Jellyfin end to end: per-viewer playback, progress, episodes, swap browser

- Host/swap send refs only; pasted Jellyfin links become refs; the host
  hands the relay its own app-obtained credential.
- Each viewer resolves with their own account (token in a header) or
  via the relay, else a clear blocked card with Link account.
- Per-account progress reporting (Playing/Progress/Stopped), 401 marks
  the account expired.
- Previous/next episode in the controls (< > / Shift+P/N), floating
  Next episode pill near the end, auto-advance countdown (one
  designated swapper), track carry-over per series.
- Swap panel uses the shared MediaPicker; browser location remembered
  per server and opens on the current series.
- Fix: states are applied one at a time (a stale pause could land
  after a newer play).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -1,7 +1,7 @@
 # watch-together
 
 Watch a video with friends, in sync, with the quality of a real mpv player.
-Paste a Jellyfin link, any direct video link, or pick a file on your own disk;
+Pick from your Jellyfin library, paste any direct video link, or pick a file on your own disk;
 everyone's play, pause and seek stay together.
 
 Why not Jellyfin SyncPlay: it runs in the browser and its sync is poor.
@@ -83,12 +83,14 @@ x to forget it. Ctrl+1 / Ctrl+2 switch between Join and Host.
 
 Profile, hardware decoding (auto, off or custom; the env var
 `SYNC_RELAY_HWDEC` overrides it; applies on the next join or Reload video),
-updates, video shaders (see below), and the keyboard shortcuts (read-only).
+updates, playing the next Jellyfin episode automatically, video shaders
+(see below), and the keyboard shortcuts (read-only).
 Integrations links Jellyfin servers (below). About shows the version.
 
 Keys in a session: Space = ready / unready, Tab = side panel (people, log,
 chat, change video), Left/Right = seek 10 s, F = fullscreen, Esc = close
-panel or ask to leave, Ctrl+R = reload video, Ctrl+1..6 = Anime4K mode A, B,
+panel or ask to leave, Ctrl+R = reload video, `<` / `>` or Shift+P /
+Shift+N = previous / next Jellyfin episode, Ctrl+1..6 = Anime4K mode A, B,
 C, A+A, B+B, C+A, Ctrl+0 = shaders off.
 
 ## Ports
@@ -122,11 +124,43 @@ Keys in the browser: arrows move, Enter picks or opens, I = details,
 Esc / Backspace / Alt+Left = back (Esc first clears a search), / or Ctrl+F =
 search.
 
-For now a hosted Jellyfin pick is shared as a stream link carrying the
-host's sign-in, so everyone watches through the host's account. Per-person
-playback, watched status and progress sync are planned: see
-[docs/ROADMAP.md](docs/ROADMAP.md). Pasting a Jellyfin direct-play link
-still works like any link.
+Host from the library: pick a movie or episode and Host. Only the item
+goes to the server (which Jellyfin server and which item), never a link or
+your sign-in. Pasting a Jellyfin link (web page or stream link) does the
+same when the app can reach that Jellyfin; otherwise it is shared as a
+plain link.
+
+Watching:
+- Everyone with their own account on that Jellyfin server plays the file
+  directly with their own sign-in. Jellyfin tracks progress per account:
+  your watched state, Continue watching and resume point follow what you
+  saw (reported on start, every 10 s, on pause, resume, seek and track
+  change, and when it stops).
+- Friends without an account watch through the host: the server fetches
+  the file with the host's sign-in and passes it on (only the current item,
+  only to people in the session). They show "via host" in the member list.
+  A dedicated server relays when started with `--jellyfin <file>` (see
+  [docs/ARCHITECTURE.md](docs/ARCHITECTURE.md), Jellyfin relay).
+- Without either, the app says "This needs a Jellyfin account on ..." with
+  a button to link one; it plays as soon as you are signed in.
+
+Episodes: the ⏮ / ⏭ buttons next to the controls (or `<` / `>`,
+Shift+P / Shift+N) put up the previous or next episode for everyone. In
+the last two minutes a "Next episode" button floats in the corner. When an
+episode ends, a card shows what is next with Play next; with "Play the
+next episode automatically" (Settings, on by default) it counts down 10 s
+first, and Cancel stops it on your screen (seeking back stops it for
+everyone). Anyone with an account can put the next one up; friends
+watching via the host cannot.
+
+Audio and subtitles: the subtitles button in the controls picks tracks.
+Your choice is remembered per series (and as a default) and the closest
+match (language, then title, then codec and channels) is selected on the
+next episode. This is per person; nobody else is affected.
+
+"Change video" in the session panel (Tab) opens the same picker as the Host
+tab: the library starts on the series you are watching with the current
+season, else where you left it. File is offered to the host only.
 
 ## Video quality and shaders
 

apps/desktop/lib/src/jellyfin/accounts.dart

@@ -23,6 +23,7 @@ const _keyDeviceId = 'deviceId';
 const _keyAccounts = 'accounts';
 const _keyDefault = 'defaultServer';
 const _keyLastPick = 'lastPick';
+const _keyBrowsePrefix = 'browse:';
 
 /// One signed-in user on one server.
 class JellyfinAccount {
@@ -124,10 +125,12 @@ abstract class JellyfinStore {
 }
 
 class HiveJellyfinStore implements JellyfinStore {
+  HiveJellyfinStore({this.boxName = jellyfinBoxName});
+  final String boxName;
   Box? _box;
 
   @override
-  Future<void> open() async => _box ??= await Hive.openBox(jellyfinBoxName);
+  Future<void> open() async => _box ??= await Hive.openBox(boxName);
 
   @override
   Object? get(String key) => _box?.get(key);
@@ -461,6 +464,26 @@ class JellyfinAccounts extends ChangeNotifier {
     }
   }
 
+  /// The browser's last location on [serverId] (encoded route stack, see
+  /// `browse_scope.dart`), restored by every browser and across restarts.
+  Object? browseLocation(String serverId) {
+    try {
+      final v = _store.get('$_keyBrowsePrefix$serverId');
+      return v is String ? _tryJson(v) : null;
+    } catch (_) {
+      return null;
+    }
+  }
+
+  Future<void> saveBrowseLocation(String serverId, Object? location) async {
+    try {
+      await _store.put(
+          '$_keyBrowsePrefix$serverId', location == null ? null : jsonEncode(location));
+    } catch (e) {
+      debugPrint('save browse location failed: $e');
+    }
+  }
+
   // --------------------------------------------------------------- cache
 
   /// Short-lived memo for browse calls, so going back does not refetch.

apps/desktop/lib/src/jellyfin/browse_scope.dart

@@ -53,6 +53,94 @@ final class DetailRoute extends BrowseRoute {
   String get key => 'item:${item.id}';
 }
 
+/// A route stack as JSON for [JellyfinAccounts.saveBrowseLocation]: only
+/// ids, names and the fields the pages start from (each page loads the
+/// full item itself).
+List<Map<String, Object?>> encodeBrowseStack(List<BrowseRoute> stack) => [
+      for (final r in stack)
+        switch (r) {
+          HomeRoute() => {'r': 'home'},
+          LibraryRoute(:final folder) => {'r': 'lib', ..._itemJson(folder)},
+          SeriesRoute(:final series, :final seasonId) => {
+              'r': 'series',
+              ..._itemJson(series),
+              'seasonId': ?seasonId,
+            },
+          DetailRoute(:final item) => {'r': 'item', ..._itemJson(item)},
+        }
+    ];
+
+/// Inverse of [encodeBrowseStack]; always starts with Home. Null when
+/// [raw] is not a stack.
+List<BrowseRoute>? decodeBrowseStack(Object? raw) {
+  if (raw is! List) return null;
+  final out = <BrowseRoute>[const HomeRoute()];
+  for (final e in raw) {
+    if (e is! Map) return null;
+    final item = _itemFrom(e);
+    final route = switch (e['r']) {
+      'home' => null,
+      'lib' when item != null => LibraryRoute(item),
+      'series' when item != null =>
+        SeriesRoute(item, seasonId: e['seasonId'] is String ? e['seasonId'] as String : null),
+      'item' when item != null => DetailRoute(item),
+      _ => null,
+    };
+    if (route != null && out.every((r) => r.key != route.key)) out.add(route);
+  }
+  return out;
+}
+
+Map<String, Object?> _itemJson(JellyfinItem i) => {
+      'id': i.id,
+      'name': i.name,
+      'type': i.type,
+      if (i.isFolder) 'isFolder': true,
+      'collectionType': ?i.collectionType,
+      'seriesId': ?i.seriesId,
+      'seriesName': ?i.seriesName,
+      'seasonId': ?i.seasonId,
+      'indexNumber': ?i.indexNumber,
+      'parentIndexNumber': ?i.parentIndexNumber,
+    };
+
+JellyfinItem? _itemFrom(Map e) {
+  String? s(String k) => e[k] is String && (e[k] as String).isNotEmpty ? e[k] as String : null;
+  final id = s('id');
+  if (id == null) return null;
+  return JellyfinItem(
+    id: id,
+    name: s('name') ?? '',
+    type: s('type') ?? '',
+    isFolder: e['isFolder'] == true,
+    collectionType: s('collectionType'),
+    seriesId: s('seriesId'),
+    seriesName: s('seriesName'),
+    seasonId: e['r'] == 'series' ? null : s('seasonId'),
+    indexNumber: e['indexNumber'] is int ? e['indexNumber'] as int : null,
+    parentIndexNumber: e['parentIndexNumber'] is int ? e['parentIndexNumber'] as int : null,
+  );
+}
+
+/// Where a browser opens instead of the remembered location: a server and
+/// a route stack (e.g. the series of the episode playing).
+class BrowseStart {
+  final String serverId;
+  final List<BrowseRoute> stack;
+  const BrowseStart(this.serverId, this.stack);
+
+  /// The series page of [episode] with its season selected.
+  static BrowseStart? seriesOf(String serverId, JellyfinItem episode) {
+    final sid = episode.seriesId;
+    if (sid == null) return null;
+    return BrowseStart(serverId, [
+      const HomeRoute(),
+      SeriesRoute(JellyfinItem(id: sid, name: episode.seriesName ?? '', type: 'Series'),
+          seasonId: episode.seasonId),
+    ]);
+  }
+}
+
 /// What every browser page needs, provided by [JellyfinBrowser].
 class BrowseScope extends InheritedWidget {
   final JellyfinAccounts accounts;

apps/desktop/lib/src/jellyfin/browser.dart

@@ -36,7 +36,11 @@ class JellyfinBrowser extends StatefulWidget {
   final bool expanded;
   final VoidCallback? onOpenIntegrations;
   final Duration searchDebounce;
+  /// Opens here instead of the remembered location (the series of the
+  /// episode playing, in the session's swap panel).
+  final BrowseStart? start;
   const JellyfinBrowser({
+    this.start,
     super.key,
     required this.accounts,
     required this.onPick,
@@ -67,12 +71,32 @@ class _JellyfinBrowserState extends State<JellyfinBrowser> {
   @override
   void initState() {
     super.initState();
+    final start = widget.start;
+    if (start != null && _accounts.account(start.serverId) != null) {
+      _serverId = start.serverId;
+      _stack = start.stack.isEmpty ? const [HomeRoute()] : start.stack;
+      _remember();
+    } else {
       _serverId = widget.selected != null && _accounts.account(widget.selected!.serverId) != null
           ? widget.selected!.serverId
           : _accounts.defaultServerId;
+      _stack = _restored(_serverId);
+    }
     _accounts.addListener(_changed);
   }
 
+  /// The remembered location on [serverId], else Home.
+  List<BrowseRoute> _restored(String? serverId) =>
+      (serverId == null ? null : decodeBrowseStack(_accounts.browseLocation(serverId))) ??
+      const [HomeRoute()];
+
+  /// Every navigation is saved per server (Hive), so the next browser
+  /// (Host tab, swap panel, next start) opens where this one was.
+  void _remember() {
+    final id = _account?.serverId;
+    if (id != null) unawaited(_accounts.saveBrowseLocation(id, encodeBrowseStack(_stack)));
+  }
+
   @override
   void didUpdateWidget(JellyfinBrowser old) {
     super.didUpdateWidget(old);
@@ -104,7 +128,7 @@ class _JellyfinBrowserState extends State<JellyfinBrowser> {
     if (serverId == _account?.serverId) return;
     setState(() {
       _serverId = serverId;
-      _stack = const [HomeRoute()];
+      _stack = _restored(serverId);
       _peek.value = null;
       _clearSearch();
     });
@@ -117,12 +141,14 @@ class _JellyfinBrowserState extends State<JellyfinBrowser> {
       _clearSearch();
       if (_stack.last.key != route.key) _stack = [..._stack, route];
     });
+    _remember();
     _body.requestFocus();
   }
 
   bool _back() {
     if (_stack.length <= 1) return false;
     setState(() => _stack = _stack.sublist(0, _stack.length - 1));
+    _remember();
     _body.requestFocus();
     return true;
   }
@@ -132,6 +158,7 @@ class _JellyfinBrowserState extends State<JellyfinBrowser> {
       _clearSearch();
       _stack = _stack.sublist(0, index + 1);
     });
+    _remember();
     _body.requestFocus();
   }
 

apps/desktop/lib/src/jellyfin/picker_source.dart

@@ -3,6 +3,7 @@ import 'package:flutter/material.dart';
 import '../screens/home/picked_media.dart';
 import '../screens/home/ui.dart';
 import 'accounts.dart';
+import 'browse_scope.dart';
 import 'browser.dart';
 import 'sign_in_panel.dart';
 
@@ -15,8 +16,10 @@ class JellyfinPickerSource extends StatefulWidget {
   final VoidCallback? onOpenIntegrations;
   final VoidCallback? onToggleExpanded;
   final bool expanded;
+  final BrowseStart? start;
   const JellyfinPickerSource({
     super.key,
+    this.start,
     required this.accounts,
     required this.onPick,
     this.selected,
@@ -54,6 +57,7 @@ class _JellyfinPickerSourceState extends State<JellyfinPickerSource> {
           onOpenIntegrations: widget.onOpenIntegrations,
           onToggleExpanded: widget.onToggleExpanded,
           expanded: widget.expanded,
+          start: widget.start,
         );
       },
     );

apps/desktop/lib/src/jellyfin/progress.dart

@@ -0,0 +1,134 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:sync_relay_core/core.dart';
+
+/// What the player shows, sampled about once a second. [aid] / [sid] are
+/// mpv track ids (null = none / subtitles off).
+class PlayerSnapshot {
+  final double position;
+  final bool paused;
+  final int? aid;
+  final int? sid;
+  const PlayerSnapshot({required this.position, required this.paused, this.aid, this.sid});
+
+  @override
+  String toString() => 'PlayerSnapshot($position, paused: $paused, aid: $aid, sid: $sid)';
+}
+
+/// Playing / Progress / Stopped for one item played with this viewer's own
+/// account, so Jellyfin's watched state and Continue Watching follow what
+/// this viewer saw. Fed a [PlayerSnapshot] every tick ([update]); sends
+/// Progress every [interval] and at once on pause, resume, seek (a jump of
+/// more than 3 s from where playback should be) or a track change. Reports
+/// go out one after another; a failure is logged and handed to [onError]
+/// (the session shows one quiet toast) and never touches playback. A 401
+/// calls [onUnauthorized] and ends reporting.
+class JellyfinProgressReporter {
+  final JellyfinClient client;
+  final String itemId;
+  final JellyfinMediaSource source;
+  final String playSessionId;
+  final Duration interval;
+  final DateTime Function() _clock;
+  final void Function(Object error)? onError;
+  final VoidCallback? onUnauthorized;
+
+  JellyfinProgressReporter({
+    required this.client,
+    required this.itemId,
+    required this.source,
+    required this.playSessionId,
+    this.interval = const Duration(seconds: 10),
+    this.onError,
+    this.onUnauthorized,
+    DateTime Function()? clock,
+  }) : _clock = clock ?? DateTime.now;
+
+  Future<void> _chain = Future.value();
+  bool _playing = false;
+  bool _dead = false;
+  PlayerSnapshot? _last;
+  DateTime? _lastAt;
+  DateTime? _lastSentAt;
+
+  /// Between [start] and [stop].
+  bool get active => _playing && !_dead;
+
+  /// The report body for [s]: ticks, pause, and mpv's aid/sid mapped to
+  /// Jellyfin stream indices (-1 = subtitles off).
+  JellyfinPlaybackReport reportFor(PlayerSnapshot s) => JellyfinPlaybackReport(
+        itemId: itemId,
+        mediaSourceId: source.id,
+        playSessionId: playSessionId,
+        positionTicks: (s.position * jellyfinTicksPerSecond).round(),
+        isPaused: s.paused,
+        audioStreamIndex: s.aid == null
+            ? null
+            : source.jellyfinIndexForMpvTrack(JellyfinStreamType.audio, s.aid!),
+        subtitleStreamIndex: s.sid == null
+            ? -1
+            : source.jellyfinIndexForMpvTrack(JellyfinStreamType.subtitle, s.sid!),
+      );
+
+  /// Playing: once the media is open. Again after [stop] (played to the
+  /// end, then someone seeked back) starts reporting anew.
+  void start(PlayerSnapshot s) {
+    if (_playing || _dead) return;
+    _playing = true;
+    _mark(s);
+    _send('Playing', () => client.reportPlaybackStart(reportFor(s)));
+  }
+
+  /// Progress when due (see the class doc).
+  void update(PlayerSnapshot s, {bool force = false}) {
+    if (!_playing || _dead) return;
+    final last = _last, lastAt = _lastAt, sentAt = _lastSentAt;
+    final now = _clock();
+    var due = force || last == null || lastAt == null || sentAt == null;
+    if (!due) {
+      final elapsed = now.difference(lastAt).inMilliseconds / 1000;
+      final expected = last.position + (last.paused ? 0 : elapsed);
+      due = s.paused != last.paused ||
+          s.aid != last.aid ||
+          s.sid != last.sid ||
+          (s.position - expected).abs() > 3 ||
+          now.difference(sentAt) >= interval;
+    }
+    _last = s;
+    _lastAt = now;
+    if (!due) return;
+    _lastSentAt = now;
+    _send('Progress', () => client.reportPlaybackProgress(reportFor(s)));
+  }
+
+  /// Stopped (swap, leave, kick, window close, played to the end).
+  /// Completes when it and everything before it went out.
+  Future<void> stop(PlayerSnapshot s) {
+    if (!_playing || _dead) return _chain;
+    _playing = false;
+    _send('Stopped', () => client.reportPlaybackStopped(reportFor(s)));
+    return _chain;
+  }
+
+  void _mark(PlayerSnapshot s) {
+    _last = s;
+    _lastAt = _lastSentAt = _clock();
+  }
+
+  void _send(String what, Future<void> Function() call) {
+    _chain = _chain.then((_) async {
+      if (_dead) return;
+      try {
+        await call().timeout(const Duration(seconds: 10));
+      } catch (e) {
+        debugPrint('jellyfin $what report for $itemId failed: $e');
+        if (e is JellyfinException && e.isUnauthorized) {
+          _dead = true;
+          onUnauthorized?.call();
+        }
+        onError?.call(e);
+      }
+    });
+  }
+}

apps/desktop/lib/src/jellyfin/session_media.dart

@@ -0,0 +1,346 @@
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+import 'package:sync_relay_core/core.dart';
+
+import '../screens/home/picked_media.dart';
+import 'accounts.dart';
+import 'format.dart';
+
+// Jellyfin media in a session: turning picks and pasted links into refs
+// (the wire carries only `{serverId, itemId, ...}`), the hosted server's
+// relay credential, and how this viewer plays a ref (own account, relay,
+// or neither).
+
+/// The wire ref of a browser pick.
+JellyfinRef refForPick(JellyfinMedia m) => JellyfinRef(
+      serverId: m.serverId,
+      itemId: m.itemId,
+      mediaSourceId: m.mediaSourceId,
+      title: m.title,
+      subtitle: m.subtitle.isEmpty ? null : m.subtitle,
+      runtimeSecs: m.runtime == null ? null : m.runtime!.inMilliseconds / 1000,
+    );
+
+/// The `swap` media for a browser pick: a ref, never a URL.
+HelloMedia mediaForPick(JellyfinMedia m) => HelloMedia(
+    name: m.title.isEmpty ? 'Jellyfin item' : m.title,
+    size: 0,
+    duration: 0,
+    jellyfin: refForPick(m));
+
+/// The pick a ref stands for on a linked server (for highlighting it in
+/// the browser); null when this install has no account there.
+JellyfinMedia? pickForRef(JellyfinAccounts accounts, JellyfinRef ref) {
+  final a = accounts.account(ref.serverId);
+  if (a == null) return null;
+  return JellyfinMedia(
+    serverId: ref.serverId,
+    baseUrl: a.baseUrl,
+    itemId: ref.itemId,
+    mediaSourceId: ref.mediaSourceId,
+    title: ref.title,
+    subtitle: ref.subtitle ?? '',
+    runtime: ref.runtimeSecs == null
+        ? null
+        : Duration(milliseconds: (ref.runtimeSecs! * 1000).round()),
+  );
+}
+
+/// The ref in a `state.media` map, or null for other media.
+JellyfinRef? refOfStateMedia(Map<String, Object?>? media) {
+  final jf = media?['jellyfin'];
+  if (jf is! Map) return null;
+  try {
+    final ref = JellyfinRef.fromJson(Map<String, Object?>.from(jf));
+    return ref.serverId.isEmpty || ref.itemId.isEmpty ? null : ref;
+  } catch (_) {
+    return null;
+  }
+}
+
+/// Same item (server, item, source); titles may differ.
+bool sameJellyfinItem(JellyfinRef? a, JellyfinRef? b) =>
+    a != null &&
+    b != null &&
+    a.serverId == b.serverId &&
+    a.itemId == b.itemId &&
+    a.mediaSourceId == b.mediaSourceId;
+
+final _sourceId = RegExp(r'^[A-Za-z0-9-]{1,64}$');
+
+/// What a pasted link becomes on the wire. A recognised Jellyfin item link
+/// (`parseJellyfinLink`) becomes a ref when its ServerId is known (in the
+/// link or from `/System/Info/Public`); its `api_key` is never shared then.
+/// Anything else, or a server that does not answer, stays a plain link.
+/// The title comes from this install's account on that server when there
+/// is one.
+Future<HelloMedia> mediaForLink(JellyfinAccounts accounts, String url,
+    {Duration timeout = const Duration(seconds: 6)}) async {
+  final plain = HelloMedia(name: linkName(url), size: 0, duration: 0, url: url);
+  final link = parseJellyfinLink(url);
+  if (link == null) return plain;
+  await accounts.ensureLoaded();
+  var serverId = link.serverId;
+  if (serverId == null || serverId.isEmpty) {
+    final probe = accounts.anonymousClient(link.baseUrl);
+    try {
+      serverId = (await probe.publicInfo().timeout(timeout)).id;
+    } catch (e) {
+      debugPrint('jellyfin link: no server id from ${link.baseUrl}: $e');
+      return plain;
+    } finally {
+      probe.close();
+    }
+    if (serverId.isEmpty) return plain;
+  }
+  final src = Uri.tryParse(url)?.queryParameters['mediaSourceId'];
+  var ref = JellyfinRef(
+    serverId: serverId,
+    itemId: link.itemId,
+    mediaSourceId: src != null && _sourceId.hasMatch(src) && src != link.itemId ? src : null,
+  );
+  final account = accounts.account(serverId);
+  final client = accounts.clientFor(serverId);
+  if (account != null && client != null) {
+    try {
+      final pick = pickFor(account, await client.item(link.itemId).timeout(timeout));
+      ref = refForPick(JellyfinMedia(
+        serverId: serverId,
+        baseUrl: account.baseUrl,
+        itemId: link.itemId,
+        mediaSourceId: ref.mediaSourceId,
+        title: pick.title,
+        subtitle: pick.subtitle,
+        runtime: pick.runtime,
+      ));
+    } catch (e) {
+      if (e is JellyfinException && e.isUnauthorized) accounts.markExpired(serverId);
+    }
+  }
+  return HelloMedia(
+      name: ref.title.isEmpty ? 'Jellyfin item' : ref.title, size: 0, duration: 0, jellyfin: ref);
+}
+
+/// Display name for a link: last path segment, decoded, never the query
+/// (Jellyfin-style links carry api_key there and names are broadcast).
+String linkName(String url) {
+  final uri = Uri.tryParse(url.trim());
+  if (uri == null) return 'link';
+  final segs = uri.pathSegments.where((s) => s.isNotEmpty).toList();
+  if (segs.isNotEmpty) {
+    try {
+      return Uri.decodeComponent(segs.last);
+    } catch (_) {
+      return segs.last;
+    }
+  }
+  return uri.host.isNotEmpty ? uri.host : 'link';
+}
+
+/// The hosted server's relay login: the account for [serverId] (the
+/// hosted item's server), else the default account, when its token is not
+/// known to be expired. The device fields are exactly the ones this app
+/// sends with that token ([JellyfinAccounts.clientInfo]): Jellyfin rewrites
+/// a token's device from the request header, so the relay must not differ.
+JellyfinCredential? relayCredentialFor(JellyfinAccounts accounts, {String? serverId}) {
+  bool usable(JellyfinAccount? a) =>
+      a != null && accounts.statusOf(a.serverId) != JellyfinAccountStatus.expired;
+  var a = serverId == null ? null : accounts.account(serverId);
+  if (!usable(a)) a = accounts.defaultAccount;
+  if (!usable(a)) return null;
+  final info = accounts.clientInfo;
+  return JellyfinCredential(
+    baseUrl: a!.baseUrl,
+    serverId: a.serverId,
+    token: a.token,
+    client: info.client,
+    device: info.device,
+    deviceId: info.deviceId,
+    version: info.version,
+  );
+}
+
+/// `/j/...` URL of the current Jellyfin media on the host this client
+/// dialled, built like the `/m/...` one.
+String relayUrlFor(String host, int port, String token, String itemId) =>
+    'http://$host:$port/j/default/$token/${Uri.encodeComponent(itemId)}';
+
+// ---------------------------------------------------------------- playing
+
+/// How this viewer plays a ref.
+sealed class JellyfinPlan {
+  const JellyfinPlan();
+
+  /// `report.jf` for this plan; null when it plays nothing.
+  bool? get jfAccess;
+}
+
+/// Direct play with this install's account: the static stream, the token
+/// in [headers] (not in the URL), progress reported per [info].
+final class OwnPlay extends JellyfinPlan {
+  final JellyfinClient client;
+  final JellyfinAccount account;
+  final JellyfinPlaybackInfo info;
+  final JellyfinMediaSource source;
+  /// Full item (series, episode numbers); null if that call failed.
+  final JellyfinItem? item;
+  final String url;
+  final Map<String, String> headers;
+  const OwnPlay({
+    required this.client,
+    required this.account,
+    required this.info,
+    required this.source,
+    required this.item,
+    required this.url,
+    required this.headers,
+  });
+
+  @override
+  bool get jfAccess => true;
+}
+
+/// Through the sync server's relay (`/j/...`).
+final class RelayPlay extends JellyfinPlan {
+  final String url;
+  const RelayPlay(this.url);
+
+  @override
+  bool get jfAccess => false;
+}
+
+/// Neither: no (usable) account here and the server cannot relay.
+final class BlockedPlay extends JellyfinPlan {
+  final String serverId;
+  /// Known only when this install has (had) an account there.
+  final String? serverName;
+  /// Why the own account did not work, if there is one.
+  final String? problem;
+  const BlockedPlay({required this.serverId, this.serverName, this.problem});
+
+  @override
+  bool? get jfAccess => null;
+
+  String get message {
+    final where = serverName == null || serverName!.isEmpty ? 'that Jellyfin server' : serverName!;
+    final base = 'This needs a Jellyfin account on $where (or the host can relay)';
+    return problem == null ? base : '$base — $problem';
+  }
+}
+
+/// Picks how to play [ref]: this install's account first (PlaybackInfo
+/// with its own user; a 401 marks the account expired), else the relay
+/// when the server offers it ([relay] = `state.relay`, [relayUrl] this
+/// member's `/j/...` URL), else [BlockedPlay].
+Future<JellyfinPlan> resolveJellyfinRef(
+  JellyfinAccounts accounts,
+  JellyfinRef ref, {
+  required bool relay,
+  required String? relayUrl,
+  Duration timeout = const Duration(seconds: 15),
+}) async {
+  await accounts.ensureLoaded();
+  final account = accounts.account(ref.serverId);
+  String? problem;
+  if (account != null && accounts.statusOf(ref.serverId) == JellyfinAccountStatus.expired) {
+    problem = 'your sign-in expired, reconnect it in Integrations';
+  } else if (account != null) {
+    final client = accounts.clientFor(ref.serverId)!;
+    try {
+      final infoF = client.playbackInfo(ref.itemId, mediaSourceId: ref.mediaSourceId).timeout(timeout);
+      final itemF = client
+          .item(ref.itemId)
+          .timeout(timeout)
+          .then<JellyfinItem?>((i) => i, onError: (Object _) => null);
+      final info = await infoF;
+      final item = await itemF;
+      final source = (ref.mediaSourceId == null
+              ? null
+              : info.mediaSources.where((s) => s.id == ref.mediaSourceId).firstOrNull) ??
+          info.primarySource;
+      if (source == null) throw const JellyfinException('no playable source');
+      return OwnPlay(
+        client: client,
+        account: account,
+        info: info,
+        source: source,
+        item: item,
+        url: client.shareableStreamUrl(ref.itemId, mediaSourceId: source.id).toString(),
+        headers: client.authHeaders,
+      );
+    } catch (e) {
+      debugPrint('jellyfin resolve ${ref.itemId} with own account failed: $e');
+      if (e is JellyfinException && e.isUnauthorized) {
+        accounts.markExpired(ref.serverId);
+        problem = 'your sign-in expired, reconnect it in Integrations';
+      } else if (e is JellyfinException && e.statusCode == 404) {
+        problem = 'your account cannot see this item';
+      } else {
+        problem = 'could not reach it';
+      }
+    }
+  }
+  if (relay && relayUrl != null && relayUrl.isNotEmpty) return RelayPlay(relayUrl);
+  return BlockedPlay(serverId: ref.serverId, serverName: account?.displayName, problem: problem);
+}
+
+// ------------------------------------------------------------ next episode
+
+/// A neighbouring episode as this viewer can put it up.
+class EpisodeLink {
+  final JellyfinItem item;
+  final JellyfinMedia pick;
+  const EpisodeLink(this.item, this.pick);
+
+  /// "S1E7 Battle with the Heroes".
+  String get label => [?item.episodeLabel, item.name].join(' ');
+}
+
+/// The episodes before and after the one [plan] plays, with its account.
+/// Both null for movies, at the ends of a series, or on failure.
+Future<({EpisodeLink? previous, EpisodeLink? next})> findAdjacentEpisodes(OwnPlay plan,
+    {Duration timeout = const Duration(seconds: 15)}) async {
+  const none = (previous: null, next: null);
+  final item = plan.item;
+  if (item == null || item.kind != JellyfinItemKind.episode || item.seriesId == null) return none;
+  try {
+    final around = await plan.client.adjacentEpisodes(item).timeout(timeout);
+    EpisodeLink? link(JellyfinItem? i) => i == null ? null : EpisodeLink(i, pickFor(plan.account, i));
+    return (previous: link(around.previous), next: link(around.next));
+  } catch (e) {
+    debugPrint('episode lookup failed: $e');
+    return none;
+  }
+}
+
+/// When the floating "Next episode" pill appears: the last two minutes of
+/// [runtime] (all of it for shorter media). One place to switch it to the
+/// item's outro / credits segment later.
+Duration nextPromptStart(JellyfinItem? item, Duration runtime) {
+  const lead = Duration(minutes: 2);
+  return runtime > lead ? runtime - lead : Duration.zero;
+}
+
+/// Who performs the auto-advance swap, so several counting clients do not
+/// swap twice: the lowest member id among members that play the item with
+/// their own account (`jf[serverId] == true`, not stale). Only what every
+/// client sees in `state` decides (who put the item up is not in it: a
+/// late joiner never saw that swap), so all clients agree.
+String? autoAdvanceSwapper(List<MemberView> members, String serverId) {
+  final eligible = [
+    for (final m in members)
+      if (!m.stale && m.jf[serverId] == true) m
+  ];
+  if (eligible.isEmpty) return null;
+  eligible.sort((a, b) => compareMemberIds(a.id, b.id));
+  return eligible.first.id;
+}
+
+/// "m2" before "m10": numeric suffix order, then plain text.
+int compareMemberIds(String a, String b) {
+  final na = int.tryParse(a.replaceFirst(RegExp(r'^\D+'), ''));
+  final nb = int.tryParse(b.replaceFirst(RegExp(r'^\D+'), ''));
+  if (na != null && nb != null && na != nb) return na.compareTo(nb);
+  return a.compareTo(b);
+}

apps/desktop/lib/src/jellyfin/track_prefs.dart

@@ -0,0 +1,189 @@
+import 'dart:convert';
+
+import 'package:flutter/foundation.dart';
+import 'package:sync_relay_core/core.dart';
+
+import 'accounts.dart';
+
+// Per-viewer audio/subtitle carry-over: the last choice is kept per series
+// (and as a global fallback) and matched against the next Jellyfin item's
+// tracks with core's `matchTrack`. Local only; nothing goes on the wire.
+
+const trackPrefsBoxName = 'track_prefs';
+const _keyGlobal = 'global';
+
+/// One mpv track as media_kit lists it ([id] is mpv's `aid` / `sid`).
+class MpvTrack {
+  final int id;
+  final JellyfinStreamType type;
+  final String? language;
+  final String? title;
+  final String? codec;
+  final int? channels;
+  final bool isDefault;
+  const MpvTrack({
+    required this.id,
+    required this.type,
+    this.language,
+    this.title,
+    this.codec,
+    this.channels,
+    this.isDefault = false,
+  });
+
+  /// As a stream for [matchTrack]; its index is the mpv id.
+  JellyfinMediaStream get asStream => JellyfinMediaStream(
+      index: id,
+      type: type,
+      language: language,
+      title: title,
+      codec: codec,
+      channels: channels,
+      isDefault: isDefault);
+
+  /// Menu text: "English (eac3 2ch)", "Track 2".
+  String get label {
+    final name = title ?? language ?? 'Track $id';
+    final extra = [?codec, if (channels != null) '${channels}ch'].join(' ');
+    final lang = title != null && language != null ? ' [$language]' : '';
+    return extra.isEmpty ? '$name$lang' : '$name$lang ($extra)';
+  }
+}
+
+/// A viewer's audio/subtitle choice as traits (indices shift between
+/// files). [subtitlesOff] wins over [subtitle].
+class TrackChoice {
+  final TrackPreference? audio;
+  final TrackPreference? subtitle;
+  final bool subtitlesOff;
+  const TrackChoice({this.audio, this.subtitle, this.subtitlesOff = false});
+
+  Map<String, Object?> toJson() => {
+        'audio': ?_prefToJson(audio),
+        'subtitle': ?_prefToJson(subtitle),
+        'subtitlesOff': subtitlesOff,
+      };
+
+  static TrackChoice? fromJson(Object? j) {
+    if (j is! Map) return null;
+    return TrackChoice(
+      audio: _prefFromJson(j['audio'], JellyfinStreamType.audio),
+      subtitle: _prefFromJson(j['subtitle'], JellyfinStreamType.subtitle),
+      subtitlesOff: j['subtitlesOff'] == true,
+    );
+  }
+
+  /// The choice behind mpv's [aid] / [sid] (null = none / off): traits from
+  /// the Jellyfin [source] when this viewer has it (title, channels,
+  /// forced/HI flags), else from mpv's [tracks].
+  factory TrackChoice.of({
+    required int? aid,
+    required int? sid,
+    JellyfinMediaSource? source,
+    List<MpvTrack> tracks = const [],
+  }) {
+    TrackPreference? pref(JellyfinStreamType type, int? id) {
+      if (id == null) return null;
+      if (source != null) {
+        final index = source.jellyfinIndexForMpvTrack(type, id);
+        final s = index == null ? null : source.streamAt(index);
+        if (s != null) return TrackPreference.fromStream(s);
+      }
+      final t = tracks.where((t) => t.type == type && t.id == id).firstOrNull;
+      return t == null ? null : TrackPreference.fromStream(t.asStream);
+    }
+
+    return TrackChoice(
+      audio: pref(JellyfinStreamType.audio, aid),
+      subtitle: pref(JellyfinStreamType.subtitle, sid),
+      subtitlesOff: sid == null,
+    );
+  }
+}
+
+Map<String, Object?>? _prefToJson(TrackPreference? p) => p == null
+    ? null
+    : {
+        'language': ?p.language,
+        'title': ?p.title,
+        'codec': ?p.codec,
+        'channels': ?p.channels,
+        if (p.isForced) 'forced': true,
+        if (p.isHearingImpaired) 'hi': true,
+      };
+
+TrackPreference? _prefFromJson(Object? j, JellyfinStreamType type) {
+  if (j is! Map) return null;
+  String? s(Object? v) => v is String && v.isNotEmpty ? v : null;
+  return TrackPreference(
+    type: type,
+    language: s(j['language']),
+    title: s(j['title']),
+    codec: s(j['codec']),
+    channels: j['channels'] is int ? j['channels'] as int : null,
+    isForced: j['forced'] == true,
+    isHearingImpaired: j['hi'] == true,
+  );
+}
+
+/// mpv tracks to select for [choice] on a new item. Matches against the
+/// Jellyfin [source]'s streams when this viewer has them (mapped to mpv ids
+/// with [JellyfinMediaSource.mpvTrackId]), else against mpv's [tracks].
+/// Null fields keep the player's default; [subtitlesOff] turns them off.
+({int? aid, int? sid, bool subtitlesOff}) chooseTracks(TrackChoice choice,
+    {JellyfinMediaSource? source, List<MpvTrack> tracks = const []}) {
+  int? pick(TrackPreference? pref) {
+    if (pref == null) return null;
+    if (source != null) {
+      final s = matchTrack(pref, source.mediaStreams);
+      return s == null ? null : source.mpvTrackId(s.index);
+    }
+    return matchTrack(pref, [for (final t in tracks) t.asStream])?.index;
+  }
+
+  return (
+    aid: pick(choice.audio),
+    sid: choice.subtitlesOff ? null : pick(choice.subtitle),
+    subtitlesOff: choice.subtitlesOff,
+  );
+}
+
+/// The last choice per series and overall, in their own Hive box.
+class TrackPrefs {
+  TrackPrefs({JellyfinStore? store}) : _store = store ?? HiveJellyfinStore(boxName: trackPrefsBoxName);
+  final JellyfinStore _store;
+  Future<void>? _open;
+
+  Future<void> _ready() => _open ??= _store.open().catchError((Object e) {
+        debugPrint('open track prefs failed: $e');
+      });
+
+  /// The series' choice, else the global one.
+  Future<TrackChoice?> load({String? seriesId}) async {
+    await _ready();
+    try {
+      Object? read(String key) {
+        final v = _store.get(key);
+        return v is String ? jsonDecode(v) : null;
+      }
+
+      return (seriesId == null ? null : TrackChoice.fromJson(read('series:$seriesId'))) ??
+          TrackChoice.fromJson(read(_keyGlobal));
+    } catch (e) {
+      debugPrint('read track prefs failed: $e');
+      return null;
+    }
+  }
+
+  /// Saves [choice] as the global one and, with [seriesId], the series'.
+  Future<void> save(TrackChoice choice, {String? seriesId}) async {
+    await _ready();
+    try {
+      final v = jsonEncode(choice.toJson());
+      await _store.put(_keyGlobal, v);
+      if (seriesId != null) await _store.put('series:$seriesId', v);
+    } catch (e) {
+      debugPrint('save track prefs failed: $e');
+    }
+  }
+}

apps/desktop/lib/src/playback/playback_controller.dart

@@ -5,6 +5,9 @@ import 'package:flutter/widgets.dart';
 import 'package:media_kit/media_kit.dart';
 import 'package:media_kit_video/media_kit_video.dart';
 import 'package:signals/signals_flutter.dart';
+import 'package:sync_relay_core/core.dart' show JellyfinStreamType;
+
+import '../jellyfin/track_prefs.dart' show MpvTrack;
 
 import '../shaders/shader_assets.dart';
 import '../shaders/shader_presets.dart';
@@ -356,16 +359,89 @@ class PlaybackController {
     }
   }
 
-  Future<void> openUrl(String url) async {
+  /// Opens [url] paused. [headers] go with every request for it (mpv
+  /// `http-header-fields`): a Jellyfin token travels there, not in the URL.
+  Future<void> openUrl(String url, {Map<String, String>? headers}) async {
     if (!_ready) return;
     try {
-      await player.open(Media(url), play: false);
+      // An empty map, not null: media_kit caches headers per URI.
+      await player.open(Media(url, httpHeaders: headers ?? const {}), play: false);
     } catch (e, st) {
-      debugPrint('open $url failed: $e\n$st');
+      debugPrint('open ${Uri.tryParse(url)?.replace(query: '') ?? 'media'} failed: $e\n$st');
       rethrow;
     }
   }
 
+  /// The audio / subtitle tracks of the open file (mpv's track-list).
+  List<MpvTrack> get tracks {
+    final p = _player;
+    if (p == null) return const [];
+    MpvTrack? of(dynamic t, JellyfinStreamType type) {
+      final id = int.tryParse('${t.id}');
+      if (id == null) return null;
+      return MpvTrack(
+        id: id,
+        type: type,
+        language: t.language as String?,
+        title: t.title as String?,
+        codec: t.codec as String?,
+        channels: (t.channelscount ?? t.audiochannels) as int?,
+        isDefault: t.isDefault == true,
+      );
+    }
+
+    return [
+      for (final t in p.state.tracks.audio) ?of(t, JellyfinStreamType.audio),
+      for (final t in p.state.tracks.subtitle) ?of(t, JellyfinStreamType.subtitle),
+    ];
+  }
+
+  /// Waits (bounded) until the open file's tracks are listed and mpv has
+  /// selected its audio track, so a report or a carried-over choice sees
+  /// the real selection.
+  Future<List<MpvTrack>> waitForTracks({Duration timeout = const Duration(seconds: 5)}) async {
+    final end = DateTime.now().add(timeout);
+    while (_player != null && DateTime.now().isBefore(end)) {
+      final t = tracks;
+      final hasAudio = t.any((x) => x.type == JellyfinStreamType.audio);
+      if (t.isNotEmpty && (!hasAudio || (await currentTrackIds()).aid != null)) return t;
+      await Future.delayed(const Duration(milliseconds: 100));
+    }
+    return tracks;
+  }
+
+  /// mpv's selected audio and subtitle track ids (null = none / off).
+  Future<({int? aid, int? sid})> currentTrackIds() async {
+    final p = _player;
+    if (p == null) return (aid: null, sid: null);
+    try {
+      final dynamic platform = p.platform;
+      final aid = int.tryParse('${await platform?.getProperty('current-tracks/audio/id')}');
+      final sid = int.tryParse('${await platform?.getProperty('current-tracks/sub/id')}');
+      return (aid: aid, sid: sid);
+    } catch (_) {
+      return (aid: null, sid: null);
+    }
+  }
+
+  /// Selects tracks by mpv id; a null [aid] keeps audio, [subtitlesOff]
+  /// turns subtitles off, else a null [sid] keeps them.
+  Future<void> selectTracks({int? aid, int? sid, bool subtitlesOff = false}) async {
+    final p = _player;
+    if (p == null) return;
+    try {
+      final dynamic platform = p.platform;
+      if (aid != null) await platform?.setProperty('aid', '$aid');
+      if (subtitlesOff) {
+        await platform?.setProperty('sid', 'no');
+      } else if (sid != null) {
+        await platform?.setProperty('sid', '$sid');
+      }
+    } catch (e) {
+      debugPrint('select tracks failed: $e');
+    }
+  }
+
   double get positionSecs {
     final p = _player;
     if (p == null) return 0;

apps/desktop/lib/src/screens/home/connect_flow.dart

@@ -1,6 +1,7 @@
 import 'dart:io';
 
 import 'package:flutter/foundation.dart';
+import 'package:sync_relay_core/core.dart' show HelloMedia;
 
 import '../../session/session_coordinator.dart';
 import '../../state/session_state.dart';
@@ -91,11 +92,11 @@ class ConnectFlow extends ChangeNotifier {
   }
 
   /// [edit] fills the card's fields into a copy of the last form, so the
-  /// other card's saved values survive. [linkOverride] (host only) is played
-  /// as the link but never stored in the form: the interim Jellyfin stream
-  /// URL carries a token.
+  /// other card's saved values survive. [media] (host only) is put up
+  /// instead of the form's link or file (a Jellyfin ref; the pick itself is
+  /// remembered in the Jellyfin box, not the form).
   Future<void> submit(ConnectMode mode, void Function(ConnectForm f) edit,
-      {String? linkOverride}) async {
+      {HelloMedia? media}) async {
     if (busy != null) return;
     final myAttempt = ++_attempt;
     final form = _session.lastForm.copy();
@@ -113,15 +114,10 @@ class ConnectFlow extends ChangeNotifier {
     notices[mode] = null;
     _notify();
 
-    final ConnectParams params;
+    ConnectParams params;
     try {
-      params = await buildParams(
-          mode,
-          linkOverride == null || mode != ConnectMode.host
-              ? form
-              : (form.copy()
-                ..mediaPath = ''
-                ..linkUrl = linkOverride));
+      params = await buildParams(mode, form);
+      if (media != null && mode == ConnectMode.host) params = params.withMedia(media);
     } catch (e) {
       if (myAttempt != _attempt) return;
       busy = null;

apps/desktop/lib/src/screens/home/host_tab.dart

@@ -1,7 +1,9 @@
 import 'package:flutter/material.dart';
 import 'package:signals/signals_flutter.dart';
+import 'package:sync_relay_core/core.dart' show HelloMedia;
 
 import '../../jellyfin/accounts.dart';
+import '../../jellyfin/session_media.dart';
 import '../../state/session_state.dart';
 import 'connect_flow.dart';
 import 'connect_status.dart';
@@ -48,20 +50,17 @@ class HostFields {
   }
 }
 
-/// INTERIM(jellyfin-protocol): until the protocol carries a Jellyfin item,
-/// the host plays it as a link: this install's authorised static stream URL
-/// (token in the query, so viewers stream with the host's sign-in and the
-/// URL must not be persisted). Throws [FormatException] with a user-facing
-/// message when the server is not linked any more.
-String interimJellyfinLink(JellyfinAccounts accounts, JellyfinMedia media) {
-  final client = accounts.clientFor(media.serverId);
-  if (client == null) {
+/// What hosting a picked Jellyfin item sends: its ref (no URL, no token).
+/// Throws [FormatException] with a user-facing message when the server is
+/// not linked any more or its sign-in expired.
+HelloMedia hostJellyfinMedia(JellyfinAccounts accounts, JellyfinMedia media) {
+  if (accounts.account(media.serverId) == null) {
     throw const FormatException('that Jellyfin server is not linked any more — pick again');
   }
   if (accounts.statusOf(media.serverId) == JellyfinAccountStatus.expired) {
     throw const FormatException('Jellyfin sign-in expired — reconnect it in Integrations');
   }
-  return client.streamUrl(media.itemId, mediaSourceId: media.mediaSourceId).toString();
+  return mediaForPick(media);
 }
 
 /// Below this width the server column moves under the media picker.
@@ -79,10 +78,10 @@ class HostTab extends StatelessWidget {
   void _host() {
     if (flow.busy != null) return;
     final media = fields.media.selection;
-    String? link;
+    HelloMedia? jellyfinMedia;
     if (media is JellyfinMedia) {
       try {
-        link = interimJellyfinLink(fields.jellyfin, media);
+        jellyfinMedia = hostJellyfinMedia(fields.jellyfin, media);
       } on FormatException catch (e) {
         flow.showError(ConnectMode.host, CardError('Check the form', e.message));
         return;
@@ -96,7 +95,7 @@ class HostTab extends StatelessWidget {
         ..hostSecret = fields.secret.text
         ..mediaPath = media is FileMedia ? media.path : ''
         ..linkUrl = media is LinkMedia ? media.url : '',
-      linkOverride: link,
+      media: jellyfinMedia,
     );
   }
 

apps/desktop/lib/src/screens/home/media_picker.dart

@@ -3,6 +3,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 
 import '../../jellyfin/accounts.dart';
+import '../../jellyfin/browse_scope.dart' show BrowseStart;
 import '../../jellyfin/picker_source.dart';
 import '../../widgets/media_input.dart';
 import 'picked_media.dart';
@@ -114,8 +115,17 @@ class MediaPicker extends StatefulWidget {
   /// Jellyfin source only: the browser's "bigger" toggle.
   final VoidCallback? onToggleExpanded;
   final bool expanded;
+  /// Where the Jellyfin browser opens instead of its remembered location.
+  final BrowseStart? jellyfinStart;
+  /// False hides the File source (only the host can serve a file).
+  final bool allowFile;
+  /// Shown under the Link field instead of the default help.
+  final String? linkHelp;
   const MediaPicker({
     super.key,
+    this.jellyfinStart,
+    this.allowFile = true,
+    this.linkHelp,
     required this.controller,
     this.onChanged,
     this.onSubmit,
@@ -221,6 +231,7 @@ class _MediaPickerState extends State<MediaPicker> {
           onOpenIntegrations: widget.onOpenIntegrations,
           onToggleExpanded: widget.onToggleExpanded,
           expanded: widget.expanded,
+          start: widget.jellyfinStart,
         ),
       MediaKind.link => _FieldRow(
           key: const ValueKey('media-link'),
@@ -236,7 +247,9 @@ class _MediaPickerState extends State<MediaPicker> {
             icon: const Icon(Icons.content_paste, size: 18),
             label: const Text('Paste'),
           ),
-          help: 'A direct http(s) link to a video file; everyone streams it from there.',
+          help: widget.linkHelp ??
+              'A direct http(s) link to a video file; everyone streams it from there. '
+                  'Jellyfin links are shared as the item, without your sign-in.',
           notice: _c.notice,
         ),
       MediaKind.file => _FieldRow(
@@ -260,17 +273,17 @@ class _MediaPickerState extends State<MediaPicker> {
       child: SegmentedButton<MediaKind>(
         key: const ValueKey('media-source'),
         showSelectedIcon: false,
-        segments: const [
-          ButtonSegment(
+        segments: [
+          const ButtonSegment(
               value: MediaKind.jellyfin,
               icon: Icon(Icons.video_library_outlined),
               label: Text('Jellyfin')),
-          ButtonSegment(value: MediaKind.link, icon: Icon(Icons.link), label: Text('Link')),
-          ButtonSegment(
+          const ButtonSegment(value: MediaKind.link, icon: Icon(Icons.link), label: Text('Link')),
+          const ButtonSegment(
               value: MediaKind.file,
               icon: Icon(Icons.insert_drive_file_outlined),
               label: Text('File')),
-        ],
+        ].where((s) => widget.allowFile || s.value != MediaKind.file).toList(),
         selected: {source},
         onSelectionChanged: (s) => _c.source = s.first,
       ),

apps/desktop/lib/src/screens/home/settings_page.dart

@@ -17,6 +17,7 @@ const sessionShortcuts = [
   ('F', 'Toggle fullscreen'),
   ('Tab', 'Open / close the people & chat panel'),
   ('Ctrl+R', 'Reload the video'),
+  ('> or Shift+N', 'Put up the next Jellyfin episode'),
   ('Ctrl+1…6', 'Shaders: Anime4K mode A, B, C, A+A, B+B, C+A'),
   ('Ctrl+0', 'Shaders off'),
   ('Esc', 'Close panel or fullscreen, else ask to leave'),
@@ -34,6 +35,7 @@ class SettingsPage extends StatelessWidget {
         const PageTitle('Settings'),
         const _Section(title: 'Profile', child: ProfileEditor()),
         const _Section(title: 'Player', child: _HwdecSetting()),
+        const _Section(title: 'Jellyfin', child: _AutoAdvanceSetting()),
         _Section(title: 'Updates', child: _UpdateSettings(controller: updates)),
         const _Section(title: 'Keyboard shortcuts', child: _ShortcutList()),
         const _Section(title: 'Video quality & shaders', child: _ShaderSettings()),
@@ -290,6 +292,26 @@ class _UpdateSettings extends StatelessWidget {
   }
 }
 
+class _AutoAdvanceSetting extends StatelessWidget {
+  const _AutoAdvanceSetting();
+
+  @override
+  Widget build(BuildContext context) {
+    final s = AppSettings.instance;
+    return SignalBuilder(
+      builder: (context) => SwitchListTile(
+        key: const ValueKey('auto-advance'),
+        contentPadding: EdgeInsets.zero,
+        title: const Text('Play the next episode automatically'),
+        subtitle: const Text('When an episode ends, a 10 s countdown puts up the next one; '
+            'anyone can cancel it on their screen.'),
+        value: s.autoAdvance.value,
+        onChanged: s.setAutoAdvance,
+      ),
+    );
+  }
+}
+
 class _ShortcutList extends StatelessWidget {
   const _ShortcutList();
 

apps/desktop/lib/src/screens/session/jellyfin_widgets.dart

@@ -0,0 +1,328 @@
+import 'package:flutter/material.dart';
+import 'package:sync_relay_core/core.dart' show JellyfinStreamType;
+
+import '../../jellyfin/session_media.dart';
+import '../../jellyfin/track_prefs.dart';
+import '../../session/session_coordinator.dart' show AutoAdvance, autoAdvanceSecs;
+
+// Jellyfin pieces of the session screen. Plain widgets fed by the
+// coordinator's signals, so tests can pump them without the player.
+
+/// Previous / next episode in the video controls. Nothing when there is
+/// no such episode or this viewer cannot put it up (no account).
+class EpisodeSkipButton extends StatelessWidget {
+  final EpisodeLink? episode;
+  final bool next;
+  final VoidCallback onPressed;
+  final FocusNode? focusNode;
+  const EpisodeSkipButton(
+      {super.key, required this.episode, required this.next, required this.onPressed, this.focusNode});
+
+  @override
+  Widget build(BuildContext context) {
+    final e = episode;
+    if (e == null) return const SizedBox.shrink();
+    return Tooltip(
+      message: '${next ? 'Next' : 'Previous'}: ${e.label}  (${next ? '> or Shift+N' : '< or Shift+P'})',
+      child: IconButton(
+        key: ValueKey(next ? 'episode-next' : 'episode-previous'),
+        focusNode: focusNode,
+        color: Colors.white,
+        iconSize: 22,
+        visualDensity: VisualDensity.compact,
+        icon: Icon(next ? Icons.skip_next_rounded : Icons.skip_previous_rounded),
+        onPressed: onPressed,
+      ),
+    );
+  }
+}
+
+/// Floating "Next episode ›" near the end of an episode: faint at rest,
+/// lit on hover. Lives outside the auto-hiding controls, so it shows in
+/// fullscreen and with the controls hidden.
+class NextEpisodePill extends StatefulWidget {
+  final EpisodeLink episode;
+  final VoidCallback onPressed;
+  const NextEpisodePill({super.key, required this.episode, required this.onPressed});
+
+  @override
+  State<NextEpisodePill> createState() => _NextEpisodePillState();
+}
+
+class _NextEpisodePillState extends State<NextEpisodePill> {
+  bool _hover = false;
+
+  @override
+  Widget build(BuildContext context) {
+    final primary = Theme.of(context).colorScheme.primary;
+    return MouseRegion(
+      cursor: SystemMouseCursors.click,
+      onEnter: (_) => setState(() => _hover = true),
+      onExit: (_) => setState(() => _hover = false),
+      child: Tooltip(
+        message: 'Next: ${widget.episode.label}',
+        child: AnimatedScale(
+          duration: const Duration(milliseconds: 150),
+          scale: _hover ? 1.06 : 1,
+          child: AnimatedOpacity(
+            duration: const Duration(milliseconds: 150),
+            opacity: _hover ? 1 : 0.45,
+            child: GestureDetector(
+              key: const ValueKey('next-episode-pill'),
+              onTap: widget.onPressed,
+              child: AnimatedContainer(
+                duration: const Duration(milliseconds: 150),
+                padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 9),
+                decoration: BoxDecoration(
+                  color: Colors.black.withValues(alpha: 0.75),
+                  borderRadius: BorderRadius.circular(999),
+                  border: Border.all(color: _hover ? primary : Colors.white24),
+                  boxShadow: _hover
+                      ? [BoxShadow(color: primary.withValues(alpha: 0.45), blurRadius: 16)]
+                      : const [],
+                ),
+                child: const Row(
+                  mainAxisSize: MainAxisSize.min,
+                  children: [
+                    Text('Next episode', style: TextStyle(color: Colors.white, fontSize: 13)),
+                    SizedBox(width: 4),
+                    Icon(Icons.chevron_right, color: Colors.white, size: 18),
+                  ],
+                ),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+/// At the end of an episode: "Next: S1E7 title" with Play now, and while
+/// the auto-advance countdown runs, the seconds left and Cancel.
+class EndOfEpisodeCard extends StatelessWidget {
+  final EpisodeLink next;
+  final AutoAdvance? countdown;
+  final VoidCallback onPlayNow;
+  final VoidCallback onCancel;
+  const EndOfEpisodeCard({
+    super.key,
+    required this.next,
+    required this.countdown,
+    required this.onPlayNow,
+    required this.onCancel,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final t = Theme.of(context).textTheme;
+    final c = countdown;
+    return Card(
+      key: const ValueKey('end-of-episode'),
+      color: Colors.black.withValues(alpha: 0.85),
+      child: Padding(
+        padding: const EdgeInsets.fromLTRB(16, 12, 12, 12),
+        child: ConstrainedBox(
+          constraints: const BoxConstraints(maxWidth: 380),
+          child: Column(
+            mainAxisSize: MainAxisSize.min,
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [
+              Text(c == null ? 'Up next' : 'Next episode in ${c.secondsLeft} s',
+                  style: t.labelLarge?.copyWith(color: Colors.white70)),
+              const SizedBox(height: 4),
+              Text('Next: ${next.label}',
+                  maxLines: 2, overflow: TextOverflow.ellipsis, style: t.titleMedium),
+              if (c != null) ...[
+                const SizedBox(height: 8),
+                LinearProgressIndicator(value: c.secondsLeft / autoAdvanceSecs),
+              ],
+              const SizedBox(height: 10),
+              Row(
+                mainAxisAlignment: MainAxisAlignment.end,
+                children: [
+                  if (c != null)
+                    TextButton(
+                        key: const ValueKey('auto-advance-cancel'),
+                        onPressed: onCancel,
+                        child: const Text('Cancel')),
+                  const SizedBox(width: 8),
+                  FilledButton.icon(
+                    key: const ValueKey('play-next'),
+                    onPressed: onPlayNow,
+                    icon: const Icon(Icons.skip_next_rounded, size: 18),
+                    label: Text(c == null ? 'Play next' : 'Play now'),
+                  ),
+                ],
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+/// This viewer cannot play the Jellyfin media: say why and offer to link
+/// an account (never a silent stall).
+class JellyfinBlockedCard extends StatelessWidget {
+  final BlockedPlay blocked;
+  final VoidCallback onLinkAccount;
+  final VoidCallback onRetry;
+  const JellyfinBlockedCard(
+      {super.key, required this.blocked, required this.onLinkAccount, required this.onRetry});
+
+  @override
+  Widget build(BuildContext context) {
+    final t = Theme.of(context).textTheme;
+    return Card(
+      key: const ValueKey('jellyfin-blocked'),
+      color: Colors.black.withValues(alpha: 0.85),
+      child: Padding(
+        padding: const EdgeInsets.all(20),
+        child: ConstrainedBox(
+          constraints: const BoxConstraints(maxWidth: 440),
+          child: Column(
+            mainAxisSize: MainAxisSize.min,
+            children: [
+              const Icon(Icons.lock_outline, color: Colors.orange, size: 32),
+              const SizedBox(height: 10),
+              Text(blocked.message, textAlign: TextAlign.center, style: t.titleSmall),
+              const SizedBox(height: 6),
+              Text('Link your own account in Integrations, or ask the host to relay it.',
+                  textAlign: TextAlign.center, style: t.bodySmall?.copyWith(color: Colors.grey)),
+              const SizedBox(height: 14),
+              Wrap(
+                spacing: 8,
+                children: [
+                  FilledButton(
+                      key: const ValueKey('link-jellyfin-account'),
+                      onPressed: onLinkAccount,
+                      child: const Text('Link a Jellyfin account')),
+                  TextButton(onPressed: onRetry, child: const Text('Try again')),
+                ],
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+/// Small member-list badge: plays the Jellyfin item through the host.
+class ViaHostBadge extends StatelessWidget {
+  const ViaHostBadge({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return Tooltip(
+      message: 'No Jellyfin account here: watches through the host',
+      child: Container(
+        key: const ValueKey('via-host'),
+        padding: const EdgeInsets.symmetric(horizontal: 6, vertical: 1),
+        decoration: BoxDecoration(
+          color: Colors.white10,
+          borderRadius: BorderRadius.circular(999),
+          border: Border.all(color: Colors.white24),
+        ),
+        child: const Text('via host', style: TextStyle(fontSize: 10, color: Colors.white70)),
+      ),
+    );
+  }
+}
+
+/// A track pick from [TracksControlButton]: audio id, subtitle id, or off.
+typedef TrackPick = ({int? aid, int? sid, bool subtitlesOff});
+
+/// Audio / subtitle menu for the controls bar. The choice is remembered
+/// for the next Jellyfin item (per viewer).
+class TracksControlButton extends StatelessWidget {
+  final FocusNode? focusNode;
+  final List<MpvTrack> Function() tracks;
+  final Future<({int? aid, int? sid})> Function() current;
+  final void Function(TrackPick pick) onPick;
+  final ValueChanged<bool>? onMenuOpen;
+  const TracksControlButton({
+    super.key,
+    this.focusNode,
+    required this.tracks,
+    required this.current,
+    required this.onPick,
+    this.onMenuOpen,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return Tooltip(
+      message: 'Audio and subtitles',
+      child: IconButton(
+        key: const ValueKey('tracks-button'),
+        focusNode: focusNode,
+        color: Colors.white,
+        iconSize: 20,
+        visualDensity: VisualDensity.compact,
+        icon: const Icon(Icons.subtitles_outlined),
+        onPressed: () => _open(context),
+      ),
+    );
+  }
+
+  Future<void> _open(BuildContext context) async {
+    final list = tracks();
+    final button = context.findRenderObject() as RenderBox;
+    final overlay = Navigator.of(context).overlay!.context.findRenderObject() as RenderBox;
+    final position = RelativeRect.fromRect(
+      Rect.fromPoints(
+        button.localToGlobal(Offset.zero, ancestor: overlay),
+        button.localToGlobal(button.size.bottomRight(Offset.zero), ancestor: overlay),
+      ),
+      Offset.zero & overlay.size,
+    );
+    final navigator = Navigator.of(context);
+    final now = await current();
+    if (!navigator.mounted) return;
+    final audio = list.where((t) => t.type == JellyfinStreamType.audio).toList();
+    final subs = list.where((t) => t.type == JellyfinStreamType.subtitle).toList();
+    PopupMenuItem<TrackPick> header(String text) => PopupMenuItem(
+        enabled: false,
+        height: 28,
+        child: Text(text, style: const TextStyle(fontSize: 12, color: Colors.grey)));
+    onMenuOpen?.call(true);
+    final pick = await showMenu<TrackPick>(
+      context: navigator.context,
+      position: position,
+      popUpAnimationStyle: AnimationStyle.noAnimation,
+      constraints: const BoxConstraints(minWidth: 280, maxWidth: 420),
+      items: [
+        header('Audio'),
+        if (audio.isEmpty)
+          const PopupMenuItem(enabled: false, height: 32, child: Text('None')),
+        for (final t in audio)
+          CheckedPopupMenuItem(
+            value: (aid: t.id, sid: null, subtitlesOff: false),
+            checked: now.aid == t.id,
+            height: 36,
+            child: Text(t.label, maxLines: 1, overflow: TextOverflow.ellipsis),
+          ),
+        const PopupMenuDivider(),
+        header('Subtitles'),
+        CheckedPopupMenuItem(
+          value: (aid: null, sid: null, subtitlesOff: true),
+          checked: now.sid == null,
+          height: 36,
+          child: const Text('Off'),
+        ),
+        for (final t in subs)
+          CheckedPopupMenuItem(
+            value: (aid: null, sid: t.id, subtitlesOff: false),
+            checked: now.sid == t.id,
+            height: 36,
+            child: Text(t.label, maxLines: 1, overflow: TextOverflow.ellipsis),
+          ),
+      ],
+    );
+    onMenuOpen?.call(false);
+    if (pick != null) onPick(pick);
+  }
+}

apps/desktop/lib/src/screens/session/swap_panel.dart

@@ -0,0 +1,136 @@
+import 'package:flutter/material.dart';
+
+import '../../jellyfin/accounts.dart';
+import '../../jellyfin/browse_scope.dart' show BrowseStart;
+import '../home/media_picker.dart';
+
+/// "Change video" in a session: the same [MediaPicker] as Home's Host tab
+/// (Jellyfin browser, Link, File) and a button that puts the pick up for
+/// everyone. File is offered to the host only (the file streams from the
+/// host's disk). [onSwap] returns an error text, or null when sent.
+class SwapPanel extends StatefulWidget {
+  final MediaPickerController controller;
+  final JellyfinAccounts accounts;
+  final bool isHost;
+  final BrowseStart? jellyfinStart;
+  final Future<String?> Function(PickedMedia media) onSwap;
+  final VoidCallback onClose;
+  final VoidCallback? onOpenIntegrations;
+  const SwapPanel({
+    super.key,
+    required this.controller,
+    required this.accounts,
+    required this.isHost,
+    required this.onSwap,
+    required this.onClose,
+    this.jellyfinStart,
+    this.onOpenIntegrations,
+  });
+
+  @override
+  State<SwapPanel> createState() => _SwapPanelState();
+}
+
+class _SwapPanelState extends State<SwapPanel> {
+  bool _busy = false;
+  String? _error;
+
+  @override
+  void initState() {
+    super.initState();
+    final c = widget.controller;
+    if (!widget.isHost && c.source == MediaKind.file) c.source = MediaKind.link;
+  }
+
+  Future<void> _swap() async {
+    final media = widget.controller.selection;
+    if (media == null || _busy) return;
+    setState(() {
+      _busy = true;
+      _error = null;
+    });
+    String? error;
+    try {
+      error = await widget.onSwap(media);
+    } catch (e) {
+      error = '$e';
+    }
+    if (!mounted) return;
+    setState(() {
+      _busy = false;
+      _error = error;
+    });
+    if (error == null) widget.onClose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final t = Theme.of(context).textTheme;
+    return Material(
+      key: const ValueKey('swap-panel'),
+      elevation: 12,
+      borderRadius: BorderRadius.circular(16),
+      clipBehavior: Clip.antiAlias,
+      child: Padding(
+        padding: const EdgeInsets.fromLTRB(20, 12, 12, 16),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.stretch,
+          children: [
+            Row(
+              children: [
+                Expanded(child: Text('Change video', style: t.titleLarge)),
+                IconButton(
+                    tooltip: 'Close (Esc)', icon: const Icon(Icons.close), onPressed: widget.onClose),
+              ],
+            ),
+            const SizedBox(height: 8),
+            Expanded(
+              child: Padding(
+                padding: const EdgeInsets.only(right: 8),
+                child: MediaPicker(
+                  controller: widget.controller,
+                  jellyfin: widget.accounts,
+                  enabled: !_busy,
+                  allowFile: widget.isHost,
+                  jellyfinStart: widget.jellyfinStart,
+                  onOpenIntegrations: widget.onOpenIntegrations,
+                  onSubmit: _swap,
+                ),
+              ),
+            ),
+            const SizedBox(height: 12),
+            ListenableBuilder(
+              listenable: widget.controller,
+              builder: (context, _) {
+                final sel = widget.controller.selection;
+                return Row(
+                  children: [
+                    Expanded(
+                      child: Text(
+                        _error ?? (sel == null ? 'Pick something to watch' : 'Put up: ${sel.label}'),
+                        maxLines: 2,
+                        overflow: TextOverflow.ellipsis,
+                        style: t.bodyMedium?.copyWith(
+                            color: _error != null ? Theme.of(context).colorScheme.error : null),
+                      ),
+                    ),
+                    const SizedBox(width: 12),
+                    FilledButton.icon(
+                      key: const ValueKey('swap-go'),
+                      onPressed: sel == null || _busy ? null : _swap,
+                      icon: _busy
+                          ? const SizedBox(
+                              width: 16, height: 16, child: CircularProgressIndicator(strokeWidth: 2))
+                          : const Icon(Icons.swap_horiz),
+                      label: const Text('Put it up for everyone'),
+                    ),
+                  ],
+                );
+              },
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+}

apps/desktop/lib/src/screens/session_screen.dart

@@ -4,6 +4,8 @@ import 'package:media_kit_video/media_kit_video.dart';
 import 'package:signals/signals_flutter.dart';
 import 'package:sync_relay_core/core.dart';
 
+import '../jellyfin/browse_scope.dart' show BrowseStart;
+import '../jellyfin/session_media.dart';
 import '../session/health.dart';
 import '../session/session_coordinator.dart';
 import '../shaders/shader_menu.dart';
@@ -17,6 +19,10 @@ import '../widgets/shown_frame_probe.dart';
 import '../widgets/text_focus.dart';
 import '../widgets/window_buttons.dart';
 import '../widgets/window_drag_layer.dart';
+import 'home/integrations_page.dart';
+import 'home/media_picker.dart';
+import 'session/jellyfin_widgets.dart';
+import 'session/swap_panel.dart';
 
 class SessionScreen extends StatefulWidget {
   const SessionScreen({super.key});
@@ -38,7 +44,10 @@ class _SessionScreenState extends State<SessionScreen> {
   DateTime? _lastKeyAt;
   final _chat = TextEditingController();
   final _chatFocus = FocusNode();
-  final _swapLink = TextEditingController();
+  // "Change video": the shared media picker over the video.
+  final _swapOpen = signal(false);
+  MediaPickerController? _swapPicker;
+  bool _integrationsOpen = false;
   late final void Function() _stopKickWatch;
   late final void Function() _stopSheetWatch;
   late final void Function() _stopPlayerWatch;
@@ -54,6 +63,7 @@ class _SessionScreenState extends State<SessionScreen> {
     super.initState();
     final session = SessionState.instance;
     _noFocus = FocusNode(skipTraversal: true, canRequestFocus: false);
+    session.coordinator.jellyfin.ensureLoaded();
     session.coordinator.playback.shownFrame = _frameProbe.sample;
     HardwareKeyboard.instance.addHandler(_globalKey);
     _stopKickWatch = effect(() {
@@ -144,14 +154,70 @@ class _SessionScreenState extends State<SessionScreen> {
     _stopShaderWatch();
     _chat.dispose();
     _chatFocus.dispose();
-    _swapLink.dispose();
+    _swapPicker?.dispose();
     _noFocus.dispose();
     super.dispose();
   }
 
+  /// Opens the swap panel: the browser starts on the series of the
+  /// episode playing (season selected, episode highlighted), else where it
+  /// was last.
+  void _openSwap() {
+    final coord = SessionState.instance.coordinator;
+    coord.markInput();
+    final ref = coord.currentRef.peek();
+    final accounts = coord.jellyfin;
+    final pick = ref == null ? null : pickForRef(accounts, ref);
+    final plan = coord.jellyfinPlan.peek();
+    _swapPicker?.dispose();
+    _swapPicker = MediaPickerController(
+      jellyfin: pick,
+      source: pick != null || (accounts.loaded && !accounts.isEmpty)
+          ? MediaKind.jellyfin
+          : MediaKind.link,
+    );
+    _swapStart = ref != null && plan is OwnPlay && plan.item != null
+        ? BrowseStart.seriesOf(ref.serverId, plan.item!)
+        : null;
+    _sheetOpen.value = false;
+    _swapOpen.value = true;
+  }
+
+  BrowseStart? _swapStart;
+
+  void _closeSwap() {
+    _swapOpen.value = false;
+    FocusManager.instance.primaryFocus?.unfocus();
+  }
+
+  /// Integrations over the session (link an account for a blocked item).
+  Future<void> _openIntegrations() async {
+    if (_integrationsOpen) return;
+    _integrationsOpen = true;
+    try {
+      await Navigator.of(context, rootNavigator: true).push(MaterialPageRoute<void>(
+        builder: (_) => Scaffold(
+          appBar: AppBar(title: const Text('Integrations')),
+          body: IntegrationsPage(jellyfin: SessionState.instance.coordinator.jellyfin),
+        ),
+      ));
+    } finally {
+      _integrationsOpen = false;
+    }
+  }
+
   bool _globalKey(KeyEvent event) {
     if (event is! KeyDownEvent) return false;
     if (SessionState.instance.route.peek() != AppRoute.session) return false;
+    if (_integrationsOpen) return false;
+    if (_swapOpen.peek()) {
+      // The picker owns the keyboard; Esc outside a field closes it.
+      if (event.logicalKey == LogicalKeyboardKey.escape && !textInputFocused()) {
+        _closeSwap();
+        return true;
+      }
+      return false;
+    }
     if (textInputFocused()) return false;
     final now = DateTime.now().toUtc();
     if (_lastKeyAt != null && now.difference(_lastKeyAt!).inMilliseconds < 350) {
@@ -177,6 +243,20 @@ class _SessionScreenState extends State<SessionScreen> {
       coord.toggleReady();
       return true;
     }
+    // mpv's playlist keys (< >) and Shift+P / Shift+N: Jellyfin episodes.
+    final shift = HardwareKeyboard.instance.isShiftPressed;
+    if (event.character == '>' || (shift && event.logicalKey == LogicalKeyboardKey.keyN)) {
+      if (coord.nextEpisode.peek() == null) return false;
+      _lastKeyAt = now;
+      coord.playNextEpisode();
+      return true;
+    }
+    if (event.character == '<' || (shift && event.logicalKey == LogicalKeyboardKey.keyP)) {
+      if (coord.previousEpisode.peek() == null) return false;
+      _lastKeyAt = now;
+      coord.playPreviousEpisode();
+      return true;
+    }
     if (event.logicalKey == LogicalKeyboardKey.tab) {
       _lastKeyAt = now;
       _sheetOpen.value = !_sheetOpen.peek();
@@ -254,12 +334,35 @@ class _SessionScreenState extends State<SessionScreen> {
         ),
       ],
       bottomButtonBar: [
+        SignalBuilder(
+          builder: (context) => EpisodeSkipButton(
+            focusNode: _noFocus,
+            episode: coord.previousEpisode.value,
+            next: false,
+            onPressed: coord.playPreviousEpisode,
+          ),
+        ),
+        SignalBuilder(
+          builder: (context) => EpisodeSkipButton(
+            focusNode: _noFocus,
+            episode: coord.nextEpisode.value,
+            next: true,
+            onPressed: coord.playNextEpisode,
+          ),
+        ),
         const MaterialDesktopVolumeButton(),
         _ReadyControlButton(focusNode: _noFocus),
         _MarkAllReadyControlButton(focusNode: _noFocus),
         _ReloadVideoControlButton(focusNode: _noFocus, onPressed: _reloadVideo),
         const MaterialDesktopPositionIndicator(),
         const Spacer(),
+        TracksControlButton(
+          focusNode: _noFocus,
+          tracks: () => coord.playback.tracks,
+          current: coord.playback.currentTrackIds,
+          onPick: (p) => coord.selectTrack(aid: p.aid, sid: p.sid, subtitlesOff: p.subtitlesOff),
+          onMenuOpen: (open) => _shaderMenuOpen = open,
+        ),
         ShaderControlButton(
           focusNode: _noFocus,
           renderMode: coord.playback.renderMode,
@@ -320,8 +423,10 @@ class _SessionScreenState extends State<SessionScreen> {
         MaterialDesktopVideoControls(state),
         _healthOverlay(),
         _waitingOverlay(),
+        _jellyfinOverlay(),
         _toastsOverlay(),
         _sheetOverlay(),
+        _swapOverlay(),
         _leaveOverlay(),
         Positioned.fill(
           child: SignalBuilder(
@@ -329,7 +434,7 @@ class _SessionScreenState extends State<SessionScreen> {
               final sheetOpen = _sheetOpen.value;
               final confirm = _confirmLeave.value;
               return WindowDragLayer(
-                enabled: !confirm,
+                enabled: !confirm && !_swapOpen.value,
                 exclusions: [
                   (s) => Rect.fromLTWH(0, s.height - 120, s.width, 120),
                   if (sheetOpen) (s) => Rect.fromLTWH(s.width - 380, 0, 380, s.height),
@@ -469,6 +574,94 @@ class _SessionScreenState extends State<SessionScreen> {
     );
   }
 
+  /// Jellyfin: the blocked card, the end-of-episode card (countdown) and
+  /// the "Next episode" pill. Outside the auto-hiding controls, so they
+  /// also show in fullscreen.
+  Widget _jellyfinOverlay() {
+    final coord = SessionState.instance.coordinator;
+    return Positioned.fill(
+      child: SignalBuilder(
+        builder: (context) {
+          final blocked = coord.jellyfinBlocked.value;
+          final next = coord.nextEpisode.value;
+          final countdown = coord.autoAdvance.value;
+          final finished = coord.serverState.value?.transport == 'finished';
+          final pill = coord.nextPromptVisible.value;
+          return Stack(
+            children: [
+              if (blocked != null)
+                Center(
+                  child: JellyfinBlockedCard(
+                    blocked: blocked,
+                    onLinkAccount: _openIntegrations,
+                    onRetry: coord.retryJellyfin,
+                  ),
+                ),
+              if (next != null && (finished || countdown != null))
+                Positioned(
+                  right: 24,
+                  bottom: 110,
+                  child: EndOfEpisodeCard(
+                    next: next,
+                    countdown: countdown,
+                    onPlayNow: coord.playNextEpisode,
+                    onCancel: coord.cancelAutoAdvance,
+                  ),
+                )
+              else if (next != null && pill)
+                Positioned(
+                  right: 24,
+                  bottom: 96,
+                  child: NextEpisodePill(episode: next, onPressed: coord.playNextEpisode),
+                ),
+            ],
+          );
+        },
+      ),
+    );
+  }
+
+  Widget _swapOverlay() {
+    final coord = SessionState.instance.coordinator;
+    return SignalBuilder(
+      builder: (context) {
+        final picker = _swapPicker;
+        if (!_swapOpen.value || picker == null) return const SizedBox.shrink();
+        return Positioned.fill(
+          child: Stack(
+            children: [
+              Positioned.fill(
+                child: GestureDetector(
+                  onTap: _closeSwap,
+                  child: Container(color: Colors.black54),
+                ),
+              ),
+              Positioned.fill(
+                child: Padding(
+                  padding: const EdgeInsets.fromLTRB(32, 48, 32, 32),
+                  child: Center(
+                    child: ConstrainedBox(
+                      constraints: const BoxConstraints(maxWidth: 1400),
+                      child: SwapPanel(
+                        controller: picker,
+                        accounts: coord.jellyfin,
+                        isHost: coord.hostFile != null,
+                        jellyfinStart: _swapStart,
+                        onSwap: coord.swapPicked,
+                        onClose: _closeSwap,
+                        onOpenIntegrations: _openIntegrations,
+                      ),
+                    ),
+                  ),
+                ),
+              ),
+            ],
+          ),
+        );
+      },
+    );
+  }
+
   Widget _toastsOverlay() {
     final coord = SessionState.instance.coordinator;
     return Positioned(
@@ -526,7 +719,7 @@ class _SessionScreenState extends State<SessionScreen> {
                       child: _SheetPanel(
                         chat: _chat,
                         chatFocus: _chatFocus,
-                        swapLink: _swapLink,
+                        onChangeVideo: _openSwap,
                         onClose: () => _sheetOpen.value = false,
                         onLeave: () {
                           _sheetOpen.value = false;
@@ -697,10 +890,10 @@ class _ToastCardState extends State<_ToastCard> {
 class _SheetPanel extends StatelessWidget {
   final TextEditingController chat;
   final FocusNode chatFocus;
-  final TextEditingController swapLink;
+  final VoidCallback onChangeVideo;
   final VoidCallback onClose;
   final VoidCallback onLeave;
-  const _SheetPanel({required this.chat, required this.chatFocus, required this.swapLink, required this.onClose, required this.onLeave});
+  const _SheetPanel({required this.chat, required this.chatFocus, required this.onChangeVideo, required this.onClose, required this.onLeave});
 
   @override
   Widget build(BuildContext context) {
@@ -750,7 +943,12 @@ class _SheetPanel extends StatelessWidget {
                 const Divider(height: 20),
                 Text('Users (${members.length})', style: sectionStyle),
                 const SizedBox(height: 2),
-                for (final m in members) _MemberRow(member: m, isSelf: m.id == coord.sync.memberId),
+                for (final m in members)
+                  _MemberRow(
+                    member: m,
+                    isSelf: m.id == coord.sync.memberId,
+                    viaHost: viaHostOf(m, coord.currentRef.value),
+                  ),
                 const Divider(height: 20),
                 Text('Activity', style: sectionStyle),
                 const SizedBox(height: 6),
@@ -790,34 +988,14 @@ class _SheetPanel extends StatelessWidget {
                   ],
                 ),
                 const SizedBox(height: 12),
-                Text('Share a link', style: sectionStyle),
-                const SizedBox(height: 8),
-                Row(
-                  crossAxisAlignment: CrossAxisAlignment.start,
-                  children: [
-                    Expanded(
-                      child: TextField(
-                        controller: swapLink,
-                        decoration: const InputDecoration(labelText: 'Swap to link URL', border: OutlineInputBorder(), isDense: true),
-                      ),
-                    ),
-                    const SizedBox(width: 8),
-                    ValueListenableBuilder<TextEditingValue>(
-                      valueListenable: swapLink,
-                      builder: (context, value, _) {
-                        final link = value.text.trim();
-                        return IconButton(
+                SizedBox(
+                  width: double.infinity,
+                  child: OutlinedButton.icon(
+                    key: const ValueKey('change-video'),
                     icon: const Icon(Icons.swap_horiz),
-                          onPressed: link.isEmpty
-                              ? null
-                              : () {
-                                  coord.swapLink(link);
-                                  swapLink.clear();
-                                },
-                        );
-                      },
+                    label: const Text('Change video'),
+                    onPressed: onChangeVideo,
                   ),
-                  ],
                 ),
                 const Divider(height: 20),
                 SizedBox(
@@ -880,10 +1058,14 @@ class _StatusChip extends StatelessWidget {
   }
 }
 
+/// The member plays the current Jellyfin item through the host's relay.
+bool viaHostOf(MemberView m, JellyfinRef? ref) => ref != null && m.jf[ref.serverId] == false;
+
 class _MemberRow extends StatelessWidget {
   final MemberView member;
   final bool isSelf;
-  const _MemberRow({required this.member, required this.isSelf});
+  final bool viaHost;
+  const _MemberRow({required this.member, required this.isSelf, this.viaHost = false});
 
   @override
   Widget build(BuildContext context) {
@@ -920,6 +1102,7 @@ class _MemberRow extends StatelessWidget {
                       status.$1,
                       style: theme.textTheme.bodySmall?.copyWith(color: theme.textTheme.bodySmall?.color?.withValues(alpha: 0.75)),
                     ),
+                    if (viaHost) ...[const SizedBox(width: 6), const ViaHostBadge()],
                   ],
                 ),
               ],

apps/desktop/lib/src/session/session_coordinator.dart

@@ -4,8 +4,14 @@ import 'package:flutter/widgets.dart';
 import 'package:signals/signals_flutter.dart';
 import 'package:sync_relay_core/core.dart';
 
+import '../jellyfin/accounts.dart';
+import '../jellyfin/progress.dart';
+import '../jellyfin/session_media.dart';
+import '../jellyfin/track_prefs.dart';
 import '../playback/playback_controller.dart';
+import '../screens/home/picked_media.dart';
 import '../sfx/sfx.dart';
+import '../state/settings.dart';
 import '../sync/state_diff.dart';
 import '../sync/sync_client.dart';
 import '../sync/user_seek.dart';
@@ -21,19 +27,7 @@ class ConnectCancelled implements Exception {
 
 /// Display name for a link: last path segment, decoded, never the query
 /// (Jellyfin-style links carry api_key there and names are broadcast).
-String linkDisplayName(String url) {
-  final uri = Uri.tryParse(url.trim());
-  if (uri == null) return 'link';
-  final segs = uri.pathSegments.where((s) => s.isNotEmpty).toList();
-  if (segs.isNotEmpty) {
-    try {
-      return Uri.decodeComponent(segs.last);
-    } catch (_) {
-      return segs.last;
-    }
-  }
-  return uri.host.isNotEmpty ? uri.host : 'link';
-}
+String linkDisplayName(String url) => linkName(url);
 
 class ConnectParams {
   final String host;
@@ -45,6 +39,9 @@ class ConnectParams {
   final String linkUrl;
   /// Sent in hello by the hosting app's own client (see AppConfig.hostKey).
   final String hostKey;
+  /// Put up with a `swap` right after joining (a Jellyfin ref or a link);
+  /// wins over [linkUrl].
+  final HelloMedia? media;
   const ConnectParams({
     required this.host,
     required this.port,
@@ -54,9 +51,37 @@ class ConnectParams {
     this.mediaPath = '',
     this.linkUrl = '',
     this.hostKey = '',
+    this.media,
   });
+
+  ConnectParams withMedia(HelloMedia? media) => ConnectParams(
+        host: host,
+        port: port,
+        secret: secret,
+        name: name,
+        avatar: avatar,
+        mediaPath: mediaPath,
+        linkUrl: media == null ? linkUrl : '',
+        hostKey: hostKey,
+        media: media,
+      );
 }
 
+/// The end-of-episode countdown (auto-advance). Every client with the
+/// setting on shows it; only [swapper] puts the next episode up.
+class AutoAdvance {
+  final int mediaId;
+  final int secondsLeft;
+  final EpisodeLink next;
+  /// This client performs the swap (see [autoAdvanceSwapper]).
+  final bool swapper;
+  const AutoAdvance(
+      {required this.mediaId, required this.secondsLeft, required this.next, required this.swapper});
+}
+
+/// Seconds of the end-of-episode countdown.
+const autoAdvanceSecs = 10;
+
 class ToastItem {
   final int id;
   final String text;
@@ -76,6 +101,13 @@ String? stateMediaUrl(StateBroadcast state) {
 
 class SessionCoordinator {
   final SfxService sfx;
+  /// Linked Jellyfin servers: how this viewer plays Jellyfin refs.
+  final JellyfinAccounts jellyfin;
+  /// Audio/subtitle carry-over between Jellyfin items.
+  final TrackPrefs trackPrefs;
+  /// Set by the hosting app: makes a local file the hosted one (File swap);
+  /// null when this app is not the host.
+  Future<({String name, int size})?> Function(String path)? hostFile;
   final SyncClient sync = SyncClient();
   final PlaybackController playback = PlaybackController();
   final StateDiff diff = StateDiff();
@@ -89,6 +121,21 @@ class SessionCoordinator {
   final kickReason = signal<String?>(null);
   final starving = signal<String?>(null);
 
+  /// The current media's Jellyfin ref (null for links and files).
+  final currentRef = signal<JellyfinRef?>(null);
+  /// How this viewer plays [currentRef]; null while resolving.
+  final jellyfinPlan = signal<JellyfinPlan?>(null);
+  /// Set when this viewer cannot play the Jellyfin media: no account and
+  /// no relay. The session shows it with a way to link an account.
+  final jellyfinBlocked = signal<BlockedPlay?>(null);
+  /// Neighbouring episodes this viewer can put up (own account only).
+  final previousEpisode = signal<EpisodeLink?>(null);
+  final nextEpisode = signal<EpisodeLink?>(null);
+  /// The floating "Next episode" pill near the end of an episode.
+  final nextPromptVisible = signal(false);
+  /// End-of-episode countdown; null when none runs here.
+  final autoAdvance = signal<AutoAdvance?>(null);
+
   late final Computed<MemberView?> selfMember = computed(() {
     final r = serverState.value;
     if (r == null || sync.memberId.isEmpty) return null;
@@ -139,8 +186,25 @@ class SessionCoordinator {
   int _toastId = 0;
   ConnectParams? _params;
   bool _everConnected = false;
+  Map<String, String>? _openHeaders;
 
-  SessionCoordinator({this.sfx = const NoopSfxService()});
+  // Jellyfin: the resolved ref, the mediaId it belongs to, a generation
+  // that stale resolutions check, and the progress reporter.
+  JellyfinRef? _jfRef;
+  int _jfMediaId = -1;
+  int _jfGen = 0;
+  JellyfinProgressReporter? _reporter;
+  PlayerSnapshot? _lastSnap;
+  bool _jfToastShown = false;
+  Timer? _advanceTimer;
+  int _advanceDoneFor = -1;
+  String _blockedKey = '';
+  bool _jellyfinListening = false;
+
+  SessionCoordinator(
+      {this.sfx = const NoopSfxService(), JellyfinAccounts? jellyfin, TrackPrefs? trackPrefs})
+      : jellyfin = jellyfin ?? JellyfinAccounts.instance,
+        trackPrefs = trackPrefs ?? TrackPrefs();
 
   /// Player lifetime = one session: created here on connect, disposed by
   /// [leave]. Never reused across sessions (a GPU-side video freeze sticks
@@ -175,9 +239,10 @@ class SessionCoordinator {
     try {
       await playback.recreate();
       final url = _openUrl;
+      final headers = _openHeaders;
       _openUrl = null;
       _clearPendingSeek();
-      if (url != null) await _openMedia(url);
+      if (url != null) await _openMedia(url, headers: headers);
     } catch (e, st) {
       debugPrint('video reload failed: $e\n$st');
       health.value =
@@ -221,6 +286,12 @@ class SessionCoordinator {
     _seekGate.reset();
     _clearPendingSeek();
     _lastEventId = -1;
+    _resetJellyfin();
+    _jfToastShown = false;
+    if (!_jellyfinListening) {
+      _jellyfinListening = true;
+      jellyfin.addListener(_onAccountsChanged);
+    }
     markInput();
     _subscribe();
     feedLog.value = [];
@@ -252,13 +323,10 @@ class SessionCoordinator {
         health.value = const HealthStatus(
             HealthSeverity.info, 'connected — waiting for host media…');
       }
-      if (params.linkUrl.isNotEmpty) {
-        sync.sendSwap(HelloMedia(
-            name: linkDisplayName(params.linkUrl),
-            size: 0,
-            duration: 0,
-            url: params.linkUrl));
-      }
+      final media = params.media ??
+          (params.linkUrl.isEmpty ? null : await mediaForLink(jellyfin, params.linkUrl));
+      if (epoch != _epoch) throw const ConnectCancelled();
+      if (media != null) sync.sendSwap(media);
       _startTicker();
     } catch (e) {
       if (epoch != _epoch) throw const ConnectCancelled();
@@ -286,19 +354,23 @@ class SessionCoordinator {
     });
   }
 
-  Future<void> _openMedia(String url) async {
-    if (url == _openUrl) return;
+  /// Opens [url] (with [headers] on every request); false on failure.
+  Future<bool> _openMedia(String url, {Map<String, String>? headers}) async {
+    if (url == _openUrl) return true;
     _openUrl = url;
+    _openHeaders = headers;
     diff.reset();
     _opening = true;
     try {
-      await playback.openUrl(url);
+      await playback.openUrl(url, headers: headers);
       health.value =
           const HealthStatus(HealthSeverity.ok, 'connected');
+      return true;
     } catch (e) {
       debugPrint('open media failed: $e');
       health.value =
           HealthStatus(HealthSeverity.error, 'cannot open media: $e');
+      return false;
     } finally {
       _opening = false;
     }
@@ -308,15 +380,57 @@ class SessionCoordinator {
     return 'http://$_wsHost:$_wsPort/m/default/${sync.token}/${Uri.encodeComponent(name)}';
   }
 
-  Future<void> _onState(StateBroadcast r) async {
+  StateBroadcast? _queuedState;
+  bool _applying = false;
+
+  /// States are applied one at a time, newest first: two applies running
+  /// interleaved could land an older pause after a newer play (seen with
+  /// three viewers readying at once). A state that arrives meanwhile
+  /// replaces any still waiting.
+  void _onState(StateBroadcast r) {
     _lastStateAt = DateTime.now().toUtc();
     serverState.value = r;
+    _queuedState = r;
+    if (_applying) return;
+    _applying = true;
+    () async {
+      try {
+        while (_queuedState != null) {
+          final next = _queuedState!;
+          _queuedState = null;
+          try {
+            await _applyState(next);
+          } catch (e, st) {
+            debugPrint('apply state failed: $e\n$st');
+          }
+        }
+      } finally {
+        _applying = false;
+      }
+    }();
+  }
+
+  Future<void> _applyState(StateBroadcast r) async {
     _trackSelfReady(r);
     _seekGate.observe(r, sync.memberId);
     final newEvent = r.eventId != _lastEventId;
     _lastEventId = r.eventId;
     if (r.mediaId != _mediaId) {
       _mediaId = r.mediaId;
+      final ref = refOfStateMedia(r.media);
+      // Back after a dropped connection on the same item played with our
+      // own account: nothing to resolve or reopen.
+      final same = ref != null &&
+          r.mediaId == _jfMediaId &&
+          sameJellyfinItem(ref, _jfRef) &&
+          jellyfinPlan.peek() is OwnPlay;
+      if (!same) {
+        _seekGate.reset();
+        _clearPendingSeek();
+        _leaveJellyfinItem();
+        if (ref != null) {
+          await _playJellyfin(ref, r);
+        } else {
           var url = stateMediaUrl(r);
           if ((url == null || url.isEmpty) && sync.token.isNotEmpty) {
             final name = (r.media?['name'] as String?) ?? '';
@@ -327,9 +441,12 @@ class SessionCoordinator {
           } else {
             _openUrl = null;
           }
+        }
+      }
       _seekGate.reset();
       _clearPendingSeek();
     }
+    _jellyfinTransport(r);
     if (!_playerReady || _openUrl == null) {
       _wasPlayAllowed = false;
       _updateStarving(r, 0);
@@ -475,6 +592,7 @@ class SessionCoordinator {
     // Stop, not pause: a paused player keeps filling its cache from the
     // host's media URL.
     _openUrl = null;
+    await _stopJellyfin();
     try {
       await playback.stop();
     } catch (_) {}
@@ -504,8 +622,10 @@ class SessionCoordinator {
         eventId: r.eventId,
         duration: known ? playback.durationSecs : 0,
         mediaId: known ? r.mediaId : 0,
+        jf: _jfAccessFor(r),
       );
       _checkSeekLanded(r);
+      unawaited(_tickJellyfin(r));
     }
     if (!_manualClose &&
         kickReason.peek() == null &&
@@ -661,10 +781,362 @@ class SessionCoordinator {
     sync.sendKick(memberId, reason: reason);
   }
 
+  /// A pasted link: a recognised Jellyfin item link goes up as a ref
+  /// (see [mediaForLink]), anything else as the link.
   Future<void> swapLink(String url) async {
     markInput();
-    sync.sendSwap(HelloMedia(
-        name: linkDisplayName(url), size: 0, duration: 0, url: url));
+    sync.sendSwap(await mediaForLink(jellyfin, url));
+  }
+
+  /// A Jellyfin pick (browser, next / previous episode) goes up as a ref.
+  void swapJellyfin(JellyfinMedia media) {
+    markInput();
+    sync.sendSwap(mediaForPick(media));
+  }
+
+  /// The host's File swap: the server takes the file, then the swap puts
+  /// it up. Returns an error text, or null when sent.
+  Future<String?> swapFile(String path) async {
+    markInput();
+    final host = hostFile;
+    if (host == null) return 'only the host can share a file';
+    final file = await host(path);
+    if (file == null) return 'file not found — check the path';
+    sync.sendSwap(HelloMedia(name: file.name, size: file.size, duration: 0));
+    return null;
+  }
+
+  /// Any picker selection.
+  Future<String?> swapPicked(PickedMedia media) async {
+    switch (media) {
+      case LinkMedia(:final url):
+        await swapLink(url);
+      case JellyfinMedia():
+        swapJellyfin(media);
+      case FileMedia(:final path):
+        return swapFile(path);
+    }
+    return null;
+  }
+
+  void playNextEpisode() {
+    final n = nextEpisode.peek();
+    if (n != null) swapJellyfin(n.pick);
+  }
+
+  void playPreviousEpisode() {
+    final p = previousEpisode.peek();
+    if (p != null) swapJellyfin(p.pick);
+  }
+
+  /// Hides the countdown here; this client will not auto-advance this
+  /// item (if it is the swapper, nobody does).
+  void cancelAutoAdvance() {
+    _advanceTimer?.cancel();
+    _advanceTimer = null;
+    final a = autoAdvance.peek();
+    if (a != null) _advanceDoneFor = a.mediaId;
+    autoAdvance.value = null;
+  }
+
+  // ------------------------------------------------------------- jellyfin
+
+  void _pushToast(String text) {
+    _toastId++;
+    toasts.value = [
+      ...toasts.peek(),
+      ToastItem(id: _toastId, text: text, at: DateTime.now().toUtc())
+    ];
+  }
+
+  void _resetJellyfin() {
+    _jfGen++;
+    _jfRef = null;
+    _jfMediaId = -1;
+    _reporter = null;
+    _lastSnap = null;
+    _openHeaders = null;
+    _blockedKey = '';
+    currentRef.value = null;
+    jellyfinPlan.value = null;
+    jellyfinBlocked.value = null;
+    previousEpisode.value = null;
+    nextEpisode.value = null;
+    nextPromptVisible.value = false;
+    _advanceTimer?.cancel();
+    _advanceTimer = null;
+    _advanceDoneFor = -1;
+    autoAdvance.value = null;
+  }
+
+  /// The current item is being replaced: Stopped goes out (not awaited:
+  /// reports are sent in order), per-item state clears.
+  void _leaveJellyfinItem() {
+    final reporter = _reporter;
+    final snap = _snapNow();
+    _resetJellyfin();
+    if (reporter != null && snap != null) unawaited(reporter.stop(snap));
+  }
+
+  /// Leave / kick / window close: Stopped, bounded so leaving never hangs.
+  Future<void> _stopJellyfin() async {
+    final reporter = _reporter;
+    final snap = _snapNow();
+    _resetJellyfin();
+    if (reporter == null || snap == null) return;
+    try {
+      await reporter.stop(snap).timeout(const Duration(milliseconds: 1500));
+    } catch (_) {}
+  }
+
+  /// The last sampled tracks with the position as of now.
+  PlayerSnapshot? _snapNow() {
+    if (!_playerReady) return _lastSnap;
+    final last = _lastSnap;
+    return PlayerSnapshot(
+      position: playback.positionSecs,
+      paused: !playback.player.state.playing,
+      aid: last?.aid,
+      sid: last?.sid,
+    );
+  }
+
+  Future<PlayerSnapshot?> _snapshot() async {
+    if (!_playerReady) return null;
+    final ids = await playback.currentTrackIds();
+    if (!_playerReady) return null;
+    return _lastSnap = PlayerSnapshot(
+      position: playback.positionSecs,
+      paused: !playback.player.state.playing,
+      aid: ids.aid,
+      sid: ids.sid,
+    );
+  }
+
+  String? _relayUrlFor(JellyfinRef ref) {
+    if (sync.token.isEmpty) return null;
+    final welcome = sync.relayUrl;
+    if (welcome != null &&
+        welcome.contains('/${sync.token}/') &&
+        welcome.endsWith('/${Uri.encodeComponent(ref.itemId)}')) {
+      return welcome;
+    }
+    return relayUrlFor(_wsHost, _wsPort, sync.token, ref.itemId);
+  }
+
+  Map<String, bool>? _jfAccessFor(StateBroadcast r) {
+    final ref = _jfRef;
+    final access = jellyfinPlan.peek()?.jfAccess;
+    if (ref == null || access == null || r.mediaId != _jfMediaId) return null;
+    return {ref.serverId: access};
+  }
+
+  /// Resolves [ref] for this viewer and opens it: own account (direct
+  /// play, progress reports, neighbouring episodes), the relay, or the
+  /// blocked state. Then carries the audio/subtitle choice over.
+  Future<void> _playJellyfin(JellyfinRef ref, StateBroadcast r) async {
+    final gen = ++_jfGen;
+    _jfRef = ref;
+    _jfMediaId = r.mediaId;
+    currentRef.value = ref;
+    // Until it resolves nothing is open: no syncing the previous media.
+    final prevUrl = _openUrl;
+    _openUrl = null;
+    _opening = true;
+    if (_playerReady) {
+      try {
+        await playback.player.pause();
+      } catch (_) {}
+    }
+    final JellyfinPlan plan;
+    try {
+      plan = await resolveJellyfinRef(jellyfin, ref, relay: r.relay, relayUrl: _relayUrlFor(ref));
+    } finally {
+      if (gen == _jfGen) _opening = false;
+    }
+    if (gen != _jfGen) return;
+    jellyfinPlan.value = plan;
+    switch (plan) {
+      case BlockedPlay():
+        jellyfinBlocked.value = plan;
+        _blockedKey = _accountKey(ref.serverId);
+        try {
+          await playback.stop();
+        } catch (_) {}
+        return;
+      case RelayPlay(:final url):
+        jellyfinBlocked.value = null;
+        // Same relay URL (resumed member): the player still has it.
+        if (url == prevUrl) {
+          _openUrl = url;
+          return;
+        }
+        if (!await _openMedia(url) || gen != _jfGen) return;
+      case OwnPlay(:final url, :final headers):
+        jellyfinBlocked.value = null;
+        if (!await _openMedia(url, headers: headers) || gen != _jfGen) return;
+        final reporter = JellyfinProgressReporter(
+          client: plan.client,
+          itemId: ref.itemId,
+          source: plan.source,
+          playSessionId: plan.info.playSessionId,
+          onUnauthorized: () => jellyfin.markExpired(ref.serverId),
+          onError: (e) {
+            if (_jfToastShown) return;
+            _jfToastShown = true;
+            _pushToast('Jellyfin progress not saved: ${e is JellyfinException && e.isUnauthorized ? 'sign-in expired' : 'server unreachable'}');
+          },
+        );
+        unawaited(_findEpisodes(plan, gen));
+        // Playing carries the tracks: wait (bounded) until the file is in.
+        await playback.waitForTracks();
+        if (gen != _jfGen) return;
+        final snap = await _snapshot();
+        if (gen != _jfGen || snap == null) return;
+        // Installed once started: the per-state restart (after the end)
+        // must not send the first Playing without the tracks.
+        _reporter = reporter..start(snap);
+    }
+    await _applyTrackChoice(plan, gen);
+  }
+
+  Future<void> _findEpisodes(OwnPlay plan, int gen) async {
+    final around = await findAdjacentEpisodes(plan);
+    if (gen != _jfGen) return;
+    previousEpisode.value = around.previous;
+    nextEpisode.value = around.next;
+    final r = serverState.peek();
+    if (r != null) _jellyfinTransport(r);
+  }
+
+  Future<void> _applyTrackChoice(JellyfinPlan plan, int gen) async {
+    final own = plan is OwnPlay ? plan : null;
+    final choice = await trackPrefs.load(seriesId: own?.item?.seriesId);
+    if (choice == null || gen != _jfGen || !_playerReady) return;
+    final tracks = await playback.waitForTracks();
+    if (gen != _jfGen) return;
+    final pick = chooseTracks(choice, source: own?.source, tracks: tracks);
+    await playback.selectTracks(aid: pick.aid, sid: pick.sid, subtitlesOff: pick.subtitlesOff);
+  }
+
+  /// A track picked in the player: applied, remembered for the next
+  /// Jellyfin item (per series and overall), reported.
+  Future<void> selectTrack({int? aid, int? sid, bool subtitlesOff = false}) async {
+    markInput();
+    await playback.selectTracks(aid: aid, sid: sid, subtitlesOff: subtitlesOff);
+    final ids = await playback.currentTrackIds();
+    final plan = jellyfinPlan.peek();
+    final own = plan is OwnPlay ? plan : null;
+    await trackPrefs.save(
+        TrackChoice.of(aid: ids.aid, sid: ids.sid, source: own?.source, tracks: playback.tracks),
+        seriesId: own?.item?.seriesId);
+    final snap = await _snapshot();
+    if (snap != null) _reporter?.update(snap, force: true);
+  }
+
+  Future<void> _tickJellyfin(StateBroadcast r) async {
+    final reporter = _reporter;
+    if (_jfRef == null || r.mediaId != _jfMediaId) return;
+    final snap = await _snapshot();
+    if (snap == null) return;
+    if (reporter != null && identical(reporter, _reporter) && r.transport != 'finished') {
+      reporter.update(snap);
+    }
+    final next = nextEpisode.peek();
+    final duration = playback.durationSecs;
+    var show = false;
+    if (next != null && duration > 0 && autoAdvance.peek() == null && r.transport != 'finished') {
+      final item = (jellyfinPlan.peek() as OwnPlay?)?.item;
+      final at = nextPromptStart(item, Duration(milliseconds: (duration * 1000).round()));
+      show = snap.position * 1000 >= at.inMilliseconds;
+    }
+    nextPromptVisible.value = show;
+  }
+
+  /// Per state: played to the end -> Stopped (Jellyfin marks it watched)
+  /// and the auto-advance countdown; seeked back from the end -> Playing
+  /// again.
+  void _jellyfinTransport(StateBroadcast r) {
+    final ref = _jfRef;
+    if (ref == null || r.mediaId != _jfMediaId) return;
+    final reporter = _reporter;
+    final finished = r.transport == 'finished';
+    if (reporter != null && _openUrl != null && !_opening) {
+      final snap = _snapNow();
+      if (finished && reporter.active && snap != null) {
+        unawaited(reporter.stop(PlayerSnapshot(
+            position: r.position, paused: true, aid: snap.aid, sid: snap.sid)));
+      } else if (!finished && !reporter.active && snap != null) {
+        reporter.start(snap);
+      }
+    }
+    if (!finished) {
+      if (autoAdvance.peek() != null) cancelAutoAdvance();
+      _advanceDoneFor = -1;
+      return;
+    }
+    nextPromptVisible.value = false;
+    final next = nextEpisode.peek();
+    if (next == null ||
+        !AppSettings.instance.autoAdvance.peek() ||
+        _advanceDoneFor == r.mediaId ||
+        autoAdvance.peek()?.mediaId == r.mediaId) {
+      return;
+    }
+    autoAdvance.value = AutoAdvance(
+        mediaId: r.mediaId, secondsLeft: autoAdvanceSecs, next: next, swapper: _isSwapper(r, ref));
+    _advanceTimer?.cancel();
+    _advanceTimer = Timer.periodic(const Duration(seconds: 1), (_) => _advanceTick());
+  }
+
+  bool _isSwapper(StateBroadcast r, JellyfinRef ref) =>
+      autoAdvanceSwapper(r.members, ref.serverId) == sync.memberId;
+
+  void _advanceTick() {
+    final a = autoAdvance.peek();
+    final r = serverState.peek();
+    final ref = _jfRef;
+    if (a == null || r == null || ref == null || r.mediaId != a.mediaId || r.transport != 'finished') {
+      cancelAutoAdvance();
+      return;
+    }
+    final left = a.secondsLeft - 1;
+    if (left > 0) {
+      autoAdvance.value = AutoAdvance(
+          mediaId: a.mediaId, secondsLeft: left, next: a.next, swapper: _isSwapper(r, ref));
+      return;
+    }
+    // Decided on the latest state: one swapper among the clients counting.
+    final swap = _isSwapper(r, ref);
+    cancelAutoAdvance();
+    if (swap) swapJellyfin(a.next.pick);
+  }
+
+  String _accountKey(String serverId) =>
+      '${jellyfin.account(serverId)?.token}|${jellyfin.statusOf(serverId).name}';
+
+  /// A blocked viewer links (or reconnects) the account: try again.
+  void _onAccountsChanged() {
+    final blocked = jellyfinBlocked.peek();
+    if (blocked == null) return;
+    final key = _accountKey(blocked.serverId);
+    if (key == _blockedKey) return;
+    _blockedKey = key;
+    final status = jellyfin.statusOf(blocked.serverId);
+    if (jellyfin.account(blocked.serverId) == null ||
+        status == JellyfinAccountStatus.expired ||
+        status == JellyfinAccountStatus.checking) {
+      return;
+    }
+    retryJellyfin();
+  }
+
+  /// "Try again" on the blocked card (and after linking an account).
+  void retryJellyfin() {
+    final r = serverState.peek();
+    final ref = refOfStateMedia(r?.media);
+    if (r == null || ref == null) return;
+    unawaited(_playJellyfin(ref, r));
   }
 
   void _scheduleReconnect({bool manual = false}) {
@@ -790,6 +1262,7 @@ class SessionCoordinator {
     _seekTimer = null;
     _seekGate.reset();
     reconnecting.value = false;
+    await _stopJellyfin();
     _playerReady = false;
     try {
       await playback.dispose();
@@ -806,6 +1279,10 @@ class SessionCoordinator {
 
   Future<void> dispose() async {
     await leave(silent: true);
+    if (_jellyfinListening) {
+      _jellyfinListening = false;
+      jellyfin.removeListener(_onAccountsChanged);
+    }
     await _stateSub?.cancel();
     await _feedSub?.cancel();
     await _kickSub?.cancel();

apps/desktop/lib/src/state/server_isolate.dart

@@ -131,6 +131,27 @@ class ServerIsolate {
     if (!_stopping) crash?.call(_lastError ?? 'the server stopped unexpectedly');
   }
 
+  /// Makes [path] the hosted file (the in-session File swap). Returns its
+  /// name and size for the `swap` that puts it up, or null when the file
+  /// is missing or the server is gone.
+  Future<({String name, int size})?> setFile(String path,
+      {Duration timeout = const Duration(seconds: 5)}) async {
+    if (_exited.isCompleted) return null;
+    final reply = ReceivePort('server file');
+    try {
+      _stop.send({'t': 'file', 'path': path, 'reply': reply.sendPort});
+      final msg = await reply.first.timeout(timeout);
+      if (msg is Map && msg['ok'] == true) {
+        return (name: msg['name'] as String, size: msg['size'] as int);
+      }
+      return null;
+    } catch (_) {
+      return null;
+    } finally {
+      reply.close();
+    }
+  }
+
   /// Asks the server to close its sockets and exit; kills the isolate if it
   /// has not exited within [timeout].
   Future<void> stop({Duration timeout = const Duration(seconds: 3)}) async {

apps/desktop/lib/src/state/session_state.dart

@@ -6,6 +6,8 @@ import 'package:flutter/widgets.dart';
 import 'package:signals/signals_flutter.dart';
 import 'package:sync_relay_core/core.dart';
 
+import '../jellyfin/accounts.dart';
+import '../jellyfin/session_media.dart';
 import '../sfx/sfx.dart';
 import '../session/health.dart';
 import '../session/session_coordinator.dart';
@@ -154,6 +156,7 @@ class SessionState {
   final SfxService sfx = const NoopSfxService();
   late final SessionCoordinator coordinator = SessionCoordinator(sfx: sfx);
   final lastForm = ConnectForm();
+  JellyfinAccounts get jellyfin => JellyfinAccounts.instance;
   /// Set when the hosted server died mid-session; Home shows it on the
   /// Host card and clears it.
   final serverCrash = signal<String?>(null);
@@ -232,6 +235,14 @@ class SessionState {
       if (op != _op) throw const ConnectCancelled();
       final hostKey = newHostKey();
       _setupCrash = null;
+      // A pasted Jellyfin link goes up as a ref like a browser pick.
+      final media = params.media ??
+          (params.linkUrl.isEmpty ? null : await mediaForLink(jellyfin, params.linkUrl));
+      if (op != _op) throw const ConnectCancelled();
+      // Guests without an account watch through the server, with the
+      // host's own sign-in (the hosted item's server, else the default).
+      await jellyfin.ensureLoaded(validate: false);
+      final relay = relayCredentialFor(jellyfin, serverId: media?.jellyfin?.serverId);
       late final ServerIsolate server;
       try {
         server = await ServerIsolate.start(
@@ -241,6 +252,7 @@ class SessionState {
             name: 'server',
             mediaPath: params.mediaPath,
             hostKey: hostKey,
+            jellyfin: relay,
           ),
           onLog: (line) => debugPrint('[server] $line'),
           onCrash: (cause) => _onServerCrash(server, cause),
@@ -256,6 +268,8 @@ class SessionState {
         throw const ConnectCancelled();
       }
       _server = server;
+      coordinator.hostFile = (path) async =>
+          identical(_server, server) ? server.setFile(path) : null;
       status.value =
           HealthStatus(HealthSeverity.ok, 'hosting on port ${server.port}');
       try {
@@ -265,8 +279,8 @@ class SessionState {
           secret: params.secret,
           name: params.name,
           avatar: params.avatar,
-          linkUrl: params.linkUrl,
           hostKey: hostKey,
+          media: media,
         ));
         if (op != _op) throw const ConnectCancelled();
       } catch (e) {
@@ -353,6 +367,7 @@ class SessionState {
   }
 
   Future<void> stopServer() async {
+    coordinator.hostFile = null;
     _stopKickWatch?.call();
     _stopKickWatch = null;
     final server = _server;

apps/desktop/lib/src/state/settings.dart

@@ -16,6 +16,7 @@ const _keyAutoCheckUpdates = 'autoCheckUpdates';
 const _keyShaderPreset = 'shaderPreset';
 const _keyShaderQuality = 'shaderQuality';
 const _keyCustomShaders = 'customShaders';
+const _keyAutoAdvance = 'autoAdvance';
 
 enum HwdecMode { auto, off, custom }
 
@@ -25,6 +26,8 @@ class AppSettings {
   final hwdecMode = signal(HwdecMode.auto);
   final hwdecCustom = signal('');
   final autoCheckUpdates = signal(true);
+  /// Jellyfin episodes: at the end, count down 10 s and put up the next.
+  final autoAdvance = signal(true);
 
   /// Video shaders: one choice, used on join and changed both here and
   /// in the session (Ctrl+0..6, the shader button).
@@ -59,6 +62,8 @@ class AppSettings {
       if (custom is String) hwdecCustom.value = custom;
       final auto = box.get(_keyAutoCheckUpdates);
       if (auto is bool) autoCheckUpdates.value = auto;
+      final advance = box.get(_keyAutoAdvance);
+      if (advance is bool) autoAdvance.value = advance;
       final preset = box.get(_keyShaderPreset);
       shaderPreset.value =
           ShaderPreset.values.where((p) => p.name == preset).firstOrNull ??
@@ -91,6 +96,11 @@ class AppSettings {
     _put(_keyAutoCheckUpdates, on);
   }
 
+  void setAutoAdvance(bool on) {
+    autoAdvance.value = on;
+    _put(_keyAutoAdvance, on);
+  }
+
   void setShaderPreset(ShaderPreset preset) {
     shaderPreset.value = preset;
     _put(_keyShaderPreset, preset.name);

apps/desktop/lib/src/sync/sync_client.dart

@@ -36,6 +36,9 @@ class SyncClient {
   String token = '';
   String memberId = '';
   String? mediaUrl;
+  /// This member's `/j/...` URL from `welcome` (Jellyfin media the server
+  /// relays); private like [token].
+  String? relayUrl;
   StateBroadcast? lastState;
   Completer<WelcomeMessage>? _pendingWelcome;
 
@@ -89,6 +92,7 @@ class SyncClient {
       token = welcome.token;
       memberId = welcome.memberId;
       mediaUrl = welcome.mediaUrl;
+      relayUrl = welcome.relayUrl;
       if (welcome.state != null) {
         try {
           lastState = StateBroadcast.fromJson(welcome.state!);
@@ -214,6 +218,7 @@ class SyncClient {
     required int eventId,
     double duration = 0,
     int mediaId = 0,
+    Map<String, bool>? jf,
   }) {
     final safeBuffered = buffered.isNaN || buffered < 0 ? 0.0 : buffered;
     _send(
@@ -223,6 +228,7 @@ class SyncClient {
         eventId: eventId,
         duration: duration.isFinite && duration > 0 ? duration : 0,
         mediaId: mediaId,
+        jf: jf,
       ).toJson(),
     );
   }
@@ -254,6 +260,7 @@ class SyncClient {
     token = '';
     memberId = '';
     mediaUrl = null;
+    relayUrl = null;
     lastState = null;
   }
 

apps/desktop/test/jellyfin_accounts_test.dart

@@ -7,7 +7,7 @@ import 'package:sync_relay_core/core.dart';
 import 'package:watch_together/src/jellyfin/accounts.dart';
 import 'package:watch_together/src/jellyfin/format.dart';
 import 'package:watch_together/src/jellyfin/sign_in.dart';
-import 'package:watch_together/src/screens/home/host_tab.dart' show interimJellyfinLink, mediaSummary;
+import 'package:watch_together/src/screens/home/host_tab.dart' show mediaSummary;
 import 'package:watch_together/src/screens/home/media_picker.dart';
 
 /// Captured Jellyfin 10.11 answers shared with packages/core's client tests.
@@ -342,22 +342,6 @@ void main() {
       expect(m.subtitle, 'Black Summoner · S1E6');
       expect(m.runtime, isNotNull);
     });
-
-    test('INTERIM: the host plays a Jellyfin pick as its authorised stream link', () async {
-      final (accounts, _) = await linkedAccounts();
-      const m = JellyfinMedia(
-          serverId: fixtureServerId, baseUrl: 'https://example.invalid', itemId: 'abc', title: 't');
-      final url = Uri.parse(interimJellyfinLink(accounts, m));
-      expect(url.path, '/Videos/abc/stream');
-      expect(url.queryParameters['static'], 'true');
-      expect(url.queryParameters['api_key'], 'TEST_ACCESS_TOKEN');
-      expect(
-          () => interimJellyfinLink(
-              accounts, const JellyfinMedia(serverId: 'gone', baseUrl: 'x', itemId: 'i', title: 't')),
-          throwsFormatException);
-      accounts.markExpired(fixtureServerId);
-      expect(() => interimJellyfinLink(accounts, m), throwsFormatException);
-    });
   });
 
   group('format', () {

apps/desktop/test/jellyfin_e2e_test.dart

@@ -0,0 +1,448 @@
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:media_kit/media_kit.dart';
+import 'package:sync_relay_core/core.dart';
+import 'package:sync_relay_server/server.dart';
+import 'package:watch_together/src/jellyfin/accounts.dart';
+import 'package:watch_together/src/jellyfin/session_media.dart';
+import 'package:watch_together/src/jellyfin/track_prefs.dart';
+import 'package:watch_together/src/session/session_coordinator.dart';
+
+// Two account holders and a guest watch Jellyfin episodes together over a
+// real sync server, real mpv and a local fake Jellyfin (never a real one):
+// account holders direct-play with their own token and report progress,
+// the guest plays through the server's /j relay with the host credential.
+
+final _tmp = Platform.environment['WT_TEST_TMP'] ?? Directory.systemTemp.path;
+const _sid = 'f00dfeedf00dfeedf00dfeedf00dfeed';
+const _series = '5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e5e';
+const _ep1 = 'e1e1e1e1e1e1e1e1e1e1e1e1e1e1e1e1';
+const _ep2 = 'e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2e2';
+
+/// 20 s, h264 + two audio tracks (Japanese first, English second).
+Future<String> _media() async {
+  final path = '$_tmp/jellyfin_e2e_20s.mkv';
+  if (await File(path).exists()) return path;
+  final r = await Process.run('ffmpeg', [
+    '-y', '-v', 'error',
+    '-f', 'lavfi', '-i', 'testsrc2=size=320x180:rate=24',
+    '-f', 'lavfi', '-i', 'sine=frequency=440:sample_rate=48000',
+    '-f', 'lavfi', '-i', 'sine=frequency=660:sample_rate=48000',
+    '-map', '0:v', '-map', '1:a', '-map', '2:a',
+    '-t', '20', '-c:v', 'libx264', '-preset', 'ultrafast', '-g', '24', '-pix_fmt', 'yuv420p',
+    '-c:a', 'aac',
+    '-metadata:s:a:0', 'language=jpn', '-metadata:s:a:0', 'title=Japanese',
+    '-metadata:s:a:1', 'language=eng', '-metadata:s:a:1', 'title=English',
+    path,
+  ]);
+  if (r.exitCode != 0) fail('ffmpeg failed: ${r.stderr}');
+  return path;
+}
+
+class _Call {
+  final String method;
+  final String path;
+  final String auth;
+  final Map<String, dynamic>? body;
+  _Call(this.method, this.path, this.auth, this.body);
+}
+
+/// Just enough Jellyfin: public info, users, PlaybackInfo, items, episodes,
+/// the static stream with ranges, and the three Sessions reports. Every
+/// request is recorded with its Authorization header.
+class _FakeJellyfin {
+  final String file;
+  final tokens = {'ATOKEN': 'ua', 'CTOKEN': 'uc', 'HOSTTOKEN': 'uh'};
+  final calls = <_Call>[];
+  late HttpServer _server;
+  _FakeJellyfin(this.file);
+
+  String get base => 'http://127.0.0.1:${_server.port}';
+
+  Future<void> start() async {
+    _server = await HttpServer.bind(InternetAddress.loopbackIPv4, 0);
+    _server.listen(_handle);
+  }
+
+  Future<void> stop() => _server.close(force: true);
+
+  static Map<String, String> authFields(String header) => {
+        for (final m in RegExp(r'(\w+)="([^"]*)"').allMatches(header))
+          m.group(1)!: Uri.decodeComponent(m.group(2)!),
+      };
+
+  Map<String, Object?> _item(String id) => {
+        'Id': id,
+        'Name': id == _ep1 ? 'Pilot' : 'Second',
+        'Type': 'Episode',
+        'ServerId': _sid,
+        'SeriesId': _series,
+        'SeriesName': 'Fake Show',
+        'SeasonId': 'seas1',
+        'ParentIndexNumber': 1,
+        'IndexNumber': id == _ep1 ? 1 : 2,
+        'RunTimeTicks': 20 * jellyfinTicksPerSecond,
+      };
+
+  Future<void> _handle(HttpRequest req) async {
+    final auth = req.headers.value('authorization') ?? '';
+    final bodyText = await utf8.decoder.bind(req).join();
+    Map<String, dynamic>? body;
+    try {
+      body = bodyText.isEmpty ? null : jsonDecode(bodyText) as Map<String, dynamic>;
+    } catch (_) {}
+    calls.add(_Call(req.method, req.uri.path, auth, body));
+    final res = req.response;
+    Future<void> json(Object v) async {
+      res.headers.contentType = ContentType.json;
+      res.write(jsonEncode(v));
+      await res.close();
+    }
+
+    final path = req.uri.path;
+    if (path == '/System/Info/Public') {
+      return json({'Id': _sid, 'ServerName': 'Fake Jellyfin', 'Version': '10.11.11'});
+    }
+    final token = authFields(auth)['Token'] ?? req.uri.queryParameters['api_key'];
+    final user = tokens[token];
+    if (user == null) {
+      res.statusCode = 401;
+      return res.close();
+    }
+    if (path == '/Users/Me') return json({'Id': user, 'Name': user, 'ServerId': _sid});
+    final m = RegExp(r'^/Items/(\w+)(/PlaybackInfo)?$').firstMatch(path);
+    if (m != null && m.group(2) != null) {
+      return json({
+        'PlaySessionId': 'ps-$user-${m.group(1)}',
+        'MediaSources': [
+          {
+            'Id': m.group(1),
+            'SupportsDirectPlay': true,
+            'MediaStreams': [
+              {'Index': 0, 'Type': 'Video', 'Codec': 'h264'},
+              {'Index': 1, 'Type': 'Audio', 'Language': 'jpn', 'Title': 'Japanese', 'Codec': 'aac'},
+              {'Index': 2, 'Type': 'Audio', 'Language': 'eng', 'Title': 'English', 'Codec': 'aac'},
+            ],
+          }
+        ],
+      });
+    }
+    if (m != null) return json(_item(m.group(1)!));
+    if (path == '/Shows/$_series/Episodes') {
+      return json({'Items': [_item(_ep1), _item(_ep2)], 'TotalRecordCount': 2});
+    }
+    if (path.startsWith('/Sessions/Playing')) {
+      res.statusCode = 204;
+      return res.close();
+    }
+    if (RegExp(r'^/Videos/\w+/stream$').hasMatch(path)) return _stream(req);
+    res.statusCode = 404;
+    await res.close();
+  }
+
+  Future<void> _stream(HttpRequest req) async {
+    final f = File(file);
+    final size = await f.length();
+    final res = req.response;
+    res.headers.set('Accept-Ranges', 'bytes');
+    res.headers.contentType = ContentType('video', 'x-matroska');
+    var start = 0, end = size - 1;
+    final range = RegExp(r'bytes=(\d*)-(\d*)').firstMatch(req.headers.value('range') ?? '');
+    if (range != null) {
+      start = int.tryParse(range.group(1)!) ?? 0;
+      end = int.tryParse(range.group(2)!) ?? size - 1;
+      if (end >= size) end = size - 1;
+      res.statusCode = 206;
+      res.headers.set('Content-Range', 'bytes $start-$end/$size');
+    }
+    res.contentLength = end - start + 1;
+    try {
+      await res.addStream(f.openRead(start, end + 1));
+      await res.close();
+    } catch (_) {}
+  }
+
+  List<_Call> sessions({String? token}) => [
+        for (final c in calls)
+          if (c.path.startsWith('/Sessions/Playing') &&
+              (token == null || authFields(c.auth)['Token'] == token))
+            c
+      ];
+
+  List<_Call> streams(String token) => [
+        for (final c in calls)
+          if (c.path.startsWith('/Videos/') && authFields(c.auth)['Token'] == token) c
+      ];
+}
+
+Future<void> _poll(FutureOr<bool> Function() cond, String what,
+    {Duration timeout = const Duration(seconds: 30)}) async {
+  final deadline = DateTime.now().add(timeout);
+  while (DateTime.now().isBefore(deadline)) {
+    if (await cond()) return;
+    await Future.delayed(const Duration(milliseconds: 200));
+  }
+  fail('timed out waiting for $what');
+}
+
+Future<JellyfinAccounts> _account(String base, String token, String userId, String device) async {
+  final a = JellyfinAccounts(store: MemoryJellyfinStore(), deviceName: device);
+  await a.ensureLoaded(validate: false);
+  await a.link(
+    baseUrl: base,
+    server: const JellyfinServerInfo(id: _sid, name: 'Fake Jellyfin', version: '10.11.11'),
+    auth: JellyfinAuthResult(
+        accessToken: token, user: JellyfinUser(id: userId, name: userId), serverId: _sid),
+  );
+  return a;
+}
+
+String _kind(_Call c) => c.path.split('/').last;
+
+void main() {
+  test(
+    'account holders direct-play and report, the guest plays through the relay, all in sync',
+    timeout: const Timeout(Duration(minutes: 4)),
+    () async {
+      MediaKit.ensureInitialized();
+      final jelly = _FakeJellyfin(await _media());
+      await jelly.start();
+      const relayCred = (client: 'Watch Together', device: 'HostBox', deviceId: 'host-dev-1', version: '9.9.9');
+      final server = SyncServer(AppConfig(
+        port: 0,
+        secret: 'jf',
+        name: 'jf',
+        jellyfin: JellyfinCredential(
+          baseUrl: jelly.base,
+          serverId: _sid,
+          token: 'HOSTTOKEN',
+          client: relayCred.client,
+          device: relayCred.device,
+          deviceId: relayCred.deviceId,
+          version: relayCred.version,
+        ),
+      ));
+      await server.start();
+      final accA = await _account(jelly.base, 'ATOKEN', 'ua', 'A-PC');
+      final accC = await _account(jelly.base, 'CTOKEN', 'uc', 'C-PC');
+      final accB = JellyfinAccounts(store: MemoryJellyfinStore());
+      await accB.ensureLoaded(validate: false);
+      final a = SessionCoordinator(jellyfin: accA, trackPrefs: TrackPrefs(store: MemoryJellyfinStore()));
+      final b = SessionCoordinator(jellyfin: accB, trackPrefs: TrackPrefs(store: MemoryJellyfinStore()));
+      final c = SessionCoordinator(jellyfin: accC, trackPrefs: TrackPrefs(store: MemoryJellyfinStore()));
+      final all = [a, b, c];
+      ConnectParams params(String name, [HelloMedia? media]) => ConnectParams(
+          host: '127.0.0.1', port: server.boundPort, secret: 'jf', name: name, media: media);
+      try {
+        // A hosts the episode as a ref: no URL or token on the wire.
+        await a.connect(params('alice', const HelloMedia(
+            name: 'Pilot',
+            size: 0,
+            duration: 0,
+            jellyfin: JellyfinRef(serverId: _sid, itemId: _ep1, title: 'Pilot', subtitle: 'Fake Show · S1E1'))));
+        await _poll(() => a.serverState.peek()?.media?['jellyfin'] != null, 'ref on the server');
+        expect(a.serverState.peek()!.media!.containsKey('url'), isFalse);
+        expect(a.serverState.peek()!.relay, isTrue);
+        await b.connect(params('guest'));
+        await c.connect(params('carol'));
+        for (final x in all) {
+          await x.playback.player.setVolume(0);
+        }
+        await _poll(() => all.every((x) => x.playback.durationSecs > 19), 'all three opened the item');
+        expect(a.jellyfinPlan.peek(), isA<OwnPlay>());
+        await _poll(() {
+          final members = a.serverState.peek()?.members ?? const [];
+          final jf = {for (final m in members) m.name: m.jf[_sid]};
+          return jf['alice'] == true && jf['carol'] == true && jf['guest'] == false;
+        }, 'jf access in the member list');
+        expect(a.nextEpisode.peek()?.item.id, _ep2);
+        expect(b.nextEpisode.peek(), isNull, reason: 'guests cannot resolve the next one');
+
+        for (final x in all) {
+          x.toggleReady();
+        }
+        await _poll(() => all.every((x) => x.playback.player.state.playing), 'all playing');
+        await Future.delayed(const Duration(seconds: 4));
+        final pos = [for (final x in all) x.playback.positionSecs];
+        // ignore: avoid_print
+        print('positions after 4 s: $pos');
+        for (final p in pos) {
+          expect((p - pos.first).abs(), lessThan(1.0), reason: 'in sync: $pos');
+        }
+
+        // Pause (A unreadies): an immediate Progress with IsPaused.
+        a.toggleReady();
+        await _poll(() => !a.playback.player.state.playing, 'held');
+        await _poll(
+            () => jelly.sessions(token: 'ATOKEN').any((s) =>
+                _kind(s) == 'Progress' && s.body?['IsPaused'] == true),
+            'paused progress');
+        a.toggleReady();
+        await _poll(() => all.every((x) => x.playback.player.state.playing), 'playing again');
+
+        // Account holders see the "Next episode" prompt (this item is
+        // shorter than its 2 min lead); the guest cannot put it up.
+        await _poll(() => a.nextPromptVisible.peek(), 'next prompt');
+        expect(b.nextPromptVisible.peek(), isFalse);
+
+        // Alice and the guest pick English; it carries to the next episode.
+        await a.selectTrack(aid: 2);
+        await b.selectTrack(aid: 2);
+        await _poll(
+            () => jelly.sessions(token: 'ATOKEN').any((s) =>
+                _kind(s) == 'Progress' && s.body?['AudioStreamIndex'] == 2),
+            'track change reported');
+
+        // Near the end: finished -> Stopped, then one auto-advance swap.
+        a.seekTo(16);
+        await _poll(() => a.serverState.peek()?.transport == 'finished', 'finished',
+            timeout: const Duration(seconds: 20));
+        final finishedId = a.serverState.peek()!.mediaId;
+        await _poll(() => a.autoAdvance.peek() != null && c.autoAdvance.peek() != null,
+            'both account holders count down');
+        expect(b.autoAdvance.peek(), isNull);
+        final swappers = [a.autoAdvance.peek()!.swapper, c.autoAdvance.peek()!.swapper];
+        expect(swappers.where((s) => s), hasLength(1),
+            reason: 'exactly one designated swapper: the lowest member id (alice, m1)');
+        expect(a.autoAdvance.peek()!.swapper, isTrue);
+        await _poll(() => (a.serverState.peek()?.mediaId ?? 0) > finishedId, 'advanced',
+            timeout: const Duration(seconds: 20));
+        await Future.delayed(const Duration(seconds: 3));
+        expect(a.serverState.peek()!.mediaId, finishedId + 1, reason: 'no double swap');
+        expect(refOfStateMedia(a.serverState.peek()!.media)!.itemId, _ep2);
+        await _poll(() => all.every((x) => x.playback.durationSecs > 19 && x.jellyfinPlan.peek() != null),
+            'all opened the next episode');
+        expect(b.jellyfinPlan.peek(), isA<RelayPlay>());
+        expect((b.jellyfinPlan.peek() as RelayPlay).url, endsWith('/$_ep2'));
+        await _poll(() async => (await a.playback.currentTrackIds()).aid == 2, 'alice keeps English');
+        await _poll(() async => (await b.playback.currentTrackIds()).aid == 2, 'guest keeps English');
+        expect((await c.playback.currentTrackIds()).aid, 1, reason: 'carol never chose');
+        expect(a.previousEpisode.peek()?.item.id, _ep1);
+        expect(a.nextEpisode.peek(), isNull);
+
+        await a.leave();
+        await c.leave();
+        await Future.delayed(const Duration(milliseconds: 300));
+
+        // Progress only from account holders, exactly their own device.
+        final infoA = accA.clientInfo, infoC = accC.clientInfo;
+        void ownHeader(_Call call, JellyfinClientInfo info, String token) {
+          final f = _FakeJellyfin.authFields(call.auth);
+          expect(f, {
+            'Client': info.client,
+            'Device': info.device,
+            'DeviceId': info.deviceId,
+            'Version': info.version,
+            'Token': token,
+          }, reason: '${call.method} ${call.path}');
+        }
+
+        final sessions = jelly.sessions();
+        expect(sessions, isNotEmpty);
+        expect(sessions.every((s) => ['ATOKEN', 'CTOKEN'].contains(_FakeJellyfin.authFields(s.auth)['Token'])),
+            isTrue, reason: 'no reports from the guest or the relay credential');
+        final aCalls = jelly.sessions(token: 'ATOKEN');
+        for (final s in aCalls) {
+          ownHeader(s, infoA, 'ATOKEN');
+        }
+        for (final s in jelly.sessions(token: 'CTOKEN')) {
+          ownHeader(s, infoC, 'CTOKEN');
+        }
+        final ep1 = [for (final s in aCalls) if (s.body?['ItemId'] == _ep1) _kind(s)];
+        final ep2 = [for (final s in aCalls) if (s.body?['ItemId'] == _ep2) _kind(s)];
+        // ignore: avoid_print
+        print('alice reports: ep1 $ep1, ep2 $ep2');
+        expect(ep1.first, 'Playing');
+        expect(ep1, contains('Progress'));
+        expect(ep1.last, 'Stopped');
+        expect(ep1.where((k) => k == 'Stopped'), hasLength(1));
+        final stopped1 = aCalls.lastWhere((s) => s.body?['ItemId'] == _ep1);
+        expect(stopped1.body!['PositionTicks'], greaterThan(19 * jellyfinTicksPerSecond),
+            reason: 'played to the end');
+        expect(stopped1.body!['PlaySessionId'], 'ps-ua-$_ep1');
+        expect(ep2.first, 'Playing');
+        expect(ep2.last, 'Stopped', reason: 'leaving reports Stopped');
+        final playing = aCalls.firstWhere((s) => _kind(s) == 'Playing');
+        expect(playing.body!['AudioStreamIndex'], 1, reason: 'mpv aid 1 = Jellyfin index 1');
+        expect(playing.body!['SubtitleStreamIndex'], -1);
+        final stopped2 = aCalls.lastWhere((s) => s.body?['ItemId'] == _ep2);
+        expect(stopped2.body!['PlaySessionId'], 'ps-ua-$_ep2');
+        expect(aCalls.lastWhere((s) => _kind(s) != 'Stopped' && s.body?['ItemId'] == _ep2)
+            .body!['AudioStreamIndex'], 2, reason: 'English carried over and reported');
+
+        // Streams: own token with own fields; the relay with exactly the
+        // configured credential.
+        expect(jelly.streams('ATOKEN'), isNotEmpty);
+        for (final s in jelly.streams('ATOKEN')) {
+          ownHeader(s, infoA, 'ATOKEN');
+        }
+        final relayed = jelly.streams('HOSTTOKEN');
+        expect(relayed, isNotEmpty, reason: 'the guest played through the relay');
+        for (final s in relayed) {
+          expect(_FakeJellyfin.authFields(s.auth), {
+            'Client': relayCred.client,
+            'Device': relayCred.device,
+            'DeviceId': relayCred.deviceId,
+            'Version': relayCred.version,
+            'Token': 'HOSTTOKEN',
+          });
+        }
+        expect(jelly.calls.any((c) => c.path.startsWith('/Videos/') && c.auth.isEmpty), isFalse,
+            reason: 'no token-less (api_key) stream requests');
+      } finally {
+        for (final x in all) {
+          await x.dispose();
+        }
+        await server.stop();
+        await jelly.stop();
+      }
+    },
+  );
+
+  test(
+    'a guest with no account and no relay sees the blocked state, then plays after linking',
+    timeout: const Timeout(Duration(minutes: 2)),
+    () async {
+      MediaKit.ensureInitialized();
+      final jelly = _FakeJellyfin(await _media());
+      await jelly.start();
+      final server = SyncServer(const AppConfig(port: 0, secret: '', name: 'nr'));
+      await server.start();
+      final accA = await _account(jelly.base, 'ATOKEN', 'ua', 'A-PC');
+      final accB = JellyfinAccounts(store: MemoryJellyfinStore());
+      await accB.ensureLoaded(validate: false);
+      final a = SessionCoordinator(jellyfin: accA, trackPrefs: TrackPrefs(store: MemoryJellyfinStore()));
+      final b = SessionCoordinator(jellyfin: accB, trackPrefs: TrackPrefs(store: MemoryJellyfinStore()));
+      try {
+        await a.connect(ConnectParams(
+            host: '127.0.0.1',
+            port: server.boundPort,
+            secret: '',
+            name: 'alice',
+            media: const HelloMedia(
+                name: 'Pilot', size: 0, duration: 0, jellyfin: JellyfinRef(serverId: _sid, itemId: _ep1))));
+        await b.connect(ConnectParams(host: '127.0.0.1', port: server.boundPort, secret: '', name: 'bob'));
+        await _poll(() => b.jellyfinBlocked.peek() != null, 'blocked');
+        expect(b.serverState.peek()!.relay, isFalse);
+        expect(b.jellyfinBlocked.peek()!.message, contains('needs a Jellyfin account'));
+        // Linking an account (Integrations) retries by itself.
+        await accB.link(
+            baseUrl: jelly.base,
+            server: const JellyfinServerInfo(id: _sid, name: 'Fake Jellyfin', version: '10.11.11'),
+            auth: const JellyfinAuthResult(
+                accessToken: 'CTOKEN', user: JellyfinUser(id: 'uc', name: 'uc'), serverId: _sid));
+        await _poll(() => b.jellyfinPlan.peek() is OwnPlay && b.playback.durationSecs > 19,
+            'plays with the new account');
+        expect(b.jellyfinBlocked.peek(), isNull);
+      } finally {
+        await a.dispose();
+        await b.dispose();
+        await server.stop();
+        await jelly.stop();
+      }
+    },
+  );
+}

apps/desktop/test/jellyfin_session_test.dart

@@ -0,0 +1,591 @@
+import 'dart:convert';
+
+import 'package:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:sync_relay_core/core.dart';
+import 'package:watch_together/src/jellyfin/accounts.dart';
+import 'package:watch_together/src/jellyfin/browse_scope.dart';
+import 'package:watch_together/src/jellyfin/progress.dart';
+import 'package:watch_together/src/jellyfin/session_media.dart';
+import 'package:watch_together/src/jellyfin/track_prefs.dart';
+import 'package:watch_together/src/screens/home/host_tab.dart' show hostJellyfinMedia;
+import 'package:watch_together/src/screens/home/media_picker.dart';
+import 'package:watch_together/src/screens/session/jellyfin_widgets.dart';
+import 'package:watch_together/src/screens/session/swap_panel.dart';
+import 'package:watch_together/src/screens/session_screen.dart' show viaHostOf;
+import 'package:watch_together/src/session/session_coordinator.dart' show AutoAdvance;
+
+import 'jellyfin_accounts_test.dart';
+import 'jellyfin_browser_test.dart' show app, setSize, settle;
+
+const episodeId = 'b18826be994070a79f9b52bc0f66f052'; // Black Summoner S1E6
+const nextEpisodeId = '74c50bdbf83e8fef231dd7710058e197'; // S1E7
+const seriesId = 'e9aec9c14a1fcab775111844112b4cf7';
+const seasonId = 'fb0b77cfda15445f9319ed9d753dba23';
+const playSessionId = 'fc428dbbeb9c46a7885fa053bd46f7e7';
+
+const episodeRef = JellyfinRef(
+    serverId: fixtureServerId, itemId: episodeId, title: 'Rice and Thieves and Heroes');
+
+/// The fake plus playback: PlaybackInfo, the Black Summoner episodes and
+/// the three Sessions reports (recorded with their bodies).
+FakeJellyfin playbackFake() {
+  final fake = FakeJellyfin();
+  fake.fixture('POST', '/Items/$episodeId/PlaybackInfo', 'playback_info');
+  fake.on('GET', '/Shows/$seriesId/Episodes',
+      (_, _) => JellyfinHttpResponse(200, jellyfinFixture('bs_episodes')));
+  for (final path in ['/Sessions/Playing', '/Sessions/Playing/Progress', '/Sessions/Playing/Stopped']) {
+    fake.on('POST', path, (_, body) {
+      reports.add((path: path, body: jsonDecode(body!) as Map<String, dynamic>));
+      return const JellyfinHttpResponse(204, '');
+    });
+  }
+  return fake;
+}
+
+final reports = <({String path, Map<String, dynamic> body})>[];
+
+JellyfinMediaSource fixtureSource() => JellyfinPlaybackInfo.fromJson(
+        jsonDecode(jellyfinFixture('playback_info')) as Map<String, dynamic>)
+    .primarySource!;
+
+MemberView member(String id, String name, {Map<String, bool> jf = const {}, bool stale = false}) =>
+    MemberView(
+        id: id, name: name, ready: true, inSet: true, buffered: 10, stale: stale, jf: jf);
+
+void main() {
+  setUp(reports.clear);
+
+  group('resolve a ref', () {
+    test('own account: PlaybackInfo with its own user, static stream, token in the header',
+        () async {
+      final (accounts, fake) = await linkedAccounts(http: playbackFake());
+      final plan = await resolveJellyfinRef(accounts, episodeRef,
+          relay: true, relayUrl: 'http://h:1/j/default/t/$episodeId');
+      expect(plan, isA<OwnPlay>());
+      plan as OwnPlay;
+      expect(plan.jfAccess, isTrue);
+      expect(plan.info.playSessionId, playSessionId);
+      expect(plan.source.id, episodeId);
+      expect(plan.item?.seriesId, seriesId);
+      final info = fake.requests.firstWhere((r) => r.uri.path.endsWith('/PlaybackInfo'));
+      expect(info.uri.queryParameters['userId'], fixtureUserId);
+      expect(info.headers['Authorization'], contains('Token="TEST_ACCESS_TOKEN"'));
+      final url = Uri.parse(plan.url);
+      expect(url.path, '/Videos/$episodeId/stream');
+      expect(url.queryParameters['static'], 'true');
+      expect(url.queryParameters.containsKey('api_key'), isFalse, reason: 'token in a header only');
+      expect(plan.headers['Authorization'], accounts.clientInfo.authorizationHeader('TEST_ACCESS_TOKEN'));
+    });
+
+    test('no account: the relay URL when the server relays', () async {
+      final accounts = JellyfinAccounts(store: MemoryJellyfinStore(), httpFactory: FakeJellyfin.new);
+      final plan = await resolveJellyfinRef(accounts, episodeRef,
+          relay: true, relayUrl: 'http://h:1/j/default/t/$episodeId');
+      expect(plan, isA<RelayPlay>());
+      expect((plan as RelayPlay).url, 'http://h:1/j/default/t/$episodeId');
+      expect(plan.jfAccess, isFalse);
+    });
+
+    test('neither: blocked with a clear message, never a silent stall', () async {
+      final accounts = JellyfinAccounts(store: MemoryJellyfinStore(), httpFactory: FakeJellyfin.new);
+      final plan = await resolveJellyfinRef(accounts, episodeRef, relay: false, relayUrl: null);
+      expect(plan, isA<BlockedPlay>());
+      expect((plan as BlockedPlay).message,
+          'This needs a Jellyfin account on that Jellyfin server (or the host can relay)');
+      expect(plan.jfAccess, isNull);
+    });
+
+    test('a 401 marks the account expired and falls back to the relay', () async {
+      final fake = playbackFake()
+        ..on('POST', '/Items/$episodeId/PlaybackInfo', (_, _) => const JellyfinHttpResponse(401, ''));
+      final (accounts, _) = await linkedAccounts(http: fake);
+      final plan = await resolveJellyfinRef(accounts, episodeRef, relay: true, relayUrl: 'http://r');
+      expect(plan, isA<RelayPlay>());
+      expect(accounts.statusOf(fixtureServerId), JellyfinAccountStatus.expired);
+      final blocked = await resolveJellyfinRef(accounts, episodeRef, relay: false, relayUrl: null);
+      expect((blocked as BlockedPlay).message, contains('on Example Server'));
+      expect(blocked.message, contains('sign-in expired'));
+    });
+
+    test('relay URL is built like the /m one', () {
+      expect(relayUrlFor('10.0.0.2', 8080, 'tok', episodeId),
+          'http://10.0.0.2:8080/j/default/tok/$episodeId');
+    });
+  });
+
+  group('wire media', () {
+    test('a pick goes up as a ref without URL or token', () async {
+      final (accounts, _) = await linkedAccounts();
+      const pick = JellyfinMedia(
+          serverId: fixtureServerId,
+          baseUrl: 'https://example.invalid',
+          itemId: episodeId,
+          title: 'Rice and Thieves and Heroes',
+          subtitle: 'Black Summoner · S1E6',
+          runtime: Duration(minutes: 23));
+      final media = hostJellyfinMedia(accounts, pick);
+      expect(media.url, isNull);
+      expect(media.jellyfin!.itemId, episodeId);
+      expect(media.jellyfin!.subtitle, 'Black Summoner · S1E6');
+      expect(media.jellyfin!.runtimeSecs, 23 * 60);
+      expect(jsonEncode(SwapIntent(media: media).toJson()), isNot(contains('TEST_ACCESS_TOKEN')));
+      expect(() => hostJellyfinMedia(accounts, const JellyfinMedia(serverId: 'gone', baseUrl: 'x', itemId: 'i', title: 't')),
+          throwsFormatException);
+      accounts.markExpired(fixtureServerId);
+      expect(() => hostJellyfinMedia(accounts, pick), throwsFormatException);
+    });
+
+    test('a pasted Jellyfin link becomes a ref (ServerId from /System/Info/Public, no api_key)',
+        () async {
+      final (accounts, fake) = await linkedAccounts();
+      final media = await mediaForLink(accounts,
+          'https://example.invalid/Videos/$episodeId/stream?static=true&api_key=SOMEONES_TOKEN');
+      expect(media.url, isNull);
+      expect(media.jellyfin!.serverId, fixtureServerId);
+      expect(media.jellyfin!.itemId, episodeId);
+      expect(media.jellyfin!.title, 'Rice and Thieves and Heroes', reason: 'title via own account');
+      expect(media.name, 'Rice and Thieves and Heroes');
+      expect(jsonEncode(media.toJson()), isNot(contains('SOMEONES_TOKEN')));
+      expect(fake.count('GET', '/System/Info/Public'), 1);
+      // Never sent with the pasted token.
+      expect(fake.requests.every((r) => !'${r.uri}${r.headers}'.contains('SOMEONES_TOKEN')), isTrue);
+
+      // A web UI link carries the ServerId: no lookup.
+      final web = await mediaForLink(accounts,
+          'https://example.invalid/web/#/details?id=$episodeId&serverId=$fixtureServerId');
+      expect(web.jellyfin!.serverId, fixtureServerId);
+      expect(fake.count('GET', '/System/Info/Public'), 1);
+    });
+
+    test('other links, or an unreachable Jellyfin, stay plain links', () async {
+      final fake = FakeJellyfin()..offline = true;
+      final accounts = JellyfinAccounts(store: MemoryJellyfinStore(), httpFactory: () => fake);
+      const url = 'https://jelly.example/Items/$episodeId/Download?api_key=x';
+      final media = await mediaForLink(accounts, url);
+      expect(media.jellyfin, isNull);
+      expect(media.url, url);
+      expect(media.name, 'Download');
+      final plain = await mediaForLink(accounts, 'https://cdn.example/movie.mkv');
+      expect(plain.url, 'https://cdn.example/movie.mkv');
+      expect(plain.name, 'movie.mkv');
+    });
+
+    test('relay credential: the account token with exactly its own device fields', () async {
+      final (accounts, _) = await linkedAccounts();
+      final cred = relayCredentialFor(accounts, serverId: fixtureServerId)!;
+      final info = accounts.clientInfo;
+      expect(cred.token, 'TEST_ACCESS_TOKEN');
+      expect(cred.serverId, fixtureServerId);
+      expect(cred.baseUrl, 'https://example.invalid');
+      expect([cred.client, cred.device, cred.deviceId, cred.version],
+          [info.client, info.device, info.deviceId, info.version]);
+      expect(cred.device, 'Test PC');
+      // Another server's item: the default account still relays its own.
+      expect(relayCredentialFor(accounts, serverId: 'other')!.serverId, fixtureServerId);
+      accounts.markExpired(fixtureServerId);
+      expect(relayCredentialFor(accounts, serverId: fixtureServerId), isNull);
+      final none = JellyfinAccounts(store: MemoryJellyfinStore());
+      await none.ensureLoaded(validate: false);
+      expect(relayCredentialFor(none), isNull);
+    });
+  });
+
+  group('progress', () {
+    late JellyfinAccounts accounts;
+    late DateTime now;
+    late JellyfinProgressReporter reporter;
+    final errors = <Object>[];
+    var unauthorized = 0;
+
+    setUp(() async {
+      (accounts, _) = await linkedAccounts(http: playbackFake());
+      now = DateTime(2026, 1, 1, 20);
+      errors.clear();
+      unauthorized = 0;
+      reporter = JellyfinProgressReporter(
+        client: accounts.clientFor(fixtureServerId)!,
+        itemId: episodeId,
+        source: fixtureSource(),
+        playSessionId: playSessionId,
+        clock: () => now,
+        onError: errors.add,
+        onUnauthorized: () => unauthorized++,
+      );
+    });
+
+    Future<void> idle() => reporter.stop(const PlayerSnapshot(position: 0, paused: true))
+        .then((_) {});
+
+    test('Playing, Progress every 10 s and on pause / seek / track change, Stopped', () async {
+      // English audio (mpv aid 2 = Jellyfin index 2), English full subs (sid 1 = 3).
+      reporter.start(const PlayerSnapshot(position: 0, paused: true, aid: 2, sid: 1));
+      void at(int secs, double pos, {bool paused = false, int? aid = 2, int? sid = 1}) {
+        now = DateTime(2026, 1, 1, 20).add(Duration(seconds: secs));
+        reporter.update(PlayerSnapshot(position: pos, paused: paused, aid: aid, sid: sid));
+      }
+
+      at(1, 0); // resume -> Progress
+      at(2, 1);
+      at(5, 4); // nothing due
+      at(11, 10); // 10 s since the last one
+      at(12, 11, paused: true); // pause
+      at(13, 11, paused: true);
+      at(14, 300, paused: true); // seek
+      at(15, 300, paused: true, sid: null); // subtitles off
+      await reporter.stop(const PlayerSnapshot(position: 300.5, paused: true, aid: 2));
+
+      expect(reports.map((r) => r.path.split('/').last), [
+        'Playing',
+        'Progress', // resumed
+        'Progress', // 10 s
+        'Progress', // paused
+        'Progress', // seek
+        'Progress', // track change
+        'Stopped',
+      ]);
+      final playing = reports.first.body;
+      expect(playing['ItemId'], episodeId);
+      expect(playing['MediaSourceId'], episodeId);
+      expect(playing['PlaySessionId'], playSessionId);
+      expect(playing['PlayMethod'], 'DirectPlay');
+      expect(playing['IsPaused'], isTrue);
+      expect(playing['AudioStreamIndex'], 2);
+      expect(playing['SubtitleStreamIndex'], 3);
+      expect(reports[2].body['PositionTicks'], 10 * jellyfinTicksPerSecond);
+      expect(reports[3].body['IsPaused'], isTrue);
+      expect(reports[4].body['PositionTicks'], 300 * jellyfinTicksPerSecond);
+      expect(reports[5].body['SubtitleStreamIndex'], -1);
+      expect(reports.last.body, {
+        'ItemId': episodeId,
+        'MediaSourceId': episodeId,
+        'PlaySessionId': playSessionId,
+        'PositionTicks': 3005000000,
+      });
+      expect(errors, isEmpty);
+    });
+
+    test('played to the end, then seeked back: a fresh Playing', () async {
+      reporter.start(const PlayerSnapshot(position: 0, paused: false));
+      await reporter.stop(const PlayerSnapshot(position: 1440, paused: true));
+      expect(reporter.active, isFalse);
+      reporter.update(const PlayerSnapshot(position: 1440, paused: true));
+      reporter.start(const PlayerSnapshot(position: 600, paused: false));
+      await idle();
+      expect(reports.map((r) => r.path.split('/').last), ['Playing', 'Stopped', 'Playing', 'Stopped']);
+    });
+
+    test('failures are handed on and never throw; a 401 ends reporting', () async {
+      final fake = playbackFake()
+        ..on('POST', '/Sessions/Playing/Progress', (_, _) => const JellyfinHttpResponse(500, ''));
+      (accounts, _) = await linkedAccounts(http: fake);
+      final r = JellyfinProgressReporter(
+        client: accounts.clientFor(fixtureServerId)!,
+        itemId: episodeId,
+        source: fixtureSource(),
+        playSessionId: playSessionId,
+        clock: () => now,
+        onError: errors.add,
+        onUnauthorized: () => unauthorized++,
+      );
+      r.start(const PlayerSnapshot(position: 0, paused: false));
+      r.update(const PlayerSnapshot(position: 0, paused: true));
+      await r.stop(const PlayerSnapshot(position: 1, paused: true));
+      expect(errors, hasLength(1));
+      expect(unauthorized, 0);
+      expect(reports.map((r) => r.path.split('/').last), ['Playing', 'Stopped']);
+
+      fake.on('POST', '/Sessions/Playing', (_, _) => const JellyfinHttpResponse(401, ''));
+      reports.clear();
+      r.start(const PlayerSnapshot(position: 0, paused: false));
+      r.update(const PlayerSnapshot(position: 0, paused: true));
+      await r.stop(const PlayerSnapshot(position: 1, paused: true));
+      expect(unauthorized, 1);
+      expect(reports, isEmpty, reason: 'nothing after the 401');
+      expect(r.active, isFalse);
+    });
+  });
+
+  group('episodes', () {
+    test('neighbours of an episode with the clicker\'s account', () async {
+      final (accounts, _) = await linkedAccounts(http: playbackFake());
+      final plan = await resolveJellyfinRef(accounts, episodeRef, relay: false, relayUrl: null)
+          as OwnPlay;
+      final around = await findAdjacentEpisodes(plan);
+      expect(around.previous, isNull, reason: 'S1E6 is first in the fixture');
+      expect(around.next!.item.id, nextEpisodeId);
+      expect(around.next!.label, 'S1E7 Battle with the Heroes');
+      final media = mediaForPick(around.next!.pick);
+      expect(media.jellyfin!.itemId, nextEpisodeId);
+      expect(media.jellyfin!.subtitle, 'Black Summoner · S1E7');
+    });
+
+    test('the floating prompt starts two minutes before the end', () {
+      expect(nextPromptStart(null, const Duration(minutes: 24)), const Duration(minutes: 22));
+      expect(nextPromptStart(null, const Duration(seconds: 90)), Duration.zero);
+    });
+
+    test('one auto-advance swapper: the lowest id among members with their own account', () {
+      final members = [
+        member('m10', 'Ann', jf: {fixtureServerId: true}),
+        member('m2', 'Bob', jf: {fixtureServerId: true}),
+        member('m1', 'Guest', jf: {fixtureServerId: false}),
+        member('m0', 'Old', jf: {fixtureServerId: true}, stale: true),
+        member('m3', 'Fresh'),
+      ];
+      expect(autoAdvanceSwapper(members, fixtureServerId), 'm2');
+      expect(autoAdvanceSwapper(members.reversed.toList(), fixtureServerId), 'm2',
+          reason: 'order does not matter: every client agrees');
+      expect(autoAdvanceSwapper(members, 'other-server'), isNull);
+      expect(compareMemberIds('m9', 'm10'), lessThan(0));
+    });
+
+    test('member badge: via host only for relay viewers of the current item', () {
+      expect(viaHostOf(member('m1', 'G', jf: {fixtureServerId: false}), episodeRef), isTrue);
+      expect(viaHostOf(member('m1', 'G', jf: {fixtureServerId: true}), episodeRef), isFalse);
+      expect(viaHostOf(member('m1', 'G'), episodeRef), isFalse);
+      expect(viaHostOf(member('m1', 'G', jf: {fixtureServerId: false}), null), isFalse);
+    });
+  });
+
+  group('track carry-over', () {
+    test('choice from Jellyfin streams carries to the next episode by traits', () {
+      final source = fixtureSource();
+      // mpv aid 2 / sid 2: English eac3 audio, "English (Signs)" subtitles.
+      final choice = TrackChoice.of(aid: 2, sid: 2, source: source);
+      expect(choice.audio!.language, 'eng');
+      expect(choice.subtitle!.title, 'English (Signs) [Generated]');
+      // Next file: same tracks in another order (English audio first).
+      final next = JellyfinMediaSource(id: 'n', mediaStreams: [
+        const JellyfinMediaStream(index: 0, type: JellyfinStreamType.video),
+        const JellyfinMediaStream(
+            index: 1, type: JellyfinStreamType.audio, language: 'eng', title: 'English', codec: 'eac3', channels: 2),
+        const JellyfinMediaStream(
+            index: 2, type: JellyfinStreamType.audio, language: 'jpn', title: 'Japanese', codec: 'eac3', channels: 2),
+        const JellyfinMediaStream(
+            index: 3, type: JellyfinStreamType.subtitle, language: 'eng', title: 'English (Full Subtitle)'),
+        const JellyfinMediaStream(
+            index: 4, type: JellyfinStreamType.subtitle, language: 'eng', title: 'English (Signs)'),
+      ]);
+      final pick = chooseTracks(choice, source: next);
+      expect(pick.aid, 1, reason: 'English is mpv aid 1 there');
+      expect(pick.sid, 2, reason: 'Signs, not Full');
+      expect(pick.subtitlesOff, isFalse);
+      final off = chooseTracks(TrackChoice.of(aid: 1, sid: null, source: source), source: next);
+      expect(off.aid, 2, reason: 'Japanese');
+      expect(off.subtitlesOff, isTrue);
+    });
+
+    test('relay viewers match on mpv\'s track list', () {
+      const tracks = [
+        MpvTrack(id: 1, type: JellyfinStreamType.audio, language: 'jpn', title: 'Japanese', codec: 'aac'),
+        MpvTrack(id: 2, type: JellyfinStreamType.audio, language: 'eng', title: 'English', codec: 'aac'),
+        MpvTrack(id: 1, type: JellyfinStreamType.subtitle, language: 'eng', title: 'Signs'),
+        MpvTrack(id: 2, type: JellyfinStreamType.subtitle, language: 'eng', title: 'Full'),
+      ];
+      final choice = TrackChoice.of(aid: 2, sid: 2, tracks: tracks);
+      expect(choice.audio!.title, 'English');
+      final pick = chooseTracks(choice, tracks: const [
+        MpvTrack(id: 1, type: JellyfinStreamType.audio, language: 'en', title: 'English'),
+        MpvTrack(id: 2, type: JellyfinStreamType.audio, language: 'ja', title: 'Japanese'),
+        MpvTrack(id: 1, type: JellyfinStreamType.subtitle, language: 'en', title: 'Full Subtitles'),
+        MpvTrack(id: 2, type: JellyfinStreamType.subtitle, language: 'en', title: 'Signs & Songs'),
+      ]);
+      expect(pick.aid, 1);
+      expect(pick.sid, 1);
+    });
+
+    test('kept per series with a global fallback', () async {
+      final prefs = TrackPrefs(store: MemoryJellyfinStore());
+      expect(await prefs.load(seriesId: 'a'), isNull);
+      final eng = TrackChoice.of(aid: 2, sid: null, source: fixtureSource());
+      await prefs.save(eng, seriesId: 'a');
+      final jpn = TrackChoice.of(aid: 1, sid: 1, source: fixtureSource());
+      await prefs.save(jpn, seriesId: 'b');
+      expect((await prefs.load(seriesId: 'a'))!.audio!.language, 'eng');
+      expect((await prefs.load(seriesId: 'a'))!.subtitlesOff, isTrue);
+      expect((await prefs.load(seriesId: 'b'))!.audio!.language, 'jpn');
+      expect((await prefs.load(seriesId: 'new'))!.audio!.language, 'jpn', reason: 'global = last');
+      expect((await prefs.load())!.subtitle!.title, 'English (Full Subtitle)');
+    });
+  });
+
+  group('browser location', () {
+    test('route stacks round-trip and survive in the Jellyfin box', () async {
+      final (accounts, _) = await linkedAccounts();
+      final stack = [
+        const HomeRoute(),
+        const LibraryRoute(
+            JellyfinItem(id: 'lib1', name: 'Shows', type: 'CollectionFolder', collectionType: 'tvshows')),
+        SeriesRoute(const JellyfinItem(id: seriesId, name: 'Black Summoner', type: 'Series'),
+            seasonId: seasonId),
+      ];
+      await accounts.saveBrowseLocation(fixtureServerId, encodeBrowseStack(stack));
+      final back = decodeBrowseStack(accounts.browseLocation(fixtureServerId))!;
+      expect(back.map((r) => r.key), stack.map((r) => r.key));
+      expect((back[1] as LibraryRoute).folder.collectionType, 'tvshows');
+      expect((back[2] as SeriesRoute).seasonId, seasonId);
+      expect(decodeBrowseStack('junk'), isNull);
+    });
+
+    testWidgets('the browser reopens where it was, per server', (tester) async {
+      await setSize(tester, const Size(1600, 1000));
+      final (accounts, _) = await linkedAccounts();
+      await accounts.saveBrowseLocation(fixtureServerId, encodeBrowseStack([
+        const HomeRoute(),
+        SeriesRoute(const JellyfinItem(id: arifuretaId, name: 'Arifureta', type: 'Series'),
+            seasonId: season2Id),
+      ]));
+      final c = MediaPickerController(source: MediaKind.jellyfin);
+      addTearDown(c.dispose);
+      await tester.pumpWidget(app(MediaPicker(controller: c, jellyfin: accounts)));
+      await settle(tester);
+      final s2 = tester.widget<ChoiceChip>(find.byKey(const ValueKey('season-$season2Id')));
+      expect(s2.selected, isTrue);
+      // Back to Home is remembered too.
+      await tester.tap(find.byTooltip('Back (Esc)'));
+      await settle(tester);
+      expect(decodeBrowseStack(accounts.browseLocation(fixtureServerId))!.map((r) => r.key), ['home']);
+    });
+  });
+
+  group('session widgets', () {
+    final next = EpisodeLink(
+        const JellyfinItem(
+            id: nextEpisodeId, name: 'Battle with the Heroes', type: 'Episode',
+            parentIndexNumber: 1, indexNumber: 7),
+        const JellyfinMedia(
+            serverId: fixtureServerId, baseUrl: 'b', itemId: nextEpisodeId, title: 'Battle with the Heroes'));
+
+    testWidgets('next / previous buttons: tooltip, hidden without an episode', (tester) async {
+      var pressed = 0;
+      await tester.pumpWidget(app(Row(children: [
+        EpisodeSkipButton(episode: null, next: false, onPressed: () {}),
+        EpisodeSkipButton(episode: next, next: true, onPressed: () => pressed++),
+      ])));
+      expect(find.byKey(const ValueKey('episode-previous')), findsNothing);
+      expect(find.byTooltip('Next: S1E7 Battle with the Heroes  (> or Shift+N)'), findsOneWidget);
+      await tester.tap(find.byKey(const ValueKey('episode-next')));
+      expect(pressed, 1);
+    });
+
+    testWidgets('end card: Next prompt, countdown with Cancel', (tester) async {
+      var play = 0, cancel = 0;
+      await tester.pumpWidget(app(EndOfEpisodeCard(
+          next: next, countdown: null, onPlayNow: () => play++, onCancel: () => cancel++)));
+      expect(find.text('Next: S1E7 Battle with the Heroes'), findsOneWidget);
+      expect(find.byKey(const ValueKey('auto-advance-cancel')), findsNothing);
+      await tester.tap(find.byKey(const ValueKey('play-next')));
+      expect(play, 1);
+
+      await tester.pumpWidget(app(EndOfEpisodeCard(
+          next: next,
+          countdown: AutoAdvance(mediaId: 3, secondsLeft: 7, next: next, swapper: false),
+          onPlayNow: () => play++,
+          onCancel: () => cancel++)));
+      expect(find.text('Next episode in 7 s'), findsOneWidget);
+      await tester.tap(find.byKey(const ValueKey('auto-advance-cancel')));
+      expect(cancel, 1);
+    });
+
+    testWidgets('next-episode pill: faint at rest, lit on hover, click puts it up', (tester) async {
+      var pressed = 0;
+      await tester.pumpWidget(app(Align(child: NextEpisodePill(episode: next, onPressed: () => pressed++))));
+      double opacity() => tester.widget<AnimatedOpacity>(find.descendant(
+          of: find.byType(NextEpisodePill), matching: find.byType(AnimatedOpacity))).opacity;
+      expect(opacity(), lessThan(0.5));
+      final mouse = await tester.createGesture(kind: PointerDeviceKind.mouse);
+      await mouse.addPointer(location: Offset.zero);
+      addTearDown(mouse.removePointer);
+      await mouse.moveTo(tester.getCenter(find.byKey(const ValueKey('next-episode-pill'))));
+      await tester.pumpAndSettle();
+      expect(opacity(), 1);
+      await tester.tap(find.byKey(const ValueKey('next-episode-pill')));
+      expect(pressed, 1);
+    });
+
+    testWidgets('blocked card offers to link an account', (tester) async {
+      var link = 0;
+      await tester.pumpWidget(app(JellyfinBlockedCard(
+          blocked: const BlockedPlay(serverId: fixtureServerId, serverName: 'Example Server'),
+          onLinkAccount: () => link++,
+          onRetry: () {})));
+      expect(find.text('This needs a Jellyfin account on Example Server (or the host can relay)'),
+          findsOneWidget);
+      await tester.tap(find.byKey(const ValueKey('link-jellyfin-account')));
+      expect(link, 1);
+    });
+
+    testWidgets('swap panel: the shared picker, File only for the host', (tester) async {
+      await setSize(tester, const Size(1400, 900));
+      final (accounts, _) = await linkedAccounts();
+      final c = MediaPickerController(source: MediaKind.link);
+      addTearDown(c.dispose);
+      final swapped = <PickedMedia>[];
+      var closed = 0;
+      await tester.pumpWidget(app(SwapPanel(
+        controller: c,
+        accounts: accounts,
+        isHost: false,
+        onSwap: (m) async {
+          swapped.add(m);
+          return null;
+        },
+        onClose: () => closed++,
+      )));
+      await settle(tester);
+      expect(find.widgetWithText(ButtonSegment<MediaKind>, 'File'), findsNothing);
+      expect(find.text('File'), findsNothing);
+      expect(find.text('Jellyfin'), findsOneWidget);
+      await tester.enterText(find.byType(TextField), 'https://cdn.example/movie.mkv');
+      await tester.pump();
+      await tester.tap(find.byKey(const ValueKey('swap-go')));
+      await settle(tester);
+      expect(swapped, [const LinkMedia('https://cdn.example/movie.mkv')]);
+      expect(closed, 1);
+
+      // The Jellyfin source is the library browser; a pick goes up as is.
+      await tester.tap(find.text('Jellyfin'));
+      await settle(tester);
+      expect(find.byKey(const ValueKey('media-jellyfin')), findsOneWidget);
+
+      await tester.pumpWidget(app(SwapPanel(
+          controller: c, accounts: accounts, isHost: true, onSwap: (_) async => 'x', onClose: () {})));
+      await settle(tester);
+      expect(find.text('File'), findsOneWidget);
+    });
+
+    testWidgets('swap panel opens on the series of the episode playing, episode highlighted',
+        (tester) async {
+      await setSize(tester, const Size(1600, 1000));
+      final (accounts, _) = await linkedAccounts();
+      // Somewhere else remembered: the series start wins.
+      await accounts.saveBrowseLocation(fixtureServerId, encodeBrowseStack([const HomeRoute()]));
+      final eps = (jsonDecode(jellyfinFixture('episodes')) as Map)['Items'] as List;
+      final ep = JellyfinItem.fromJson((eps.firstWhere((e) => e['SeasonId'] == season2Id) as Map)
+          .cast<String, dynamic>());
+      final pick = pickForRef(accounts,
+          JellyfinRef(serverId: fixtureServerId, itemId: ep.id, title: ep.name))!;
+      final c = MediaPickerController(jellyfin: pick, source: MediaKind.jellyfin);
+      addTearDown(c.dispose);
+      await tester.pumpWidget(app(SwapPanel(
+        controller: c,
+        accounts: accounts,
+        isHost: false,
+        jellyfinStart: BrowseStart.seriesOf(fixtureServerId, ep),
+        onSwap: (_) async => null,
+        onClose: () {},
+      )));
+      await settle(tester, 10);
+      expect(tester.widget<ChoiceChip>(find.byKey(const ValueKey('season-$season2Id'))).selected,
+          isTrue);
+      expect(find.text('Put up: ${pick.label}'), findsOneWidget);
+      final row = tester.widget<Material>(find
+          .ancestor(of: find.byKey(ValueKey('episode-${ep.id}')), matching: find.byType(Material))
+          .first);
+      expect((row.shape as RoundedRectangleBorder).side.color, isNot(Colors.transparent),
+          reason: 'the episode playing is highlighted');
+    });
+  });
+}

apps/desktop/test/server_isolate_test.dart

@@ -7,6 +7,7 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:hive_ce/hive.dart';
 import 'package:media_kit/media_kit.dart';
 import 'package:sync_relay_core/core.dart';
+import 'package:watch_together/src/jellyfin/accounts.dart';
 import 'package:watch_together/src/session/session_coordinator.dart';
 import 'package:watch_together/src/state/server_isolate.dart';
 import 'package:watch_together/src/state/session_state.dart';
@@ -162,4 +163,59 @@ void main() {
       await session.stopServer();
     }
   });
+
+  test('host path: a Jellyfin pick goes up as a ref with the host relay; File swap',
+      timeout: const Timeout(Duration(minutes: 2)), () async {
+    MediaKit.ensureInitialized();
+    final tmp = Platform.environment['WT_TEST_TMP'] ?? Directory.systemTemp.path;
+    Hive.init('$tmp/hive_isolate_jf_test');
+    const sid = 'abcdefabcdefabcdefabcdefabcdef12';
+    final accounts = JellyfinAccounts.instance;
+    await accounts.ensureLoaded(validate: false);
+    // An unreachable Jellyfin: only the wire and the relay flag matter here.
+    await accounts.link(
+        baseUrl: 'http://127.0.0.1:9',
+        server: const JellyfinServerInfo(id: sid, name: 'J', version: '10.11.11'),
+        auth: const JellyfinAuthResult(
+            accessToken: 'HOSTTOKEN', user: JellyfinUser(id: 'u', name: 'u'), serverId: sid));
+    final session = SessionState.instance;
+    final port = await _freePort();
+    _Raw? friend;
+    final file = File('$tmp/host file swap.mkv')..writeAsBytesSync(List.filled(4096, 7));
+    try {
+      await session.host(
+          ConnectParams(
+              host: '',
+              port: port,
+              secret: '',
+              name: 'host',
+              media: const HelloMedia(
+                  name: 'Pilot',
+                  size: 0,
+                  duration: 0,
+                  jellyfin: JellyfinRef(serverId: sid, itemId: 'e1e1e1e1e1e1e1e1e1e1e1e1e1e1e1e1', title: 'Pilot'))),
+          ConnectForm());
+      await session.coordinator.playback.player.setVolume(0);
+      friend = await _Raw.join(port, 'friend');
+      final state = await friend.next('state', where: (m) => m['media'] != null);
+      final media = state['media'] as Map;
+      expect(media['jellyfin'], isA<Map>());
+      expect(media.containsKey('url'), isFalse);
+      expect(state['relay'], isTrue, reason: "the host's own sign-in relays for guests");
+      expect(jsonEncode(state), isNot(contains('HOSTTOKEN')));
+
+      expect(await session.coordinator.swapFile(file.path), isNull);
+      final swapped = await friend.next('state',
+          where: (m) => (m['media'] as Map?)?['name'] == 'host file swap.mkv');
+      expect((swapped['media'] as Map)['jellyfin'], isNull);
+      expect(swapped['relay'], isNull);
+      expect(await session.coordinator.swapFile('$tmp/missing.mkv'), contains('not found'));
+    } finally {
+      await friend?.ws.close();
+      await session.coordinator.leave(silent: true);
+      await session.stopServer();
+      await accounts.signOut(sid);
+      if (file.existsSync()) file.deleteSync();
+    }
+  });
 }

docs/ARCHITECTURE.md

@@ -26,7 +26,10 @@ an `AppConfig.toMap()` (primitives only, so it crosses isolates). It starts a
 `SyncServer` (bound to all IPv4 interfaces) and reports on the `events` port:
 `ready` (with the port and a `stop` SendPort), `error` (start failed), and
 every log record as `log`. Sending `{'t':'stop'}` to the `stop` port closes
-all sockets and returns, and the isolate exits.
+all sockets and returns, and the isolate exits. `{'t':'file', 'path', 'reply'}`
+on the same port makes a local file the hosted one and answers its name and
+size (`ServerIsolate.setFile`): the host's in-session File swap then sends a
+`swap` with that name and size, which the server matches to the file.
 
 - **Hosting from the app**: `SessionState.host()` spawns an isolate running
   `serve` (`ServerIsolate`), waits for `ready`, then joins it over
@@ -96,7 +99,10 @@ Loosely modeled on Syncplay, with a different readiness design.
   position, bumps `eventId` and records who sent it (`seekBy`, `seekSeq` in
   `state` for that event); flags are untouched. Clients diff each `state`
   broadcast by `eventId` (`StateDiff`): new event means seek to the computed
-  server position, transport change means play/pause. Between events: drift
+  server position, transport change means play/pause. The coordinator
+  applies states one at a time, newest first (a state arriving meanwhile
+  replaces any still waiting): interleaved applies could land an older
+  pause after a newer play. Between events: drift
   over 5 s for more than 2 s seeks, ahead by more than 1.5 s sets rate 0.95
   until level, otherwise nothing.
 - **User seeks**: the player is a `SyncPlayer` whose public `seek` is the
@@ -141,7 +147,10 @@ Three sources, same sync.
 
 - **Link**: the media field holds an http(s) URL. It travels as `media.url`
   in `swap` and `state`, and as `mediaUrl` in `welcome`. Each app plays it
-  directly; the server is only the clock.
+  directly; the server is only the clock. A pasted link that
+  `parseJellyfinLink` recognises goes up as a Jellyfin ref instead when the
+  ServerId is known (in the link, else `/System/Info/Public`), so its
+  `api_key` is never shared (`mediaForLink`, host and swap alike).
 - **Host local file**: `SyncServer.setLocalFile` / `mediaPath` makes the file
   the session media. `GET /m/<sid>/<token>/<name>` serves it with a Range
   table, gated by the viewer's token. The server builds the URL per viewer
@@ -319,6 +328,66 @@ errors leave it out).
   subscription does).
 - No progress reporting in the server: watched state is per client.
 
+## Jellyfin in a session
+
+Client side (`lib/src/jellyfin/session_media.dart`, `progress.dart`,
+`track_prefs.dart`, wired in `SessionCoordinator`):
+- **Resolve**: a `state` whose media is a ref is resolved per viewer
+  (`resolveJellyfinRef`): an account for that ServerId that is not expired
+  -> PlaybackInfo with its own user (PlaySessionId, media source; `/Items/{id}`
+  alongside for series and episode numbers), then mpv plays the static
+  stream with the token in `http-header-fields` (`Authorization:
+  MediaBrowser` with this install's fields), not in the URL: `OwnPlay`,
+  `report.jf {serverId: true}`. Else, when `state.relay`, `welcome.relayUrl`
+  or `/j/default/<token>/<itemId>` on the dialled host: `RelayPlay`,
+  `jf: false`. Else `BlockedPlay`: the session shows "This needs a
+  Jellyfin account on <server> (or the host can relay)" with a button that
+  opens Integrations over the session; linking (or reconnecting) the
+  account retries by itself. A 401 marks the account expired. The member
+  list shows "via host" for members whose `jf` is false for the current
+  item. A reconnect to the same item with `OwnPlay` keeps playing as is.
+- **Progress** (`JellyfinProgressReporter`, `OwnPlay` only): Playing once the
+  file is open and mpv has picked its tracks; Progress every 10 s and at
+  once on pause, resume, a seek (position more than 3 s from where playback
+  should be) or a track change; Stopped on swap, leave, kick, window close
+  (bounded to 1.5 s inside the graceful leave) and at `finished` (position =
+  duration, so Jellyfin marks it played); seeking back from the end sends
+  Playing again. Reports carry `PositionTicks`, `IsPaused` and mpv's
+  `aid`/`sid` as Jellyfin stream indices (`jellyfinIndexForMpvTrack`,
+  `SubtitleStreamIndex -1` = off). They go out in order on one chain;
+  failures are logged, one quiet toast per session, playback is never
+  touched; a 401 marks the account expired and ends reporting.
+- **Episodes**: with `OwnPlay` on an episode, `adjacentEpisodes` (one
+  `/Shows/{id}/Episodes` call; `episodeBefore` / `episodeAfter`) gives the
+  previous and next episode. The controls show previous / next buttons
+  (also `<` `>`, Shift+P / Shift+N); from `nextPromptStart` (last 2 min of
+  the runtime; the single place to switch to an outro segment later) a
+  floating "Next episode" pill shows outside the auto-hiding controls. Any
+  of them swaps to that episode's ref with the clicker's account. Guests
+  (relay, blocked) see none of it.
+- **Auto-advance** (Settings, on by default): at `finished` with a known
+  next episode, every client with the setting on shows a 10 s countdown
+  card (Cancel / Play now; without the setting, a "Next" card with Play
+  next). Exactly one client swaps: `autoAdvanceSwapper`, the lowest member
+  id among non-stale members whose `jf` for that server is true. Only what
+  every client sees in `state` decides it (who put the item up is not in
+  `state`; a late joiner never saw that swap), so clients agree without a
+  wire change. Cancel is local: it stops the countdown on that screen, and
+  the swapper's Cancel stops the swap; a seek by anyone ends `finished`
+  and with it every countdown.
+- **Tracks**: the controls' subtitles button lists mpv's audio and subtitle
+  tracks. A pick is applied, reported, and saved as a `TrackChoice`
+  (language, title, codec, channels, forced/HI: from the Jellyfin streams
+  with `OwnPlay`, else from mpv's track list) per series and as the global
+  fallback in the `track_prefs` Hive box. On the next Jellyfin item it is
+  matched with `matchTrack` against the source's streams (mapped to mpv ids
+  with `mpvTrackId`) or mpv's track list, and selected locally. Nothing goes
+  on the wire.
+- **Swap panel**: "Change video" in the side panel opens the shared
+  `MediaPicker` over the video (`screens/session/swap_panel.dart`); Link
+  goes through `mediaForLink`, a Jellyfin pick as a ref, File (host only)
+  through `ServerIsolate.setFile` and a matching `swap`.
+
 ## Desktop UI
 
 One `HomeScreen` (`screens/home/`) with a single top bar (`top_bar.dart`):
@@ -339,7 +408,7 @@ Jellyfin source the browser fills the height and can be enlarged, which
 turns the column into a one-row bar under it. Text fields have fixed or capped widths (720 px max) so
 they stay compact on ultrawide screens. Submit state (busy, cancel,
 per-tab errors, server crash) is `ConnectFlow`. Settings (profile, hardware
-decoding, updates, video shaders, shortcuts), Integrations
+decoding, Jellyfin auto-advance, updates, video shaders, shortcuts), Integrations
 (linked Jellyfin servers) and About open in the same body. Settings persist
 in two Hive boxes: `connect_form` (last form and recents; saved even when a
 join fails) and `settings`. Link media names are derived from the URL path
@@ -369,11 +438,17 @@ Jellyfin on the desktop (`lib/src/jellyfin/`, over the core client):
   hover/focus from 1400 px browser width.
 - Picking an item gives a `JellyfinMedia` (serverId, baseUrl, itemId,
   mediaSourceId?, title, subtitle, runtime; no credentials). The Host tab
-  remembers the last pick in the `jellyfin` box. Interim until the protocol
-  carries Jellyfin items: `interimJellyfinLink` in `host_tab.dart`
-  (`INTERIM(jellyfin-protocol)`) hosts it as a link to the host's
-  authorised static stream URL; `ConnectFlow.submit(linkOverride:)` keeps
-  that token-bearing URL out of the saved form.
+  remembers the last pick in the `jellyfin` box and hosts it as a ref
+  (`hostJellyfinMedia`, `ConnectFlow.submit(media:)`); the hosted server
+  gets the relay credential (`relayCredentialFor`: the account of the
+  item's server, else the default one, not expired; its token with
+  exactly `JellyfinAccounts.clientInfo`'s device fields).
+- Browser location: every navigation saves the route stack per server
+  (`browse:<serverId>` in the `jellyfin` box, `encodeBrowseStack`: ids,
+  names and the fields pages start from), so the Host tab, the swap panel
+  and the next start open where the browser was. A `BrowseStart` overrides
+  it: the swap panel opens on the series of the episode playing, its
+  season selected and the episode highlighted.
 
 Window chrome is frameless (`window_manager`): every screen brings its own
 drag area and min/max/close buttons (Home's top bar; the session uses

docs/DEVELOPMENT.md

@@ -46,7 +46,8 @@ and `e2e_check` (simulated viewers against a live server).
 - `cd packages/core && dart test`, `cd packages/server && dart test`.
 - `cd apps/desktop && flutter test test/<file>`.
 - Real-mpv tests: `sync_playback_e2e`, `coord_presence`, `video_reload_e2e`,
-  `seek_drag_e2e`, `end_of_file_e2e`, `readahead_e2e`. The sync and
+  `seek_drag_e2e`, `end_of_file_e2e`, `readahead_e2e`, `jellyfin_e2e` (a
+  local fake Jellyfin over HTTP; tests never talk to a real Jellyfin). The sync and
   end-of-file ones expect `~/Videos/chiyo.mp4`; others generate media with
   ffmpeg into `WT_TEST_TMP`. Headless mpv (no video output attached) won't
   open video-only files, so test media needs an audio track. Tests always log

docs/HOW-IT-WORKS.md

@@ -17,7 +17,9 @@ A five-minute tour. Details: [ARCHITECTURE.md](ARCHITECTURE.md), wire format:
         +----------------------------------------+
 
  video bytes come from somewhere else:
-   - a link (Jellyfin, any http/https URL): each app fetches it directly
+   - a link (any http/https URL): each app fetches it directly
+   - a Jellyfin item: each app plays it with its own Jellyfin account,
+     friends without one through the server (/j/... endpoint)
    - a file on the host's disk: the server streams it (/m/... endpoint)
 ```
 
@@ -26,8 +28,10 @@ A five-minute tour. Details: [ARCHITECTURE.md](ARCHITECTURE.md), wire format:
 - **Server**: keeps one shared clock and the list of people. It never sees
   video frames, only "position 123 s, playing". There is exactly one server
   and one watch session on it.
-- **Jellyfin** (or any web host): where a link's video lives. The server does
-  not touch it today; each app downloads it itself.
+- **Jellyfin** (or any web host): where the video lives. For a Jellyfin
+  item the server only knows which item it is; each app signs in with its
+  own account and reports what it watched. For friends without an account
+  the server fetches the item with the host's sign-in and passes it on.
 
 ## Ways to run
 
@@ -71,7 +75,9 @@ anyone except the host.
 ## Where video comes from
 
 - **Link**: you paste an http(s) URL. Every app plays it directly with mpv.
-  Works for a Jellyfin direct-download link or any file on the web.
+  A pasted Jellyfin link becomes the Jellyfin item below when possible.
+- **Jellyfin item**: picked in the app's library browser. Shared as "this
+  item on this Jellyfin server", never as a link with someone's sign-in.
 - **Local file (host only)**: you pick a file on your disk. The server
   streams it to everyone, host included, over HTTP with range requests, each
   with a per-person token. Nothing is stored or converted.

docs/ROADMAP.md

@@ -24,8 +24,7 @@ off by deleting it in the same commit as the code. Wire changes also edit
      next suspect is media_kit's context switching on the raster thread
      with NVIDIA.
    - Link conveniences: a link swap in session updates the remembered media;
-     show the open link with an open-in-browser button; the session's swap
-     panel reuses Home's `MediaPicker`.
+     show the open link with an open-in-browser button.
    - Time UI: remaining time, scrubber preview.
    - mpv / mpv.net shortcut parity.
    - Sounds: replace `NoopSfxService` (cues already fire). Candidates:
@@ -38,32 +37,25 @@ off by deleting it in the same commit as the code. Wire changes also edit
    - Avatar caching: serve avatar bytes once by hash instead of base64 in
      every `state` broadcast.
    - The `state` broadcast carries the full media URL, which can include an
-     `api_key`.
+     `api_key` (recognised Jellyfin links become refs; other links do not).
    - TLS: document a reverse proxy in front of the server.
    - Playlist: `queue-add`, `queue-skip`, auto-advance like a swap.
    - Sidecar subtitles.
 
 ## Epic: Jellyfin
 
-- Each viewer logs in to Jellyfin themselves (Quick Connect or password).
-- Several Jellyfin servers can be linked, keyed by `ServerId`.
-- The sync server shares only `{ServerId, ItemId}`. Pasted Jellyfin links are
-  recognised and reduced to that pair.
-- Viewers with an account direct-play `/Videos/{id}/stream?static=true`
-  with their own token and report Playing / Progress / Stopped, so watched
-  state and Continue Watching update per account.
-- Guests without an account play through the sync server, which fetches with a
-  credential that stays server-side (the host's own or a configured one).
-- Next episode: the successor in `/Shows/{seriesId}/Episodes` (NextUp means
-  first unwatched, not next-after-X); audio and subtitle track matching by language, then title,
-  then codec/channels.
-- Library browser; anyone can put up items.
-
-Spike facts (Jellyfin 10.11.11): `/Videos/{id}/stream?static=true&mediaSourceId=`
-serves the original with byte ranges (206). PlaybackInfo gives `PlaySessionId`
-and DirectPlay. All audio and subtitle tracks are embedded in the mkv. Quick
-Connect is enabled but `/QuickConnect/Initiate` returned 400: investigate
-(likely missing client/device fields in the auth header).
+What is left (the rest is in [ARCHITECTURE.md](ARCHITECTURE.md), "Jellyfin
+in a session"):
+- Queue: put several library items (a season, a pick list) up as a
+  playlist that advances like a swap (shares `queue-add` / `queue-skip`
+  with the backlog's Playlist item).
+- The "Next episode" prompt from the item's Outro / credits segment instead
+  of the last two minutes (`nextPromptStart`).
+- Auto-advance cancel for everyone: today Cancel is per screen (the
+  designated swapper's Cancel stops the swap; a seek stops all). A shared
+  cancel needs a wire message.
+- Sidecar (external) subtitle streams of Jellyfin items: only embedded
+  tracks are mapped to mpv today.
 
 ## Deferred
 

packages/core/lib/src/jellyfin/client.dart

@@ -426,6 +426,16 @@ class JellyfinClient {
         await episodes(seriesId, withMediaStreams: withMediaStreams), episode.id);
   }
 
+  /// The episodes before and after [episode] in its series (one
+  /// `/Shows/{id}/Episodes` call; see [episodeBefore] / [episodeAfter]).
+  Future<({JellyfinItem? previous, JellyfinItem? next})> adjacentEpisodes(
+      JellyfinItem episode) async {
+    final seriesId = episode.seriesId;
+    if (seriesId == null) return (previous: null, next: null);
+    final list = await episodes(seriesId);
+    return (previous: episodeBefore(list, episode.id), next: episodeAfter(list, episode.id));
+  }
+
   // -------------------------------------------------------------- images
 
   /// Image URL for caching and display. Images need no token on Jellyfin,
@@ -594,3 +604,20 @@ JellyfinItem? episodeAfter(List<JellyfinItem> episodes, String episodeId) {
   }
   return null;
 }
+
+/// The predecessor of [episodeId] in [episodes], the mirror of
+/// [episodeAfter]: crossing seasons, skipping other copies of the same
+/// episode. Null when it is first or not in the list.
+JellyfinItem? episodeBefore(List<JellyfinItem> episodes, String episodeId) {
+  final at = episodes.indexWhere((e) => e.id == episodeId);
+  if (at < 0) return null;
+  final cur = episodes[at];
+  for (var i = at - 1; i >= 0; i--) {
+    final e = episodes[i];
+    final sameEpisode = cur.indexNumber != null &&
+        e.indexNumber == cur.indexNumber &&
+        e.parentIndexNumber == cur.parentIndexNumber;
+    if (!sameEpisode) return e;
+  }
+  return null;
+}

packages/core/test/jellyfin_client_test.dart

@@ -235,6 +235,22 @@ void main() {
       expect(episodeAfter(eps, eps.last.id), isNull);
       expect(episodeAfter(eps, 'nope'), isNull);
     });
+
+    test('adjacentEpisodes: previous mirrors next across seasons and copies', () async {
+      http.on('GET', '/Shows/550eff23b37ec61082c988678ccc214c/Episodes', fixture: 'episodes');
+      final eps = await client.episodes('550eff23b37ec61082c988678ccc214c');
+      final s3e2 = eps.firstWhere((e) => e.episodeLabel == 'S3E2');
+      final around = await client.adjacentEpisodes(s3e2);
+      // S3E1 exists twice: the predecessor is the copy right before S3E2.
+      expect(around.previous!.episodeLabel, 'S3E1');
+      expect(around.next!.episodeLabel, 'S3E3');
+      final s3e1 = eps.lastWhere((e) => e.episodeLabel == 'S3E1');
+      expect(episodeBefore(eps, s3e1.id)!.episodeLabel, 'S2E12');
+      expect(episodeBefore(eps, eps.first.id), isNull);
+      expect(episodeBefore(eps, 'nope'), isNull);
+      expect((await client.adjacentEpisodes(const JellyfinItem(id: 'x', name: 'm', type: 'Movie'))).next,
+          isNull);
+    });
   });
 
   group('images', () {

packages/server/lib/src/serve.dart

@@ -14,7 +14,11 @@ import 'sync_server.dart';
 /// `{'t':'error','message':m}`, and forwards log records as
 /// `{'t':'log','level','logger','message'[,'error']}`. Sending
 /// `{'t':'stop'}` to the `stop` port stops the server; the returned future
-/// completes once it is down. Without [events] a start failure throws.
+/// completes once it is down. `{'t':'file','path':p,'reply':SendPort}` makes
+/// a file on this machine the hosted file (the hosting app's in-session file
+/// swap; a following `swap` with its name and size puts it up) and answers
+/// `{'ok':true,'name':n,'size':s}` or `{'ok':false}`. Without [events] a
+/// start failure throws.
 Future<void> serve(Map<String, Object?> config, {SendPort? events}) async {
   StreamSubscription<pkg_logging.LogRecord>? logs;
   if (events != null) {
@@ -39,7 +43,20 @@ Future<void> serve(Map<String, Object?> config, {SendPort? events}) async {
   final control = ReceivePort('serve control');
   events?.send({'t': 'ready', 'port': server.boundPort, 'stop': control.sendPort});
   await for (final msg in control) {
-    if (msg is Map && msg['t'] == 'stop') break;
+    if (msg is! Map) continue;
+    if (msg['t'] == 'stop') break;
+    if (msg['t'] == 'file' && msg['path'] is String && msg['reply'] is SendPort) {
+      final reply = msg['reply'] as SendPort;
+      try {
+        final ok = await server.setLocalFile(msg['path'] as String);
+        final media = server.session.media;
+        reply.send(ok && media != null
+            ? {'ok': true, 'name': media.name, 'size': media.size}
+            : {'ok': false});
+      } catch (_) {
+        reply.send({'ok': false});
+      }
+    }
   }
   control.close();
   await server.stop();

packages/server/test/serve_isolate_test.dart

@@ -51,6 +51,31 @@ void main() {
     errors.close();
   });
 
+  test('serve: the file control message makes a local file the hosted one', () async {
+    final events = ReceivePort();
+    final exit = ReceivePort();
+    final dir = Directory.systemTemp.createTempSync('serve_file_');
+    final file = File('${dir.path}/ep 2.mkv')..writeAsBytesSync(List.filled(1000, 1));
+    await Isolate.spawn(_run, (const AppConfig(port: 0, secret: '', name: 'f').toMap(), events.sendPort),
+        onExit: exit.sendPort);
+    final ready = await events.firstWhere((m) => m is Map && m['t'] == 'ready') as Map;
+    final stop = ready['stop'] as SendPort;
+    Future<Object?> ask(String path) async {
+      final reply = ReceivePort();
+      stop.send({'t': 'file', 'path': path, 'reply': reply.sendPort});
+      final r = await reply.first.timeout(const Duration(seconds: 5));
+      reply.close();
+      return r;
+    }
+
+    expect(await ask(file.path), {'ok': true, 'name': 'ep 2.mkv', 'size': 1000});
+    expect(await ask('${dir.path}/missing.mkv'), {'ok': false});
+    stop.send({'t': 'stop'});
+    await exit.first.timeout(const Duration(seconds: 10));
+    events.close();
+    dir.deleteSync(recursive: true);
+  });
+
   test('serve reports a bind failure as an error event', () async {
     final blocker = await ServerSocket.bind(InternetAddress.anyIPv4, 0);
     final events = ReceivePort();