yt-dlp for page links in every Link mode; app icon and Linux launcher entry

yt-dlp: a managed, checksum-verified, daily-updated yt-dlp in the app and
the dedicated server (--[no-]yt-dlp, --yt-dlp-dir). Pasted links are
probed: direct files stay links, pages are resolved for title, uploader,
duration and thumbnail. Everyone fetches it: mpv's ytdl hook on the
managed copy. I pass it on / the server fetches it: the best single-file
format, re-resolved once when its URL expires. Relay names never split
the /r/ path; viewers of server-fetched pages wait for the relay to go
live. No wire change.

Icon: two stars orbiting a play button (assets/icon/icon.svg, PNGs, the
Windows .ico). GTK app id moe.senkochan.watch_together; release builds
install their .desktop file and icons into ~/.local/share so Wayland
shows the icon; the window icon is set for X11. README shows the icon.

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

apps/desktop/assets/icon/icon.svg

@@ -0,0 +1,9 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256">
+<defs><linearGradient id="bg" x1="0" y1="0" x2="1" y2="1"><stop offset="0" stop-color="#2d2547"/><stop offset="1" stop-color="#14111d"/></linearGradient><linearGradient id="t1" gradientUnits="userSpaceOnUse" x1="50.7" y1="148.7" x2="184.6" y2="71.4"><stop offset="0" stop-color="#f0795a" stop-opacity="0"/><stop offset="0.45" stop-color="#f0795a" stop-opacity="0.85"/><stop offset="1" stop-color="#ffc56b"/></linearGradient><linearGradient id="t2" gradientUnits="userSpaceOnUse" x1="205.3" y1="107.3" x2="71.4" y2="184.6"><stop offset="0" stop-color="#ffc56b" stop-opacity="0"/><stop offset="0.45" stop-color="#ffc56b" stop-opacity="0.85"/><stop offset="1" stop-color="#f0795a"/></linearGradient></defs>
+<rect x="8" y="8" width="240" height="240" rx="56" fill="url(#bg)"/>
+<circle cx="128" cy="128" r="80" fill="none" stroke="#ffffff" stroke-opacity="0.10" stroke-width="6"/>
+<path d="M205.27 107.29 A80 80 0 0 1 71.43 184.57" fill="none" stroke="url(#t2)" stroke-width="7" stroke-linecap="butt"/><path d="M50.73 148.71 A80 80 0 0 1 184.57 71.43" fill="none" stroke="url(#t1)" stroke-width="7" stroke-linecap="butt"/>
+<path d="M110 96 L110 160 L162 128 Z" fill="#fff1d6" stroke="#fff1d6" stroke-width="16" stroke-linejoin="round"/>
+<path d="M71.4 161.6 Q74.7 181.3 94.4 184.6 Q74.7 187.8 71.4 207.6 Q68.2 187.8 48.4 184.6 Q68.2 181.3 71.4 161.6 Z" fill="#f0795a"/>
+<path d="M184.6 40.4 Q188.9 67.1 215.6 71.4 Q188.9 75.8 184.6 102.4 Q180.2 75.8 153.6 71.4 Q180.2 67.1 184.6 40.4 Z" fill="#ffc56b"/>
+</svg>

apps/desktop/lib/main.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:io';
 
 import 'package:flutter/material.dart';
@@ -7,6 +8,8 @@ import 'package:sync_relay_core/core.dart';
 import 'package:window_manager/window_manager.dart';
 
 import 'app.dart';
+import 'src/playback/yt_dlp_app.dart';
+import 'src/platform/desktop_entry.dart';
 import 'src/screens/home/ui.dart';
 import 'src/state/session_state.dart';
 import 'src/state/settings.dart';
@@ -60,6 +63,10 @@ Future<void> main(List<String> args) async {
     debugPrint('load connect form failed: $e\n$st');
   }
   MediaKit.ensureInitialized();
+  // yt-dlp for web page links: downloaded on first run, kept current.
+  AppYtDlp.instance.warmUp();
+  // Linux: the launcher entry and icon Wayland needs (release installs).
+  unawaited(installDesktopEntry());
   runApp(const WatchTogetherApp());
 }
 

apps/desktop/lib/src/platform/desktop_entry.dart

@@ -0,0 +1,54 @@
+import 'dart:io';
+
+import 'package:flutter/foundation.dart';
+
+import '../update/updater.dart' show findInstallRoot;
+
+/// The app's id: GTK's application id, so the Wayland `app_id` the
+/// compositor matches to [desktopFileName] for the window's icon.
+const appId = 'moe.senkochan.watch_together';
+const desktopFileName = '$appId.desktop';
+
+/// Linux release installs (an unpacked tarball) carry no launcher entry, so
+/// Wayland shows a generic icon. On start: write the `.desktop` file into
+/// `~/.local/share/applications` (Exec = this binary) and the icon into
+/// the hicolor theme, only when something changed (a moved install, a new
+/// icon). Never in debug runs; failures only log.
+Future<void> installDesktopEntry({String? executable, String? dataHome, String? home}) async {
+  if (!Platform.isLinux || kDebugMode) return;
+  try {
+    final exe = executable ?? Platform.resolvedExecutable;
+    final root = findInstallRoot(exe, windows: false);
+    if (root == null) return;
+    final share = dataHome ?? Platform.environment['XDG_DATA_HOME'] ??
+        '${home ?? Platform.environment['HOME']}/.local/share';
+    final icons = '${root.path}/data/flutter_assets/assets/icon';
+    for (final size in const [16, 32, 48, 64, 128, 256, 512]) {
+      final src = File('$icons/icon_$size.png');
+      if (!src.existsSync()) continue;
+      final dst = File('$share/icons/hicolor/${size}x$size/apps/$appId.png');
+      if (dst.existsSync() && dst.lengthSync() == src.lengthSync()) continue;
+      await dst.parent.create(recursive: true);
+      await src.copy(dst.path);
+    }
+    final entry = desktopEntryText(exe);
+    final file = File('$share/applications/$desktopFileName');
+    if (file.existsSync() && file.readAsStringSync() == entry) return;
+    await file.parent.create(recursive: true);
+    await file.writeAsString(entry);
+  } catch (e) {
+    debugPrint('desktop entry: $e');
+  }
+}
+
+@visibleForTesting
+String desktopEntryText(String exe) => '''[Desktop Entry]
+Type=Application
+Name=Watch together
+Comment=Watch videos in sync with friends
+Exec="$exe"
+Icon=$appId
+StartupWMClass=$appId
+Categories=AudioVideo;Video;Player;Network;
+Terminal=false
+''';

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

@@ -16,6 +16,7 @@ import '../sync/state_diff.dart';
 import '../sync/user_seek.dart';
 import 'frame_watchdog.dart';
 import 'media_marks.dart';
+import 'yt_dlp_app.dart' show ytdlFormat;
 
 /// Owns one mpv [Player] (and its [VideoController]) per session: created
 /// by [init] on join, released by [dispose] on leave, swapped by
@@ -60,6 +61,26 @@ class PlaybackController {
   /// Called once when the watchdog sees a frozen picture.
   void Function()? onFrozen;
 
+  /// mpv's yt-dlp hook could not open the current link (its error text).
+  void Function(String error)? onYtdlError;
+
+  /// Points mpv's yt-dlp hook at [path] (the app's managed copy) for web
+  /// page links, at most 1080p. Once per player.
+  Future<void> useYtDlp(String path) async {
+    final p = _player;
+    if (p == null || identical(p, _ytdlSetOn)) return;
+    try {
+      final dynamic platform = p.platform;
+      await platform?.setProperty('script-opts', 'ytdl_hook-ytdl_path=$path');
+      await platform?.setProperty('ytdl-format', ytdlFormat);
+      _ytdlSetOn = p;
+    } catch (e) {
+      debugPrint('yt-dlp path not set: $e');
+    }
+  }
+
+  Player? _ytdlSetOn;
+
   /// Fingerprint of the picture on screen, installed by the video view
   /// (`ShownFrameProbe.sample`). Without it the watchdog stays idle.
   Future<int?> Function()? shownFrame;
@@ -298,6 +319,11 @@ class PlaybackController {
   // an error there while shaders are on is a shader that failed to load
   // or compile (mpv then renders without it).
   void _onLog(PlayerLog log) {
+    if (log.prefix == 'ytdl_hook' && (log.level == 'error' || log.level == 'fatal')) {
+      final text = log.text.trim().replaceFirst(RegExp(r'^ERROR:\s*'), '');
+      if (text.isNotEmpty) onYtdlError?.call(text);
+      return;
+    }
     if (log.prefix != 'libmpv_render') return;
     if (log.text.contains('suspected software renderer')) {
       _setRenderMode(RenderMode.softwareGl);

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

@@ -0,0 +1,47 @@
+import 'dart:async';
+import 'dart:io';
+
+import 'package:path_provider/path_provider.dart';
+import 'package:sync_relay_core/core.dart';
+
+/// mpv's `ytdl-format` for links every player opens itself.
+const ytdlFormat = 'bv*[height<=1080]+ba/b';
+
+/// The app's yt-dlp (see [YtDlp]): in the app-support folder, shared with
+/// the hosted server. [probe] remembers what pasted links are for a while,
+/// so the Link preview and the swap ask once.
+class AppYtDlp {
+  static final instance = AppYtDlp();
+
+  /// [ytDlp]: a given one (tests); default in the app-support folder.
+  AppYtDlp([YtDlp? ytDlp]) : _ytDlp = ytDlp == null ? null : Future.value(ytDlp);
+
+  Future<YtDlp>? _ytDlp;
+  Future<YtDlp> get ytDlp => _ytDlp ??= () async {
+        final base = await getApplicationSupportDirectory();
+        return YtDlp(dir(base.path));
+      }();
+
+  static String dir(String appSupport) => '$appSupport${Platform.pathSeparator}yt-dlp';
+
+  /// Gets yt-dlp ready in the background (download on first run, a daily
+  /// update check afterwards).
+  void warmUp() => unawaited(ytDlp.then((y) => y.ensure()).catchError((_) => null));
+
+  final _probes = <String, (DateTime, Future<LinkProbe>)>{};
+  static const _probeTtl = Duration(minutes: 10);
+
+  Future<LinkProbe> probe(String url) {
+    final now = DateTime.now();
+    _probes.removeWhere((_, v) => now.difference(v.$1) > _probeTtl);
+    final hit = _probes[url];
+    if (hit != null) return hit.$2;
+    final f = ytDlp.then((y) => probeLink(Uri.parse(url), ytDlp: y));
+    _probes[url] = (now, f);
+    f.catchError((Object _) {
+      _probes.remove(url);
+      return LinkProbe.file(Uri(), -1);
+    });
+    return f;
+  }
+}

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

@@ -1,6 +1,7 @@
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
+import 'dart:math';
 
 import 'package:flutter/widgets.dart';
 import 'package:signals/signals_flutter.dart';
@@ -12,6 +13,7 @@ import '../jellyfin/session_media.dart';
 import '../jellyfin/track_prefs.dart';
 import '../playback/media_marks.dart';
 import '../playback/playback_controller.dart';
+import '../playback/yt_dlp_app.dart';
 import '../schedule/anilist.dart';
 import '../screens/home/picked_media.dart';
 import '../sfx/sfx.dart';
@@ -132,7 +134,10 @@ final class _FileOrigin extends _RelayOrigin {
 
 final class _LinkOrigin extends _RelayOrigin {
   final String url;
-  const _LinkOrigin(this.url);
+  /// What the link is (a page goes through [ytDlp]).
+  final LinkProbe probe;
+  final YtDlp ytDlp;
+  const _LinkOrigin(this.url, this.probe, this.ytDlp);
 }
 
 /// A Jellyfin item: served with this install's account, else with the
@@ -159,6 +164,8 @@ class SessionCoordinator {
   /// 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;
+  /// The app's yt-dlp and link probes (tests pass their own).
+  final AppYtDlp ytDlp;
   final SyncClient sync = SyncClient();
   /// Member pictures by `avatarHash`, fetched from the server.
   late final AvatarCache avatars = AvatarCache(sync);
@@ -293,8 +300,9 @@ class SessionCoordinator {
   bool _jellyfinListening = false;
 
   SessionCoordinator(
-      {this.sfx = const NoopSfxService(), JellyfinAccounts? jellyfin, TrackPrefs? trackPrefs})
-      : jellyfin = jellyfin ?? JellyfinAccounts.instance,
+      {this.sfx = const NoopSfxService(), JellyfinAccounts? jellyfin, TrackPrefs? trackPrefs, AppYtDlp? ytDlp})
+      : ytDlp = ytDlp ?? AppYtDlp.instance,
+        jellyfin = jellyfin ?? JellyfinAccounts.instance,
         trackPrefs = trackPrefs ?? TrackPrefs();
 
   /// Player lifetime = one session: created here on connect, disposed by
@@ -304,6 +312,7 @@ class SessionCoordinator {
     if (_playerReady) return;
     try {
       playback.onFrozen = () => unawaited(reloadVideo(auto: true));
+      playback.onYtdlError = (e) => health.value = HealthStatus(HealthSeverity.error, "can't open this link: $e");
       playback.onUserSeek = (d) => _userSeek(d.inMicroseconds / 1e6);
       await playback.init();
       _playerReady = true;
@@ -456,6 +465,7 @@ class SessionCoordinator {
     diff.reset();
     _opening = true;
     try {
+      await _prepareYtDlp(url);
       await playback.openUrl(url, headers: headers);
       health.value =
           const HealthStatus(HealthSeverity.ok, 'connected');
@@ -470,8 +480,30 @@ class SessionCoordinator {
     }
   }
 
+  /// A web link (not this server's): mpv's yt-dlp hook gets the app's
+  /// managed yt-dlp, downloaded first if needed; a media file name does
+  /// not wait for that.
+  Future<void> _prepareYtDlp(String url) async {
+    final uri = Uri.tryParse(url);
+    if (uri == null || !(uri.isScheme('http') || uri.isScheme('https'))) return;
+    if (uri.host == _wsHost && uri.port == _wsPort) return;
+    try {
+      final y = await ytDlp.ytDlp;
+      final ready = y.ensure();
+      final path = hasMediaExtension(uri)
+          ? y.path
+          : await ready.timeout(const Duration(seconds: 90), onTimeout: () => null);
+      if (path != null) await playback.useYtDlp(path);
+    } catch (e) {
+      debugPrint('yt-dlp not ready: $e');
+    }
+  }
+
   bool _relayWaitShown = false;
 
+  /// The server-fetched media this viewer opens once it is live.
+  int _awaitLiveFor = -1;
+
   /// Relayed through a member whose channel is down: say who everyone is
   /// waiting for (the buffer still plays what it has).
   void _relayStatus(StateBroadcast r) {
@@ -494,7 +526,7 @@ class SessionCoordinator {
   }
 
   String _relayMediaUrlFor(String name, int mediaId) =>
-      'http://$_wsHost:$_wsPort/r/default/${sync.token}/$mediaId/${Uri.encodeComponent(name)}';
+      'http://$_wsHost:$_wsPort/r/default/${sync.token}/$mediaId/${relayUrlName(name)}';
 
   /// Serves [bytes] for media [mediaId] on this member's relay channel.
   /// The server only pulls while someone watches through it.
@@ -617,9 +649,19 @@ class SessionCoordinator {
           _startRelaySource(r.mediaId, FileRelayBytes(File(origin.path)), announce: true);
         } else if (origin is _LinkOrigin) {
           await _openMedia(origin.url);
-          _startRelaySource(r.mediaId, HttpRelayBytes(Uri.parse(origin.url)), announce: true);
+          _startRelaySource(
+              r.mediaId, LinkRelayBytes(Uri.parse(origin.url), ytDlp: origin.ytDlp, probe: origin.probe),
+              announce: true);
         } else if (relay != null && !mine) {
-          await _openMedia(_relayMediaUrlFor(name, r.mediaId));
+          if (relay.fetch && !relay.live) {
+            // The server is still getting it (yt-dlp takes seconds; mpv
+            // gives up on a silent request after 5): open once it is live.
+            _openUrl = null;
+            _awaitLiveFor = r.mediaId;
+            health.value = const HealthStatus(HealthSeverity.info, 'the server is getting the video…');
+          } else {
+            await _openMedia(_relayMediaUrlFor(name, r.mediaId));
+          }
         } else {
           var url = stateMediaUrl(r);
           if ((url == null || url.isEmpty) && sync.token.isNotEmpty) {
@@ -635,6 +677,9 @@ class SessionCoordinator {
       }
       _seekGate.reset();
       _clearPendingSeek();
+    } else if (_awaitLiveFor == r.mediaId && (stateMediaRelay(r)?.live ?? false)) {
+      _awaitLiveFor = -1;
+      await _openMedia(_relayMediaUrlFor((r.media?['name'] as String?) ?? '', r.mediaId));
     }
     _jellyfinTransport(r);
     _relayStatus(r);
@@ -1060,8 +1105,11 @@ class SessionCoordinator {
       if (ref != null && client != null) {
         bytes = await jellyfinArt(client, ref.itemId);
       } else if (ref == null && (media.url ?? '').isNotEmpty) {
-        // A web link: its name is a URL tail ("1"), not a show; never guess.
-        bytes = null;
+        // A web link is not a show: never guess. A page's thumbnail is
+        // its banner.
+        final thumb = (await _probeFor(media.url!))?.info?.thumbnail;
+        final uri = thumb == null ? null : Uri.tryParse(thumb);
+        bytes = uri == null ? null : (banner: await fetchImage(uri, const {}, RelayConstants.maxBannerBytes), poster: null);
       } else {
         final name = ref == null ? media.name : jellyfinTitle(ref.title, ref.subtitle).$1;
         bytes = await aniListArt(_aniList ??= AniListClient(), name);
@@ -1089,33 +1137,58 @@ class SessionCoordinator {
       _swap(media.copyWith(relay: const MediaRelay()));
       return null;
     }
+    LinkProbe? probe;
+    String? probeError;
+    try {
+      probe = await ytDlp.probe(url).timeout(const Duration(seconds: 45));
+    } catch (e) {
+      probeError = '$e';
+    }
+    // A page is named by its title, never its URL tail ("1", "watch").
+    final uri = Uri.tryParse(url) ?? Uri();
+    final name = probe?.title ?? (probe != null || hasMediaExtension(uri) || uri.host.isEmpty ? media.name : uri.host);
     if (relay == LinkRelay.direct) {
-      _swap(media);
+      _swap(HelloMedia(name: name, size: 0, duration: 0, url: url));
       return null;
     }
-    // Relayed: it must be a single file the relay can range-read (not a
-    // page like YouTube, which only the player can resolve).
-    final probe = HttpRelayBytes(Uri.parse(url));
-    final int size;
-    try {
-      size = await probe.size().timeout(const Duration(seconds: 15));
-    } catch (e) {
-      return relay == LinkRelay.me
-          ? 'cannot pass this link on: $e'
-          : 'cannot check this link: $e';
-    } finally {
-      await probe.close();
-    }
     if (relay == LinkRelay.me) {
-      _pendingOrigin = _LinkOrigin(url);
-      _swap(HelloMedia(name: media.name, size: size, duration: 0, relay: const MediaRelay()));
-    } else {
-      _swap(HelloMedia(
-          name: media.name, size: size, duration: 0, url: url, relay: const MediaRelay(fetch: true)));
+      // This computer reads it: a file, or a page's single-file format.
+      if (probe == null) return 'cannot pass this link on: $probeError';
+      final problem = probe.relayProblem;
+      if (problem != null) return problem;
+      final y = await ytDlp.ytDlp;
+      final check = LinkRelayBytes(uri, ytDlp: y, probe: probe);
+      final int size;
+      try {
+        size = await check.size().timeout(const Duration(seconds: 15));
+      } catch (e) {
+        return 'cannot pass this link on: $e';
+      } finally {
+        await check.close();
+      }
+      _pendingOrigin = _LinkOrigin(url, probe, y);
+      _swap(HelloMedia(name: name, size: size, duration: 0, relay: const MediaRelay()));
+      return null;
     }
+    // The server reads it with its own yt-dlp; only a page this app knows
+    // has no single file is refused here (the server may reach what this
+    // computer cannot).
+    if (probe != null && probe.isPage && probe.info != null && probe.info!.single == null) {
+      return noSingleFileText;
+    }
+    _swap(HelloMedia(
+        name: name, size: max(0, probe?.size ?? 0), duration: 0, url: url, relay: const MediaRelay(fetch: true)));
     return null;
   }
 
+  Future<LinkProbe?> _probeFor(String url) async {
+    try {
+      return await ytDlp.probe(url).timeout(const Duration(seconds: 45));
+    } catch (_) {
+      return null;
+    }
+  }
+
   /// A Jellyfin pick (browser, next / previous episode) goes up as a ref,
   /// relayed by this member for viewers without an account.
   void swapJellyfin(JellyfinMedia media) {

apps/desktop/lib/src/shell/library_link.dart

@@ -1,10 +1,11 @@
 import 'dart:async';
 import 'dart:convert';
-import 'dart:io';
 
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
+import 'package:sync_relay_core/core.dart' show LinkProbe, hasMediaExtension, notAVideoText;
 
+import '../playback/yt_dlp_app.dart';
 import '../screens/home/media_picker.dart';
 import '../state/connect_prefs.dart';
 import 'motion.dart';
@@ -109,49 +110,49 @@ class LinkPreview {
   const LinkPreview({required this.title, required this.subtitle, this.thumbnail});
 }
 
-/// GET [uri] and return the body (oEmbed).
-typedef OEmbedGetter = Future<String> Function(Uri uri);
+/// What a link is (see [AppYtDlp.probe]).
+typedef LinkProber = Future<LinkProbe> Function(String url);
 
-Future<String> defaultOEmbedGet(Uri uri) async {
-  final client = HttpClient()..connectionTimeout = const Duration(seconds: 6);
-  try {
-    final req = await client.getUrl(uri);
-    final res = await req.close().timeout(const Duration(seconds: 8));
-    if (res.statusCode != 200) throw HttpException('status ${res.statusCode}', uri: uri);
-    return await res.transform(utf8.decoder).join().timeout(const Duration(seconds: 8));
-  } finally {
-    client.close(force: true);
-  }
-}
-
-bool isYouTubeLink(Uri uri) {
-  final h = uri.host.toLowerCase();
-  return h == 'youtu.be' || h == 'youtube.com' || h.endsWith('.youtube.com');
-}
+Future<LinkProbe> defaultLinkProber(String url) => AppYtDlp.instance.probe(url);
 
 String _host(Uri uri) => uri.host.startsWith('www.') ? uri.host.substring(4) : uri.host;
 
-/// The preview of [url]: YouTube links ask YouTube's oEmbed for the title,
-/// channel and thumbnail; anything else (or a failed lookup) shows the
-/// file name and host. Null for text that is not an http(s) link.
-Future<LinkPreview?> previewLink(String url, {OEmbedGetter get = defaultOEmbedGet}) async {
+/// "3:07", "1:02:03".
+String clockText(double seconds) {
+  final s = seconds.round();
+  final h = s ~/ 3600, m = s % 3600 ~/ 60, sec = (s % 60).toString().padLeft(2, '0');
+  return h > 0 ? '$h:${m.toString().padLeft(2, '0')}:$sec' : '$m:$sec';
+}
+
+/// The preview of [url]: a web page shows yt-dlp's title, uploader,
+/// duration and thumbnail (or why it is not a video); a media file (by
+/// name or by probe) its file name and host. Null for text that is not an http(s) link.
+Future<LinkPreview?> previewLink(String url, {LinkProber probe = defaultLinkProber}) async {
   final uri = Uri.tryParse(url.trim());
   if (uri == null || !(uri.scheme == 'http' || uri.scheme == 'https') || uri.host.isEmpty) return null;
-  final plain = LinkPreview(title: LinkMedia(url.trim()).label, subtitle: _host(uri));
-  if (!isYouTubeLink(uri)) return plain;
+  final host = _host(uri);
+  // A media file name needs no lookup.
+  if (hasMediaExtension(uri)) return LinkPreview(title: LinkMedia(url.trim()).label, subtitle: host);
+  final LinkProbe p;
   try {
-    final body = await get(Uri.https('www.youtube.com', '/oembed', {'url': url.trim(), 'format': 'json'}));
-    final j = jsonDecode(body);
-    if (j is! Map || j['title'] is! String) return plain;
-    final author = j['author_name'];
-    return LinkPreview(
-      title: j['title'] as String,
-      subtitle: [_host(uri), if (author is String && author.isNotEmpty) author].join(' · '),
-      thumbnail: j['thumbnail_url'] is String ? j['thumbnail_url'] as String : null,
-    );
-  } catch (_) {
-    return plain;
+    p = await probe(url.trim());
+  } catch (e) {
+    return LinkPreview(title: LinkMedia(url.trim()).label, subtitle: '$host · $e');
   }
+  final info = p.info;
+  if (!p.isPage) return LinkPreview(title: LinkMedia(url.trim()).label, subtitle: host);
+  if (info == null) {
+    return LinkPreview(title: p.title ?? host, subtitle: '$host · ${notAVideoText(p.ytDlpError)}');
+  }
+  return LinkPreview(
+    title: p.title ?? host,
+    subtitle: [
+      host,
+      if (info.uploader.isNotEmpty) info.uploader,
+      if (info.duration case final d? when d > 0) clockText(d),
+    ].join(' · '),
+    thumbnail: info.thumbnail,
+  );
 }
 
 /// "today", "yesterday", "3 days ago", "last week", "5 weeks ago", ...
@@ -195,14 +196,14 @@ class LibraryLinkSource extends StatefulWidget {
   /// Puts the link up; returns an error text, or null when sent.
   final Future<String?> Function(LinkMedia media) onPutUp;
   final RecentLinks recents;
-  final OEmbedGetter oembed;
+  final LinkProber probe;
   const LibraryLinkSource({
     super.key,
     required this.controller,
     required this.onPutUp,
     required this.recents,
     this.offlineHint,
-    this.oembed = defaultOEmbedGet,
+    this.probe = defaultLinkProber,
   });
 
   @override
@@ -246,7 +247,7 @@ class _LibraryLinkSourceState extends State<LibraryLinkSource> {
       if (mounted) setState(() {});
       return;
     }
-    final p = await previewLink(url, get: widget.oembed);
+    final p = await previewLink(url, probe: widget.probe);
     _previews[url] = p;
     if (mounted) setState(() {});
   }
@@ -272,7 +273,7 @@ class _LibraryLinkSourceState extends State<LibraryLinkSource> {
       error = '$e';
     }
     if (error == null) {
-      final p = _previews[url] ?? await previewLink(url, get: widget.oembed);
+      final p = _previews[url] ?? await previewLink(url, probe: widget.probe);
       unawaited(widget.recents.add(RecentLink(
         url: url,
         title: p?.title ?? LinkMedia(url).label,
@@ -346,7 +347,7 @@ class _LibraryLinkSourceState extends State<LibraryLinkSource> {
               Text('Watch from a link', textAlign: TextAlign.center, style: t.headlineSmall),
               const SizedBox(height: 6),
               Text(
-                'A video file, YouTube, a Jellyfin link… Ctrl+V or drop it anywhere to bring it here.',
+                'A video file, a page (YouTube, X, …) or a Jellyfin link. Ctrl+V or drop it anywhere to bring it here.',
                 textAlign: TextAlign.center,
                 style: TextStyle(color: scheme.onSurfaceVariant),
               ),

apps/desktop/lib/src/shell/library_tab.dart

@@ -83,7 +83,7 @@ class LibraryTab extends StatefulWidget {
   final VoidCallback? onOpenIntegrations;
   /// Defaults to [RecentLinks.instance].
   final RecentLinks? recentLinks;
-  final OEmbedGetter oembed;
+  final LinkProber probe;
   /// The Files source (tests inject one); defaults to [FilesPage].
   final Widget Function(BuildContext context, {required bool online, required bool relayed,
       required Future<String?> Function(String path) onPlay, String? nowPlayingPath})? filesBuilder;
@@ -100,7 +100,7 @@ class LibraryTab extends StatefulWidget {
     this.jellyfinStart,
     this.onOpenIntegrations,
     this.recentLinks,
-    this.oembed = defaultOEmbedGet,
+    this.probe = defaultLinkProber,
     this.filesBuilder,
     this.now = DateTime.now,
   });
@@ -245,7 +245,7 @@ class _LibraryTabState extends State<LibraryTab> {
           controller: _c,
           offlineHint: _hint,
           recents: widget.recentLinks ?? RecentLinks.instance,
-          oembed: widget.oembed,
+          probe: widget.probe,
           onPutUp: _put,
         ),
       MediaKind.file => _files(context),

apps/desktop/lib/src/shell/settings_tab.dart

@@ -2,10 +2,12 @@ import 'dart:async';
 
 import 'package:flutter/material.dart';
 import 'package:signals/signals_flutter.dart';
+import 'package:sync_relay_core/core.dart' show YtDlp;
 
 import '../controls/player_settings.dart';
 import '../jellyfin/accounts.dart';
 import '../jellyfin/accounts_panel.dart';
+import '../playback/yt_dlp_app.dart';
 import '../schedule/animeflow.dart';
 import '../screens/home/about_page.dart';
 import '../screens/home/settings_page.dart';
@@ -107,6 +109,7 @@ class SettingsTab extends StatelessWidget {
             child: Column(crossAxisAlignment: CrossAxisAlignment.stretch, children: playerSettingRows()),
           ),
           const SettingsPanel(title: 'Custom shaders', child: CustomShaderFiles()),
+          const SettingsPanel(title: 'yt-dlp', child: YtDlpSettings()),
         ];
       case SettingsSection.integrations:
         final accounts = jellyfin ?? JellyfinAccounts.instance;
@@ -352,6 +355,67 @@ class RecentServersPanel extends StatelessWidget {
   }
 }
 
+/// The app's yt-dlp (web page links): its version, "Update now", and the
+/// last error.
+class YtDlpSettings extends StatefulWidget {
+  /// Defaults to [AppYtDlp.instance]'s.
+  final Future<YtDlp>? ytDlp;
+  const YtDlpSettings({super.key, this.ytDlp});
+
+  @override
+  State<YtDlpSettings> createState() => _YtDlpSettingsState();
+}
+
+class _YtDlpSettingsState extends State<YtDlpSettings> {
+  late final Future<YtDlp> _y = widget.ytDlp ?? AppYtDlp.instance.ytDlp;
+
+  @override
+  Widget build(BuildContext context) {
+    final scheme = Theme.of(context).colorScheme;
+    return FutureBuilder<YtDlp>(
+      future: _y,
+      builder: (context, snap) {
+        final y = snap.data;
+        if (y == null) return const SizedBox.shrink();
+        return StreamBuilder<void>(
+          stream: y.changes,
+          builder: (context, _) {
+            final err = y.lastError;
+            return Column(
+              crossAxisAlignment: CrossAxisAlignment.stretch,
+              children: [
+                ListTile(
+                  contentPadding: EdgeInsets.zero,
+                  leading: const Icon(Icons.travel_explore),
+                  title: Text(y.busy
+                      ? 'Downloading…'
+                      : y.version == null
+                          ? 'Not downloaded yet'
+                          : 'Version ${y.version}'),
+                  subtitle: err == null
+                      ? null
+                      : Text(err, key: const ValueKey('ytdlp-error'), style: TextStyle(color: scheme.error)),
+                  trailing: TextButton(
+                    onPressed: y.busy
+                        ? null
+                        : () => y.path == null ? y.ensure() : y.update(force: true),
+                    child: const Text('Update now'),
+                  ),
+                ),
+                Text(
+                  'Plays links to web pages (YouTube, X, …) in all three link modes. '
+                  'Downloaded and kept up to date by the app; checked once a day.',
+                  style: TextStyle(color: scheme.onSurfaceVariant, fontSize: 12),
+                ),
+              ],
+            );
+          },
+        );
+      },
+    );
+  }
+}
+
 /// AnimeFlow (the Schedule tab's source): connected as whom, with which
 /// rights, or why not.
 class AnimeFlowCard extends StatefulWidget {

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

@@ -8,6 +8,7 @@ import 'package:sync_relay_core/core.dart';
 
 import '../jellyfin/accounts.dart';
 import '../jellyfin/session_media.dart';
+import '../playback/yt_dlp_app.dart';
 import '../sfx/sfx.dart';
 import '../sfx/synth_sfx.dart';
 import '../session/health.dart';
@@ -165,6 +166,16 @@ class SessionState {
   /// Set when the hosted server died mid-session; Home shows it on the
   /// Host card and clears it.
   final serverCrash = signal<String?>(null);
+
+  /// The app's yt-dlp folder for the hosted server; '' (the server's own
+  /// default) when the app-support folder is not available.
+  static Future<String> _sharedYtDlpDir() async {
+    try {
+      return (await AppYtDlp.instance.ytDlp).dir;
+    } catch (_) {
+      return '';
+    }
+  }
   ServerIsolate? _server;
   String? _setupCrash;
 
@@ -258,6 +269,7 @@ class SessionState {
             mediaPath: params.mediaPath,
             hostKey: hostKey,
             jellyfin: relay,
+            ytDlpDir: await _sharedYtDlpDir(),
           ),
           onLog: (line) => debugPrint('[server] $line'),
           onCrash: (cause) => _onServerCrash(server, cause),

apps/desktop/linux/CMakeLists.txt

@@ -7,7 +7,7 @@ project(runner LANGUAGES CXX)
 set(BINARY_NAME "watch_together")
 # The unique GTK application identifier for this application. See:
 # https://wiki.gnome.org/HowDoI/ChooseApplicationID
-set(APPLICATION_ID "com.example.watch_together")
+set(APPLICATION_ID "moe.senkochan.watch_together")
 
 # Explicitly opt in to modern CMake behaviors to avoid warnings with recent
 # versions of CMake.

apps/desktop/linux/runner/my_application.cc

@@ -54,6 +54,19 @@ static void my_application_activate(GApplication* application) {
 
   gtk_window_set_default_size(window, 1280, 720);
 
+  // The window icon (X11; Wayland takes it from the .desktop file the app
+  // installs for its application id).
+  {
+    g_autofree gchar* exe = g_file_read_link("/proc/self/exe", nullptr);
+    if (exe != nullptr) {
+      g_autofree gchar* dir = g_path_get_dirname(exe);
+      g_autofree gchar* icon = g_build_filename(
+          dir, "data", "flutter_assets", "assets", "icon", "icon_256.png",
+          nullptr);
+      gtk_window_set_icon_from_file(window, icon, nullptr);
+    }
+  }
+
   g_autoptr(FlDartProject) project = fl_dart_project_new();
   fl_dart_project_set_dart_entrypoint_arguments(
       project, self->dart_entrypoint_arguments);

apps/desktop/pubspec.yaml

@@ -38,3 +38,4 @@ flutter:
   uses-material-design: true
   assets:
     - assets/shaders/anime4k/
+    - assets/icon/

apps/desktop/test/library_rows_test.dart

@@ -189,23 +189,21 @@ void main() {
       expect(decodeRecentLinks(jsonEncode([{'url': ''}, {'url': 'https://a/b.mkv'}])).single.title, 'b.mkv');
     });
 
-    test('preview: YouTube via oEmbed, other links by file name, failures fall back', () async {
-      Uri? asked;
-      final yt = await previewLink('https://www.youtube.com/watch?v=abc', get: (uri) async {
-        asked = uri;
-        return jsonEncode({'title': 'A video', 'author_name': 'Chan', 'thumbnail_url': 'https://i.ytimg/x.jpg'});
-      });
-      expect(asked!.host, 'www.youtube.com');
-      expect(asked!.path, '/oembed');
-      expect(asked!.queryParameters, {'url': 'https://www.youtube.com/watch?v=abc', 'format': 'json'});
-      expect((yt!.title, yt.subtitle, yt.thumbnail), ('A video', 'youtube.com · Chan', 'https://i.ytimg/x.jpg'));
+    test('preview: a page by yt-dlp, a file by its name, else why not', () async {
+      final yt = await previewLink('https://www.youtube.com/watch?v=abc',
+          probe: (url) async => LinkProbe.page(Uri.parse(url),
+              info: const YtDlpInfo(
+                  title: 'A video', uploader: 'Chan', duration: 187, thumbnail: 'https://i.ytimg/x.jpg')));
+      expect((yt!.title, yt.subtitle, yt.thumbnail), ('A video', 'youtube.com · Chan · 3:07', 'https://i.ytimg/x.jpg'));
 
       final file = await previewLink('https://cdn.example/dir/My%20Movie.mkv?sig=1',
-          get: (_) => throw StateError('no lookup for plain links'));
+          probe: (url) async => LinkProbe.file(Uri.parse(url), 10));
       expect((file!.title, file.subtitle, file.thumbnail), ('My Movie.mkv', 'cdn.example', null));
 
-      final down = await previewLink('https://youtu.be/abc', get: (_) async => throw Exception('offline'));
-      expect((down!.title, down.subtitle), ('abc', 'youtu.be'));
+      final page = await previewLink('https://example.com/a',
+          probe: (url) async => LinkProbe.page(Uri.parse(url), pageTitle: 'Example', ytDlpError: 'Unsupported URL'));
+      expect((page!.title, page.subtitle),
+          ('Example', "example.com · Not a video (and yt-dlp couldn't read it: Unsupported URL)"));
       expect(await previewLink('not a link'), isNull);
     });
 

apps/desktop/test/library_tab_test.dart

@@ -108,10 +108,9 @@ Future<Harness> pumpLibrary(
         jellyfinStart: start,
         recentLinks: h.recents,
         now: () => fixtureNow,
-        oembed: (uri) async => jsonEncode({
-          'title': 'A video',
-          'author_name': 'Chan',
-        }),
+        probe: (url) async => url.endsWith('.mkv')
+            ? LinkProbe.file(Uri.parse(url), 1)
+            : LinkProbe.page(Uri.parse(url), info: const YtDlpInfo(title: 'A video', uploader: 'Chan')),
         filesBuilder: (context, {required online, required relayed, required onPlay, nowPlayingPath}) =>
             FilesStub(online: online, relayed: relayed, onPlay: onPlay),
         onPutUp: (m) async {

apps/desktop/test/relay_e2e_test.dart

@@ -7,6 +7,7 @@ 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/track_prefs.dart';
+import 'package:watch_together/src/playback/yt_dlp_app.dart';
 import 'package:watch_together/src/screens/home/picked_media.dart';
 import 'package:watch_together/src/session/session_coordinator.dart';
 
@@ -67,7 +68,10 @@ void main() {
   Future<SessionCoordinator> member(String name) async {
     final acc = JellyfinAccounts(store: MemoryJellyfinStore());
     await acc.ensureLoaded(validate: false);
-    final c = SessionCoordinator(jellyfin: acc, trackPrefs: TrackPrefs(store: MemoryJellyfinStore()));
+    final c = SessionCoordinator(
+        jellyfin: acc,
+        trackPrefs: TrackPrefs(store: MemoryJellyfinStore()),
+        ytDlp: AppYtDlp(YtDlp('$_tmp/relay_e2e_no_ytdlp', enabled: false)));
     all.add(c);
     await c.connect(ConnectParams(host: '127.0.0.1', port: server.boundPort, secret: 'pw', name: name));
     await c.playback.player.setVolume(0);
@@ -150,7 +154,7 @@ void main() {
       await playTogether([alice, bob]);
       expect(hits.length, greaterThan(before));
 
-      // A page instead of a file is refused up front.
+      // A page yt-dlp cannot read is refused up front.
       final page = await HttpServer.bind(InternetAddress.loopbackIPv4, 0);
       page.listen((r) {
         r.response.headers.contentType = ContentType.html;
@@ -158,7 +162,7 @@ void main() {
         r.response.close();
       });
       expect(await alice.swapPicked(LinkMedia('http://127.0.0.1:${page.port}/watch?v=x', relay: LinkRelay.me)),
-          contains('cannot pass this link on'));
+          contains('Not a video'));
       await page.close(force: true);
     } finally {
       await origin.close(force: true);