Errors: refuse links the probe can't play (with Put it up anyway), plain error texts, and others see who can't play

report.error / state.members[].error (optional, no protocol bump): an
errored member is out of the ready gate until its player opens the media
or the media changes; others see "Bob can't play this: ..." and a mark
on the avatar; your own pill offers Retry (reload).

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

README.md

@@ -145,7 +145,10 @@ folder to Files, or fill Link).
   what it is (a page's title, uploader, length and thumbnail, else the
   file name); in a server, pick how the
   others get it (everyone fetches it, the server fetches it, or through
-  you). Your last 12 links are listed under it.
+  you). Your last 12 links are listed under it. A link that does not
+  open here (needs cookies, 403, 404, not a video) says why and goes up
+  only with "Put it up anyway"; in the player, whoever cannot play it is
+  named ("Bob can't play this: Not allowed (403)") and nobody waits for them.
 - **Files**: video folders you add on this computer, grouped by series
   (click a series to list its episodes), or any file through Browse. The others stream it from you.
 

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

@@ -16,7 +16,10 @@ enum LinkRelay { direct, server, me }
 final class LinkMedia extends PickedMedia {
   final String url;
   final LinkRelay relay;
-  const LinkMedia(this.url, {this.relay = LinkRelay.direct});
+  /// Put it up even though this computer's probe found a problem
+  /// (`LinkProbe.problem`): the server or a friend may still open it.
+  final bool anyway;
+  const LinkMedia(this.url, {this.relay = LinkRelay.direct, this.anyway = false});
 
   @override
   String get label {

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

@@ -182,6 +182,10 @@ class SessionCoordinator {
   final toasts = signal<List<ToastItem>>([]);
   final reconnecting = signal(false);
   final starving = signal<String?>(null);
+  /// Why this player cannot open the current media, in plain words
+  /// ([playErrorText]); empty while it can. It rides in `report.error`, so
+  /// the server stops waiting for this member and the others see it.
+  final playerError = signal('');
 
   /// The current media's Jellyfin ref (null for links and files).
   final currentRef = signal<JellyfinRef?>(null);
@@ -318,6 +322,12 @@ class SessionCoordinator {
   int _advanceDoneFor = -1;
   String _blockedKey = '';
   bool _jellyfinListening = false;
+  // The mediaId [playerError] belongs to, and the player's duration when
+  // it came: a new duration means the media opened after all.
+  int _playerErrorFor = -1;
+  Duration _playerErrorDuration = Duration.zero;
+  // Members' last `error`, by id, so a new one toasts once.
+  Map<String, String> _memberErrors = const {};
 
   SessionCoordinator(
       {this.sfx = const NoopSfxService(), JellyfinAccounts? jellyfin, TrackPrefs? trackPrefs, AppYtDlp? ytDlp})
@@ -332,8 +342,8 @@ 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.onYtdlError = _setPlayerError;
-      playback.onLoadError = (e) => health.value = HealthStatus(HealthSeverity.error, "can't play this: $e");
+      playback.onLoadError = _setPlayerError;
       playback.onUserSeek = (d) => _userSeek(d.inMicroseconds / 1e6);
       await playback.init();
       _playerReady = true;
@@ -345,6 +355,35 @@ class SessionCoordinator {
     }
   }
 
+  void _setPlayerError(String raw) {
+    debugPrint('player cannot open media $_mediaId: $raw');
+    _playerErrorFor = _mediaId;
+    _playerErrorDuration = playback.duration.peek();
+    playerError.value = playErrorText(raw);
+  }
+
+  /// Clears [playerError] once the media opened (a new duration) or the
+  /// server moved to another media.
+  void _checkPlayerError(int mediaId) {
+    if (playerError.peek().isEmpty) return;
+    final d = playback.duration.peek();
+    if (_playerErrorFor != mediaId || (d > Duration.zero && d != _playerErrorDuration)) {
+      playerError.value = '';
+    }
+  }
+
+  /// A member's new `error` toasts once (the pill is hidden while playing).
+  void _toastMemberErrors(StateBroadcast r) {
+    final now = {for (final m in r.members) if (m.error.isNotEmpty) m.id: m.error};
+    for (final m in r.members) {
+      final e = now[m.id];
+      if (e != null && m.id != sync.memberId && _memberErrors[m.id] != e) {
+        _pushToast("${m.name} can't play this: $e", actor: m.name);
+      }
+    }
+    _memberErrors = now;
+  }
+
   bool _reloadingVideo = false;
 
   /// "Reload video" (button, Ctrl+R, frozen-picture watchdog): fresh
@@ -398,6 +437,8 @@ class SessionCoordinator {
     diff.reset();
     _mediaId = -1;
     _openUrl = null;
+    playerError.value = '';
+    _memberErrors = const {};
     _lastReady = false;
     _restoringReady = false;
     _lastOut = false;
@@ -495,8 +536,7 @@ class SessionCoordinator {
       return true;
     } catch (e) {
       debugPrint('open media failed: $e');
-      health.value =
+      _setPlayerError('$e');
-          HealthStatus(HealthSeverity.error, 'cannot open media: $e');
       return false;
     } finally {
       _opening = false;
@@ -614,6 +654,8 @@ class SessionCoordinator {
   void _onState(StateBroadcast r) {
     _lastStateAt = DateTime.now().toUtc();
     serverState.value = r;
+    _toastMemberErrors(r);
+    _checkPlayerError(r.mediaId);
     _maybeSendArt(r);
     _queuedState = r;
     if (_applying) return;
@@ -917,6 +959,8 @@ class SessionCoordinator {
       // Duration only once the open media is the server's current one.
       // Sitting out: still a report (it keeps this member fresh), empty.
       final known = !_lastOut && !_opening && _openUrl != null && _mediaId == r.mediaId;
+      _checkPlayerError(r.mediaId);
+      final error = playerError.peek();
       sync.sendReport(
         position: _lastOut ? 0 : playback.positionSecs,
         buffered: _lastOut ? 0 : playback.bufferedSecsAhead,
@@ -924,6 +968,7 @@ class SessionCoordinator {
         duration: known ? playback.durationSecs : 0,
         mediaId: known ? r.mediaId : 0,
         jf: _jfAccessFor(r),
+        error: known && _playerErrorFor == r.mediaId ? error : '',
       );
       if (!_lastOut) {
         _checkSeekLanded(r);
@@ -1244,10 +1289,13 @@ class SessionCoordinator {
   /// A pasted link: a recognised Jellyfin item link goes up as a ref
   /// (see [mediaForLink]) that this member relays for viewers without an
   /// account (with the link's key, which stays here); anything else as the
-  /// link, or relayed per [relay]. Returns an error text, or null when sent.
+  /// link, or relayed per [relay]. A link this computer cannot open (its
-  Future<String?> swapLink(String url, {LinkRelay relay = LinkRelay.direct}) async {
+  /// probe's [LinkProbe.problem], or unreachable) is refused with the
+  /// reason in plain words unless [anyway]. Returns an error text, or null
+  /// when sent.
+  Future<String?> swapLink(String url, {LinkRelay relay = LinkRelay.direct, bool anyway = false}) async {
     markInput();
-    _lastPick = LinkMedia(url, relay: relay);
+    _lastPick = LinkMedia(url, relay: relay, anyway: anyway);
     final media = await mediaForLink(jellyfin, url);
     if (media.jellyfin != null) {
       _pendingOrigin = _JellyfinOrigin(url);
@@ -1261,6 +1309,8 @@ class SessionCoordinator {
     } catch (e) {
       probeError = '$e';
     }
+    final problem = probe == null ? playErrorText(probeError ?? '') : probe.problem;
+    if (problem != null && !anyway) return problem;
     // 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);
@@ -1271,9 +1321,9 @@ class SessionCoordinator {
     if (relay == LinkRelay.me) {
       // This computer reads it: a file, or a page's formats (one file,
       // separate video and audio tracks, or segmented playlists).
-      if (probe == null) return 'cannot pass this link on: $probeError';
+      if (probe == null) return problem;
-      final problem = probe.relayProblem;
+      final relayProblem = probe.relayProblem;
-      if (problem != null) return problem;
+      if (relayProblem != null) return relayProblem;
       final y = await ytDlp.ytDlp;
       final check = LinkRelayMedia(uri, ytDlp: y, probe: probe);
       var size = 0;
@@ -1352,8 +1402,8 @@ class SessionCoordinator {
   /// Any picker selection.
   Future<String?> swapPicked(PickedMedia media) async {
     switch (media) {
-      case LinkMedia(:final url, :final relay):
+      case LinkMedia(:final url, :final relay, :final anyway):
-        return swapLink(url, relay: relay);
+        return swapLink(url, relay: relay, anyway: anyway);
       case JellyfinMedia():
         swapJellyfin(media);
       case FileMedia(:final path):

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

@@ -379,7 +379,7 @@ class AppShellState extends State<AppShell> with SingleTickerProviderStateMixin
       if (error != null || !mounted) return error;
     }
     // Alone, a link plays direct: there is nobody to pass it on to.
-    if (media is LinkMedia && session.solo.peek()) media = LinkMedia(media.url);
+    if (media is LinkMedia && session.solo.peek()) media = LinkMedia(media.url, anyway: media.anyway);
     final error = await session.coordinator.swapPicked(media);
     if (error != null || !mounted) return error;
     final f = session.lastForm;

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

@@ -19,6 +19,9 @@ class AvatarInfo {
   final bool ready, buffering, relaying, stale, host, self;
   /// Sitting out: dimmed, with an "away" mark.
   final bool out;
+  /// Why their player cannot open the media (`members[].error`): an error
+  /// mark; empty when it can.
+  final String error;
   const AvatarInfo({
     this.id = '',
     required this.name,
@@ -31,6 +34,7 @@ class AvatarInfo {
     this.host = false,
     this.self = false,
     this.out = false,
+    this.error = '',
   });
 }
 
@@ -78,7 +82,7 @@ ImageProvider? memberAvatarImage(MemberView m, SessionCoordinator coord) {
 }
 
 /// Your own avatar from the profile (also offline).
-AvatarInfo selfAvatarInfo({bool ready = false, bool host = false, bool out = false}) {
+AvatarInfo selfAvatarInfo({bool ready = false, bool host = false, bool out = false, String error = ''}) {
   final p = Profile.instance;
   final png = p.picture.value;
   final name = p.name.value;
@@ -90,6 +94,7 @@ AvatarInfo selfAvatarInfo({bool ready = false, bool host = false, bool out = fal
     host: host,
     self: true,
     out: out,
+    error: error,
   );
 }
 
@@ -104,7 +109,7 @@ AvatarInfo memberAvatarInfo(MemberView m, StateBroadcast? r, SessionCoordinator
     color: self ? Profile.instance.color.value : colorForName(m.name),
     image: memberAvatarImage(m, coord),
     ready: m.ready,
-    buffering: !m.stale && m.ready && playing && m.buffered < r!.bufferNeed,
+    buffering: !m.stale && m.ready && m.error.isEmpty && playing && m.buffered < r!.bufferNeed,
     relaying: relay != null && relay.source.isNotEmpty && relay.source == m.id,
     stale: m.stale,
     // The state marks the host (`members[].host`); your own app also
@@ -112,6 +117,7 @@ AvatarInfo memberAvatarInfo(MemberView m, StateBroadcast? r, SessionCoordinator
     host: m.host || (self && coord.hostFile != null),
     self: self,
     out: m.out,
+    error: m.error,
   );
 }
 
@@ -138,7 +144,7 @@ class PartyWatch extends StatelessWidget {
 /// Circle avatar with a status ring outside it and a gap in the background
 /// colour, so overlapping neighbours never hide the status. Crown = host,
 /// tower = passing the video on, spinner = buffering, dimmed = stale,
-/// dimmed with a moon = sitting out.
+/// dimmed with a moon = sitting out, red "!" = cannot play the media.
 class StatusAvatar extends StatelessWidget {
   final AvatarInfo info;
   final double size;
@@ -222,6 +228,17 @@ class StatusAvatar extends StatelessWidget {
                 child: Icon(Icons.bedtime, size: (badge * 0.8).clamp(10.0, 24.0), color: Colors.blueGrey.shade200),
               ),
             ),
+          if (info.error.isNotEmpty)
+            Positioned(
+              key: const ValueKey('error-mark'),
+              right: -3,
+              top: -3,
+              child: Container(
+                padding: const EdgeInsets.all(1),
+                decoration: BoxDecoration(shape: BoxShape.circle, color: bg),
+                child: Icon(Icons.error, size: (badge * 0.8).clamp(10.0, 24.0), color: Colors.redAccent.shade200),
+              ),
+            ),
           if (badges && info.relaying)
             Positioned(
               right: -3,
@@ -287,7 +304,9 @@ class _AvatarStackState extends State<AvatarStack> {
                   left: i * step,
                   top: 0,
                   child: Tooltip(
-                    message: visible[i].name,
+                    message: visible[i].error.isEmpty
+                        ? visible[i].name
+                        : "${visible[i].name} can't play this: ${visible[i].error}",
                     child: StatusAvatar(info: visible[i], size: size),
                   ),
                 ),

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

@@ -3,7 +3,7 @@ import 'dart:convert';
 
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
-import 'package:sync_relay_core/core.dart' show LinkProbe, hasMediaExtension, notAVideoText;
+import 'package:sync_relay_core/core.dart' show LinkProbe, hasMediaExtension, parseJellyfinLink, playErrorText;
 
 import '../playback/yt_dlp_app.dart';
 import '../screens/home/media_picker.dart';
@@ -107,7 +107,10 @@ class LinkPreview {
   /// "youtube.com · Channel", or the host.
   final String subtitle;
   final String? thumbnail;
-  const LinkPreview({required this.title, required this.subtitle, this.thumbnail});
+  /// Why this computer cannot open it, in plain words ([LinkProbe.problem]);
+  /// null when it looks playable.
+  final String? problem;
+  const LinkPreview({required this.title, required this.subtitle, this.thumbnail, this.problem});
 }
 
 /// What a link is (see [AppYtDlp.probe]).
@@ -125,24 +128,30 @@ String clockText(double seconds) {
 }
 
 /// 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
+/// duration and thumbnail; a media file its file name and host; a link
-/// name or by probe) its file name and host. Null for text that is not an http(s) link.
+/// that does not open, why ([LinkPreview.problem]). 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 host = _host(uri);
-  // A media file name needs no lookup.
+  // A Jellyfin item goes up as the item (see `mediaForLink`), not the page.
-  if (hasMediaExtension(uri)) return LinkPreview(title: LinkMedia(url.trim()).label, subtitle: host);
+  if (parseJellyfinLink(url.trim()) != null) return LinkPreview(title: host, subtitle: '$host · Jellyfin');
+  final file = hasMediaExtension(uri);
   final LinkProbe p;
   try {
     p = await probe(url.trim());
   } catch (e) {
-    return LinkPreview(title: LinkMedia(url.trim()).label, subtitle: '$host · $e');
+    final problem = playErrorText('$e');
+    return LinkPreview(title: LinkMedia(url.trim()).label, subtitle: '$host · $problem', problem: problem);
   }
   final info = p.info;
   if (!p.isPage) return LinkPreview(title: LinkMedia(url.trim()).label, subtitle: host);
-  if (info == null) {
+  final problem = p.problem;
-    return LinkPreview(title: p.title ?? host, subtitle: '$host · ${notAVideoText(p.ytDlpError)}');
+  if (info == null || problem != null) {
+    // A media file name that did not answer as one keeps its name.
+    final title = file ? LinkMedia(url.trim()).label : p.title ?? host;
+    return LinkPreview(title: title, subtitle: '$host · ${problem ?? 'Not a video'}', problem: problem);
   }
   return LinkPreview(
     title: p.title ?? host,
@@ -221,6 +230,8 @@ class _LibraryLinkSourceState extends State<LibraryLinkSource> {
   Timer? _debounce;
   bool _busy = false;
   String? _error;
+  /// [_error] is the probe's problem: "Put it up anyway" is offered.
+  bool _canForce = false;
 
   @override
   void initState() {
@@ -242,7 +253,12 @@ class _LibraryLinkSourceState extends State<LibraryLinkSource> {
     if (url == _previewUrl) return;
     _debounce?.cancel();
     _debounce = Timer(const Duration(milliseconds: 350), () => _preview(url));
-    if (mounted) setState(() => _error = null);
+    if (mounted) {
+      setState(() {
+        _error = null;
+        _canForce = false;
+      });
+    }
   }
 
   Future<void> _preview(String url) async {
@@ -263,19 +279,27 @@ class _LibraryLinkSourceState extends State<LibraryLinkSource> {
     } catch (_) {}
   }
 
-  Future<void> _go() async {
+  Future<void> _go({bool anyway = false}) async {
     final url = _c.link.text.trim();
     if (url.isEmpty || _busy) return;
     setState(() {
       _busy = true;
       _error = null;
+      _canForce = false;
     });
-    String? error;
+    // What the probe found refuses it here, with "Put it up anyway": the
-    try {
+    // server or a friend (with cookies) may still open it.
-      error = await widget.onPutUp(LinkMedia(url, relay: widget.solo ? LinkRelay.direct : _c.linkRelay));
+    final problem = anyway ? null : (_previews[url] ?? await previewLink(url, probe: widget.probe))?.problem;
-    } catch (e) {
+    String? error = problem;
-      error = '$e';
+    if (problem == null) {
+      try {
+        error = await widget.onPutUp(
+            LinkMedia(url, relay: widget.solo ? LinkRelay.direct : _c.linkRelay, anyway: anyway));
+      } catch (e) {
+        error = '$e';
+      }
     }
+    final canForce = problem != null;
     if (error == null) {
       final p = _previews[url] ?? await previewLink(url, probe: widget.probe);
       unawaited(widget.recents.add(RecentLink(
@@ -289,6 +313,7 @@ class _LibraryLinkSourceState extends State<LibraryLinkSource> {
     setState(() {
       _busy = false;
       _error = error;
+      _canForce = canForce;
     });
   }
 
@@ -373,6 +398,14 @@ class _LibraryLinkSourceState extends State<LibraryLinkSource> {
                   textAlign: TextAlign.center,
                   style: t.bodySmall?.copyWith(color: _error != null ? scheme.error : Colors.grey),
                 ),
+                if (_canForce)
+                  Center(
+                    child: TextButton(
+                      key: const ValueKey('link-put-up-anyway'),
+                      onPressed: _busy ? null : () => _go(anyway: true),
+                      child: Text(solo ? 'Play it anyway' : 'Put it up anyway'),
+                    ),
+                  ),
               ],
               AnimatedSize(
                 duration: easeTime,
@@ -475,9 +508,9 @@ class _PreviewCard extends StatelessWidget {
                       const SizedBox(height: 4),
                       Text(
                         p?.subtitle ?? 'Paste an http(s) address',
-                        maxLines: 1,
+                        maxLines: 2,
                         overflow: TextOverflow.ellipsis,
-                        style: const TextStyle(color: Colors.grey),
+                        style: TextStyle(color: p?.problem != null ? scheme.error : Colors.grey),
                       ),
                     ],
                   ),

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

@@ -103,6 +103,7 @@ class PartyStrip extends StatelessWidget {
                   info: selfAvatarInfo(
                     ready: self?.ready ?? false,
                     host: online && !solo && coord.hostFile != null,
+                    error: online ? coord.playerError.value : '',
                   ),
                   size: stripAvatarSize,
                   ring: online,
@@ -553,6 +554,8 @@ class _MemberTile extends StatelessWidget {
         ? 'reconnecting…'
         : m.out
         ? 'sitting out'
+        : m.error.isNotEmpty
+        ? "can't play this: ${m.error}"
         : info.buffering
         ? 'buffering ${m.buffered.toStringAsFixed(1)} s'
         : m.ready

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

@@ -11,11 +11,12 @@ import 'avatar.dart';
 import 'motion.dart';
 
 /// What the player's status pill says, most pressing first.
-enum StatusKind { reconnecting, problem, connecting, finished, loading, you, waiting }
+enum StatusKind { reconnecting, problem, connecting, finished, loading, you, cannotPlay, waiting }
 
-/// The pill's button: stop reconnecting, retry, or mark yourself ready
+/// The pill's button: stop reconnecting, retry (reconnect), reload the
-/// (the whole pill).
+/// video (your player could not open it), or mark yourself ready (the
-enum StatusAction { cancel, retry, ready }
+/// whole pill).
+enum StatusAction { cancel, retry, reload, ready }
 
 /// One status line: [text], a muted [detail], a coloured [tone] for
 /// problems (warn, error), the members it is about ([who]; [self] for you)
@@ -55,18 +56,24 @@ String _sentence(String s) => s.isEmpty ? s : s[0].toUpperCase() + s.substring(1
 
 /// The player's status from the session's signals; null when there is
 /// nothing to say (playing, connected, everyone ready). [slowConnect]:
-/// connecting has taken over 2 s.
+/// connecting has taken over 2 s. [playerError]: why your player cannot
+/// open the media (the coordinator's `playerError`).
 StatusView? playerStatusFor({
   required HealthStatus health,
   bool reconnecting = false,
   StateBroadcast? state,
   MemberView? self,
   bool slowConnect = false,
+  String playerError = '',
 }) {
   if (reconnecting) {
     return const StatusView(StatusKind.reconnecting, 'Reconnecting…',
         tone: HealthSeverity.warn, action: StatusAction.cancel);
   }
+  if (playerError.isNotEmpty && state?.media != null && !(self?.out ?? false)) {
+    return StatusView(StatusKind.problem, "Can't play this: $playerError",
+        tone: HealthSeverity.error, action: StatusAction.reload, short: "Can't play this");
+  }
   if (health.severity == HealthSeverity.warn || health.severity == HealthSeverity.error) {
     return StatusView(StatusKind.problem, _sentence(health.message),
         tone: health.severity, action: StatusAction.retry);
@@ -81,6 +88,12 @@ StatusView? playerStatusFor({
   if (r.transport == 'finished') {
     return const StatusView(StatusKind.finished, 'Finished · seek back or pick the next video', short: 'Finished');
   }
+  // Members whose player cannot open it: the server does not wait for
+  // them; say why instead of "waiting for".
+  final failed = [
+    for (final m in r.members)
+      if (m.error.isNotEmpty && !m.out && (self == null || m.id != self.id)) m,
+  ];
   // As the server holds playback: someone in the ready set short of the
   // minimum buffer.
   final need = r.bufferNeed;
@@ -92,12 +105,22 @@ StatusView? playerStatusFor({
           who: [m], self: you, progress: p, detail: '${(p * 100).round()}%');
     }
   }
+  if (failed.isNotEmpty) {
+    final f = failed.first;
+    final who = nameList([for (final m in failed) m.name]);
+    final unready = self != null && !self.ready;
+    return StatusView(StatusKind.cannotPlay, "$who can't play this: ${f.error}",
+        who: failed,
+        short: "$who can't play this",
+        detail: unready ? "Press Space when you're ready" : null,
+        action: unready ? StatusAction.ready : null);
+  }
   if (self != null && !self.ready) {
     return StatusView(StatusKind.you, "Press Space when you're ready",
         who: [self], self: true, action: StatusAction.ready, detail: 'or click here', short: 'Press Space when ready');
   }
   // Members sitting out are never waited for nor counted.
-  final active = [for (final m in r.members) if (!m.stale && !m.out) m];
+  final active = [for (final m in r.members) if (!m.stale && !m.out && m.error.isEmpty) m];
   final others = [
     for (final m in active)
       if ((self == null || m.id != self.id) && !(m.inSet && m.ready)) m,
@@ -117,6 +140,7 @@ StatusView? playerStatusNow({bool slowConnect = false}) {
     state: c.serverState.value,
     self: c.selfMember.value,
     slowConnect: slowConnect,
+    playerError: c.playerError.value,
   );
 }
 
@@ -164,6 +188,8 @@ class _PlayerStatusState extends State<PlayerStatus> {
         coord.cancelReconnect();
       case StatusAction.retry:
         coord.retry();
+      case StatusAction.reload:
+        unawaited(coord.reloadVideo());
       case StatusAction.ready:
         coord.toggleReady();
     }
@@ -266,6 +292,7 @@ class _StatusLine extends StatelessWidget {
         return null;
       case StatusKind.loading:
       case StatusKind.you:
+      case StatusKind.cannotPlay:
       case StatusKind.waiting:
         final r = coord.serverState.value;
         final infos = [

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

@@ -219,6 +219,7 @@ class SyncClient {
     double duration = 0,
     int mediaId = 0,
     Map<String, bool>? jf,
+    String error = '',
   }) {
     final safeBuffered = buffered.isNaN || buffered < 0 ? 0.0 : buffered;
     _send(
@@ -229,6 +230,7 @@ class SyncClient {
         duration: duration.isFinite && duration > 0 ? duration : 0,
         mediaId: mediaId,
         jf: jf,
+        error: error,
       ).toJson(),
     );
   }

apps/desktop/test/library_rows_test.dart

@@ -202,8 +202,11 @@ void main() {
 
       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),
+      expect((page!.title, page.subtitle, page.problem),
-          ('Example', "example.com · Not a video (and yt-dlp couldn't read it: Unsupported URL)"));
+          ('Example', 'example.com · Not a video page yt-dlp knows', 'Not a video page yt-dlp knows'));
+      final refused = await previewLink('https://cdn.example/b.mp4',
+          probe: (url) async => LinkProbe.page(Uri.parse(url), ytDlpError: 'odd', status: 403));
+      expect((refused!.title, refused.problem), ('b.mp4', 'Not allowed (403)'));
       expect(await previewLink('not a link'), isNull);
     });
 

apps/desktop/test/library_tab_test.dart

@@ -110,7 +110,9 @@ Future<Harness> pumpLibrary(
         now: () => fixtureNow,
         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')),
+            : url.contains('bilibili')
+                ? LinkProbe.page(Uri.parse(url), ytDlpError: 'HTTP Error 412: Precondition Failed')
+                : LinkProbe.page(Uri.parse(url), info: const YtDlpInfo(title: 'A video', uploader: 'Chan')),
         filesBuilder: (context, {required solo, required relayed, required onPlay, nowPlayingPath}) =>
             FilesStub(solo: solo, relayed: relayed, onPlay: onPlay),
         onPutUp: (m) async {
@@ -296,6 +298,18 @@ void main() {
     await settle(tester, 10);
     expect(h.controller.link.text, url);
 
+    // A link the probe cannot open: the reason, not put up; "anyway" is.
+    const bili = 'https://www.bilibili.com/video/BV1';
+    await tester.enterText(find.byKey(const ValueKey('link-field')), bili);
+    await settle(tester, 10);
+    await tester.tap(find.byKey(const ValueKey('link-put-up')));
+    await settle(tester, 10);
+    expect(find.text(needsCookiesText), findsOneWidget);
+    expect(h.put, hasLength(1));
+    await tester.tap(find.byKey(const ValueKey('link-put-up-anyway')));
+    await settle(tester, 10);
+    expect((h.put.last as LinkMedia).anyway, isTrue);
+
     expect(tester.takeException(), isNull);
   });
 

apps/desktop/test/player_status_test.dart

@@ -112,6 +112,19 @@ void main() {
       expect(w.who.map((m) => m.name), ['Bob', 'Mika']);
     });
 
+    test("can't play: yours with Retry (reload); others' instead of waiting", () {
+      var v = playerStatusFor(health: ok, state: held([me]), self: me, playerError: 'Not allowed (403)')!;
+      expect((v.kind, v.text, v.action), (StatusKind.problem, "Can't play this: Not allowed (403)", StatusAction.reload));
+      final bob = MemberView(id: 'b', name: 'Bob', ready: false, inSet: false, buffered: 0, stale: false,
+          error: 'Not allowed (403)');
+      v = playerStatusFor(health: ok, state: held([me, bob, mv('m', 'Mika', ready: true)]), self: me)!;
+      expect((v.kind, v.text, v.action), (StatusKind.cannotPlay, "Bob can't play this: Not allowed (403)", null));
+      expect(v.who.single.id, 'b');
+      final notMe = mv('me', 'Me');
+      v = playerStatusFor(health: ok, state: held([notMe, bob]), self: notMe)!;
+      expect((v.kind, v.action), (StatusKind.cannotPlay, StatusAction.ready));
+    });
+
     test('names read as a sentence', () {
       expect(nameList(['Bob']), 'Bob');
       expect(nameList(['Bob', 'Mika']), 'Bob and Mika');

docs/ARCHITECTURE.md

@@ -113,8 +113,17 @@ Loosely modeled on Syncplay, with a different readiness design.
   setting "Unready when the video changes", `AppSettings.unreadyOnSwap`,
   default off, sends `ready=false` itself on a new `mediaId`; not for the
   first state of a session, and a reconnect does not restore a ready that
-  a swap meanwhile would have dropped). Stale, leave and sitting out
+  a swap meanwhile would have dropped). Stale, leave, sitting out and a
-  remove from the set.
+  player error remove from the set.
+- **Player error** (`EngineMember.error`, `report.error`,
+  `state.members[].error`): a member whose player cannot open the current
+  media says why in its reports; the server takes it out of the set at
+  once (like sitting out, but automatic: `ready`/`force` do not put it
+  back, its ready flag is kept), so the others start without it. A report
+  without it (the media opened, after a reload too) or a swap clears it:
+  back in the set like a join while not PLAYING; while PLAYING from its
+  next frame if it is ready (the others then hold for its buffer, as for a
+  stale member coming back), else from its `ready`.
 - **Sitting out** (`EngineMember.out`, `state.members[].out`): a member
   stays connected (chat, feed, party, nudges) but is never in the set and
   never ready: no `ready` or `force` reaches it, a swap leaves it out, its
@@ -263,9 +272,18 @@ or a 5xx is retried, at most 3 times per read and 4 s apart at most; a
 (older ffmpeg ignores `reconnect_max_retries`). A load that fails (mpv's
 fatal "No video or audio streams selected", or an EDL track that cannot
 be opened) before a duration is known is reported once per open
-(`onLoadError`) and shows as "can't play this: ..." with ffmpeg's HTTP
+(`onLoadError`), with ffmpeg's HTTP status when this player gets
-status when this player gets ffmpeg's log (ffmpeg logs through one mpv
+ffmpeg's log (ffmpeg logs through one mpv instance per process, the
-instance per process, the first one alive). The cache is in RAM:
+first one alive). That, a yt-dlp hook error and a failed `openUrl` become
+the coordinator's `playerError` in plain words (`playErrorText`, core
+`link_probe.dart`: 412/precondition/login/cookies/sign in → "This site
+needs cookies — Settings → Player → yt-dlp → Cookies", 403 → "Not allowed
+(403)", 404/410 → "Not found (404)", "Unsupported URL" → "Not a video
+page yt-dlp knows", network errors → "Couldn't reach the site", anything
+else as is). It rides in `report.error` (see "Player error" in the sync
+model) until the media opens (a new duration) or the server's `mediaId`
+moves on; the pill shows "Can't play this: ..." with Retry (Reload
+video). The cache is in RAM:
 media_kit sets `cache-on-disk` without a `cache-dir`, and mpv falls back. mpv
 ignores invalid values silently, so every pin is read back and a mismatch is
 logged and kept in `pinMismatches`. Measured against the `/m` endpoint
@@ -647,15 +665,23 @@ all three link modes. Nothing is bundled or installed by hand.
   video/audio type, or a generic one on a media file name, is a file
   (`looksLikeMediaFile`); anything else goes to yt-dlp, and when yt-dlp
   cannot read it the page's `og:title` / `<title>` is kept with yt-dlp's
-  reason ("Not a video (and yt-dlp couldn't read it: ...)"). The app
+  reason and the GET's HTTP status. `LinkProbe.problem`: why it will not
-  probes on paste (`AppYtDlp.probe`, remembered 10 minutes) for the Link
+  play, in plain words (`playErrorText` of yt-dlp's reason, else of a 4xx
-  preview and the swap: a page is named by its title, never its URL tail,
+  status), null for a file or a page yt-dlp read. The app probes on paste
-  and its thumbnail goes up as the banner (no poster).
+  (`AppYtDlp.probe`, remembered 10 minutes; media file names too, not a
+  Jellyfin item link) for the
+  Link preview and the swap: a page is named by its title, never its URL
+  tail, and its thumbnail goes up as the banner (no poster). A link with a
+  problem, or one the probe cannot reach ("Couldn't reach the site"), is
+  not put up in any mode: the Link page shows the reason (preview and
+  under the button) and offers "Put it up anyway" (`LinkMedia.anyway`),
+  for when the server or a friend with cookies may still open it;
+  `swapLink` refuses it the same way for any other caller.
 - **Everyone fetches it**: the swap sends the page URL. Before opening an
   external link every app points mpv's hook at its managed copy
   (`script-opts=ytdl_hook-ytdl_path=...`, `ytdl-format=bv*[height<=1080]+ba/b`,
   once per player), waiting for the download unless the URL names a media
-  file. A hook error shows as "can't open this link: ...". The hook (mpv
+  file. A hook error is a player error (see the mpv settings under "Media"). The hook (mpv
   0.41) gives mpv the first requested format's `http_headers` (User-Agent
   as `user-agent`; Referer, Cookie, X-Forwarded-For as file-local
   `http-header-fields`, which win over the empty list media_kit sets on
@@ -924,7 +950,13 @@ always scrolls the page). Space never presses a focused button
   `StateBroadcast.bufferNeed`, the gate's own need at the current
   position: less near the end, none at finished; their avatar with the progress round it), you not
   ready (a click marks you ready) and who everyone waits for (avatars,
-  "2/3 ready"); nothing otherwise, info never. 34 px avatars, a main line
+  "2/3 ready"); nothing otherwise, info never. Your own `playerError`
+  comes right after reconnecting ("Can't play this: ...", Retry reloads
+  the video); members with `members[].error` show as "Bob can't play
+  this: ..." (before your ready prompt, which then rides in the detail
+  line) and are never in "waiting for". A member's new error also toasts
+  once (the pill is hidden while playing); avatars carry a red error mark
+  and the members card says "can't play this: ...". 34 px avatars, a main line
   and a muted detail line. Frosted glass, colour only for problems; it fades through
   between kinds. The mini shows its short line in its hover bar. ⚙ in both
   control designs opens the player settings card (`controls/

docs/PROTOCOL.md

@@ -40,7 +40,7 @@ with different `proto` refuse each other at `hello` (`proto mismatch`).
 {"t":"swap","media":{"name":"","size":0,"duration":0,"jellyfin":{<ref>}}}
 {"t":"swap","media":{"name":"","size":123,"duration":0,"url":"...","relay":{}}}
 {"t":"report","position":123.1,"buffered":6.2,"eventId":41,
- "duration":1440.5,"mediaId":2,"jf":{"<serverId>":true}}
+ "duration":1440.5,"mediaId":2,"jf":{"<serverId>":true},"error":"Not allowed (403)"}
 {"t":"ping","c":1767225600000}
 {"t":"chat","text":"..."}
 {"t":"out","target":"<memberId>","out":true}
@@ -72,6 +72,17 @@ Field notes:
   client plays the item with its own account, `false` = through the relay.
   Sticky: a report without `jf` keeps the last one. At most 8 entries, keys
   up to 64 characters; others are dropped.
+- `report.error` (optional, omitted when empty): short plain text saying
+  why this client's player cannot open the media `report.mediaId` (e.g.
+  `Not allowed (403)`). The client sends it in every report while that
+  lasts and drops it once the media opens (a reload included). The server
+  keeps it per member (one line, cut to 120 characters) only for the
+  current `mediaId`: a report without it, or for another `mediaId`,
+  clears it, and so does a swap. An errored member is out of the ready
+  gate: out of the set, a `ready` or `force` does not put it back; when
+  the error clears it is in the set again like a join (unless `playing`,
+  then from its `ready`). Optional on both sides: older servers ignore it,
+  older clients ignore `members[].error`.
 - `ping.c`: the client's clock in epoch ms; answered with `pong`.
 - `user.avatar`: base64 PNG, at most 256 KiB of characters (else
   `rejected: ...`). `name` is trimmed, empty becomes `?`, cut to 32
@@ -113,7 +124,7 @@ Field notes:
  "serverTime":"<ISO-8601 UTC>","mediaId":1,
  "media":{name,size,duration,url?,jellyfin?,relay?,swapBy?,art?}|absent,
  "members":[{"id","name","avatarHash"?,"ready","inSet","buffered","stale","jf"?,
-   "host"?,"out"?}],
+   "host"?,"out"?,"error"?}],
  "seekBy":"m1","seekSeq":3,"relay":true}
 {"t":"pong","c":1767225600000,"s":1767225600012}
 {"t":"feed","actor":"","action":"","target":"","reason":"","at":"<ISO-8601>"}
@@ -145,7 +156,9 @@ Field notes:
   (omitted when the member has no picture) names the picture's bytes (see
   "Avatars"). `members[].host` (omitted when false): the member sent the
   server's `hostKey` (see `hello.hostKey`). `members[].out` (omitted when
-  false): the member sits out (see `out`).
+  false): the member sits out (see `out`). `members[].error` (omitted when
+  empty): the member's player cannot open the current media (see
+  `report.error`).
 - `pong.c` echoes the ping's `c`; `pong.s` is the server's clock in epoch ms
   (the clock `serverTime` uses). With `t3` the local receive time, the offset
   is `s - (c + t3) / 2`, accurate to half the round trip.

packages/core/lib/src/constants.dart

@@ -50,6 +50,8 @@ abstract class RelayConstants {
   static const int maxBannerBytes = 768 * 1024;
   static const int maxNameLength = 32;
   static const int maxChatLength = 500;
+  /// Characters of `report.error` the server keeps.
+  static const int maxMemberErrorLength = 120;
   /// Nudges one member may send: at most this many per second and per
   /// minute; the server drops the rest silently.
   static const int nudgesPerSec = 3;

packages/core/lib/src/link_probe.dart

@@ -75,6 +75,38 @@ String notAVideoText(String? ytDlpError) =>
 /// The text for a page with no video a relay can read.
 const noRelayFormatText = "This page has no video a relay can read. Choose 'Everyone fetches it' instead.";
 
+/// The plain-words texts of [playErrorText].
+const needsCookiesText = 'This site needs cookies — Settings → Player → yt-dlp → Cookies';
+const notAllowedText = 'Not allowed (403)';
+const notFoundText = 'Not found (404)';
+const unsupportedUrlText = 'Not a video page yt-dlp knows';
+const unreachableText = "Couldn't reach the site";
+const _plainTexts = {needsCookiesText, notAllowedText, notFoundText, unsupportedUrlText, unreachableText};
+
+final _cookiesHint = RegExp(r'\b412\b|precondition|log ?in\b|logged|cookies|sign ?in\b', caseSensitive: false);
+final _forbidden = RegExp(r'(^|[\s(:])403\b|forbidden', caseSensitive: false);
+final _notFound = RegExp(r'(^|[\s(:])404\b|\b410\b|not found', caseSensitive: false);
+final _unreachable = RegExp(
+    r'SocketException|HandshakeException|TimeoutException|timed out|failed host lookup|connection (refused|reset|closed)|'
+    r'network is unreachable|no route to host|name or service not known|getaddrinfo|unable to download webpage',
+    caseSensitive: false);
+
+/// Why a link or media cannot be played, in plain words, from the raw
+/// error of yt-dlp, ffmpeg/mpv or the link probe; anything it does not
+/// know comes back as is (one line, at most 100 characters).
+String playErrorText(String raw) {
+  final s = raw.trim();
+  // First: its message quotes the URL, which may say anything.
+  if (s.toLowerCase().contains('unsupported url')) return unsupportedUrlText;
+  if (_cookiesHint.hasMatch(s)) return needsCookiesText;
+  if (_forbidden.hasMatch(s)) return notAllowedText;
+  if (_notFound.hasMatch(s)) return notFoundText;
+  if (_unreachable.hasMatch(s)) return unreachableText;
+  final line = s.replaceAll(RegExp(r'\s+'), ' ');
+  if (line.isEmpty) return "Couldn't open it";
+  return line.length > 100 ? '${line.substring(0, 99)}…' : line;
+}
+
 class LinkProbeException implements Exception {
   final String message;
   const LinkProbeException(this.message);
@@ -94,15 +126,30 @@ class LinkProbe {
   final String? pageTitle;
   /// Why yt-dlp could not read the page.
   final String? ytDlpError;
+  /// The HTTP status of the probe's GET; 0 when unknown.
+  final int status;
   const LinkProbe.file(this.url, this.size)
       : isPage = false,
         info = null,
         pageTitle = null,
-        ytDlpError = null;
+        ytDlpError = null,
-  const LinkProbe.page(this.url, {this.info, this.pageTitle, this.ytDlpError})
+        status = 0;
+  const LinkProbe.page(this.url, {this.info, this.pageTitle, this.ytDlpError, this.status = 0})
       : isPage = true,
         size = -1;
 
+  /// Why nobody may be able to play this link ([playErrorText]), or null
+  /// when it looks playable: a page yt-dlp could not read, or a link
+  /// answering 4xx.
+  String? get problem {
+    if (!isPage || info != null) return null;
+    final err = ytDlpError == null ? null : playErrorText(ytDlpError!);
+    // A 4xx says more than yt-dlp's words it has no plain text for.
+    final known = err != null && _plainTexts.contains(err);
+    if (!known && status >= 400 && status < 500) return playErrorText('HTTP Error $status');
+    return err;
+  }
+
   /// The name to show: yt-dlp's title, the page's, else the host; null
   /// for a file (named by its file name).
   String? get title {
@@ -134,12 +181,14 @@ Future<LinkProbe> probeLink(Uri url, {YtDlp? ytDlp, HttpClient? client}) async {
   try {
     String? body;
     Object? getError;
+    var status = 0;
     try {
       final req = await c.getUrl(url).timeout(const Duration(seconds: 15));
       req.headers
         ..set(HttpHeaders.rangeHeader, 'bytes=0-0')
         ..set(HttpHeaders.acceptEncodingHeader, 'identity');
       final res = await req.close().timeout(const Duration(seconds: 15));
+      status = res.statusCode;
       final type = res.headers.contentType?.mimeType ?? '';
       if (looksLikeMediaFile(status: res.statusCode, contentType: type, url: url)) {
         await res.drain<void>().catchError((_) {});
@@ -155,7 +204,7 @@ Future<LinkProbe> probeLink(Uri url, {YtDlp? ytDlp, HttpClient? client}) async {
     String? ytErr;
     if (ytDlp != null) {
       try {
-        return LinkProbe.page(url, info: await ytDlp.resolve(url.toString()));
+        return LinkProbe.page(url, info: await ytDlp.resolve(url.toString()), status: status);
       } catch (e) {
         ytErr = '$e';
       }
@@ -170,7 +219,7 @@ Future<LinkProbe> probeLink(Uri url, {YtDlp? ytDlp, HttpClient? client}) async {
         body = await _readText(await req.close().timeout(const Duration(seconds: 15)));
       } catch (_) {}
     }
-    return LinkProbe.page(url, pageTitle: body == null ? null : htmlTitle(body), ytDlpError: ytErr);
+    return LinkProbe.page(url, pageTitle: body == null ? null : htmlTitle(body), ytDlpError: ytErr, status: status);
   } finally {
     if (client == null) c.close(force: true);
   }

packages/core/lib/src/protocol.dart

@@ -435,13 +435,17 @@ class ReportMessage {
   /// Jellyfin access by `ServerId`: true = plays with its own account,
   /// false = through the server's relay. Null leaves the last one in place.
   final Map<String, bool>? jf;
+  /// Why the player cannot open [mediaId] (short plain text); empty while
+  /// it can.
+  final String error;
   const ReportMessage(
       {required this.position,
       required this.buffered,
       required this.eventId,
       this.duration = 0,
       this.mediaId = 0,
-      this.jf});
+      this.jf,
+      this.error = ''});
 
   Map<String, Object?> toJson() => {
         't': 'report',
@@ -451,6 +455,7 @@ class ReportMessage {
         if (duration > 0) 'duration': duration,
         if (mediaId != 0) 'mediaId': mediaId,
         if (jf != null) 'jf': jf,
+        if (error.isNotEmpty) 'error': error,
       };
 
   factory ReportMessage.fromJson(Map<String, Object?> json) {
@@ -462,10 +467,20 @@ class ReportMessage {
       duration: finiteDouble(json['duration'], 'duration'),
       mediaId: finiteInt(json['mediaId'], 'mediaId'),
       jf: jfAccessFromJson(json['jf']),
+      error: memberErrorFromJson(json['error']),
     );
   }
 }
 
+/// Reads a `report.error` / `members[].error`: trimmed, single line, at
+/// most [RelayConstants.maxMemberErrorLength] characters; empty otherwise.
+String memberErrorFromJson(Object? value) {
+  if (value is! String) return '';
+  final line = value.replaceAll(RegExp(r'\s+'), ' ').trim();
+  const max = RelayConstants.maxMemberErrorLength;
+  return line.length > max ? line.substring(0, max) : line;
+}
+
 /// Reads a `jf` map (`{serverId: bool}`), dropping non-bool entries and
 /// keys over 64 characters, at most 8 entries (it rides in every `state`);
 /// null when absent or not a map.
@@ -582,6 +597,9 @@ class MemberView {
   final bool host;
   /// Sitting out: connected, outside the ready gate, not playing.
   final bool out;
+  /// Why its player cannot open the current media (`report.error`); empty
+  /// while it can. Errored: outside the ready gate.
+  final String error;
   const MemberView({
     required this.id,
     required this.name,
@@ -593,6 +611,7 @@ class MemberView {
     this.jf = const {},
     this.host = false,
     this.out = false,
+    this.error = '',
   });
 
   Map<String, Object?> toJson() => {
@@ -606,6 +625,7 @@ class MemberView {
         if (jf.isNotEmpty) 'jf': jf,
         if (host) 'host': true,
         if (out) 'out': true,
+        if (error.isNotEmpty) 'error': error,
       };
 
   factory MemberView.fromJson(Map<String, Object?> json) => MemberView(
@@ -619,6 +639,7 @@ class MemberView {
         jf: jfAccessFromJson(json['jf']) ?? const {},
         host: json['host'] == true,
         out: json['out'] == true,
+        error: memberErrorFromJson(json['error']),
       );
 }
 

packages/core/lib/src/sync_engine.dart

@@ -56,6 +56,9 @@ class EngineMember {
   bool host = false;
   /// Sitting out: never in the set, never ready, its buffer ignored.
   bool out = false;
+  /// Its player cannot open the current media (`report.error`): outside
+  /// the ready gate until a report clears it or the media changes.
+  String error = '';
   DateTime lastSeen;
   EngineMember({
     required this.id,
@@ -97,6 +100,7 @@ class EngineMember {
         jf: jf,
         host: host,
         out: out,
+        error: error,
       );
 }
 
@@ -197,6 +201,7 @@ class SyncEngine {
     final wasStale = isStale(member);
     member.lastSeen = now;
     if (!member.out &&
+        member.error.isEmpty &&
         !member.inSet &&
         (member.ready || (wasStale && transport != Transport.playing))) {
       member.inSet = true;
@@ -307,12 +312,12 @@ class SyncEngine {
     _seen(member);
     // Sitting out: back first ([applyOut]), then ready.
     if (member.out) return;
-    if (member.ready == ready && member.inSet) {
+    if (member.ready == ready && (member.inSet || member.error.isNotEmpty)) {
       evaluate();
       return;
     }
     member.ready = ready;
-    if (ready) member.inSet = true;
+    if (ready && member.error.isEmpty) member.inSet = true;
     feed.add(FeedMessage(
         actor: member.name,
         action: ready ? 'ready' : 'unready',
@@ -328,13 +333,13 @@ class SyncEngine {
       for (final member in members.values) {
         if (member.out) continue;
         member.ready = ready;
-        if (ready) member.inSet = true;
+        if (ready && member.error.isEmpty) member.inSet = true;
       }
     } else {
       final member = byId(target);
       if (member == null || member.out) return;
       member.ready = ready;
-      if (ready) member.inSet = true;
+      if (ready && member.error.isEmpty) member.inSet = true;
       feed.add(FeedMessage(
           actor: actorName,
           action: ready ? 'force-ready' : 'force-unready',
@@ -366,7 +371,7 @@ class SyncEngine {
     member.out = out;
     member.ready = false;
     member.buffered = 0;
-    member.inSet = !out && transport != Transport.playing;
+    member.inSet = !out && member.error.isEmpty && transport != Transport.playing;
     feed.add(FeedMessage(
         actor: actor.name, action: out ? 'out' : 'back', target: self ? null : member.name, at: now));
     evaluate();
@@ -408,6 +413,7 @@ class SyncEngine {
     // (a stale member rejoins the set with its next frame if still ready).
     final t = now;
     for (final member in members.values) {
+      member.error = '';
       member.inSet = !member.out && !isStale(member, t);
       member.buffered = 0;
     }
@@ -416,10 +422,11 @@ class SyncEngine {
   }
 
   void applyReport(String token, double reportPosition, double buffered, int reportEventId,
-      {double duration = 0, int mediaId = 0, Map<String, bool>? jf}) {
+      {double duration = 0, int mediaId = 0, Map<String, bool>? jf, String error = ''}) {
     final member = members[token];
     if (member == null) return;
     if (!reportPosition.isFinite) return;
+    _setError(member, mediaId == this.mediaId ? error : '');
     _seen(member);
     if (jf != null) member.jf = Map.unmodifiable(jf);
     member.buffered = member.out || !buffered.isFinite || buffered < 0 ? 0 : buffered;
@@ -433,6 +440,21 @@ class SyncEngine {
     evaluate();
   }
 
+  /// An error takes the member out of the set (the gate stops waiting for
+  /// it); clearing it puts it back like a join: in the set unless playing
+  /// (then from its next `ready`).
+  void _setError(EngineMember member, String error) {
+    if (member.error == error) return;
+    member.error = error;
+    if (error.isNotEmpty) {
+      member.inSet = false;
+    } else if (!member.out) {
+      member.inSet = transport != Transport.playing;
+    }
+    // Leaving the set may let the others start.
+    evaluate();
+  }
+
   void sweepStale() {
     var changed = false;
     for (final member in members.values) {

packages/core/test/sync_engine_test.dart

@@ -85,6 +85,52 @@ void main() {
     });
   });
 
+  group('player errors', () {
+    void fail(String token, String error, {int? mediaId}) => engine.applyReport(
+        token, engine.positionAt(), 0, engine.eventId,
+        mediaId: mediaId ?? engine.mediaId, error: error);
+
+    test('an errored member leaves the gate; clearing puts it back', () {
+      join('a', 'alice');
+      join('b', 'bob');
+      engine.applyReady('a', true);
+      engine.applyReady('b', true);
+      buffer('a', 4.0);
+      expect(engine.transport, Transport.held, reason: 'bob has no buffer');
+      fail('b', "Not allowed (403)");
+      final b = engine.members['b']!;
+      expect([b.error, b.inSet], ['Not allowed (403)', false]);
+      expect(engine.transport, Transport.playing, reason: 'alice plays alone');
+      final view = engine.broadcast().members;
+      expect(view.last.toJson()['error'], 'Not allowed (403)');
+      expect(view.first.toJson().containsKey('error'), isFalse);
+      engine.applyReady('b', true);
+      expect(b.inSet, isFalse, reason: 'ready does not bring it back while errored');
+      // A report of another media does not set it; a clean one clears it.
+      fail('b', 'x', mediaId: engine.mediaId - 1);
+      expect(b.error, isEmpty);
+      expect(b.inSet, isTrue, reason: 'ready and playing: back like a stale return');
+      expect(engine.transport, Transport.held, reason: 'bob is buffering');
+    });
+
+    test('a swap clears it; held, clearing puts it in the set', () {
+      join('a', 'alice');
+      join('b', 'bob');
+      fail('b', 'Not found (404)');
+      engine.applySwap('a', const HelloMedia(name: 'n', size: 1, duration: 0, url: 'u'));
+      final b = engine.members['b']!;
+      expect([b.error, b.inSet], ['', true]);
+      fail('b', 'Not found (404)');
+      expect(b.inSet, isFalse);
+      buffer('b', 4.0);
+      expect([b.error, b.inSet], ['', true]);
+      expect(ReportMessage.fromJson({
+        't': 'report', 'position': 0, 'buffered': 0, 'eventId': 0,
+        'error': '  a\nb  ${'x' * 200}'}).error.length,
+          RelayConstants.maxMemberErrorLength);
+    });
+  });
+
   group('membership + gate', () {
     test('join while held lands in the set, playback stays held', () {
       join('a', 'alice');

packages/core/test/yt_dlp_test.dart

@@ -115,6 +115,24 @@ void main() {
     });
   });
 
+  test('play errors in plain words; a probe refuses unread pages and 4xx links', () {
+    expect(playErrorText('[BiliBili] BV1x: Unable to download webpage: HTTP Error 412: Precondition Failed'),
+        needsCookiesText);
+    expect(playErrorText('Sign in to confirm your age'), needsCookiesText);
+    expect(playErrorText('the video server answered HTTP error 403 Forbidden'), notAllowedText);
+    expect(playErrorText('HTTP Error 404: Not Found'), notFoundText);
+    expect(playErrorText('Unsupported URL: https://example.com/login/403'), unsupportedUrlText);
+    expect(playErrorText('cannot open the link: SocketException: Failed host lookup'), unreachableText);
+    expect(playErrorText('the video stream could not be opened'), 'the video stream could not be opened');
+    expect(playErrorText(notAllowedText), notAllowedText);
+    final u = Uri.parse('https://x/v.mp4');
+    expect(LinkProbe.page(u, ytDlpError: 'HTTP Error 412: Precondition Failed').problem, needsCookiesText);
+    expect(LinkProbe.page(u, ytDlpError: 'odd failure', status: 403).problem, notAllowedText);
+    expect(LinkProbe.page(u, ytDlpError: 'odd failure').problem, 'odd failure');
+    expect(LinkProbe.page(u, info: YtDlpInfo.parse({'title': 'x', 'formats': []}), status: 404).problem, isNull);
+    expect(LinkProbe.file(u, 10).problem, isNull);
+  });
+
   test('viewer URL: one track plain, several an mpv EDL with %length% framing', () {
     expect(relayViewerUrl('http://h:1/r/default/t/3', 'a/b c'), 'http://h:1/r/default/t/3/a_b%20c');
     const v = 'http://h:1/r/default/t/3/0/x', a = 'http://h:1/r/default/t/3/1/x';

packages/server/lib/src/server_hub.dart

@@ -428,7 +428,7 @@ void mountSyncRoute(
               final report = ReportMessage.fromJson(decoded);
               hub.engine.applyReport(
                   token, report.position, report.buffered, report.eventId,
-                  duration: report.duration, mediaId: report.mediaId, jf: report.jf);
+                  duration: report.duration, mediaId: report.mediaId, jf: report.jf, error: report.error);
               hub.changed();
             case 'ping':
               final ping = PingMessage.fromJson(decoded);