Preserve playback position on watchdog recovery

server/index.js

@@ -46,6 +46,20 @@ const MAX_YT_DLP_OUTPUT_BYTES = 8 * 1024 * 1024;
 const RELAY_BRANCH_PAUSE_BYTES = Math.floor(MAX_RELAY_BRANCH_QUEUE_BYTES / 2);
 const JPEG_SOI = Buffer.from([0xff, 0xd8]);
 const JPEG_EOI = Buffer.from([0xff, 0xd9]);
+const BEST_EFFORT_RESUME_MAX_SECONDS = 30 * 24 * 60 * 60;
+const RECORDED_MEDIA_EXTENSIONS = new Set([
+  '.avi',
+  '.flv',
+  '.m4v',
+  '.mkv',
+  '.mov',
+  '.mp4',
+  '.mpeg',
+  '.mpg',
+  '.ogv',
+  '.webm',
+  '.wmv',
+]);
 
 const defaults = {
   fps: clampInteger(process.env.DEFAULT_FPS, 24, 1, 30),
@@ -169,8 +183,10 @@ app.post('/api/session', async (request, response) => {
     options,
     duration: null,
     metadataStatus,
+    metadataProbePromise: null,
     seekSeconds: 0,
     seekGeneration: 0,
+    forceSplitPlayback: false,
     createdAt: Date.now(),
     lastUsedAt: Date.now(),
   });
@@ -201,7 +217,7 @@ app.get('/api/session/:sessionId', (request, response) => {
   response.json(formatSessionPayload(session));
 });
 
-app.post('/api/session/:sessionId/seek', (request, response) => {
+app.post('/api/session/:sessionId/seek', async (request, response) => {
   const session = getSession(request.params.sessionId);
 
   if (!session) {
@@ -209,11 +225,6 @@ app.post('/api/session/:sessionId/seek', (request, response) => {
     return;
   }
 
-  if (!isSessionSeekable(session)) {
-    response.status(409).json({ error: 'This stream is not seekable.' });
-    return;
-  }
-
   const requestedSeconds = Number(request.body?.time);
 
   if (!Number.isFinite(requestedSeconds)) {
@@ -221,21 +232,42 @@ app.post('/api/session/:sessionId/seek', (request, response) => {
     return;
   }
 
-  const seekSeconds = clampNumber(requestedSeconds, 0, session.duration);
+  const allowBestEffort = request.body?.allowBestEffort === true;
+
+  if (!isSessionSeekable(session) && allowBestEffort && session.metadataStatus !== 'unavailable') {
+    await ensureSessionDuration(session);
+  }
+
+  const canSeekExactly = isSessionSeekable(session);
+  const canResumeBestEffort = allowBestEffort && canBestEffortResumeWithoutDuration(session);
+
+  if (!canSeekExactly && !canResumeBestEffort) {
+    response.status(409).json({ error: 'This stream is not seekable.' });
+    return;
+  }
+
+  const seekSeconds = canSeekExactly
+    ? clampNumber(requestedSeconds, 0, session.duration)
+    : clampNumber(requestedSeconds, 0, BEST_EFFORT_RESUME_MAX_SECONDS);
   const playback = playbacks.get(session.id);
+  const stopReason = allowBestEffort ? 'client_recovery_seek' : 'client_seek';
 
   session.seekSeconds = seekSeconds;
   session.seekGeneration += 1;
   session.lastUsedAt = Date.now();
 
+  if (!canSeekExactly && canResumeBestEffort && PLAYBACK_CONNECTION_MODE === 'relay') {
+    session.forceSplitPlayback = true;
+  }
+
   if (playback && !playback.closed) {
-    playback.stop('client_seek');
+    playback.stop(stopReason);
     if (playbacks.get(session.id) === playback) {
       playbacks.delete(session.id);
     }
   }
 
-  logInfo(`session seeked id=${shortId(session.id)} time=${seekSeconds.toFixed(3)} duration=${session.duration.toFixed(3)}`);
+  logInfo(`session seeked id=${shortId(session.id)} reason=${stopReason} time=${seekSeconds.toFixed(3)} duration=${Number.isFinite(session.duration) ? session.duration.toFixed(3) : 'unknown'} exact=${canSeekExactly}`);
   response.json(formatSessionPayload(session));
 });
 
@@ -701,7 +733,26 @@ function hasRecordedDuration(session) {
   return Number.isFinite(session.duration) && session.duration > 0;
 }
 
+function canBestEffortResumeWithoutDuration(session) {
+  return session.sourceKind === 'youtube'
+    || isLikelyRecordedMediaUrl(session.originalUrl)
+    || isLikelyRecordedMediaUrl(session.url);
+}
+
+function isLikelyRecordedMediaUrl(value) {
+  try {
+    const parsed = new URL(value);
+    return RECORDED_MEDIA_EXTENSIONS.has(path.extname(parsed.pathname).toLowerCase());
+  } catch {
+    return false;
+  }
+}
+
 function getSessionPlaybackConnectionMode(session) {
+  if (session.forceSplitPlayback) {
+    return 'split';
+  }
+
   if (PLAYBACK_CONNECTION_MODE === 'relay' && hasRecordedDuration(session)) {
     return 'split';
   }
@@ -710,26 +761,48 @@ function getSessionPlaybackConnectionMode(session) {
 }
 
 function startSessionMetadataProbe(session) {
-  void probeSessionDuration(session).then((duration) => {
+  void ensureSessionDuration(session);
+}
+
+function ensureSessionDuration(session) {
+  if (hasRecordedDuration(session)) {
+    return Promise.resolve(session.duration);
+  }
+
+  if (session.metadataProbePromise) {
+    return session.metadataProbePromise;
+  }
+
+  session.metadataStatus = 'pending';
+
+  const probePromise = probeSessionDuration(session).then((duration) => {
     const current = sessions.get(session.id);
 
     if (current !== session) {
-      return;
+      return duration;
     }
 
     session.duration = duration;
     session.metadataStatus = Number.isFinite(duration) ? 'ready' : 'unavailable';
+    return duration;
   }).catch((error) => {
     const current = sessions.get(session.id);
 
-    if (current !== session) {
-      return;
+    if (current === session) {
+      session.duration = null;
+      session.metadataStatus = 'unavailable';
+      logWarn(`duration probe failed id=${shortId(session.id)} error=${oneLine(error.message)}`);
     }
 
-    session.duration = null;
-    session.metadataStatus = 'unavailable';
-    logWarn(`duration probe failed id=${shortId(session.id)} error=${oneLine(error.message)}`);
+    return null;
+  }).finally(() => {
+    if (session.metadataProbePromise === probePromise) {
+      session.metadataProbePromise = null;
+    }
   });
+
+  session.metadataProbePromise = probePromise;
+  return probePromise;
 }
 
 async function probeSessionDuration(session) {