Enable recorded stream seeking

AGENTS.md

@@ -6,18 +6,18 @@ This project is a web video player for clients that can decode audio and still i
 
 The UI intentionally has only two screens:
 
-- URL entry screen with a stream URL input, a `Next` button, and globally stored recently played URLs.
+- URL entry screen with a stream URL input, a `Next` button, globally stored recently played URLs, and globally stored favorites.
 - Fullscreen player screen with JPEG frames drawn to a canvas and native audio playback through an `<audio>` element.
 - Playback controls are overlay controls toggled by tapping/clicking the frame area, similar to YouTube.
 - Do not reintroduce debug panels, frame counters, settings forms, explanatory marketing copy, or visible ffmpeg details into the normal UI.
 
-The backend stores recently played URLs globally, not per-browser. The default path is `data/recent-urls.json`, configurable with `RECENT_URLS_PATH`. Docker Compose persists this through the `frame-stream-data` volume.
+The backend stores recently played URLs and favorites globally, not per-browser. The default recent URL path is `data/recent-urls.json`, configurable with `RECENT_URLS_PATH`. The default favorites path is `data/favorites.json`, configurable with `FAVORITES_PATH`. Docker Compose persists both through the `frame-stream-data` volume.
 
 ## Core Architecture
 
 The app is plain Node/Express plus browser JavaScript:
 
-- `server/index.js`: API, WebSocket, source proxy/relay, ffmpeg process lifecycle, recent URL persistence.
+- `server/index.js`: API, WebSocket, source proxy/relay, ffmpeg process lifecycle, recent URL and favorites persistence.
 - `public/index.html`: frontend markup.
 - `public/app.js`: URL submission, WebSocket frame receiving, audio element coordination, canvas drawing, overlay controls.
 - `public/styles.css`: two-screen player UI.
@@ -28,6 +28,8 @@ Main public endpoints:
 
 - `POST /api/session`: validates the stream URL, stores recent URL, creates a short-lived playback session.
 - `GET /api/recent-urls`: returns global recent URL entries with `url`, redacted `displayUrl`, and `lastPlayedAt`.
+- `GET /api/favorites`: returns global favorite entries with `title` and `url`.
+- `PUT /api/favorites`: replaces the global favorites list. Each favorite has a user-provided `title` and stream `url`.
 - `GET /audio/:sessionId`: serves MP3 audio to the browser audio element.
 - `WS /frames/:sessionId`: sends timed JPEG frame packets to the browser.
 - `GET /api/health`: exposes basic health and active playback connection mode.
@@ -73,6 +75,8 @@ The regression history matters:
 
 Default code behavior is `split` when no mode is set. The Compose example uses `relay` because it is the mode to try for IPTV streams.
 
+Finite-duration sessions are treated as recorded video and seekable. When the configured mode is `relay`, recorded sessions switch to the seek-capable `split` path once duration metadata is known; live/unknown-duration streams stay in relay mode.
+
 ## ffmpeg Pipelines
 
 All ffmpeg command builders live near the bottom of `server/index.js`.
@@ -170,6 +174,8 @@ Runtime:
 - `PLAYBACK_CONNECTION_MODE`: `split`, `relay`, or `single`.
 - `RECENT_URLS_PATH`: recent URL JSON path.
 - `RECENT_URL_LIMIT`: recent URL count, default `12`.
+- `FAVORITES_PATH`: favorites JSON path.
+- `FAVORITES_LIMIT`: favorites count, default `50`.
 - `MAX_WS_BUFFER_BYTES`: server-side WebSocket JPEG frame backlog cap, default `2097152`.
 - `MAX_AUDIO_QUEUE_BYTES`: single-mode audio output queue cap, default `16777216`.
 - `MAX_RELAY_BRANCH_QUEUE_BYTES`: relay per-branch compressed-input queue cap, default `16777216`.
@@ -218,6 +224,7 @@ Start a mode locally:
 
 ```sh
 PORT=3014 RECENT_URLS_PATH=/tmp/carplay-relay-recent.json \
+  FAVORITES_PATH=/tmp/carplay-relay-favorites.json \
   FFMPEG_LOG_LEVEL=warning FFMPEG_INPUT_SEEKABLE=0 \
   PLAYBACK_CONNECTION_MODE=relay npm start
 ```
@@ -225,7 +232,7 @@ PORT=3014 RECENT_URLS_PATH=/tmp/carplay-relay-recent.json \
 After smoke testing, remove generated assets:
 
 ```sh
-rm -f public/_relay-smoke.ts /tmp/carplay-*-recent.json
+rm -f public/_relay-smoke.ts /tmp/carplay-*-recent.json /tmp/carplay-*-favorites.json
 ```
 
 ## Security Notes

README.md

@@ -39,7 +39,7 @@ docker compose -f docker-compose-example.yml up --build
 
 The app uses CPU decoding by default, so no video device is required. The compose example includes commented VAAPI/NVIDIA passthrough options for future hardware-accelerated `ffmpeg` setups, but hardware acceleration is usually only useful when server CPU is saturated.
 
-Recently played URLs are stored globally by the backend. In Docker Compose, they are persisted in the `frame-stream-data` named volume.
+Recently played URLs and favorites are stored globally by the backend. In Docker Compose, they are persisted in the `frame-stream-data` named volume.
 
 `ffmpeg` worker lifecycle, stderr warnings/errors, and source proxy open/close events are written to stdout/stderr, so they appear in `docker logs`. For more detail while debugging a stream, set `FFMPEG_LOG_LEVEL=info` in Docker Compose and run:
 
@@ -61,6 +61,8 @@ Available playback modes:
 - `relay`: One source connection from the backend, then the compressed input bytes are teed into separate audio and frame `ffmpeg` workers. This is intended for IPTV hosts that stop early or reject multiple active connections.
 - `single`: One source connection and one `ffmpeg` worker with both audio and frame outputs. This is the simplest one-connection fallback, but audio and frame delivery can affect each other.
 
+Finite-duration streams are treated as recorded video and become seekable once metadata is available. If the app is configured for `relay`, recorded streams switch to the seek-capable `split` path; live or unknown-duration streams stay in relay mode.
+
 Relay mode uses bounded per-worker input queues so one branch can briefly lag without immediately stalling the other. Tune the cap with `MAX_RELAY_BRANCH_QUEUE_BYTES`; the default is `16777216`.
 
 ## Tuning

docker-compose-example.yml

@@ -19,6 +19,7 @@ services:
       MAX_AUDIO_QUEUE_BYTES: "16777216"
       MAX_RELAY_BRANCH_QUEUE_BYTES: "16777216"
       RECENT_URLS_PATH: /app/data/recent-urls.json
+      FAVORITES_PATH: /app/data/favorites.json
     extra_hosts:
       - "host.docker.internal:host-gateway"
     volumes:

public/app.js

@@ -5,8 +5,20 @@ const elements = {
   url: document.querySelector('#stream-url'),
   next: document.querySelector('#next'),
   entryMessage: document.querySelector('#entry-message'),
+  libraryPanel: document.querySelector('#library-panel'),
   recentPanel: document.querySelector('#recent-panel'),
   recentList: document.querySelector('#recent-list'),
+  favoritesPanel: document.querySelector('#favorites-panel'),
+  favoritesList: document.querySelector('#favorites-list'),
+  editFavorites: document.querySelector('#edit-favorites'),
+  favoritesModal: document.querySelector('#favorites-modal'),
+  favoritesForm: document.querySelector('#favorites-form'),
+  closeFavorites: document.querySelector('#close-favorites'),
+  cancelFavorites: document.querySelector('#cancel-favorites'),
+  addFavorite: document.querySelector('#add-favorite'),
+  saveFavorites: document.querySelector('#save-favorites'),
+  favoritesEditorList: document.querySelector('#favorites-editor-list'),
+  favoritesMessage: document.querySelector('#favorites-message'),
   audio: document.querySelector('#audio'),
   canvas: document.querySelector('#screen'),
   stage: document.querySelector('#video-stage'),
@@ -28,9 +40,18 @@ const MAX_PENDING_FRAME_QUEUE_SECONDS = 2;
 const MAX_DECODED_FRAME_QUEUE_SECONDS = 3;
 const MIN_PENDING_FRAME_QUEUE = 12;
 const MIN_DECODED_FRAME_QUEUE = 24;
+const IMAGE_DECODE_TIMEOUT_MS = 3000;
+const FRAME_STALL_CHECK_MS = 1000;
+const FRAME_STARTUP_STALL_RESET_MS = 10000;
+const FRAME_STALL_RESET_MS = 6000;
+const PLAYBACK_RESTART_COOLDOWN_MS = 8000;
+const PLAYBACK_RESTART_DELAY_MS = 750;
+const METADATA_REFRESH_ATTEMPTS = 20;
+const METADATA_REFRESH_INTERVAL_MS = 650;
 
 const state = {
   generation: 0,
+  streamGeneration: 0,
   session: null,
   websocket: null,
   pendingFrames: [],
@@ -42,14 +63,20 @@ const state = {
   controlsVisible: true,
   hideControlsTimer: 0,
   recentUrls: [],
+  favorites: [],
+  favoriteModalTrigger: null,
   playbackOffset: 0,
   duration: null,
   seekable: false,
   isSeeking: false,
   seekPreviewTime: 0,
+  frameWatchdogTimer: 0,
+  lastFramePacketAt: 0,
+  lastFramePaintedAt: 0,
+  lastPlaybackRestartAt: 0,
 };
 
-void loadRecentUrls();
+void loadEntryLists();
 
 elements.form.addEventListener('submit', async (event) => {
   event.preventDefault();
@@ -99,6 +126,68 @@ elements.recentList.addEventListener('click', (event) => {
   elements.form.requestSubmit();
 });
 
+elements.favoritesList.addEventListener('click', (event) => {
+  const button = event.target.closest('[data-favorite-index]');
+
+  if (!button) {
+    return;
+  }
+
+  const item = state.favorites[Number(button.dataset.favoriteIndex)];
+
+  if (!item) {
+    return;
+  }
+
+  elements.url.value = item.url;
+  elements.form.requestSubmit();
+});
+
+elements.editFavorites.addEventListener('click', () => {
+  openFavoritesModal();
+});
+
+elements.closeFavorites.addEventListener('click', () => {
+  closeFavoritesModal();
+});
+
+elements.cancelFavorites.addEventListener('click', () => {
+  closeFavoritesModal();
+});
+
+elements.addFavorite.addEventListener('click', () => {
+  elements.favoritesEditorList.append(createFavoriteEditorRow());
+  focusLastFavoriteTitle();
+});
+
+elements.favoritesEditorList.addEventListener('click', (event) => {
+  const button = event.target.closest('[data-remove-favorite]');
+
+  if (!button) {
+    return;
+  }
+
+  button.closest('.favorite-editor-row')?.remove();
+  ensureFavoriteEditorRows();
+});
+
+elements.favoritesForm.addEventListener('submit', (event) => {
+  event.preventDefault();
+  void saveFavoritesFromModal();
+});
+
+elements.favoritesModal.addEventListener('click', (event) => {
+  if (event.target === elements.favoritesModal) {
+    closeFavoritesModal();
+  }
+});
+
+window.addEventListener('keydown', (event) => {
+  if (event.key === 'Escape' && !elements.favoritesModal.hidden) {
+    closeFavoritesModal();
+  }
+});
+
 elements.stage.addEventListener('pointerup', (event) => {
   if (!state.session || event.target.closest('.controls')) {
     return;
@@ -156,6 +245,7 @@ elements.seek.addEventListener('change', () => {
 
 elements.audio.addEventListener('play', () => {
   startRenderLoop();
+  startFrameWatchdog();
   syncControlLabels();
   scheduleControlsHide();
   syncPlayhead();
@@ -195,6 +285,12 @@ elements.audio.addEventListener('error', () => {
   }
 });
 
+window.addEventListener('online', () => {
+  if (state.session && !elements.audio.paused && isFrameStreamStale(FRAME_STALL_RESET_MS)) {
+    restartPlaybackStreams();
+  }
+});
+
 function startSession(session) {
   state.session = session;
   state.playbackOffset = Number(session.seekSeconds) || 0;
@@ -203,6 +299,8 @@ function startSession(session) {
   state.isSeeking = false;
   state.seekPreviewTime = state.playbackOffset;
   state.frameCount = 0;
+  state.lastFramePacketAt = 0;
+  state.lastFramePaintedAt = 0;
   clearFrameQueue();
   syncControlLabels();
   syncPlayhead();
@@ -211,6 +309,7 @@ function startSession(session) {
   clearPlayerMessage();
 
   connectPlaybackStreams();
+  startFrameWatchdog();
   void refreshSessionMetadata(session.id);
 }
 
@@ -219,8 +318,12 @@ function connectPlaybackStreams() {
     return;
   }
 
-  const generation = state.generation;
+  const streamGeneration = state.streamGeneration + 1;
   const session = state.session;
+  const now = Date.now();
+  state.streamGeneration = streamGeneration;
+  state.lastPlaybackRestartAt = now;
+  state.lastFramePacketAt = now;
 
   if (state.websocket) {
     state.websocket.close(1000, 'client reconnecting');
@@ -234,7 +337,7 @@ function connectPlaybackStreams() {
   state.websocket = websocket;
 
   websocket.addEventListener('message', (event) => {
-    if (generation !== state.generation) {
+    if (streamGeneration !== state.streamGeneration) {
       return;
     }
 
@@ -243,18 +346,18 @@ function connectPlaybackStreams() {
       return;
     }
 
-    void handleFramePacket(event.data, generation);
+    handleFramePacket(event.data, streamGeneration);
   });
 
   websocket.addEventListener('close', () => {
-    if (generation === state.generation && state.session?.id === session.id) {
+    if (streamGeneration === state.streamGeneration && state.session?.id === session.id) {
       showPlayerMessage('Stream ended');
       setControlsVisible(true);
     }
   });
 
   websocket.addEventListener('error', () => {
-    if (generation === state.generation && state.session?.id === session.id) {
+    if (streamGeneration === state.streamGeneration && state.session?.id === session.id) {
       showPlayerMessage('Stream failed');
       setControlsVisible(true);
     }
@@ -277,18 +380,94 @@ async function playAudio() {
   }
 }
 
-function handleFramePacket(packet, generation) {
+function startFrameWatchdog() {
+  if (state.frameWatchdogTimer) {
+    return;
+  }
+
+  state.frameWatchdogTimer = window.setInterval(checkFrameWatchdog, FRAME_STALL_CHECK_MS);
+}
+
+function clearFrameWatchdog() {
+  if (!state.frameWatchdogTimer) {
+    return;
+  }
+
+  window.clearInterval(state.frameWatchdogTimer);
+  state.frameWatchdogTimer = 0;
+}
+
+function checkFrameWatchdog() {
+  if (!state.session || state.isSeeking || document.hidden || elements.audio.paused || elements.audio.ended || elements.audio.readyState === 0) {
+    return;
+  }
+
+  const resetAfterMs = state.lastFramePaintedAt > 0 ? FRAME_STALL_RESET_MS : FRAME_STARTUP_STALL_RESET_MS;
+
+  if (!isFrameStreamStale(resetAfterMs)) {
+    return;
+  }
+
+  restartPlaybackStreams();
+}
+
+function isFrameStreamStale(resetAfterMs) {
+  const now = Date.now();
+  const lastFrameAt = state.lastFramePacketAt || state.lastPlaybackRestartAt || now;
+  return now - lastFrameAt >= resetAfterMs && now - state.lastPlaybackRestartAt >= PLAYBACK_RESTART_COOLDOWN_MS;
+}
+
+function restartPlaybackStreams() {
+  if (!state.session) {
+    return;
+  }
+
+  if (state.seekable && Number.isFinite(state.duration) && state.duration > 0) {
+    state.lastPlaybackRestartAt = Date.now();
+    void seekTo(getVisiblePlaybackTime());
+    return;
+  }
+
+  const streamGeneration = state.streamGeneration + 1;
+  const sessionId = state.session.id;
+  const now = Date.now();
+
+  state.streamGeneration = streamGeneration;
+  state.lastPlaybackRestartAt = now;
+  state.lastFramePacketAt = now;
+  elements.loader.hidden = false;
+  clearPlayerMessage();
+  clearFrameQueue({ keepCurrent: true });
+
+  if (state.websocket) {
+    state.websocket.close(1000, 'frame stream stalled');
+    state.websocket = null;
+  }
+
+  elements.audio.pause();
+  elements.audio.removeAttribute('src');
+  elements.audio.load();
+
+  window.setTimeout(() => {
+    if (state.session?.id === sessionId && state.streamGeneration === streamGeneration) {
+      connectPlaybackStreams();
+    }
+  }, PLAYBACK_RESTART_DELAY_MS);
+}
+
+function handleFramePacket(packet, streamGeneration) {
   if (!(packet instanceof ArrayBuffer) || packet.byteLength <= 8) {
     return;
   }
 
   const timestamp = new DataView(packet, 0, 8).getFloat64(0, true);
 
-  if (generation !== state.generation || isLateFrame(timestamp)) {
+  if (streamGeneration !== state.streamGeneration || isLateFrame(timestamp)) {
     return;
   }
 
-  state.pendingFrames.push({ timestamp, jpeg: packet.slice(8), generation });
+  state.lastFramePacketAt = Date.now();
+  state.pendingFrames.push({ timestamp, jpeg: packet.slice(8), streamGeneration });
   trimPendingFrameQueue();
   void pumpFrameDecodeQueue();
 }
@@ -362,6 +541,7 @@ function drawReadyFrames() {
 
   state.currentBitmap = frameToDraw.bitmap;
   drawBitmap(frameToDraw.bitmap);
+  state.lastFramePaintedAt = Date.now();
   elements.loader.hidden = true;
   clearPlayerMessage();
 }
@@ -395,19 +575,19 @@ async function pumpFrameDecodeQueue() {
         return;
       }
 
-      if (frame.generation !== state.generation || isLateFrame(frame.timestamp)) {
+      if (frame.streamGeneration !== state.streamGeneration || isLateFrame(frame.timestamp)) {
         continue;
       }
 
       let bitmap;
 
       try {
-        bitmap = await decodeImage(new Blob([frame.jpeg], { type: 'image/jpeg' }));
+        bitmap = await decodeImageWithTimeout(new Blob([frame.jpeg], { type: 'image/jpeg' }));
       } catch {
         continue;
       }
 
-      if (frame.generation !== state.generation || isLateFrame(frame.timestamp)) {
+      if (frame.streamGeneration !== state.streamGeneration || isLateFrame(frame.timestamp)) {
         releaseImage(bitmap);
         continue;
       }
@@ -501,6 +681,7 @@ function isLateFrame(timestamp) {
 
 function stopSession({ showEntry: shouldShowEntry = true } = {}) {
   state.generation += 1;
+  state.streamGeneration += 1;
   state.session = null;
   state.frameCount = 0;
   state.playbackOffset = 0;
@@ -508,7 +689,10 @@ function stopSession({ showEntry: shouldShowEntry = true } = {}) {
   state.seekable = false;
   state.isSeeking = false;
   state.seekPreviewTime = 0;
+  state.lastFramePacketAt = 0;
+  state.lastFramePaintedAt = 0;
   clearHideControlsTimer();
+  clearFrameWatchdog();
 
   if (state.websocket) {
     state.websocket.close(1000, 'client stopped');
@@ -537,7 +721,7 @@ function stopSession({ showEntry: shouldShowEntry = true } = {}) {
   }
 }
 
-function clearFrameQueue() {
+function clearFrameQueue({ keepCurrent = false } = {}) {
   state.pendingFrames = [];
 
   for (const frame of state.frames) {
@@ -546,12 +730,45 @@ function clearFrameQueue() {
 
   state.frames = [];
 
-  if (state.currentBitmap) {
+  if (!keepCurrent && state.currentBitmap) {
     releaseImage(state.currentBitmap);
     state.currentBitmap = null;
   }
 }
 
+async function decodeImageWithTimeout(blob) {
+  let timedOut = false;
+  let timeoutId = 0;
+
+  const decodePromise = decodeImage(blob).then(
+    (image) => {
+      if (timedOut) {
+        releaseImage(image);
+        return null;
+      }
+
+      return image;
+    },
+    () => null,
+  );
+
+  const timeoutPromise = new Promise((resolve) => {
+    timeoutId = window.setTimeout(() => {
+      timedOut = true;
+      resolve(null);
+    }, IMAGE_DECODE_TIMEOUT_MS);
+  });
+
+  const image = await Promise.race([decodePromise, timeoutPromise]);
+  window.clearTimeout(timeoutId);
+
+  if (!image) {
+    throw new Error('Image decode failed.');
+  }
+
+  return image;
+}
+
 async function decodeImage(blob) {
   if ('createImageBitmap' in window) {
     return createImageBitmap(blob);
@@ -596,10 +813,13 @@ async function seekTo(value) {
   const sessionId = state.session.id;
 
   state.generation = generation;
+  state.streamGeneration += 1;
   state.playbackOffset = targetTime;
   state.seekPreviewTime = targetTime;
   state.isSeeking = false;
   state.frameCount = 0;
+  state.lastFramePacketAt = 0;
+  state.lastFramePaintedAt = 0;
   elements.loader.hidden = false;
   clearPlayerMessage();
   clearFrameQueue();
@@ -648,7 +868,7 @@ async function seekTo(value) {
 async function refreshSessionMetadata(sessionId) {
   const generation = state.generation;
 
-  for (let attempt = 0; attempt < 10; attempt += 1) {
+  for (let attempt = 0; attempt < METADATA_REFRESH_ATTEMPTS; attempt += 1) {
     if (generation !== state.generation || state.session?.id !== sessionId) {
       return;
     }
@@ -676,7 +896,7 @@ async function refreshSessionMetadata(sessionId) {
       return;
     }
 
-    await delay(650);
+    await delay(METADATA_REFRESH_INTERVAL_MS);
   }
 }
 
@@ -797,7 +1017,7 @@ function syncControlLabels() {
 function showEntry() {
   elements.playerScreen.hidden = true;
   elements.entryScreen.hidden = false;
-  void loadRecentUrls();
+  void loadEntryLists();
   elements.url.focus();
 }
 
@@ -822,11 +1042,18 @@ function setFormBusy(isBusy) {
   elements.url.disabled = isBusy;
   elements.next.disabled = isBusy;
 
-  for (const button of elements.recentList.querySelectorAll('button')) {
+  for (const button of elements.libraryPanel.querySelectorAll('button')) {
     button.disabled = isBusy;
   }
 }
 
+async function loadEntryLists() {
+  await Promise.all([
+    loadRecentUrls(),
+    loadFavorites(),
+  ]);
+}
+
 async function loadRecentUrls() {
   try {
     const response = await fetch('/api/recent-urls', { cache: 'no-store' });
@@ -849,12 +1076,170 @@ function renderRecentUrls() {
     ...state.recentUrls.map((item, index) => {
       const button = document.createElement('button');
       button.type = 'button';
-      button.className = 'recent-url';
+      button.className = 'url-item';
       button.dataset.recentIndex = String(index);
       button.textContent = item.displayUrl || item.url;
       return button;
     }),
   );
 
-  elements.recentPanel.hidden = state.recentUrls.length === 0;
+  if (state.recentUrls.length === 0) {
+    elements.recentList.replaceChildren(createEmptyListMessage('No recents'));
+  }
+}
+
+async function loadFavorites() {
+  try {
+    const response = await fetch('/api/favorites', { cache: 'no-store' });
+
+    if (!response.ok) {
+      throw new Error('Failed to load favorites.');
+    }
+
+    const payload = await response.json();
+    state.favorites = Array.isArray(payload.favorites) ? payload.favorites : [];
+    renderFavorites();
+  } catch {
+    state.favorites = [];
+    renderFavorites();
+  }
+}
+
+function renderFavorites() {
+  elements.favoritesList.replaceChildren(
+    ...state.favorites.map((item, index) => {
+      const button = document.createElement('button');
+      button.type = 'button';
+      button.className = 'url-item';
+      button.dataset.favoriteIndex = String(index);
+      button.textContent = item.title;
+      return button;
+    }),
+  );
+
+  if (state.favorites.length === 0) {
+    elements.favoritesList.replaceChildren(createEmptyListMessage('No favorites'));
+  }
+}
+
+function createEmptyListMessage(text) {
+  const message = document.createElement('p');
+  message.className = 'empty-list';
+  message.textContent = text;
+  return message;
+}
+
+function openFavoritesModal() {
+  state.favoriteModalTrigger = document.activeElement instanceof HTMLElement ? document.activeElement : null;
+  elements.favoritesMessage.textContent = '';
+  renderFavoriteEditorRows(state.favorites);
+  elements.favoritesModal.hidden = false;
+  elements.favoritesModal.classList.add('is-open');
+  focusFirstFavoriteField();
+}
+
+function closeFavoritesModal() {
+  elements.favoritesModal.hidden = true;
+  elements.favoritesModal.classList.remove('is-open');
+  elements.favoritesMessage.textContent = '';
+  state.favoriteModalTrigger?.focus();
+  state.favoriteModalTrigger = null;
+}
+
+function renderFavoriteEditorRows(items) {
+  const rows = items.length > 0 ? items : [{ title: '', url: '' }];
+  elements.favoritesEditorList.replaceChildren(
+    ...rows.map((item) => createFavoriteEditorRow(item)),
+  );
+}
+
+function createFavoriteEditorRow(item = { title: '', url: '' }) {
+  const row = document.createElement('div');
+  row.className = 'favorite-editor-row';
+
+  const title = document.createElement('input');
+  title.type = 'text';
+  title.placeholder = 'Title';
+  title.setAttribute('aria-label', 'Favorite title');
+  title.autocomplete = 'off';
+  title.maxLength = 120;
+  title.value = item.title ?? '';
+  title.dataset.favoriteTitle = '';
+
+  const url = document.createElement('input');
+  url.type = 'url';
+  url.placeholder = 'URL';
+  url.setAttribute('aria-label', 'Favorite URL');
+  url.autocomplete = 'off';
+  url.value = item.url ?? '';
+  url.dataset.favoriteUrl = '';
+
+  const remove = document.createElement('button');
+  remove.type = 'button';
+  remove.className = 'remove-favorite';
+  remove.dataset.removeFavorite = '';
+  remove.setAttribute('aria-label', 'Remove favorite');
+  remove.textContent = 'Remove';
+
+  row.append(title, url, remove);
+  return row;
+}
+
+function ensureFavoriteEditorRows() {
+  if (elements.favoritesEditorList.children.length === 0) {
+    elements.favoritesEditorList.append(createFavoriteEditorRow());
+  }
+}
+
+function focusFirstFavoriteField() {
+  const field = elements.favoritesEditorList.querySelector('[data-favorite-title], [data-favorite-url]');
+  field?.focus();
+}
+
+function focusLastFavoriteTitle() {
+  const rows = elements.favoritesEditorList.querySelectorAll('.favorite-editor-row');
+  const row = rows[rows.length - 1];
+  row?.querySelector('[data-favorite-title]')?.focus();
+}
+
+async function saveFavoritesFromModal() {
+  elements.favoritesMessage.textContent = '';
+  setFavoritesModalBusy(true);
+
+  try {
+    const favorites = readFavoriteEditorRows();
+    const response = await fetch('/api/favorites', {
+      method: 'PUT',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ favorites }),
+    });
+    const payload = await response.json();
+
+    if (!response.ok) {
+      throw new Error(payload.error ?? 'Failed to save favorites.');
+    }
+
+    state.favorites = Array.isArray(payload.favorites) ? payload.favorites : [];
+    renderFavorites();
+    closeFavoritesModal();
+  } catch (error) {
+    elements.favoritesMessage.textContent = error.message;
+  } finally {
+    setFavoritesModalBusy(false);
+  }
+}
+
+function readFavoriteEditorRows() {
+  return [...elements.favoritesEditorList.querySelectorAll('.favorite-editor-row')]
+    .map((row) => ({
+      title: row.querySelector('[data-favorite-title]')?.value.trim() ?? '',
+      url: row.querySelector('[data-favorite-url]')?.value.trim() ?? '',
+    }))
+    .filter((item) => item.title || item.url);
+}
+
+function setFavoritesModalBusy(isBusy) {
+  for (const field of elements.favoritesForm.querySelectorAll('input, button')) {
+    field.disabled = isBusy;
+  }
 }

public/index.html

@@ -22,8 +22,20 @@
             >
             <button id="next" type="submit">Next</button>
           </form>
-          <div id="recent-panel" class="recent-panel" aria-label="Recently played URLs" hidden>
+          <div id="library-panel" class="library-panel" aria-label="Saved streams">
-            <div id="recent-list" class="recent-list"></div>
+            <section id="recent-panel" class="url-column" aria-labelledby="recent-heading">
+              <div class="column-heading">
+                <h2 id="recent-heading">Recents</h2>
+              </div>
+              <div id="recent-list" class="url-list"></div>
+            </section>
+            <section id="favorites-panel" class="url-column" aria-labelledby="favorites-heading">
+              <div class="column-heading">
+                <h2 id="favorites-heading">Favorites</h2>
+                <button id="edit-favorites" type="button" class="small-button">Edit</button>
+              </div>
+              <div id="favorites-list" class="url-list"></div>
+            </section>
           </div>
         </div>
         <div id="entry-message" class="message" role="status" aria-live="polite"></div>
@@ -48,6 +60,22 @@
         </div>
         <audio id="audio" preload="none"></audio>
       </section>
+
+      <div id="favorites-modal" class="modal" role="dialog" aria-modal="true" aria-labelledby="favorites-modal-title" hidden>
+        <form id="favorites-form" class="modal-panel">
+          <div class="modal-heading">
+            <h2 id="favorites-modal-title">Edit Favorites</h2>
+            <button id="close-favorites" type="button" class="icon-button" aria-label="Close favorites editor">&times;</button>
+          </div>
+          <div id="favorites-editor-list" class="favorites-editor-list"></div>
+          <button id="add-favorite" type="button" class="secondary-button">Add Favorite</button>
+          <div id="favorites-message" class="modal-message" role="status" aria-live="polite"></div>
+          <div class="modal-actions">
+            <button id="cancel-favorites" type="button" class="secondary-button">Cancel</button>
+            <button id="save-favorites" type="submit" class="primary-button">Save</button>
+          </div>
+        </form>
+      </div>
     </main>
 
     <script src="/app.js" type="module"></script>

public/styles.css

@@ -64,7 +64,7 @@ button:disabled {
 
 .entry-stack {
   display: grid;
-  width: min(760px, 100%);
+  width: min(980px, 100%);
   gap: 0.75rem;
 }
 
@@ -96,7 +96,12 @@ button:disabled {
 }
 
 .url-form button,
-.control-button {
+.control-button,
+.small-button,
+.secondary-button,
+.primary-button,
+.icon-button,
+.remove-favorite {
   border: 1px solid var(--line);
   border-radius: 999px;
   color: var(--fg);
@@ -111,28 +116,61 @@ button:disabled {
   color: #070707;
 }
 
-.recent-panel {
+.library-panel {
+  display: grid;
+  grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
+  gap: 0.75rem;
+}
+
+.url-column {
   overflow: hidden;
   border: 1px solid var(--line);
-  border-radius: 28px;
+  border-radius: 24px;
   background: rgba(255, 255, 255, 0.07);
   box-shadow: 0 18px 80px rgba(0, 0, 0, 0.28);
   backdrop-filter: blur(18px);
 }
 
-.recent-list {
+.column-heading {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 0.75rem;
+  min-height: 3.2rem;
+  padding: 0.55rem 0.75rem 0.2rem 1rem;
+}
+
+.column-heading h2,
+.modal-heading h2 {
+  margin: 0;
+  font-size: 0.86rem;
+  font-weight: 800;
+  letter-spacing: 0;
+  text-transform: uppercase;
+  color: var(--soft);
+}
+
+.small-button {
+  flex: 0 0 auto;
+  min-width: 4.2rem;
+  padding: 0.45rem 0.8rem;
+  font-size: 0.84rem;
+  font-weight: 800;
+}
+
+.url-list {
   display: grid;
   max-height: min(42vh, 24rem);
   overflow: auto;
   padding: 0.35rem;
 }
 
-.recent-url {
+.url-item {
   display: block;
   width: 100%;
   overflow: hidden;
   border: 0;
-  border-radius: 20px;
+  border-radius: 16px;
   padding: 0.85rem 1rem;
   color: var(--soft);
   text-align: left;
@@ -141,13 +179,19 @@ button:disabled {
   background: transparent;
 }
 
-.recent-url:hover,
+.url-item:hover,
-.recent-url:focus {
+.url-item:focus {
   color: var(--fg);
   background: rgba(255, 255, 255, 0.09);
   outline: none;
 }
 
+.empty-list {
+  margin: 0;
+  padding: 0.85rem 1rem;
+  color: rgba(246, 241, 232, 0.42);
+}
+
 .message {
   position: fixed;
   bottom: 2rem;
@@ -242,12 +286,13 @@ canvas {
   top: -1.75rem;
   right: 1.1rem;
   left: 1.1rem;
-  height: 2.2rem;
+  height: 2.45rem;
 }
 
 .time-badge {
   position: absolute;
   top: 0;
+  pointer-events: none;
   min-width: 3.6rem;
   padding: 0.22rem 0.45rem;
   border: 1px solid var(--line);
@@ -274,10 +319,10 @@ canvas {
 .seek-slider {
   position: absolute;
   right: 0;
-  bottom: 0.18rem;
+  bottom: 0;
   left: 0;
   width: 100%;
-  height: 1rem;
+  height: 1.35rem;
   margin: 0;
   appearance: none;
   background: transparent;
@@ -365,6 +410,107 @@ audio {
   display: none;
 }
 
+.modal {
+  position: fixed;
+  inset: 0;
+  z-index: 10;
+  display: grid;
+  place-items: center;
+  padding: 1rem;
+  background: rgba(0, 0, 0, 0.72);
+  backdrop-filter: blur(12px);
+}
+
+.modal-panel {
+  display: grid;
+  width: min(860px, 100%);
+  max-height: min(760px, calc(100vh - 2rem));
+  overflow: auto;
+  gap: 0.85rem;
+  margin: 0;
+  padding: 1rem;
+  border: 1px solid var(--line);
+  border-radius: 8px;
+  background: var(--glass-strong);
+  box-shadow: 0 28px 120px rgba(0, 0, 0, 0.55);
+}
+
+.modal-heading {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 1rem;
+}
+
+.icon-button {
+  display: grid;
+  width: 2.3rem;
+  height: 2.3rem;
+  place-items: center;
+  padding: 0;
+  font-size: 1.2rem;
+  font-weight: 800;
+  line-height: 1;
+}
+
+.favorites-editor-list {
+  display: grid;
+  gap: 0.55rem;
+}
+
+.favorite-editor-row {
+  display: grid;
+  grid-template-columns: minmax(8rem, 0.8fr) minmax(12rem, 1.6fr) auto;
+  gap: 0.55rem;
+}
+
+.favorite-editor-row input {
+  min-width: 0;
+  border: 1px solid var(--line);
+  border-radius: 8px;
+  padding: 0.72rem 0.8rem;
+  color: var(--fg);
+  background: rgba(255, 255, 255, 0.08);
+  outline: none;
+}
+
+.favorite-editor-row input::placeholder {
+  color: rgba(246, 241, 232, 0.42);
+}
+
+.favorite-editor-row input:focus {
+  border-color: rgba(232, 168, 79, 0.7);
+}
+
+.secondary-button,
+.primary-button,
+.remove-favorite {
+  min-height: 2.7rem;
+  padding: 0.65rem 0.95rem;
+  font-weight: 800;
+}
+
+.primary-button {
+  border-color: transparent;
+  color: #070707;
+  background: var(--fg);
+}
+
+.modal-actions {
+  display: flex;
+  justify-content: flex-end;
+  gap: 0.65rem;
+}
+
+.modal-message {
+  min-height: 1.2rem;
+  color: var(--soft);
+}
+
+.modal-message:empty {
+  display: none;
+}
+
 [hidden] {
   display: none !important;
 }
@@ -386,6 +532,29 @@ audio {
     width: 100%;
   }
 
+  .library-panel {
+    grid-template-columns: 1fr;
+  }
+
+  .url-list {
+    max-height: 28vh;
+  }
+
+  .favorite-editor-row {
+    grid-template-columns: 1fr;
+  }
+
+  .remove-favorite,
+  .secondary-button,
+  .primary-button {
+    width: 100%;
+  }
+
+  .modal-actions {
+    display: grid;
+    grid-template-columns: 1fr 1fr;
+  }
+
   .controls {
     right: 0.75rem;
     bottom: 0.75rem;

server/index.js

@@ -24,6 +24,8 @@ const FFMPEG_INPUT_SEEKABLE = process.env.FFMPEG_INPUT_SEEKABLE ?? '0';
 const PLAYBACK_CONNECTION_MODE = parsePlaybackConnectionMode(process.env.PLAYBACK_CONNECTION_MODE ?? process.env.PLAYBACK_MODE);
 const RECENT_URLS_PATH = process.env.RECENT_URLS_PATH ?? path.join(__dirname, '..', 'data', 'recent-urls.json');
 const RECENT_URL_LIMIT = clampInteger(process.env.RECENT_URL_LIMIT, 12, 1, 50);
+const FAVORITES_PATH = process.env.FAVORITES_PATH ?? path.join(__dirname, '..', 'data', 'favorites.json');
+const FAVORITES_LIMIT = clampInteger(process.env.FAVORITES_LIMIT, 50, 1, 200);
 const SESSION_TTL_MS = 60 * 60 * 1000;
 const METADATA_PROBE_TIMEOUT_MS = 8 * 1000;
 const PLAYBACK_READY_TIMEOUT_MS = 15 * 1000;
@@ -46,9 +48,11 @@ const sourceTokens = new Map();
 const playbacks = new Map();
 let recentUrls = [];
 let recentWrite = Promise.resolve();
+let favorites = [];
+let favoritesWrite = Promise.resolve();
 
 app.disable('x-powered-by');
-app.use(express.json({ limit: '32kb' }));
+app.use(express.json({ limit: '256kb' }));
 app.use(express.static(publicDir));
 
 app.get('/api/health', (_request, response) => {
@@ -65,6 +69,34 @@ app.get('/api/recent-urls', (_request, response) => {
   });
 });
 
+app.get('/api/favorites', (_request, response) => {
+  response.json({ favorites: formatFavoritesPayload() });
+});
+
+app.put('/api/favorites', async (request, response) => {
+  let nextFavorites;
+
+  try {
+    nextFavorites = parseFavoritesPayload(request.body?.favorites);
+  } catch (error) {
+    response.status(400).json({ error: error.message });
+    return;
+  }
+
+  favorites = nextFavorites;
+  favoritesWrite = favoritesWrite.catch(() => {}).then(() => saveFavorites());
+
+  try {
+    await favoritesWrite;
+  } catch (error) {
+    console.warn(`Failed to store favorites: ${error.message}`);
+    response.status(500).json({ error: 'Failed to store favorites.' });
+    return;
+  }
+
+  response.json({ favorites: formatFavoritesPayload() });
+});
+
 app.post('/api/session', async (request, response) => {
   let url;
 
@@ -237,11 +269,14 @@ app.get('/audio/:sessionId', (request, response) => {
     return;
   }
 
-  if (PLAYBACK_CONNECTION_MODE === 'single' || PLAYBACK_CONNECTION_MODE === 'relay') {
+  const playbackMode = getSessionPlaybackConnectionMode(session);
-    getOrCreatePlayback(session).attachAudio(request, response);
+
+  if (playbackMode === 'single' || playbackMode === 'relay') {
+    getOrCreatePlayback(session, playbackMode).attachAudio(request, response);
     return;
   }
 
+  stopSharedPlaybackIfNeeded(session, playbackMode);
   streamSplitAudio(request, response, session);
 });
 
@@ -269,11 +304,14 @@ wss.on('connection', (websocket, _request, sessionId) => {
     return;
   }
 
-  if (PLAYBACK_CONNECTION_MODE === 'single' || PLAYBACK_CONNECTION_MODE === 'relay') {
+  const playbackMode = getSessionPlaybackConnectionMode(session);
-    getOrCreatePlayback(session).attachFrames(websocket);
+
+  if (playbackMode === 'single' || playbackMode === 'relay') {
+    getOrCreatePlayback(session, playbackMode).attachFrames(websocket);
     return;
   }
 
+  stopSharedPlaybackIfNeeded(session, playbackMode);
   streamSplitFrames(websocket, session);
 });
 
@@ -293,7 +331,10 @@ setInterval(() => {
   }
 }, 60 * 1000).unref();
 
-await loadRecentUrls();
+await Promise.all([
+  loadRecentUrls(),
+  loadFavorites(),
+]);
 
 server.listen(PORT, () => {
   console.log(`Frame stream app listening at http://localhost:${PORT} mode=${PLAYBACK_CONNECTION_MODE}`);
@@ -378,7 +419,19 @@ function formatSessionPayload(session) {
 }
 
 function isSessionSeekable(session) {
-  return PLAYBACK_CONNECTION_MODE !== 'relay' && Number.isFinite(session.duration) && session.duration > 0;
+  return hasRecordedDuration(session);
+}
+
+function hasRecordedDuration(session) {
+  return Number.isFinite(session.duration) && session.duration > 0;
+}
+
+function getSessionPlaybackConnectionMode(session) {
+  if (PLAYBACK_CONNECTION_MODE === 'relay' && hasRecordedDuration(session)) {
+    return 'split';
+  }
+
+  return PLAYBACK_CONNECTION_MODE;
 }
 
 function startSessionMetadataProbe(session) {
@@ -501,6 +554,25 @@ async function loadRecentUrls() {
   }
 }
 
+async function loadFavorites() {
+  try {
+    const raw = await fs.readFile(FAVORITES_PATH, 'utf8');
+    const parsed = JSON.parse(raw);
+    const items = Array.isArray(parsed?.favorites) ? parsed.favorites : [];
+
+    favorites = items
+      .map(normalizeFavorite)
+      .filter(Boolean)
+      .slice(0, FAVORITES_LIMIT);
+  } catch (error) {
+    if (error.code !== 'ENOENT') {
+      console.warn(`Failed to read favorites: ${error.message}`);
+    }
+
+    favorites = [];
+  }
+}
+
 async function addRecentUrl(url) {
   const lastPlayedAt = new Date().toISOString();
   recentUrls = [
@@ -522,6 +594,85 @@ async function saveRecentUrls() {
   await fs.rename(temporaryPath, RECENT_URLS_PATH);
 }
 
+async function saveFavorites() {
+  const directory = path.dirname(FAVORITES_PATH);
+  const temporaryPath = `${FAVORITES_PATH}.${process.pid}.tmp`;
+  const payload = `${JSON.stringify({ favorites }, null, 2)}\n`;
+
+  await fs.mkdir(directory, { recursive: true });
+  await fs.writeFile(temporaryPath, payload, 'utf8');
+  await fs.rename(temporaryPath, FAVORITES_PATH);
+}
+
+function formatFavoritesPayload() {
+  return favorites.map((item) => ({
+    title: item.title,
+    url: item.url,
+  }));
+}
+
+function parseFavoritesPayload(value) {
+  if (!Array.isArray(value)) {
+    throw new Error('Favorites must be a list.');
+  }
+
+  if (value.length > FAVORITES_LIMIT) {
+    throw new Error(`Favorites are limited to ${FAVORITES_LIMIT} items.`);
+  }
+
+  return value.map((item, index) => parseFavorite(item, index));
+}
+
+function parseFavorite(item, index) {
+  if (!item || typeof item !== 'object') {
+    throw new Error(`Favorite ${index + 1} is invalid.`);
+  }
+
+  const title = parseFavoriteTitle(item.title, index);
+  let url;
+
+  try {
+    url = parseStreamUrl(item.url);
+  } catch (error) {
+    throw new Error(`Favorite ${index + 1}: ${error.message}`);
+  }
+
+  return { title, url };
+}
+
+function normalizeFavorite(item) {
+  if (!item || typeof item !== 'object') {
+    return null;
+  }
+
+  try {
+    return {
+      title: parseFavoriteTitle(item.title, 0),
+      url: parseStreamUrl(item.url),
+    };
+  } catch {
+    return null;
+  }
+}
+
+function parseFavoriteTitle(value, index) {
+  if (typeof value !== 'string') {
+    throw new Error(`Favorite ${index + 1} needs a title.`);
+  }
+
+  const title = value.trim();
+
+  if (!title) {
+    throw new Error(`Favorite ${index + 1} needs a title.`);
+  }
+
+  if (title.length > 120) {
+    throw new Error(`Favorite ${index + 1} title is too long.`);
+  }
+
+  return title;
+}
+
 function getSession(sessionId) {
   const session = sessions.get(sessionId);
 
@@ -533,18 +684,34 @@ function getSession(sessionId) {
   return session;
 }
 
-function getOrCreatePlayback(session) {
+function getOrCreatePlayback(session, playbackMode = getSessionPlaybackConnectionMode(session)) {
   const existing = playbacks.get(session.id);
 
-  if (existing && !existing.closed) {
+  if (existing && !existing.closed && existing.mode === playbackMode) {
     return existing;
   }
 
-  const playback = PLAYBACK_CONNECTION_MODE === 'relay' ? createRelayPlayback(session) : createPlayback(session);
+  stopSharedPlaybackIfNeeded(session, playbackMode);
+
+  const playback = playbackMode === 'relay' ? createRelayPlayback(session) : createPlayback(session);
   playbacks.set(session.id, playback);
   return playback;
 }
 
+function stopSharedPlaybackIfNeeded(session, playbackMode) {
+  const existing = playbacks.get(session.id);
+
+  if (!existing || existing.closed || existing.mode === playbackMode) {
+    return;
+  }
+
+  existing.stop('playback_mode_changed');
+
+  if (playbacks.get(session.id) === existing) {
+    playbacks.delete(session.id);
+  }
+}
+
 function streamSplitAudio(request, response, session) {
   const worker = createAudioWorker(session);
   const releaseWorker = once(worker.release);
@@ -617,11 +784,11 @@ function streamSplitFrames(websocket, session) {
   const stderrTail = createFfmpegStderrTail();
   const { fps, quality, width } = session.options;
   const label = `frames:${shortId(session.id)}`;
-  let frameBuffer = Buffer.alloc(0);
   let frameIndex = 0;
   let skippedFrames = 0;
   let stopReason = 'process_exit';
   let serverClosingWebSocket = false;
+  const frameParser = createJpegFrameParser(handleJpegFrame);
 
   logger.start();
 
@@ -694,45 +861,27 @@ function streamSplitFrames(websocket, session) {
   });
 
   function handleFrameData(chunk) {
-    frameBuffer = Buffer.concat([frameBuffer, chunk]);
+    frameParser.write(chunk);
-
-    for (;;) {
-      const start = frameBuffer.indexOf(JPEG_SOI);
-
-      if (start === -1) {
-        frameBuffer = Buffer.alloc(0);
-        return;
   }
 
-      const end = frameBuffer.indexOf(JPEG_EOI, start + JPEG_SOI.length);
+  function handleJpegFrame(jpeg) {
-
-      if (end === -1) {
-        frameBuffer = start === 0 ? frameBuffer : frameBuffer.subarray(start);
-        return;
-      }
-
-      const jpeg = frameBuffer.subarray(start, end + JPEG_EOI.length);
-      frameBuffer = frameBuffer.subarray(end + JPEG_EOI.length);
     const timestamp = frameIndex / fps;
     frameIndex += 1;
 
-      if (!isWebSocketOpen(websocket)) {
-        return;
-      }
-
     const sendResult = sendFramePacket(websocket, timestamp, jpeg, () => {
       stopReason = 'websocket_send_error';
       stopProcess(ffmpeg);
     });
 
     if (sendResult === 'closed') {
-        return;
+      return false;
     }
 
     if (sendResult === 'skipped') {
       skippedFrames += 1;
     }
-    }
+
+    return true;
   }
 }
 
@@ -749,7 +898,6 @@ function createRelayPlayback(session) {
   let frameLogger = null;
   let sourceController = null;
   let sourceBytes = 0;
-  let frameBuffer = Buffer.alloc(0);
   let frameIndex = 0;
   let skippedFrames = 0;
   let stopReason = 'process_exit';
@@ -767,8 +915,10 @@ function createRelayPlayback(session) {
   let readyTimer = null;
   const audioStderr = createFfmpegStderrTail();
   const frameStderr = createFfmpegStderrTail();
+  const frameParser = createJpegFrameParser(handleJpegFrame);
 
   const playback = {
+    mode: 'relay',
     get closed() {
       return closed;
     },
@@ -987,32 +1137,13 @@ function createRelayPlayback(session) {
   }
 
   function handleFrameData(chunk) {
-    frameBuffer = Buffer.concat([frameBuffer, chunk]);
+    frameParser.write(chunk);
-
-    for (;;) {
-      const start = frameBuffer.indexOf(JPEG_SOI);
-
-      if (start === -1) {
-        frameBuffer = Buffer.alloc(0);
-        return;
   }
 
-      const end = frameBuffer.indexOf(JPEG_EOI, start + JPEG_SOI.length);
+  function handleJpegFrame(jpeg) {
-
-      if (end === -1) {
-        frameBuffer = start === 0 ? frameBuffer : frameBuffer.subarray(start);
-        return;
-      }
-
-      const jpeg = frameBuffer.subarray(start, end + JPEG_EOI.length);
-      frameBuffer = frameBuffer.subarray(end + JPEG_EOI.length);
     const timestamp = frameIndex / fps;
     frameIndex += 1;
 
-      if (!isWebSocketOpen(websocket)) {
-        return;
-      }
-
     const sendResult = sendFramePacket(websocket, timestamp, jpeg, (error) => {
       if (error && !closed) {
         stop('websocket_send_error');
@@ -1020,13 +1151,14 @@ function createRelayPlayback(session) {
     });
 
     if (sendResult === 'closed') {
-        return;
+      return false;
     }
 
     if (sendResult === 'skipped') {
       skippedFrames += 1;
     }
-    }
+
+    return true;
   }
 
   function stop(reason) {
@@ -1136,7 +1268,6 @@ function createPlayback(session) {
   let logger = null;
   let releaseSource = () => {};
   let stderr = '';
-  let frameBuffer = Buffer.alloc(0);
   let frameIndex = 0;
   let skippedFrames = 0;
   let stopReason = 'process_exit';
@@ -1144,8 +1275,10 @@ function createPlayback(session) {
   let closed = false;
   let readyTimer = null;
   const stderrTail = createFfmpegStderrTail();
+  const frameParser = createJpegFrameParser(handleJpegFrame);
 
   const playback = {
+    mode: 'single',
     get closed() {
       return closed;
     },
@@ -1339,32 +1472,13 @@ function createPlayback(session) {
   }
 
   function handleFrameData(chunk) {
-    frameBuffer = Buffer.concat([frameBuffer, chunk]);
+    frameParser.write(chunk);
-
-    for (;;) {
-      const start = frameBuffer.indexOf(JPEG_SOI);
-
-      if (start === -1) {
-        frameBuffer = Buffer.alloc(0);
-        return;
   }
 
-      const end = frameBuffer.indexOf(JPEG_EOI, start + JPEG_SOI.length);
+  function handleJpegFrame(jpeg) {
-
-      if (end === -1) {
-        frameBuffer = start === 0 ? frameBuffer : frameBuffer.subarray(start);
-        return;
-      }
-
-      const jpeg = frameBuffer.subarray(start, end + JPEG_EOI.length);
-      frameBuffer = frameBuffer.subarray(end + JPEG_EOI.length);
     const timestamp = frameIndex / fps;
     frameIndex += 1;
 
-      if (!isWebSocketOpen(websocket)) {
-        return;
-      }
-
     const sendResult = sendFramePacket(websocket, timestamp, jpeg, (error) => {
       if (error && !closed) {
         stop('websocket_send_error');
@@ -1372,13 +1486,14 @@ function createPlayback(session) {
     });
 
     if (sendResult === 'closed') {
-        return;
+      return false;
     }
 
     if (sendResult === 'skipped') {
       skippedFrames += 1;
     }
-    }
+
+    return true;
   }
 
   function stop(reason) {
@@ -1436,12 +1551,101 @@ function isWebSocketOpen(websocket) {
   return websocket?.readyState === WebSocket.OPEN;
 }
 
+function createJpegFrameParser(onFrame) {
+  let collecting = false;
+  let pendingMarkerByte = false;
+  let parts = [];
+  let byteLength = 0;
+
+  return {
+    write(chunk) {
+      const buffer = Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk);
+      let offset = 0;
+
+      while (offset < buffer.length) {
+        if (!collecting) {
+          if (pendingMarkerByte && buffer[offset] === 0xd8) {
+            collecting = true;
+            pendingMarkerByte = false;
+            parts = [JPEG_SOI];
+            byteLength = JPEG_SOI.length;
+            offset += 1;
+          } else {
+            const start = buffer.indexOf(JPEG_SOI, offset);
+
+            if (start === -1) {
+              pendingMarkerByte = buffer[buffer.length - 1] === 0xff;
+              return true;
+            }
+
+            collecting = true;
+            pendingMarkerByte = false;
+            parts = [];
+            byteLength = 0;
+            offset = start;
+          }
+        }
+
+        if (pendingMarkerByte) {
+          pendingMarkerByte = false;
+
+          if (buffer[offset] === 0xd9) {
+            appendFramePart(buffer.subarray(offset, offset + 1));
+            offset += 1;
+
+            if (!emitFrame()) {
+              return false;
+            }
+
+            continue;
+          }
+        }
+
+        const end = buffer.indexOf(JPEG_EOI, offset);
+
+        if (end === -1) {
+          appendFramePart(buffer.subarray(offset));
+          pendingMarkerByte = buffer[buffer.length - 1] === 0xff;
+          return true;
+        }
+
+        appendFramePart(buffer.subarray(offset, end + JPEG_EOI.length));
+        offset = end + JPEG_EOI.length;
+
+        if (!emitFrame()) {
+          return false;
+        }
+      }
+
+      return true;
+    },
+  };
+
+  function appendFramePart(part) {
+    if (part.length === 0) {
+      return;
+    }
+
+    parts.push(part);
+    byteLength += part.length;
+  }
+
+  function emitFrame() {
+    const frame = { parts, byteLength };
+    collecting = false;
+    pendingMarkerByte = false;
+    parts = [];
+    byteLength = 0;
+    return onFrame(frame) !== false;
+  }
+}
+
 function sendFramePacket(websocket, timestamp, jpeg, onError) {
   if (!isWebSocketOpen(websocket)) {
     return 'closed';
   }
 
-  const packetBytes = 8 + jpeg.length;
+  const packetBytes = 8 + getJpegFrameByteLength(jpeg);
 
   if (websocket.bufferedAmount > 0 && websocket.bufferedAmount + packetBytes > MAX_WS_BUFFER_BYTES) {
     return 'skipped';
@@ -1449,7 +1653,7 @@ function sendFramePacket(websocket, timestamp, jpeg, onError) {
 
   const packet = Buffer.allocUnsafe(packetBytes);
   packet.writeDoubleLE(timestamp, 0);
-  jpeg.copy(packet, 8);
+  copyJpegFrame(jpeg, packet, 8);
   websocket.send(packet, { binary: true }, (error) => {
     if (error) {
       onError(error);
@@ -1458,6 +1662,24 @@ function sendFramePacket(websocket, timestamp, jpeg, onError) {
   return 'sent';
 }
 
+function getJpegFrameByteLength(jpeg) {
+  return Buffer.isBuffer(jpeg) ? jpeg.length : jpeg.byteLength;
+}
+
+function copyJpegFrame(jpeg, packet, offset) {
+  if (Buffer.isBuffer(jpeg)) {
+    jpeg.copy(packet, offset);
+    return;
+  }
+
+  let writeOffset = offset;
+
+  for (const part of jpeg.parts) {
+    part.copy(packet, writeOffset);
+    writeOffset += part.length;
+  }
+}
+
 function createSourceInput(sessionId, kind) {
   const token = randomUUID();
   sourceTokens.set(token, { sessionId, kind, createdAt: Date.now() });