Compact HE-AAC audio saves: server lane with fdkaac, shrink saved songs from Saved videos

2026-10-18 17:28:47 +08:00
parent eef9fbf05f
commit b48d36b3dd
12 changed files with 342 additions and 22 deletions
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -128,8 +128,19 @@ JSON shapes mirror the Tauri Rust bridge exactly — don't change one side alone
 - **Broken**: `POST /api/media/:id/redownload` (now-playing ⚠ Broken button). When a
  client falls back from a cached copy (`/api/streams?nocache=1`) the server also
  re-validates its copy and refetches it if it fails — never trusts one device's error.
- Ops: `curl https://worship.hesed.sbs/api/media/stats`; files under
-  `/app/data/media` in the container.
+- **Still-picture songs**: a fast still-check lane (keyframe scene scores, or 1 fps =
+  our own looped encode) marks `still=1`, writes `<id>.<gen>.jpg` + `audio_sha256`. Saves
+  send `?still=1` → the device stores `<id>.m4a` + OPFS `art/<id>.jpg` and plays it as
+  audio with the picture; online, still songs also play audio + `/api/media/:id/art`.
+- **Compact audio (HE-AAC)**: `<id>.<gen>.he.m4a`, ~48 kbps HE-AAC v1 from **fdkaac**
+  (Debian contrib — ffmpeg's encoder is LC only), one niced lane, made for every copy and
+  moved to the front when a device asks (`prepare?audio=he` → `working` until ready).
+  Columns `he_size` (NULL = not made, 0 = failed/not smaller) + `he_sha256`. Devices ask
+  for it with Settings → "Save songs as compact audio" or Saved videos → Shrink
+  (`shrinkSaved` swaps the file in place; `ytpCompactSaves` remembers which ones).
+  Saved `.m4a` files of YouTube ids are never offered to P2P (not the server's file).
+- Ops: `curl https://worship.hesed.sbs/api/media/stats` (`compactAudio`, `compactQueued`); files under
+  `$MEDIA_DIR` (`/app/bulk/media` on prod) in the container.

 ## Lyrics · chapters · bookmarks (`server/notes.js`, `frontend/lyrics-core.js`)
 - **Shared per video** (every user sees the same copy): `video_notes` holds the live
--- a/6
+++ b/6
@@ -16,11 +16,15 @@ FROM oven/bun:1-debian
 # ca-certificates for HTTPS fetches from yt-dlp
 # ffmpeg lets yt-dlp merge bestvideo+bestaudio into a single mp4 for the
 # "Save before playing" download path (GET /api/download?mux=1)
-RUN apt-get update -qq && \
+# fdkaac (Debian contrib) encodes the compact HE-AAC audio phones can save;
+# ffmpeg's built-in AAC encoder only does AAC-LC.
+RUN sed -i 's/^Components: main$/Components: main contrib/' /etc/apt/sources.list.d/debian.sources && \
+    apt-get update -qq && \
    apt-get install -y --no-install-recommends \
      curl \
      python3 \
      ffmpeg \
+      fdkaac \
      ca-certificates && \
    rm -rf /var/lib/apt/lists/*

--- a/frontend/app.js
+++ b/frontend/app.js
@@ -412,6 +412,19 @@ const SaveQueue = (() => {
 // single-request save (HEVC copy this device can't play, too long for the
 // server cache, no worker/OPFS sync access), otherwise the save result —
 // { ok:false, paused:true } means the partial is kept and will resume.
+// Saves that hold the server's compact HE-AAC audio (this device only).
+const CompactSaves = (() => {
+  const KEY = 'ytpCompactSaves';
+  const read = () => { try { return new Set(JSON.parse(localStorage.getItem(KEY) || '[]')); } catch { return new Set(); } };
+  const write = (set) => { try { localStorage.setItem(KEY, JSON.stringify([...set])); } catch { /* storage blocked */ } };
+  return {
+    has: (id) => read().has(id),
+    mark(id) { const s = read(); if (!s.has(id)) { s.add(id); write(s); } },
+    drop(id) { const s = read(); if (s.delete(id)) write(s); },
+    clear() { write(new Set()); },
+  };
+})();
+
 async function resumableOpfsSave(videoId, qs, prepQs, onProgress, signal) {
  if (typeof window.OPFS.downloadVideo !== 'function' || typeof Worker === 'undefined') return null;
  const enc = encodeURIComponent(videoId);
@@ -442,7 +455,8 @@ async function resumableOpfsSave(videoId, qs, prepQs, onProgress, signal) {
      resumable: { etag: prep.etag, size: prep.size, sha256: prep.sha256 || null, ext: prep.ext || 'mp4' },
      onProgress: (received, total, m) => report({ phase: m && m.verifying ? 'verifying' : 'downloading', received, total }),
    });
-    if (w.ok) return { ok: true, cached: true, sha256: w.sha256 || null, expectedSha: w.expectedSha || null, size: w.size || 0 };
+    if (w.ok) return { ok: true, cached: true, sha256: w.sha256 || null, expectedSha: w.expectedSha || null, size: w.size || 0,
+      ext: prep.ext || 'mp4', compact: !!prep.compact };
    if (w.changed) continue; // the server copy was replaced — start over on the new one
    if (w.paused) return { ok: false, paused: true, error: w.error || 'connection lost', received: w.received || 0 };
    if (w.fallback) return null;
@@ -451,7 +465,7 @@ async function resumableOpfsSave(videoId, qs, prepQs, onProgress, signal) {
  return { ok: false, error: 'the server copy kept changing — try again' };
 }

-async function opfsDownload(videoId, { mux = false, retry = false, onProgress = null, signal } = {}) {
+async function opfsDownload(videoId, { mux = false, retry = false, onProgress = null, signal, compact = false } = {}) {
  if (!window.OPFS || !window.OPFS.isSupported()) {
    return { ok: false, error: 'OPFS not supported in this browser' };
  }
@@ -465,6 +479,9 @@ async function opfsDownload(videoId, { mux = false, retry = false, onProgress =
  if (hevcCapable()) params.set('hevc', '1');
  // Album-art songs come back as audio + picture instead of a video of one frame.
  params.set('still', '1');
+  // Compact audio (setting, or Shrink in Saved videos): the server's HE-AAC copy.
+  const he = (compact || data.settings.compactAudio) && !isUploadId(videoId);
+  if (he) params.set('audio', 'he');
  const qs = params.toString();
  const url = `/api/download/${encodeURIComponent(videoId)}${qs ? '?' + qs : ''}`;

@@ -477,7 +494,11 @@ async function opfsDownload(videoId, { mux = false, retry = false, onProgress =
      return { ok: false, paused: true, error: error.name === 'AbortError' ? 'Save paused' : 'Connection lost' };
    }
  }
-  const resumed = await resumableOpfsSave(videoId, qs, params.get('hevc') === '1' ? 'hevc=1&still=1' : 'still=1', onProgress, signal);
+  const prepParams = new URLSearchParams();
+  if (params.get('hevc') === '1') prepParams.set('hevc', '1');
+  prepParams.set('still', '1');
+  if (he) prepParams.set('audio', 'he');
+  const resumed = await resumableOpfsSave(videoId, qs, prepParams.toString(), onProgress, signal);
  if (resumed) return resumed;

  // Preferred path: a dedicated Web Worker does the fetch AND the OPFS writes,
@@ -488,7 +509,7 @@ async function opfsDownload(videoId, { mux = false, retry = false, onProgress =
  let workerError = null;
  if (typeof window.OPFS.downloadVideo === 'function' && typeof Worker !== 'undefined') {
    const w = await window.OPFS.downloadVideo(videoId, url, { signal });
-    if (w.ok) return { ok: true, cached: true, sha256: w.sha256 || null, expectedSha: w.expectedSha || null, size: w.size || 0 };
+    if (w.ok) return { ok: true, cached: true, sha256: w.sha256 || null, expectedSha: w.expectedSha || null, size: w.size || 0, ext: w.ext || null };
    if (w.paused) return w;
    workerError = w.error || null;
  }
@@ -570,6 +591,7 @@ async function opfsList() {
 async function opfsDelete(videoId) {
  if (!window.OPFS || !window.OPFS.isSupported()) return { ok: true };
  try { await window.OPFS.deleteVideo(videoId); } catch { /* ignore */ }
+  CompactSaves.drop(videoId);
  if (window.DeviceDB) { await window.DeviceDB.deleteFile(videoId); if (window.P2PClient) window.P2PClient.changed(); }
  return { ok: true };
 }
@@ -577,6 +599,7 @@ async function opfsDelete(videoId) {
 async function opfsClear() {
  if (!window.OPFS || !window.OPFS.isSupported()) return { ok: true };
  try { await window.OPFS.clearAll(); } catch { /* ignore */ }
+  CompactSaves.clear();
  if (window.DeviceDB) { await window.DeviceDB.clear(); if (window.P2PClient) window.P2PClient.changed(); }
  return { ok: true };
 }
@@ -674,6 +697,7 @@ const DEFAULT_SETTINGS = {
  p2pReceive: true,         // fetch from other devices when YouTube and the server can't — ON by default
  autoSavePlayed: true,     // keep every video you play for offline (background save once playback starts)
  saveBeforePlay: false,    // download (server-muxed single file) before playing instead of streaming
+  compactAudio: false,      // new saves are compact HE-AAC audio only (~⅓ of an audio save, no video)
  repeatMode: 'off',        // 'off' | 'all' — repeat the playing list when it ends
  loopOne: false,           // repeat the single current video
  shuffle: false,           // shuffle upcoming tracks when playing a list
@@ -1969,6 +1993,58 @@ async function saveStillArt(id) {
  return true;
 }

+// Saved videos: what format a saved file is in.
+function savedFormatLabel(it) {
+  if (isUploadId(it.id)) return 'Library file';
+  if (!/\.m4a$/i.test(it.name || '')) return 'Video';
+  return CompactSaves.has(it.id) ? 'Compact audio' : 'Audio';
+}
+
+function canShrinkSaved(it) {
+  const id = it && it.id;
+  return WEB && !!id && cachedIds.has(id) && !isUploadId(id) && !String(id).startsWith('edit_') && !CompactSaves.has(id);
+}
+
+// Swap a saved copy for the server's compact HE-AAC audio. The old file stays
+// until the new one is complete, so a failed shrink loses nothing.
+async function shrinkSaved(video) {
+  const id = video && video.id;
+  if (!canShrinkSaved({ id })) return { ok: false, error: 'nothing to shrink' };
+  if (downloading.has(id)) return { ok: false, error: 'it is still saving' };
+  if (current?.meta?.id === id && current.localUrl) return { ok: false, error: 'it is playing from that file — play something else first' };
+  const before = (await window.OPFS.getFileObject(id).catch(() => null))?.size || 0;
+  downloading.add(id);
+  let res;
+  try { res = await opfsDownload(id, { compact: true }); }
+  finally { downloading.delete(id); }
+  if (!res || !res.ok) return { ok: false, error: (res && res.error) || 'save failed' };
+  if (res.ext) await window.OPFS.keepOnly(id, `${id}.${res.ext}`);
+  if (res.compact) CompactSaves.mark(id);
+  await saveStillArt(id);
+  // An audio save is not the server's video file: stop offering it to other devices.
+  if (window.DeviceDB && /^m4a$/i.test(res.ext || '')) { await window.DeviceDB.deleteFile(id).catch(() => {}); window.P2PClient?.changed(); }
+  const after = (await window.OPFS.getFileObject(id).catch(() => null))?.size || 0;
+  return { ok: true, compact: !!res.compact, before, after };
+}
+
+// Shrink several saves one after another (the server converts each once).
+let shrinkRunning = false;
+async function shrinkSavedAll(ids) {
+  if (shrinkRunning) { toast('Already shrinking saved songs'); return; }
+  shrinkRunning = true;
+  let done = 0, saved = 0, failed = 0;
+  try {
+    for (const id of ids) {
+      if (current?.meta?.id === id) continue; // playing from that file right now
+      toast(`Shrinking saved songs… ${done + failed + 1}/${ids.length}`, { duration: 2500 });
+      const r = await shrinkSaved(videoById(id) || { id });
+      if (r.ok) { done++; saved += Math.max(0, r.before - r.after); } else failed++;
+    }
+  } finally { shrinkRunning = false; }
+  toast(`Shrunk ${done} song${done === 1 ? '' : 's'} · freed ${fmtBytes(saved)}${failed ? ` · ${failed} could not be shrunk` : ''}`, { duration: 6000 });
+  if (view.type === 'saved') renderSaved();
+}
+
 // Playback fields for a saved still-picture song: play it as audio and show
 // its saved picture. {} for anything else.
 async function localStill(id) {
@@ -2027,6 +2103,7 @@ async function preload(video, { quiet = false, mux = false, retry = false, direc
      cacheMutations++;
      // A still-picture song saved as audio isn't the server's video file, so
      // it is never offered to other devices as one.
+      if (res.compact) CompactSaves.mark(id); else CompactSaves.drop(id);
      saveStillArt(id).then((still) => { if (!still) recordDeviceFile(id, res); });
      warmThumb(thumbUrlFor(id, video));
      if (!quiet) toast(`Saved “${video.title}” ✓`);
--- a/frontend/autosave.test.js
+++ b/frontend/autosave.test.js
@@ -16,7 +16,7 @@ function harness({ autoPreload = true, cached = [], result = { ok: true, cached:
    SaveSlots: { acquire: async () => {}, release() {} },
    SaveQueue: { add: v => jobs.set(v.id, { status: 'queued' }), remove: id => jobs.delete(id), progress() {}, state: (id, status, message) => jobs.set(id, { status, message }) },
    API: { cacheDownload: async id => { calls.push(id); if (error) throw error; return result; } },
-    recordDeviceFile() {}, saveStillArt: async () => false, warmThumb() {}, thumbUrlFor: () => '', cacheMutations: 0,
+    recordDeviceFile() {}, saveStillArt: async () => false, CompactSaves: { mark() {}, drop() {} }, warmThumb() {}, thumbUrlFor: () => '', cacheMutations: 0,
  });
  const preload = source.slice(source.indexOf('async function preload(video,'), source.indexOf('// A device copy that failed to play.'));
  const playlists = source.slice(source.indexOf('function preloadPlaylist(pl)'), source.indexOf('// Update a single card\'s saved badge'));
--- a/frontend/opfs.js
+++ b/frontend/opfs.js
@@ -218,7 +218,7 @@
        opts.signal?.addEventListener('abort', abort, { once: true });
        worker.onmessage = (e) => {
          const m = e.data || {};
-          if (m.type === 'done')             finish({ ok: true, sha256: m.sha256 || null, expectedSha: m.expectedSha || null, size: m.size || 0 });
+          if (m.type === 'done')             finish({ ok: true, sha256: m.sha256 || null, expectedSha: m.expectedSha || null, size: m.size || 0, ext: m.ext || null });
          else if (m.type === 'unsupported') finish({ ok: false, fallback: true });
          else if (m.type === 'error')       finish({ ok: false, error: m.error });
          else if (m.type === 'paused')      finish({ ok: false, paused: true, received: m.received || 0, error: m.error });
@@ -359,6 +359,21 @@
      return items.reduce((s, i) => s + i.size, 0);
    },

+    // Remove this video's other saved files (a different format), keeping
+    // `keepName` — after a save that replaced e.g. <id>.mp4 with <id>.m4a.
+    async keepOnly(videoId, keepName) {
+      try {
+        const dir = await getRoot();
+        const drop = [];
+        for await (const [name, handle] of dir.entries()) {
+          if (handle.kind !== 'file' || name === keepName || name.endsWith('.part') || name.endsWith('.part.json')) continue;
+          const dot = name.lastIndexOf('.');
+          if ((dot > -1 ? name.slice(0, dot) : name) === videoId) drop.push(name);
+        }
+        for (const name of drop) await dir.removeEntry(name).catch(() => {});
+      } catch { /* OPFS not available */ }
+    },
+
    // Delete one video
    async deleteVideo(videoId) {
      try {
--- a/frontend/saved-page.css
+++ b/frontend/saved-page.css
@@ -1,7 +1,7 @@
 .saved-summary.saved-storage-summary { display:flex; align-items:center; justify-content:space-between; gap:12px; padding:8px 0 16px; }
 .saved-storage-text { min-width:0; color:var(--text-2); font-size:14px; font-variant-numeric:tabular-nums; }
 .saved-clear { flex:none; min-height:44px; padding:0 10px; border:0; background:transparent; color:var(--accent); font:inherit; cursor:pointer; }
-html[data-layout] .card.saved-card { display:grid; grid-template-columns:72px minmax(0,1fr) 96px; align-items:center; gap:12px; min-height:88px; }
+html[data-layout] .card.saved-card { display:grid; grid-template-columns:72px minmax(0,1fr) auto; align-items:center; gap:12px; min-height:88px; }
 html[data-layout] #cards .saved-card .thumb { grid-column:1; grid-row:1; width:100%; min-width:0; max-width:100%; flex:none; overflow:hidden; }
 html[data-layout] #cards .saved-card .thumb img { width:100%; max-width:100%; height:100%; object-fit:cover; }
 html[data-layout] .saved-card .card-info { grid-column:2; grid-row:1; min-width:0; }
@@ -14,4 +14,6 @@ html[data-layout] .saved-file-actions { grid-column:3; grid-row:1; display:flex;
 .saved-file-action.danger:hover, .saved-clear:hover { color:var(--accent); }
 .saved-file-action:focus-visible, .saved-clear:focus-visible { outline:2px solid var(--accent); outline-offset:3px; }
 .saved-file-action:disabled, .saved-clear:disabled { opacity:.5; cursor:wait; }
-@media(min-width:900px) { html[data-layout] .card.saved-card { grid-template-columns:88px minmax(0,1fr) 96px; } }
+@media(min-width:900px) { html[data-layout] .card.saved-card { grid-template-columns:88px minmax(0,1fr) auto; } }
+.saved-storage-summary .saved-shrink-all { margin-left:auto; }
+@media(max-width:420px) { html[data-layout] .saved-file-actions { gap:4px; } html[data-layout] .saved-file-action { width:40px; min-width:40px; height:40px; padding:8px; } }
--- a/frontend/saved-page.js
+++ b/frontend/saved-page.js
@@ -4,7 +4,8 @@
  const matches = (video, query) => !query || `${video.title || video.id} ${video.channel || ''}`.toLowerCase().includes(query.toLowerCase());
  const paths = {
    export: '<use href="#media-download"/>',
-    delete: '<path d="M4 7h16M9 7V4h6v3M6 7l1 13h10l1-13M10 11v6M14 11v6"/>'
+    delete: '<path d="M4 7h16M9 7V4h6v3M6 7l1 13h10l1-13M10 11v6M14 11v6"/>',
+    shrink: '<path d="M4 14h6v6M20 10h-6V4M14 10l7-7M3 21l7-7"/>'
  };
  function button(doc, kind, label, action) {
    const b = doc.createElement('button'); b.type = 'button';
@@ -13,10 +14,14 @@
    b.innerHTML = `<svg class="media-icon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">${paths[kind]}</svg>`;
    b.onclick = e => { e.stopPropagation(); action(); }; return b;
  }
-  function actions(row, video, exportFile, deleteFile) {
+  function actions(row, video, exportFile, deleteFile, shrinkFile = null) {
    const doc = row.ownerDocument, group = doc.createElement('div');
    group.className = 'saved-file-actions'; group.setAttribute('role', 'group');
    group.setAttribute('aria-label', `File actions for ${video.title || video.id}`);
+    if (shrinkFile) {
+      const b = button(doc, 'shrink', `Shrink to compact audio: ${video.title || video.id}`, async () => { b.disabled = true; try { await shrinkFile(); } finally { b.disabled = false; } });
+      group.append(b);
+    }
    group.append(button(doc, 'export', `Save to this device: ${video.title || video.id}`, exportFile), button(doc, 'delete', `Delete saved file: ${video.title || video.id}`, deleteFile));
    row.append(group);
  }
--- a/frontend/views-core.js
+++ b/frontend/views-core.js
@@ -658,7 +658,27 @@ async function renderSaved() {
  c.innerHTML = '';
  const summary = document.createElement('div');
  summary.className = 'saved-summary saved-storage-summary';
-  summary.innerHTML = `<span class="saved-storage-text">${fmtBytes(total)} · ${items.length} video${items.length === 1 ? '' : 's'} stored offline</span>`;
+  const audioCount = items.filter((it) => /\.m4a$/i.test(it.name || '')).length;
+  summary.innerHTML = `<span class="saved-storage-text">${fmtBytes(total)} · ${items.length} saved${audioCount ? ` · ${audioCount} as audio` : ''}</span>`;
+  // Every saved YouTube song not yet in compact audio can be shrunk in place.
+  const shrinkable = items.filter((it) => canShrinkSaved(it));
+  if (shrinkable.length) {
+    const shrinkAll = document.createElement('button');
+    shrinkAll.type = 'button';
+    shrinkAll.className = 'saved-clear saved-shrink-all';
+    shrinkAll.textContent = `Shrink ${shrinkable.length}`;
+    shrinkAll.title = 'Replace these saves with compact audio (HE-AAC): about a third of the space, no video';
+    shrinkAll.setAttribute('aria-label', `Shrink ${shrinkable.length} saved songs to compact audio`);
+    shrinkAll.onclick = () => {
+      const before = shrinkable.reduce((n, it) => n + (it.size || 0), 0);
+      showModal(`Shrink ${shrinkable.length} saved song${shrinkable.length === 1 ? '' : 's'}?`, document.createTextNode(
+        `They are swapped for compact audio (HE-AAC, ~48 kbps): sound only, no video, about a third of an audio save and far less than a video (now ${fmtBytes(before)}). The server converts each song once; a song keeps playing from its current copy until the new one is in place.`), [
+        { label: 'Cancel', onClick: closeModal },
+        { label: 'Shrink', onClick: () => { closeModal(); shrinkSavedAll(shrinkable.map((it) => it.id)); } },
+      ]);
+    };
+    summary.appendChild(shrinkAll);
+  }
  summary.appendChild(clearAll);
  $('listFilterBar').classList.remove('hidden');
  c.appendChild(summary);
@@ -679,13 +699,20 @@ async function renderSaved() {
        onerror="this.classList.add('no-art')" />${isCustom ? '<span class="edit-badge" title="Edited copy">✂</span>' : ''}${isUploadId(v.id) ? `<span class="upload-badge" title="On this server">${v.kind === 'audio' ? '♪' : '📁'}</span>` : ''}</div>
      <div class="card-info">
        <div class="card-title"></div>
-        <div class="card-channel saved-size">${isCustom ? '✂ edited · ' : ''}${fmtBytes(it.size)}</div>
+        <div class="card-channel saved-size">${isCustom ? '✂ edited · ' : ''}${savedFormatLabel(it)} · ${fmtBytes(it.size)}</div>
      </div>`;
    row.querySelector('.card-title').textContent = v.title || it.id;
    row.addEventListener('click', (e) => {
      if (e.target.closest('.saved-file-actions')) return;
      playFromList([v], 0, 'saved');
    });
+    const shrink = canShrinkSaved(it) ? async () => {
+      toast(`Shrinking “${v.title || v.id}”…`);
+      const r = await shrinkSaved(v);
+      toast(r.ok ? (r.compact ? `Shrunk ${fmtBytes(r.before)} → ${fmtBytes(r.after)}` : 'This song has no smaller version')
+        : '⚠ ' + (r.error || 'Could not shrink it'));
+      if (view.type === 'saved') renderSaved();
+    } : null;
    SavedPage.actions(row, v, () => exportToDevice(v), () => {
      showModal(`Delete saved file “${v.title || v.id}”?`, document.createTextNode(isCustom
        ? 'This edited copy exists only on this device and will be removed permanently.'
@@ -708,7 +735,7 @@ async function renderSaved() {
          toast('Removed saved file'); renderSaved();
        } },
      ]);
-    });
+    }, shrink);
    c.appendChild(row);
  });
  if (!c.querySelector('.saved-card')) {
@@ -959,6 +986,13 @@ async function renderSettings() {
        </span>
        <input id="setAutoPreload" type="checkbox" ${data.settings.autoPreload ? 'checked' : ''} />
      </label>
+      <label class="set-row">
+        <span>
+          Save songs as compact audio
+          <small>New saves keep only the sound, as HE-AAC (about a third of the space, no video). The server converts each song once. Shrink songs you already saved from Saved videos.</small>
+        </span>
+        <input id="setCompactAudio" type="checkbox" ${data.settings.compactAudio ? 'checked' : ''} />
+      </label>
      <label class="set-row">
        <span>
          Videos saved at once
@@ -1355,6 +1389,10 @@ async function renderSettings() {
    data.settings.autoSavePlayed = e.target.checked;
    persist();
  });
+  $('setCompactAudio').addEventListener('change', (e) => {
+    data.settings.compactAudio = e.target.checked;
+    persist();
+  });
  $('setAutoPreload').addEventListener('change', (e) => {
    data.settings.autoPreload = e.target.checked;
    persist();
--- a/server/db.js
+++ b/server/db.js
@@ -293,7 +293,8 @@ export async function initDb() {
  try { await db.execute('ALTER TABLE media_cache ADD COLUMN pinned INTEGER NOT NULL DEFAULT 0'); } catch { /* already migrated */ }
  // Still-picture songs: still = NULL (not checked yet) | 0 | 1. A still copy
  // also has <id>.<gen>.jpg, and devices may save just its m4a (audio_sha256).
-  for (const col of ['still INTEGER', 'audio_sha256 TEXT']) {
+  // he_size: NULL = no compact (HE-AAC) audio yet, 0 = could not make one.
+  for (const col of ['still INTEGER', 'audio_sha256 TEXT', 'he_size INTEGER', 'he_sha256 TEXT']) {
    try { await db.execute(`ALTER TABLE media_cache ADD COLUMN ${col}`); } catch { /* already migrated */ }
  }
  // Uploads shared from devices (PWA share target): who sent it, and whether it
@@ -680,7 +681,7 @@ const MEDIA_COLS = new Set([
  'status', 'gen', 'size', 'height', 'vcodec', 'acodec', 'duration', 'optimized',
  'meta', 'priority', 'auto', 'attempts', 'error', 'retry_at', 'created_at',
  'updated_at', 'last_access', 'hits', 'sha256',
-  'pinned', 'still', 'audio_sha256',
+  'pinned', 'still', 'audio_sha256', 'he_size', 'he_sha256',
 ]);

 function rowToObj(res, row) {
--- a/server/media-cache.js
+++ b/server/media-cache.js
@@ -168,6 +168,8 @@ function metaFromInfo(info, duration) {
 export function createMediaCache({
  dir, db, download, getInfo, getSourceUrl = id => `https://www.youtube.com/watch?v=${id}`,
  ffmpeg = 'ffmpeg', ffprobe = 'ffprobe', nice = 'nice',
+  fdkaac = 'fdkaac',         // Fraunhofer encoder CLI for the compact (HE-AAC) audio lane
+  compact = { enabled: true, bitrate: 48000 },
  maxBytes = 10 * 1024 ** 3,
  minFreeBytes = 5 * 1024 ** 3,
  autoMaxSeconds = 3 * 3600,
@@ -203,6 +205,9 @@ export function createMediaCache({
  const stillQueue = [];      // copies whose still-picture check hasn't run yet
  const stillChecks = new Map(); // videoId -> running check (dedupes the two lanes)
  let stillActive = false;
+  const heQueue = [];         // copies waiting for their compact HE-AAC audio
+  let heActive = null;
+  let heMissing = false;      // fdkaac isn't installed: the lane stays off
  const lastTouch = new Map();

  function sweepTmp(prefix) {
@@ -219,7 +224,7 @@ export function createMediaCache({
    let names = [];
    try { names = readdirSync(dir); } catch { return; }
    for (const n of names) {
-      const m = /^(.+)\.(\d+)\.(mp4|m4a|jpg)$/.exec(n);
+      const m = /^(.+)\.(\d+)\.(mp4|m4a|jpg|he\.m4a)$/.exec(n);
      if (!m || m[1] !== id || (keepGen !== null && Number(m[2]) === keepGen)) continue;
      const p = join(dir, n);
      const rm = () => { try { unlinkSync(p); } catch { /* gone */ } };
@@ -363,7 +368,7 @@ export function createMediaCache({
        status: 'ready', gen,
        size: probe.size + sizeOf(fileFor(id, gen, 'm4a')),
        height: probe.height, vcodec: probe.vcodec, acodec: probe.acodec, duration: probe.duration,
-        optimized: 0, still: null, audio_sha256: null, meta: JSON.stringify(metaFromInfo(info, probe.duration)),
+        optimized: 0, still: null, audio_sha256: null, he_size: null, he_sha256: null, meta: JSON.stringify(metaFromInfo(info, probe.duration)),
        attempts: 0, error: null, retry_at: 0, updated_at: t, last_access: t, sha256,
      };
      await db.upsertMedia(id, fields);
@@ -371,6 +376,7 @@ export function createMediaCache({
      job.status = 'ready';
      log.info?.(`[media] cached ${id} ${probe.height}p ${fmtMB(fields.size)}`);
      queueStill(id);
+      queueHe(id);
      enqueueOptimize(id);
      notifyReady(id, gen, sha256, probe, fields.meta);
      return { ...(prev || {}), video_id: id, ...fields };
@@ -498,6 +504,8 @@ export function createMediaCache({
    const oldAudio = fileFor(id, row.gen, 'm4a');
    const newAudio = fileFor(id, gen, 'm4a');
    try { linkSync(oldAudio, newAudio); } catch { copyFileSync(oldAudio, newAudio); }
+    const oldHe = fileFor(id, row.gen, 'he.m4a');
+    if (existsSync(oldHe)) { try { linkSync(oldHe, fileFor(id, gen, 'he.m4a')); } catch { copyFileSync(oldHe, fileFor(id, gen, 'he.m4a')); } }
    const oldArt = fileFor(id, row.gen, 'jpg');
    if (existsSync(oldArt)) { try { linkSync(oldArt, fileFor(id, gen, 'jpg')); } catch { copyFileSync(oldArt, fileFor(id, gen, 'jpg')); } }
    await db.upsertMedia(id, {
@@ -568,6 +576,94 @@ export function createMediaCache({
    return p;
  }

+  // Compact audio lane: the m4a re-encoded to HE-AAC v1 (AAC-LC core + SBR) at
+  // ~48 kbps, about a third of YouTube's ~128 kbps AAC-LC, for phones that
+  // save songs as audio. Every browser, iOS and Android decode HE-AAC. ffmpeg's
+  // own AAC encoder only does LC, so this needs fdkaac (Debian contrib).
+  // One at a time, niced; a device asking for one jumps the queue.
+  function queueHe(id, urgent = false) {
+    if (!compact || !compact.enabled || heMissing || heActive === id) return;
+    const i = heQueue.indexOf(id);
+    if (i >= 0) { if (urgent && i > 0) { heQueue.splice(i, 1); heQueue.unshift(id); } }
+    else if (urgent) heQueue.unshift(id);
+    else heQueue.push(id);
+    pumpHe();
+  }
+
+  function pumpHe() {
+    if (heActive || !heQueue.length) return;
+    const id = heQueue.shift();
+    heActive = id;
+    makeHe(id)
+      .catch((err) => log.warn?.(`[media] compact audio ${id} failed: ${err.message}`))
+      .finally(() => { heActive = null; pumpHe(); });
+  }
+
+  async function makeHe(id) {
+    const row = await db.getMedia(id);
+    if (!row || row.status !== 'ready' || (row.he_size !== null && row.he_size !== undefined)) return;
+    const src = fileFor(id, row.gen, 'm4a');
+    if (!existsSync(src)) return;
+    const prefix = `${id}-${now()}-he`;
+    const raw = join(tmpDir, `${prefix}.raw.m4a`);
+    const out = join(tmpDir, `${prefix}.m4a`);
+    const fail = async (why) => {
+      const cur = await db.getMedia(id);
+      if (cur && cur.status === 'ready' && cur.gen === row.gen) await db.upsertMedia(id, { he_size: 0 });
+      log.warn?.(`[media] compact audio ${id}: ${why}`);
+    };
+    try {
+      // Decoded PCM goes straight into the encoder (no temp WAV on the cache drive).
+      const sh = ['-c', `"$0" -v error -nostdin -i "$1" -f wav - | "$2" -S -p 5 -b ${Number(compact.bitrate) || 48000} -o "$3" -`,
+        ffmpeg, src, fdkaac, raw];
+      const r = nice ? await run(nice, ['-n', '19', 'sh', ...sh]) : await run('sh', sh);
+      if (r.code === 127 || /fdkaac.*not found/i.test(r.stderr)) {
+        heMissing = true;
+        heQueue.length = 0;
+        log.warn?.('[media] fdkaac is not installed — compact (HE-AAC) audio is off');
+        return;
+      }
+      if (r.code !== 0 || sizeOf(raw) < 1024) return fail('encode failed: ' + tail(r.stderr));
+      const m = await run(ffmpeg, ['-v', 'error', '-nostdin', '-y', '-i', raw, '-map', '0:a:0', '-c', 'copy',
+        '-movflags', '+faststart', '-f', 'mp4', out]);
+      if (m.code !== 0) return fail('remux failed: ' + tail(m.stderr));
+      // Gate: one AAC stream, as long as the source, decodes start to end cleanly.
+      const pr = await run(ffprobe, ['-v', 'error', '-show_entries', 'stream=codec_type,codec_name:format=duration',
+        '-of', 'json', out]);
+      let info = {};
+      try { info = JSON.parse(pr.stdout || '{}'); } catch { /* checked below */ }
+      const streams = info.streams || [];
+      const dur = Number(info.format && info.format.duration) || 0;
+      if (streams.length !== 1 || streams[0].codec_name !== 'aac') return fail('unexpected streams');
+      if (row.duration && dur < row.duration - 1.5) return fail(`too short (${dur.toFixed(1)} of ${row.duration.toFixed(1)} s)`);
+      const dec = await run(ffmpeg, ['-v', 'error', '-nostdin', '-i', out, '-f', 'null', '-']);
+      if (dec.code !== 0 || String(dec.stderr).trim()) return fail('decode check failed: ' + tail(dec.stderr));
+      const size = sizeOf(out);
+      if (size > sizeOf(src) * (1 - MIN_SAVING)) return fail(`not smaller (${fmtMB(size)} vs ${fmtMB(sizeOf(src))})`);
+      const sha = await hashFile(out);
+      const cur = await db.getMedia(id);
+      if (!cur || cur.status !== 'ready' || cur.gen !== row.gen) return; // replaced meanwhile
+      renameSync(out, fileFor(id, row.gen, 'he.m4a'));
+      await db.upsertMedia(id, { he_size: size, he_sha256: sha });
+      log.info?.(`[media] compact audio ${id}: ${fmtMB(sizeOf(src))} → ${fmtMB(size)}`);
+    } finally {
+      sweepTmp(prefix);
+    }
+  }
+
+  // Where a device's compact-audio save stands. Asking for one that isn't
+  // made yet moves it to the front of the lane.
+  async function compactAudio(id) {
+    if (!isMediaId(id) || !compact || !compact.enabled || heMissing) return { status: 'off' };
+    const row = await getReady(id);
+    if (!row) return { status: 'none' };
+    if (row.he_size === 0) return { status: 'off' };
+    const p = fileFor(id, row.gen, 'he.m4a');
+    if (row.he_size > 0 && existsSync(p)) return { status: 'ready', gen: row.gen, path: p, size: sizeOf(p), sha256: row.he_sha256, row };
+    queueHe(id, true);
+    return { status: 'working' };
+  }
+
  // Keyframes only: ~1 s for a 5-minute video. Every keyframe-to-keyframe
  // scene score must stay under STILL_MAX_SCENE.
  async function isStill(src) {
@@ -804,6 +900,8 @@ export function createMediaCache({
      active: fetchActive ? fetchActive.id : null,
      optimizing: optActive,
      optimizeQueued: optQueue.length,
+      compactQueued: heQueue.length,
+      compactAudio: heMissing ? 'fdkaac missing' : (compact && compact.enabled ? 'on' : 'off'),
    };
  }

@@ -821,7 +919,7 @@ export function createMediaCache({
    const byId = new Map(rows.map((r) => [r.video_id, r]));
    for (const name of readdirSync(dir)) {
      if (name === '.tmp') continue;
-      const m = /^(.+)\.(\d+)\.(mp4|m4a|jpg)$/.exec(name);
+      const m = /^(.+)\.(\d+)\.(mp4|m4a|jpg|he\.m4a)$/.exec(name);
      const r = m && byId.get(m[1]);
      if (!m || !r || r.status !== 'ready' || r.gen !== Number(m[2])) {
        try { unlinkSync(join(dir, name)); } catch { /* gone */ }
@@ -832,6 +930,7 @@ export function createMediaCache({
      if (r.status === 'ready') {
        if (!readyFilesExist(r)) { await db.deleteMedia(r.video_id); removeFiles(r.video_id); continue; }
        if (r.still === null || r.still === undefined) queueStill(r.video_id);
+        if (r.he_size === null || r.he_size === undefined) queueHe(r.video_id);
        if ((r.optimized || 0) < OPT_REV) enqueueOptimize(r.video_id);
      } else if (r.status === 'queued' || r.status === 'downloading' || r.status === 'validating') {
        startJob(r.video_id, r.priority === HIGH ? HIGH : LOW, !!r.auto, r);
@@ -869,6 +968,6 @@ export function createMediaCache({
    return n;
  }

-  return { init, ensureCached, redownload, verify, getReady, filePath, touch, status, stats, isMediaId, backfillHashes, adoptFile, available,
+  return { init, ensureCached, redownload, verify, getReady, filePath, touch, status, stats, isMediaId, backfillHashes, adoptFile, available, compactAudio,
    evictNow: id => evict(id, 'admin') };
 }
--- a/server/media-cache.test.js
+++ b/server/media-cache.test.js
@@ -435,6 +435,39 @@ describe('media cache jobs', () => {
    expect(await again.filePath('stilAAAAAA1', after.gen, 'jpg')).toBeTruthy();
  }, 90000);

+  // Stand-in for fdkaac (not installed on dev machines): same CLI shape, reads
+  // WAV on stdin, writes a low-bitrate AAC .m4a to -o.
+  function fakeFdkaac() {
+    const p = join(root, 'fake-fdkaac.sh');
+    writeFileSync(p, '#!/bin/sh\nwhile [ "$1" != "-o" ]; do shift; done\nout="$2"\nexec ffmpeg -v error -nostdin -y -f wav -i - -c:a aac -b:a 24k -f mp4 "$out"\n');
+    spawnSync('chmod', ['+x', p]);
+    return p;
+  }
+
+  test('compact audio lane: HE-AAC copy is made once, gated, and kept with the copy', async () => {
+    await clearDb();
+    const { cache } = makeCache({ fixture: 'still40.mp4', duration: 40, fdkaac: fakeFdkaac() });
+    await cache.init();
+    expect((await cache.compactAudio('compAAAAAA1')).status).toBe('none');
+    await cache.ensureCached('compAAAAAA1', { priority: HIGH });
+    expect(await until(async () => ((await dbmod.getMedia('compAAAAAA1')).he_size || 0) > 0, 20000)).toBe(true);
+    const he = await cache.compactAudio('compAAAAAA1');
+    expect(he.status).toBe('ready');
+    const lc = await cache.filePath('compAAAAAA1', he.gen, 'm4a');
+    expect(he.size).toBeLessThan(readFileSync(lc).length * 0.85);
+    expect(he.sha256).toBe(await sha256File(he.path));
+    expect(await cache.filePath('compAAAAAA1', he.gen, 'he.m4a')).toBe(he.path);
+  }, 60000);
+
+  test('compact audio is off (never blocks saves) when fdkaac is missing', async () => {
+    await clearDb();
+    const { cache } = makeCache({ fdkaac: join(root, 'no-such-fdkaac') });
+    await cache.init();
+    await cache.ensureCached('nofdAAAAAA1', { priority: HIGH });
+    expect(await until(async () => (await cache.compactAudio('nofdAAAAAA1')).status === 'off', 15000)).toBe(true);
+    expect((await cache.stats()).compactAudio).toBe('fdkaac missing');
+  }, 30000);
+
  test('a moving copy already done by the HEVC lane is not re-encoded for rev 3', async () => {
    await clearDb();
    const seed = makeCache({ fixture: 'fat64.mp4', duration: 64,
--- a/server/server.js
+++ b/server/server.js
@@ -1348,6 +1348,9 @@ const media = createMediaCache({
  },
  ffmpeg: FFMPEG,
  ffprobe: process.env.FFPROBE_PATH || 'ffprobe',
+  // Compact HE-AAC audio for phone saves (?audio=he). MEDIA_COMPACT_AUDIO=0 turns it off.
+  fdkaac: process.env.FDKAAC_PATH || 'fdkaac',
+  compact: { enabled: process.env.MEDIA_COMPACT_AUDIO !== '0', bitrate: envNum('MEDIA_COMPACT_BITRATE', 48000) },
  maxBytes:       envNum('MEDIA_CACHE_MAX_BYTES', 10 * 1024 ** 3),
  minFreeBytes:   envNum('MEDIA_MIN_FREE_BYTES', 5 * 1024 ** 3),
  autoMaxSeconds: envNum('MEDIA_AUTO_MAX_SECONDS', 3 * 3600),
@@ -1738,6 +1741,20 @@ registerDownloadRetryRoute(app, {
  media, priority: HIGH, clearHints: id => { prepareSkips.delete(id); streamCache.delete(id); },
 });
 const DOWNLOAD_EXPOSE = 'X-Content-SHA256, Content-Range, Content-Length, ETag, Accept-Ranges';
+function compactDownloadResponse(c, videoId, fp, he) {
+  if (fp && !c.req.header('range')) recordVideoAccess(fp, { id: videoId }).catch(() => {});
+  media.touch(videoId);
+  return rangeFileResponse(c, he.path, 'audio/mp4', 'no-store', {
+    etag: `"${videoId}.${he.gen}.he"`,
+    headers: {
+      'Content-Disposition': `attachment; filename="${videoId}.m4a"`,
+      'Access-Control-Allow-Origin': '*',
+      'Access-Control-Expose-Headers': DOWNLOAD_EXPOSE,
+      ...(he.sha256 ? { 'X-Content-SHA256': he.sha256 } : {}),
+    },
+  });
+}
+
 function cachedDownloadResponse(c, videoId, fp, row) {
  if (fp && !c.req.header('range')) recordVideoAccess(fp, { id: videoId }).catch(() => {});
  media.touch(videoId);
@@ -1797,6 +1814,20 @@ app.get('/api/download/:videoId/prepare', async (c) => {
  if (ready) {
    // ?still=1: the device would rather keep the audio + picture of an
    // album-art song than a video of one unchanging frame.
+    const stillArt = stillAudioPath(videoId, ready) ? { still: true, art: `/api/media/${videoId}/art?g=${ready.gen}` } : {};
+    // ?audio=he: the phone saves the compact HE-AAC audio (~48 kbps) instead.
+    // It is made once on the server and kept with the copy; until it exists
+    // the device polls like for any other preparing save.
+    if (c.req.query('audio') === 'he') {
+      const he = await media.compactAudio(videoId);
+      if (he.status === 'ready') {
+        media.touch(videoId);
+        return c.json({ ok: true, state: 'ready', gen: he.gen, size: he.size, sha256: he.sha256 || null,
+          etag: `"${videoId}.${he.gen}.he"`, ext: 'm4a', compact: true, ...stillArt }, 200, nocache);
+      }
+      if (he.status === 'working') return c.json({ ok: true, state: 'working', status: 'compressing' }, 200, nocache);
+      // 'off' (no encoder, or this song didn't shrink): the normal answer below.
+    }
    const stillAudio = c.req.query('still') === '1' ? stillAudioPath(videoId, ready) : null;
    if (stillAudio) {
      media.touch(videoId);
@@ -1879,6 +1910,10 @@ app.get('/api/download/:videoId', async (c) => {
  let cacheErr = null;
  try {
    const row = await media.ensureCached(videoId, { priority: HIGH });
+    if (c.req.query('audio') === 'he') {
+      const he = await media.compactAudio(videoId);
+      if (he.status === 'ready') return compactDownloadResponse(c, videoId, fp, he);
+    }
    // A device that can't decode HEVC must not save the HEVC copy — give it
    // the legacy H.264 save instead (the ?mux=1 path included).
    if (servableTo(row, c.req.query('hevc') === '1') || stillAudioPath(videoId, row) && c.req.query('still') === '1') {