YouTube chapters: extracted automatically, ticks on the seek bar and Glass scrubber, [ / ] to jump

- Server: chapters come from yt-dlp's `chapters` (creator chapters and
  description timestamps) whenever a video is resolved, kept in a yt_chapters
  table; GET /api/chapters?v= serves them (resolving once if needed, 30-day
  cache) so server-cached copies get them too. Never fails the player.
- Player: a video's shared chapters win; with none, YouTube's stand in —
  listed as "Chapters from YouTube", read-only (no edit/delete; + Chapter
  copies them into an editable list). They drive the existing seek-bar ticks
  (classic and Glass Stage), the chapter badge and the chapter list, and are
  cached offline with the video's notes.
- Keys: [ previous chapter (restarts the current one when >3 s in), ] next.

server/db.js

@@ -217,6 +217,13 @@ export async function initDb() {
   for (const col of ['owner TEXT', 'listed INTEGER NOT NULL DEFAULT 1']) {
     try { await db.execute(`ALTER TABLE uploads ADD COLUMN ${col}`); } catch { /* already there */ }
   }
+  // Chapters YouTube publishes for a video (from yt-dlp's `chapters`), cached so
+  // a server-cached copy can show them without another yt-dlp call.
+  await db.execute(`CREATE TABLE IF NOT EXISTS yt_chapters (
+    id         TEXT    PRIMARY KEY,
+    data       TEXT    NOT NULL,             -- JSON [{ t, end, title }]
+    updated_at INTEGER NOT NULL DEFAULT (unixepoch())
+  )`);
   // Optional profile protection: a password or generated key, stored only as a
   // slow salted hash (Bun.password / argon2id). NULL = the name alone opens it.
   for (const col of ['secret_hash TEXT', 'secret_kind TEXT']) {
@@ -800,3 +807,19 @@ export async function deleteUpload(id) {
 export async function touchUpload(id) {
   db.execute({ sql: 'UPDATE uploads SET plays = plays + 1 WHERE id = ?', args: [id] }).catch(() => {});
 }
+
+// ---- YouTube chapters cache -------------------------------------------------
+export async function getYtChapters(id) {
+  const r = await db.execute({ sql: 'SELECT data, updated_at FROM yt_chapters WHERE id = ?', args: [id] });
+  if (!r.rows[0]) return null;
+  let items = [];
+  try { items = JSON.parse(r.rows[0].data) || []; } catch { /* corrupt */ }
+  return { items, updatedAt: Number(r.rows[0].updated_at) };
+}
+export async function setYtChapters(id, items) {
+  await db.execute({
+    sql: `INSERT INTO yt_chapters (id, data, updated_at) VALUES (?, ?, unixepoch())
+          ON CONFLICT(id) DO UPDATE SET data = excluded.data, updated_at = excluded.updated_at`,
+    args: [id, JSON.stringify(items || [])],
+  });
+}

server/server.js

@@ -40,7 +40,7 @@ import { Readable }      from 'node:stream';
 import { tmpdir }        from 'node:os';
 import { createHash }    from 'node:crypto';
 import { brotliCompressSync, constants as zlibConstants } from 'node:zlib';
-import { initDb, upsertUser, recordVideoAccess, getUserData, createProfile, getProfile, saveProfile, setProfileSecret, createSharedPlaylist, getSharedPlaylist, queueInboxPlaylist, listInbox, deleteInboxItem, countInbox,
+import { initDb, upsertUser, recordVideoAccess, getUserData, createProfile, getProfile, saveProfile, setProfileSecret, getYtChapters, setYtChapters, createSharedPlaylist, getSharedPlaylist, queueInboxPlaylist, listInbox, deleteInboxItem, countInbox,
          getMedia, upsertMedia, deleteMedia, listMedia, listMediaLru, touchMedia, mediaStats } from './db.js';
 import { createMediaCache, HIGH, LOW, validateMedia, MediaSkip } from './media-cache.js';
 import * as notesDb from './db.js';
@@ -630,6 +630,17 @@ function parseExpiry(url) {
 // Resolve (and briefly cache) a video's playable formats via yt-dlp -J. The
 // cache spares a fresh ~2-3s yt-dlp run on every Range request the media
 // element fires; its TTL is bounded a minute inside the URLs' own expiry.
+// YouTube's own chapters (description timestamps / creator chapters) as the
+// app's chapter shape: [{ t, end, title }] sorted by start.
+function chaptersFromInfo(info) {
+  const ch = Array.isArray(info && info.chapters) ? info.chapters : [];
+  return ch
+    .map((c) => ({ t: Math.max(0, Number(c.start_time) || 0), end: Number(c.end_time) || null, title: String(c.title || '').trim().slice(0, 200) }))
+    .filter((c) => Number.isFinite(c.t) && c.title)
+    .sort((a, b) => a.t - b.t)
+    .slice(0, 500);
+}
+
 async function resolveStreamsUncached(videoId) {
   const now = Date.now();
   const cached = streamCache.get(videoId);
@@ -637,6 +648,7 @@ async function resolveStreamsUncached(videoId) {
 
   const out = await runYtdlpResilient(['-J', '--no-warnings', `https://www.youtube.com/watch?v=${videoId}`], { pooled: true });
   const info = JSON.parse(out);
+  setYtChapters(videoId, chaptersFromInfo(info)).catch(() => {});
   const raw = Array.isArray(info.formats) ? info.formats : [];
   const formats = [];
   let soonest = Infinity;
@@ -746,6 +758,26 @@ function countView(c, videoId) {
 }
 
 // GET /api/streams?v=<videoId> — meta + proxied audio/quality URLs.
+// GET /api/chapters?v=<id> — YouTube's chapters for a video ([] when it has
+// none). Served from the cache table; otherwise resolved once (the stream
+// resolver's own cache usually makes that free) and remembered for 30 days.
+// Never fails the player: errors answer an empty list.
+app.get('/api/chapters', async (c) => {
+  const id = (c.req.query('v') || '').trim();
+  const nc = { 'Cache-Control': 'no-store' };
+  if (!id || isUpload(id) || !media.isMediaId(id)) return c.json({ ok: true, chapters: [] }, 200, nc);
+  try {
+    const row = await getYtChapters(id);
+    if (row && Date.now() / 1000 - row.updatedAt < 30 * 86400) return c.json({ ok: true, chapters: row.items }, 200, nc);
+    const { info } = await resolveStreams(id);
+    const items = chaptersFromInfo(info);
+    await setYtChapters(id, items);
+    return c.json({ ok: true, chapters: items }, 200, nc);
+  } catch {
+    return c.json({ ok: true, chapters: [], unavailable: true }, 200, nc);
+  }
+});
+
 app.get('/api/streams', async (c) => {
   const videoId = (c.req.query('v') || '').replace(/[/\\:?<>|*"]/g, '').trim();
   if (!videoId) return c.json({ ok: false, error: 'missing videoId' }, 400);