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Loudness levelling (EBU R128, -14 LUFS) measured in the browser with WebAssembly

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- frontend/wasm/loudness.c → loudness-wasm.js (1.5 KB, base64-embedded; built by
  scripts/build-loudness-wasm.sh with clang or Zig's clang): K-weighting + 100 ms
  energy steps. loudness.js does the 400 ms gating (abs -70 LUFS, rel -10 LU)
  with an identical JS fallback. EBU Tech 3341 sine cases measure -23.0/-33.0
  on both engines; a real track reads -21.7 vs ffmpeg ebur128 -21.8.
- The device measures from audio it already has (saved copy or the server
  cache's m4a sidecar, songs up to 12 min, decoded natively at 22.05 kHz) and
  reports the number to /api/loudness, so each song is measured once for
  everyone; the server stores numbers only, no audio processing.
- The EQ graph gains a level stage (gain -> limiter) that eases each track
  toward -14 LUFS (-12..+9 dB). Settings -> Playback -> Level volume: on by
  default on Android/desktop, opt-in on iPhone (Web Audio stops sound when the
  screen locks there).
This commit is contained in:
Jonathan Sykes
2026-10-03 07:44:44 +08:00
parent 796293c0a5
commit ea9e11d054
10 changed files with 434 additions and 4 deletions
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23
server/server.js
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@@ -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, getYtChapters, setYtChapters, createSharedPlaylist, getSharedPlaylist, queueInboxPlaylist, listInbox, deleteInboxItem, countInbox,
import { initDb, upsertUser, recordVideoAccess, getUserData, createProfile, getProfile, saveProfile, setProfileSecret, getYtChapters, setYtChapters, getLoudness, addLoudness, 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';
@@ -766,6 +766,27 @@ function countView(c, videoId) {
}
// GET /api/streams?v=<videoId> — meta + proxied audio/quality URLs.
// Loudness levelling (EBU R128). Devices measure in the browser (WebAssembly)
// and report here; the server only stores numbers — no audio processing.
// GET /api/loudness?v=<id> → { lufs | null }
// POST /api/loudness { id, lufs } → stored (running mean of 10 reports)
app.get('/api/loudness', async (c) => {
const id = (c.req.query('v') || '').trim();
if (!media.isMediaId(id) && !isUpload(id)) return c.json({ ok: true, lufs: null });
const row = await getLoudness(id).catch(() => null);
return c.json({ ok: true, lufs: row ? Math.round(row.lufs * 10) / 10 : null }, 200, { 'Cache-Control': 'no-store' });
});
app.post('/api/loudness', async (c) => {
let body;
try { body = await c.req.json(); } catch { return c.json({ ok: false, error: 'invalid JSON' }, 400); }
const id = String(body && body.id || '').trim();
const lufs = Number(body && body.lufs);
if (!media.isMediaId(id) && !isUpload(id)) return c.json({ ok: false, error: 'invalid id' }, 400);
if (!Number.isFinite(lufs) || lufs < -60 || lufs > 0) return c.json({ ok: false, error: 'lufs out of range' }, 400);
await addLoudness(id, lufs);
return c.json({ ok: true });
});
// 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.