Extract the shared realtime audio graph owner

frontend/app-seams.test.js

@@ -21,7 +21,6 @@ test('Phase 4 preserves the exact playback, continuity, tracking and queue bodie
  {const start=app.indexOf("function startSleepTimer(minutes, { endOfSong = false } = {}) {");assert.ok(start>=0,"startSleepTimer");const body=app.slice(start,start+487);assert.equal(createHash('sha256').update(body).digest('hex'),"f0a93401ab90196096074cb607b28d52c5903e11dbdfb8ddb95114e143af2409","startSleepTimer body unchanged");}
  {const start=app.indexOf("function cancelSleepTimer() {");assert.ok(start>=0,"cancelSleepTimer");const body=app.slice(start,start+253);assert.equal(createHash('sha256').update(body).digest('hex'),"cf396ab758a70eede6af7444539a82ca15af801a9a57024dd5542067e9fa771a","cancelSleepTimer body unchanged");}
  {const start=app.indexOf("function finishSleep() {");assert.ok(start>=0,"finishSleep");const body=app.slice(start,start+662);assert.equal(createHash('sha256').update(body).digest('hex'),"7ee93bf760bad5f39f4644339963918c5b369b2acc554b8e561c1a1f070ac6fb","finishSleep body unchanged");}
- {const start=app.indexOf("const EQ = (() => {");assert.ok(start>=0,"EQ");const body=app.slice(start,start+7917);assert.equal(createHash('sha256').update(body).digest('hex'),"f0cba011c94f33e6fd0ab778021f4c97238262dfa0a8dd40bf3f17149c227528","EQ body unchanged");}
  {const start=app.indexOf("const EqRender = (() => {");assert.ok(start>=0,"EqRender");const body=app.slice(start,start+5912);assert.equal(createHash('sha256').update(body).digest('hex'),"f014dd41dafebc33f09e87be866074afd7a2443c5bb452103a435585353a828f","EqRender body unchanged");}
  {const start=app.indexOf("const Level = (() => {");assert.ok(start>=0,"Level");const body=app.slice(start,start+3892);assert.equal(createHash('sha256').update(body).digest('hex'),"e48ad7797384ac31bb8b864662fc2a546b04470b981042f016874ba750957226","Level body unchanged");}
 });

frontend/app.js

@@ -5507,7 +5507,7 @@ const EQ_PRESETS = EqParameters.presets;
 const EQ = (() => {
   const isIOS = /iPad|iPhone|iPod/.test(navigator.userAgent) || (navigator.platform === 'MacIntel' && navigator.maxTouchPoints > 1);
   const AC = window.AudioContext || window.webkitAudioContext;
-  const st = { ctx: null, filters: null, sources: new Map() };
+  const st = { ctx: null, filters: null };
   // Web Audio is off on iOS (it silences playback when the screen locks)
   // unless the user opted in through "Level volume" (Settings → Playback).
   // Live Web Audio is off on iOS (it silences playback when the screen locks)
@@ -5529,7 +5529,7 @@ const EQ = (() => {
       return false;
     }
     try {
-      st.ctx = new AC();
+      st.ctx = AudioGraph.context();
       st.filters = EQ_BANDS.map((b) => {
         const f = st.ctx.createBiquadFilter();
         f.type = b.type;
@@ -5554,11 +5554,9 @@ const EQ = (() => {
   }
 
   function attach(el) {
-    if (!el || st.sources.has(el)) return;
+    if (!el) return;
     try {
-      const src = st.ctx.createMediaElementSource(el);
-      src.connect(st.filters[0]);
-      st.sources.set(el, src);
+      AudioGraph.connect(el, st.filters[0]);
     } catch { /* already connected elsewhere */ }
   }
 

frontend/assets.json

@@ -29,6 +29,7 @@
         "/related-videos.js",
         "/related-videos.css",
         "/audio-continuity.js",
+        "/audio-graph.js",
         "/fullscreen-orientation.js",
         "/fullscreen-orientation.css",
         "/download-actions.js",

frontend/audio-graph.js

@@ -0,0 +1,69 @@
+/* One lifetime owner for the player's realtime AudioContext and media sources. */
+(function (root) {
+  'use strict';
+
+  function create(options = {}) {
+    const getConstructor = options.getConstructor || (() => root.AudioContext || root.webkitAudioContext);
+    let context = null;
+    const sources = new Map();
+    const routes = new Map();
+    const failed = new Map();
+
+    function getContext(contextOptions) {
+      if (context) return context;
+      const Constructor = getConstructor();
+      if (typeof Constructor !== 'function') throw new Error('Web Audio is unavailable');
+      context = contextOptions === undefined ? new Constructor() : new Constructor(contextOptions);
+      return context;
+    }
+
+    function source(element) {
+      if (!element) throw new TypeError('A media element is required');
+      if (sources.has(element)) return sources.get(element);
+      if (failed.has(element)) throw failed.get(element);
+      try {
+        const created = getContext().createMediaElementSource(element);
+        sources.set(element, created);
+        return created;
+      } catch (error) {
+        // MediaElementSource cannot be undone. Remember failure so a later
+        // route change can never attempt a second source for this element.
+        failed.set(element, error);
+        throw error;
+      }
+    }
+
+    function connect(element, destination) {
+      const mediaSource = source(element);
+      if (!destination) throw new TypeError('An audio destination is required');
+      if (routes.get(element) === destination) return mediaSource;
+      if (routes.has(element)) mediaSource.disconnect();
+      mediaSource.connect(destination);
+      routes.set(element, destination);
+      return mediaSource;
+    }
+
+    function routeAll(elements, destination) {
+      for (const element of elements || []) connect(element, destination);
+    }
+
+    function snapshot() {
+      return {
+        contextCreated: !!context,
+        sampleRate: context?.sampleRate || null,
+        sourceCount: sources.size,
+        failedCount: failed.size,
+        routedCount: routes.size,
+      };
+    }
+
+    return { context: getContext, source, connect, routeAll, snapshot };
+  }
+
+  const singleton = create();
+  const api = { create, context: (...args) => singleton.context(...args), source: (...args) => singleton.source(...args),
+    connect: (...args) => singleton.connect(...args), routeAll: (...args) => singleton.routeAll(...args),
+    snapshot: () => singleton.snapshot() };
+  if (typeof module !== 'undefined' && module.exports) module.exports = api;
+  else root.AudioGraph = api;
+})(typeof window !== 'undefined' ? window : globalThis);

frontend/audio-graph.test.js

@@ -0,0 +1,75 @@
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const { readFileSync } = require('node:fs');
+const { join } = require('node:path');
+const AudioGraph = require('./audio-graph');
+
+test('AudioGraph creates its context only on demand and retains the first context options', () => {
+  let contexts = 0, optionsSeen;
+  class Context {
+    constructor(options) { contexts++; optionsSeen = options; this.sampleRate = options?.sampleRate || 44100; }
+  }
+  const graph = AudioGraph.create({ getConstructor: () => Context });
+  assert.equal(graph.snapshot().contextCreated, false);
+  const first = graph.context({ sampleRate: 48000 });
+  assert.equal(graph.context({ sampleRate: 44100 }), first);
+  assert.equal(contexts, 1);
+  assert.deepEqual(optionsSeen, { sampleRate: 48000 });
+  assert.equal(first.sampleRate, 48000);
+});
+
+test('one retained MediaElementSource per element can change insert routes without recreation', () => {
+  const made = [], connects = [], disconnects = [];
+  class Context {
+    constructor() { this.sampleRate = 48000; }
+    createMediaElementSource(element) {
+      const source = { element, connect: target => connects.push([element.id, target.id]), disconnect: () => disconnects.push(element.id) };
+      made.push(source); return source;
+    }
+  }
+  const graph = AudioGraph.create({ getConstructor: () => Context });
+  const a = { id: 'video' }, b = { id: 'audio' }, standard = { id: 'standard' }, dsp = { id: 'dsp' };
+  const original = graph.connect(a, standard);
+  graph.connect(a, standard);
+  graph.routeAll([a, b], dsp);
+  graph.routeAll([a, b], standard);
+  assert.equal(made.length, 2);
+  assert.equal(graph.source(a), original);
+  assert.deepEqual(connects, [['video', 'standard'], ['video', 'dsp'], ['audio', 'dsp'], ['video', 'standard'], ['audio', 'standard']]);
+  assert.deepEqual(disconnects, ['video', 'video', 'audio']);
+  assert.deepEqual(graph.snapshot(), { contextCreated: true, sampleRate: 48000, sourceCount: 2, failedCount: 0, routedCount: 2 });
+});
+
+test('a failed source creation is remembered and is never attempted twice', () => {
+  let attempts = 0;
+  class Context {
+    constructor() { this.sampleRate = 48000; }
+    createMediaElementSource() { attempts++; throw new Error('already sourced'); }
+  }
+  const graph = AudioGraph.create({ getConstructor: () => Context }), element = {};
+  assert.throws(() => graph.source(element), /already sourced/);
+  assert.throws(() => graph.source(element), /already sourced/);
+  assert.equal(attempts, 1);
+  assert.deepEqual(graph.snapshot(), { contextCreated: true, sampleRate: 48000, sourceCount: 0, failedCount: 1, routedCount: 0 });
+});
+
+test('the extracted Standard EQ build block is identical to the original except for context ownership', () => {
+  const source = readFileSync(join(__dirname, 'app.js'), 'utf8');
+  const original = readFileSync(join(__dirname, '..', 'tests', 'fixtures', 'standard-eq-build.txt'), 'utf8').trimEnd();
+  const start = source.indexOf('  function build() {', source.indexOf('const EQ = (() => {'));
+  const end = source.indexOf('\n  function attach(el)', start);
+  assert.ok(start >= 0 && end > start, 'EQ build block exists');
+  const current = source.slice(start, end).trimEnd();
+  assert.equal(current, original.replace('st.ctx = new AC();', 'st.ctx = AudioGraph.context();'));
+  assert.match(source, /AudioGraph\.connect\(el, st\.filters\[0\]\)/);
+  assert.doesNotMatch(source, /\.createMediaElementSource\(/);
+});
+
+test('AudioGraph is a core runtime asset and is loaded before the lazy app', () => {
+  const { groups } = JSON.parse(readFileSync(join(__dirname, 'assets.json'), 'utf8'));
+  assert.ok(groups.core.files.includes('/audio-graph.js'));
+  const html = readFileSync(join(__dirname, 'index.html'), 'utf8');
+  assert.ok(html.indexOf('src="audio-graph.js"') < html.indexOf('src="section-rail.js"'));
+  const embedded = JSON.parse(html.match(/id="ytp-assets">([^<]+)<\/script>/)[1]);
+  assert.deepEqual(embedded.groups, groups);
+});

frontend/sw.js

@@ -70,6 +70,7 @@ const SHELL = [
   '/glass-panel-layout.js',
   '/theme-classic.css',
   '/recommendations.css',
+  '/audio-graph.js',
   '/flag-ui.js',
   '/export.js',
   '/async-guard.js',