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Revert "Fix #7: startup freeze (audio master clock jumps backward on cold start)"

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SteadyW 2026-06-14 13:30:14 +03:00 • committed by GitHub
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commit 667b412994
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2 changed files with 3 additions and 78 deletions
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22
app.js
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@ -44,7 +44,6 @@ let selectionBuffer = null;
let lastRenderTime = 0;
let frameCount = 0, currentFps = 0, lastFpsUpdate = 0;
let streamStartTime = 0;
let audioClockOffset = null; // anchors the audio clock so it never jumps backward (issue #7)
const CHAR_LUT = new Array(128);
for (let i = 0; i < 128; i++) CHAR_LUT[i] = String.fromCharCode(i);
@ -187,7 +186,6 @@ function connectWebSocket() {
streamStartTime = performance.now();
lastRenderTime = performance.now();
lastFpsUpdate = lastRenderTime;
audioClockOffset = null; // re-anchor for this stream
requestAnimationFrame(renderFrame);
};
@ -271,25 +269,11 @@ function renderFrame(now) {
requestAnimationFrame(renderFrame);
// ── MASTER CLOCK LOGIC ──
// The audio track is the master clock, BUT it must never jump backward
// (issue #7, the cold-start freeze). On a cold load the <audio> element can
// start late: the wall-clock fallback has already advanced playback a second
// or two, and when audio finally begins, audioEl.currentTime is back near 0.
// Snapping the master clock back to ~0 makes every buffered frame read as
// "in the future", so renderFrame() returns forever and the stream freezes
// until audio catches up. The fix: the first time audio is genuinely playing,
// capture the offset between where the wall clock already is and the audio
// clock, and add it back — so the clock follows audio's *rate* without ever
// moving backward. (When audio starts promptly the offset is ~0.)
const wallClock = (now - streamStartTime) / 1000.0;
let masterClock;
if (audioEl && audioEl.readyState >= 1 && !audioEl.paused && audioEl.currentTime > 0) {
if (audioClockOffset === null) {
audioClockOffset = Math.max(0, wallClock - audioEl.currentTime);
}
masterClock = audioEl.currentTime + audioClockOffset;
if (audioEl && audioEl.readyState >= 1 && !audioEl.paused) {
masterClock = audioEl.currentTime;
} else {
masterClock = wallClock;
masterClock = (now - streamStartTime) / 1000.0;
}
if (frameBuffer.length === 0) return;

59
experiments/freeze_repro.js
View file

@ -1,59 +0,0 @@
/*
* freeze_repro2.js — Model the COLD-START freeze (issue #7): audio starts late,
* so the wall-clock fallback renders ahead, then the master clock snaps back to
* audioEl.currentTime (~0) and playback freezes until audio catches up.
*
* Faithfully simulates: a server feeding frames at fps, a capped jitter buffer,
* a 60fps render loop, and the app.js master-clock + frame-gate logic — under
* three clock policies.
*/
function sim({ policy, audioDelayMs }) {
const fps = 24, rAF = 1000 / 60, DURATION = 6000;
const buf = [];
let lastServerFrame = -1, audioStart = null;
const renderTimes = [];
for (let t = 0; t <= DURATION; t += rAF) {
// server feeds frames in real time; jitter buffer caps at 20 (drops oldest)
const want = Math.floor(t / 1000 * fps);
while (lastServerFrame < want) buf.push({ time: ++lastServerFrame / fps });
while (buf.length > 20) buf.shift();
const audioPlaying = t >= audioDelayMs;
if (audioPlaying && audioStart === null) audioStart = t;
const audioCurrent = audioPlaying ? (t - audioStart) / 1000 : 0;
const wall = t / 1000;
// ── master clock policy ──
let master;
if (policy === 'broken') master = audioPlaying ? audioCurrent : wall;
else if (policy === 'guard') master = (audioPlaying && audioCurrent > 0) ? audioCurrent : wall;
else if (policy === 'monotonic') {
// fix: anchor audio so the clock never jumps backward
if (audioPlaying) {
if (sim._off === undefined) sim._off = wall - audioCurrent; // capture once
master = audioCurrent + sim._off;
} else master = wall;
}
// ── frame gate (verbatim from app.js) ──
if (buf.length) {
while (buf.length > 1 && buf[0].time < master - 0.1) buf.shift();
if (buf[0].time <= master + 0.05) { buf.shift(); renderTimes.push(t); }
}
}
delete sim._off;
const last = renderTimes[renderTimes.length - 1] ?? 0;
const afterAudio = renderTimes.filter(t => t > audioDelayMs).length;
const trailingStallMs = Math.round(DURATION - last); // froze until the end?
return { rendered: renderTimes.length, afterAudio, trailingStallMs };
}
const EXPECTED_AFTER = Math.round((6000 - 2000) / 1000 * 24); // ~96 frames in the 2-6s window
console.log(`audio starts 2s late (cold start). Expect ~${EXPECTED_AFTER} frames AFTER 2s if smooth:\n`);
for (const policy of ['broken', 'guard', 'monotonic']) {
const r = sim({ policy, audioDelayMs: 2000 });
const frozen = r.afterAudio < 5;
console.log(` ${policy.padEnd(10)} total ${String(r.rendered).padStart(3)} | after-audio ${String(r.afterAudio).padStart(3)}/${EXPECTED_AFTER} | `
+ (frozen ? `FROZE (stuck ${r.trailingStallMs}ms to end)` : `smooth`));
}