remotion-dev/remotion

Package: @remotion/player (setGlobalTimeAnchor, src/set-global-time-anchor.ts) Affected versions: 4.0.516 → 4.0.526 (current)

Problem

When the Web Audio clock briefly stalls at the start of playback (observed ~100–180 ms on first play after idle, and on some devices with high output latency), audioContext.currentTime stops while frames keep advancing. Once the clock resumes, video and audio stay offset by that amount for the rest of playback.

setGlobalTimeAnchor skips re-anchoring when

Math.abs(shift) < ALLOWED_GLOBAL_TIME_ANCHOR_SHIFT + latency   // 0.1 + baseLatency + outputLatency

With outputLatency of 0.2 s+ (Bluetooth headphones, some Android/Windows outputs; and 0.3 s is substituted when outputLatency is 0), the threshold is 0.3–0.6 s. A 100–180 ms offset never crosses it, so it's never corrected. The skip is right for per-frame jitter, but it also swallows a sustained mismatch.

Reproduction

Captured from a real replay at 25 fps — relative audioContext.currentTime vs. the frame being shown. Audio time is stuck at 0.1067 while frames 3→5 advance, then resumes ~100 ms behind:

const replay = [
  [0, 0], [0.064, 0], [0.1067, 3], [0.1067, 5], [0.128, 7], [0.2347, 10],
  [0.3413, 12], [0.4267, 15], [0.5333, 17], [0.64, 20], [0.7467, 22],
  [0.832, 25], [0.9387, 27],
];

const audioSyncAnchor = { value: 0 };
for (const [audioTime, frame] of replay) {
  setGlobalTimeAnchor({
    audioContext: { currentTime: audioTime, baseLatency: 1024 / 48000, outputLatency: 0.2, state: 'running' },
    audioSyncAnchor,
    absoluteTimeInSeconds: frame / 25,
    globalPlaybackRate: 1,
    logLevel: 'error',
    force: false,
  });
}
// final error: (audioTime - anchor) - frame/25  ≈ -0.10 s, and it never gets corrected