A suspended AudioContext holds currentTime still, so any clock derived from it stops

Fact

AudioContext.currentTime advances only while the context's state is running. A context constructed before any user gesture starts suspended under the autoplay policy, and a browser may suspend a running one again when the page is backgrounded or the output device changes.

While suspended it does not throw, reset, or report anything unusual: it holds whatever finite, non-zero value it had reached. Anything clocked on it — playback position, progress, a whole simulation — therefore stops dead while rendering carries on at full frame rate.

resume() returns a promise that settles only once the context is actually allowed to run, and a resume() that is not reached synchronously from a user gesture handler may never settle at all.

Why it matters

The frozen value looks exactly like a working clock. It is finite, it is not zero, and reading it twice inside one frame legitimately returns the same number even on a healthy context, so the obvious sanity checks pass.

The symptom is "everything draws, nothing moves", which points at the frame loop or at the update function — neither of which is at fault. It also hides during development, because interacting with the page to test it is itself the gesture that resumes the context.

How to apply

• Treat state === 'running' as a precondition of the clock, not just of the sound. Either gate the start of anything time-driven on it, or carry the time forward on a wall clock while suspended, anchored so it cannot jump:

  if (ctx && ctx.state === 'running') {
    anchorAudio = ctx.currentTime;
    anchorPerf = performance.now() / 1000;
    return anchorAudio;
  }
  return anchorAudio + performance.now() / 1000 - anchorPerf;

• Call resume() from inside the gesture handler, not from a timer or a continuation after an await.
• Listen for the context's statechange event rather than polling state.
• When nothing is moving, separate the two candidates before debugging either: log ctx.state and a requestAnimationFrame counter. A hidden surface delivering no frames and a frozen audio clock present identically.

Related: [[audiocontext-currenttime-is-not-audible-time]], [[hidden-surface-delivers-no-frames]].