fix(windows): stop the audio mixer from punching holes in a continuous voice - #916
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…s voice The mixer emitted at real time while the capture threads poll WASAPI and hand packets over late (15.6 ms at the default timer resolution, more under load). Every chunk whose packet had not arrived yet was zero-filled, leaving holes of up to 10 ms inside words: the crackle of #911. Real takes show ten or more such drops to digital silence in 25 s. The mixer now writes 100 ms behind real time. Timestamps still come from the frame count, so nothing moves on the timeline. A pause or a stop writes what the cushion holds up to that instant, and a source that ran dry (loopback after silence) resumes a cushion ahead so it lands when it played. Fixes #911
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Included review availability: This review used your included allowance. Your plan provides up to 8 included reviews per hour; 2 remain after this review. 📝 WalkthroughWalkthroughThe Windows audio mixer now emits audio 100 ms behind real time and tracks starvation for each source. It flushes buffered audio through pause and stop times. New tests check polling jitter, late source audio, and pause/resume timing. Recording documentation describes the timing and adds a microphone recording check. ChangesWindows audio mixer
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix Merge Risk: ⚪ Minimal · up to The Windows mixer adds buffering to tolerate delayed capture packets and preserves buffered audio across pause/resume. No concrete merge-blocking regression is established; the planned microphone recording check remains useful validation. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to Capture permissions, selected sources, and recording destinations remain unchanged. The main design uncertainty is at pause and stop: the new flush preserves queued audio but does not ensure that all pending capture packets have arrived, so recording boundaries can still contain silence. Retained concerns
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Inline comments:
Review comments at @electron/native/wgc-capture/src/audio_sample_utils.cpp:
- Around line 552-559: Update AudioMixer::setPaused and mixLoop so resuming
waits until the mixer acknowledges completion of the pause flush before
resetSources clears retained audio; notify the waiting resume path after the
flush, including when no timeline has started, and preserve the existing stop
behavior.
- Around line 728-780: Update the flush target in AudioMixer::mixLoop so
stopping uses the current time only when the mixer was still running; when
paused, flush to pausedAt even if stop arrives before the pause notification is
processed. Keep the existing emittedFrames_ and emitUntil flow unchanged.
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electron/native/wgc-capture/src/audio_sample_utils.cppelectron/native/wgc-capture/src/audio_sample_utils.helectron/native/wgc-capture/src/audio_sample_utils_test.cpptechnical-documentation/architecture/recording.mdtechnical-documentation/testing/manual-e2e-checklist.md
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…nchor its clock exactly Review of #916 (CodeRabbit), plus two placement errors the same tests exposed on a loaded machine. - A resume right behind a pause cleared the queues before mixLoop had written the cushion: the last 80 to 90 ms of voice before the pause were lost (measured). The resume now waits for the pause flush. - A stop that lands on a pause mixLoop has not handled yet flushes to the pause, not to now: the paused span is out of the video. - A source coming back after running dry is placed by the mixer's real lag, not by the cushion alone; under load the difference reached 50 ms early. - The clock is anchored in beginTimeline and at the resume instant, not when mixLoop next wakes, which placed the whole track early by the wake-up delay. mixLoop reads the shared clock under the lock. New test: an instant pause/resume keeps the voice before it (400 of 400 ms, was 310 to 320) and resumes within one chunk of the pause.
…nchor its clock exactly Review of #916 (CodeRabbit), plus two placement errors the same tests exposed on a loaded machine. - A resume right behind a pause cleared the queues before mixLoop had written the cushion: the last 80 to 90 ms of voice before the pause were lost (measured). The resume now waits for the pause flush. - A stop that lands on a pause mixLoop has not handled yet flushes to the pause, not to now: the paused span is out of the video. - A source coming back after running dry is placed by the mixer's real lag, not by the cushion alone; under load the difference reached 50 ms early. - The clock is anchored in beginTimeline and at the resume instant, not when mixLoop next wakes, which placed the whole track early by the wake-up delay. mixLoop reads the shared clock under the lock. New test: an instant pause/resume keeps the voice before it (400 of 400 ms, was 310 to 320) and resumes within one chunk of the pause.
1 participant
Fixes #911.
Cause
The crackle is in the recorded file itself, not in the editor.
AudioMixerwrote at real time, while the capture threads poll WASAPI and hand packets over late (15.6 ms at the default timer resolution, more under load).Fix
macOS already places audio by timestamp with a grace window; Linux uses another design. Only Windows was affected.
Tests
Three new cases in
audio_sample_utils_testdrive the real mixer with an emulated capture loop:Each guard was checked against a mutant: without the re-anchor the late source lands at 300 ms, without the pause flush the resume lands at 310 ms.
npm run build:native:winpasses (116 tests, stable over 6 runs).Not covered
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