fix(playback): normalize Firefox remux audio timestamps - #824
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Organization UI Review profile: CHILL Plan: Pro Plus Run ID: 📒 Files selected for processing (2)
Included review availability: Your plan provides up to 2 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughAdds AAC timestamp normalization for encoded audio and applies it to Firefox Matroska AAC remuxes. Updates AAC capability probing, the recipe version, playback tests, conformance fixtures, and attempt keys. ChangesFirefox Matroska AAC playback
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: ⚪ Minimal · up to This change normalizes Firefox Matroska AAC timestamps during remux while preserving direct play and other-browser behavior; no actionable merge-blocking risk remains after normal checks and review. Sequence Diagram(s)sequenceDiagram
participant FirefoxWebClient
participant PlaybackPlanner
participant firefoxMatroskaAACTimingQuirkV3
participant RemuxPlan
FirefoxWebClient->>PlaybackPlanner: request playback
PlaybackPlanner->>firefoxMatroskaAACTimingQuirkV3: evaluate source and request
firefoxMatroskaAACTimingQuirkV3-->>PlaybackPlanner: return audio_only_transcode quirk
PlaybackPlanner->>RemuxPlan: force AAC audio transcode
PlaybackPlanner->>RemuxPlan: appendAppliedQuirkV3
Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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Inline comments:
In `@internal/playback/transformations_v3.go`:
- Line 68: Update the AAC v3 availability check for TransformationAudioToAACV3
to require successful smoke probes for both aacTimestampNormalizeFilterV3 and
stereoDownmixBoostFilterV3, retaining the existing FFmpeg and AAC encoder checks
before advertising timestamp_normalization_v4.
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⚙️ Run configuration
Configuration used: Organization UI
Review profile: CHILL
Plan: Pro Plus
Run ID: 3dc44de7-9e31-41a1-ad26-3a5f105cdf97
📒 Files selected for processing (14)
docs/design/schemas/playback-v3/v3/fixtures/valid/capability_response.jsoninternal/playback/device_quirks_v3.gointernal/playback/device_quirks_v3_test.gointernal/playback/plan_v3.gointernal/playback/protocol_v3.gointernal/playback/protocol_v3_test.gointernal/playback/remux.gointernal/playback/remux_dv_test.gointernal/playback/testdata/protocol_v3/attempt_keys.jsoninternal/playback/testdata/protocol_v3/capability_response.jsoninternal/playback/testdata/protocol_v3/conformance_matrix.jsoninternal/playback/transcode.gointernal/playback/transcode_args_test.gointernal/playback/transformations_v3.go
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Related issue: #819
Follow-up to: #820
What was still happening
#820 fixed the AAC path used when surround audio is converted to stereo, but I found another Firefox case that could still crackle. Stereo AAC copied from Matroska into MP4/fMP4 kept the source millisecond-rounded packet timestamps. The resulting 21/22 ms steps leave small gaps and overlaps instead of a continuous AAC sample clock, and Firefox renders those gaps as audible silence.
I reproduced this on my own Silo server with the same media in Firefox, compared the generated packet timing, and checked the live FFmpeg process. Re-encoding only the audio through
aresample=async=1produced a continuous 1024-sample AAC cadence and removed the crackling.What changed
Testing
I tested the equivalent fix on my fork in production as build-109 with Firefox 154. I checked a fresh start, saved resume, rewind, fast-forward, remux, audio transcode, and direct play. The live route copied H.264 video while converting AAC audio with
aresample=async=1, and I confirmed by listening that the crackling was gone.Automated coverage includes Matroska AAC, direct-play preservation, non-Firefox and non-Matroska negatives, codec-copy preservation, seek anchors, and AAC conversion plans for DTS, EAC3, AC3, TrueHD 7.1, Opus, Vorbis, and FLAC.
Local checks:
go test ./internal/playbackFirefox/AAC/remux casesgo vet ./internal/playbackmake verify-playback-fixturesmake verify-local-pathsgit diff --checkThe complete playback package run is left to CI because the local macOS sandbox kills the unrelated fake-FFmpeg GPU and VideoToolbox probe subprocesses. The focused playback tests pass.
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Summary by CodeRabbit
Bug Fixes
Improvements