Fix WebVTT subtitle exports truncating audio and video while reporting the download as completed. When separate video/audio tracks are muxed with captions, subtitle EOF no longer ends the whole export. Short, sparse, and empty captions preserve the complete media.
Reproduced before fixing
- Installed the published v5.5.5 extension in Brave MV3 and Firefox MV2 and downloaded real local H.264/AAC HLS streams through the UI.
- Both clear TS and fMP4 sources reproduced the failure in both browsers. Eight-second streams were saved as "Completed" files containing only two video frames and two audio frames.
- Four new native FFmpeg regressions also failed, including a case where the audio outlasts the video.
Verified before release
- Passed 20 subtitle browser cases: four reproduce the old release's truncation and sixteen verify complete fixed exports with clear/encrypted TS and fMP4, explicit/implicit IVs, initialization keys, and short, sparse, or empty captions.
- Every fixed subtitle export preserves all 200 source video frames and all 376 audio frames. Fully decoded audio hashes match the source HLS exactly. Extracted subtitle text and cue timing match the input.
- Passed the separate 16-case video/audio browser matrix without subtitles, confirming the existing download path still works.
- All 323 automated tests, workspace typechecking, the security gate, and all six archive checks pass. Firefox lint reports zero errors and six existing warnings.
- Added
pnpm test:e2e:subtitlesfor repeatable local reproduction and verification. JSON evidence and saved media are retained in the printed temporary directory.
Firefox installation
GitHub Firefox XPIs are unsigned builds for temporary installation through about:debugging. Firefox Add-ons availability depends on a separate Mozilla signing and review process.