Screencast frame duplication (Math.round) causes video to be ~5% longer
than wall-clock time. Caption timestamps are wall-clock based, so the
audio track drifted ahead by ~8s at the midpoint of a 5-minute video.
Fix:
- stopRecording() saves recordingDuration in captions.json
- addNarration() reads actual video duration via ffprobe and scales
caption timestamps by videoDuration/recordingDuration ratio
- Phase 2 timeline now tracks actual cumulative position instead of
computing gaps from previous caption data (prevents MP3 frame
quantization drift)
- Also fixed findFfmpeg() → resolveFfmpeg() call in addNarration
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Nick ShirokovandClaude Opus 4.6
5acb586bbf