ThePendulum
f634dda5bb
sync_logic.py: pure delay_ms computation with the documented sign convention. Caught and fixed a sign error in my own test-fixture ground-truth doc while writing the unit tests: the audio+350ms fixture actually requires delay_ms=-350 (delay video), not +350, since the audio is already the late one. ffmpeg_export.py: ports ffdelay's two-branch command structure (offset video input vs audio input depending on delay_ms sign) plus its documented quirks (leading-zero float formatting, -ss/-t applied to both inputs for clip mode, non-fatal stream-copy warnings surfaced via stderr rather than swallowed). Added an end-to-end integration test (scripts/test_export_roundtrip.py) that independently re-detects event timing in the exported output via ffmpeg scene-change/silence detection (not the same code path used to build the export) and confirms both the positive- and negative-delay branches bring drift down from ~350ms to under 1ms.
Synthetic test clips
Generated with ffmpeg (see git history / commit for exact commands). Ground truth for validating marker capture, offset math, and lossless export.
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sync_test_INSYNC.mp4— 10s, 640x480 @30fps, black video with a 33ms white flash at t=5.000s; near-silent 1kHz tone that jumps to full volume for the same 33ms window at t=5.000s. Video and audio events are aligned (offset = 0ms). -
sync_test_OUTOFSYNC_audio+350ms.mp4— same content, but the audio track has been shifted +350ms later relative to video (via-itsoffset 0.350on the audio input, stream-copied). The flash event stays at video t=5.000s; the beep event now appears at t=5.350s. Exercises the negative-delay_ms / "delay video" branch in ffmpeg_export.py. -
sync_test_OUTOFSYNC_video+350ms.mp4— same content, but the video track has been shifted +350ms later instead (via-itsoffset 0.350on the video input). The beep stays at audio t=5.000s; the flash now appears at t=5.350s. Exercises the positive-delay_ms / "delay audio" branch in ffmpeg_export.py.
Ground truth for the app's marker/offset workflow:
- Mark Video at the flash → ~5.000s
- Mark Audio at the beep → ~5.350s
- Expected computed
delay_ms= (video_mark - audio_mark) * 1000 = -350 (audio is already the late one here, so the fix is to delay the video by 350ms to catch up to it -- not to delay the audio further. Negative delay_ms → offset the video input, per sync_logic.py's sign convention.) - Exporting
sync_test_OUTOFSYNC_audio+350ms.mp4with delay_ms = -350 should land both events at t=5.350s in the output (not back at 5.000s -- the absolute timeline shifts, only the relative sync matters).
Frame at exactly t=5.000s is frame index 150 (30fps) — useful for checking frame-step precision lands exactly on it.