# Synthetic test clips

Generated with ffmpeg (see git history / commit for exact commands). Ground truth for
validating marker capture, offset math, and lossless export.

- `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 0.350` on the audio
  input, stream-copied). The flash event stays at video t=5.000s; the beep event
  now appears at t=5.350s.

**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` = +350 (audio needs to be delayed to match video)
- Exporting `sync_test_OUTOFSYNC_audio+350ms.mp4` with delay_ms = +350 should
  reproduce (bit-for-bit, modulo container overhead) `sync_test_INSYNC.mp4`'s sync.

Frame at exactly t=5.000s is frame index 150 (30fps) — useful for checking
frame-step precision lands exactly on it.