pairwise_offsets now computes each signal's rFFT once at a shared padded
length (2*max_len) and reuses it for every pair: O(K) forward FFTs +
cheap per-pair spectrum products instead of O(K^2) full FFTs. Each
pair's lag search stays capped at +/-(la+lb)/2 — the same window the
per-pair transform used — and gcc_phat() itself is unchanged for
callers (drift windows, tests). Measured 1.8x on 6 cams x 10 min;
the advantage grows with camera count.
New test locks the cached path against direct gcc_phat, including
unequal-length signals where the padded sizes genuinely differ.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Fills the foundation stubs in ingest.py and audio_sync.py.
- ingest: ffprobe probe + mono 16 kHz WAV extraction per video (ffmpeg);
idempotent run_ingest reuses existing rows so synthetic -> ingest -> sync
works without unique-constraint collisions.
- sync: PHAT-whitened GCC-PHAT pairwise offsets with sub-sample parabolic
peak refinement, scored by peak-to-second-peak ratio; confidence-weighted
global least-squares solve with cycle-consistency rejection (>50 ms);
windowed drift estimation (ppm) with a 5 ppm deadband; disconnected
sync-graph components -> offset_ms=None (spec pitfall #5).
- Persists offset_ms/drift_ppm/sync_confidence via db.update_video_sync and
exports data/work/sync.json.
Verified on the synthetic fixture: synthetic -> ingest -> sync recovers the
ground-truth offsets (0 / +1370 / -842 ms) to <0.001 ms and drift 0 ppm,
well inside the spec M1 tolerances (+/-10 ms, +/-3 ppm). pytest: 43 passed
(24 foundation + 19 new in test_ingest.py and test_audio_sync.py).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
