Second measurement of the same recording family (ty-20261112-1133-701-0000-2.mp4):
wall clock (audio start -> audio stop) 6.477 s
video: 386 frames 6.455 s correct
audio: 294 packets 6.252 s 226 ms SHORT
Same magnitude as the original bug, opposite sign — the clock fixed the tick-rate error and
exposed the next one underneath. Audio started 49 ms before the pump, ffmpeg connected ~80 ms
after, and every chunk written in that window was dropped (dropped writes 27). The loop still
counted those frames as produced, so the track lost exactly that much time.
Now: the clock does not start until the pipe is connected, and AudioClock.Advance counts a
frame only when its write reached the pipe. A dropped write stays owed and is paid off on the
next tick, so a start-up gap costs content (silence, which there was anyway) instead of
length.
Two measurements, two different signs, one lesson: the audio track's LENGTH has to be the
clock's, and anything that removes samples without removing time — a fast tick, a dropped
write — shows up as drift no static offset can fix.
674 tests (one notification-timing flake under full-suite load; passes alone), 0 warnings.
gramps
102cb96b28
