Replaces whisper-server --convert. A zero exit that wrote nothing is an error.
Also fixes the red test's stub, which wrote an empty file and so (correctly)
tripped the no-output check.
Checked against real ffmpeg on iguana with the same argv: AAC .m4a in,
pcm_s16le 16000 Hz mono WAV out, duration preserved.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Cover art is not video; non-zero exit is the file's fault (ErrUnreadable),
a missing binary / cancelled ctx / bad output is ours. WaitDelay bounds a
cancelled probe whose child holds the pipe open.
Checked against real ffprobe on iguana: JSON shape matches the fixtures and
/etc/hosts exits 1 with 'Invalid data found when processing input'. The unit
tests drive a stub process; ffprobe is not installed on koala.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
mathiasandClaude Sonnet 5.5