_on_extract_audio clamped the duration to (timeline_duration - cursor), so with
the playhead within the requested length of the end (or any under-reported
duration) a 30s request was silently truncated to whatever remained — the user
asked for 30s and got 3s with no indication why.
Drop the clamp: pass the requested length straight to ffmpeg, which stops
cleanly at end-of-file if the source is shorter. Then ffprobe the result and,
when it comes up short, say so ("Saved 3.0s — source ended before 30.0s
requested") instead of silently shrinking. When there's room, 30s now yields
exactly 30s.
Adds core.ffmpeg.probe_duration(). Verified end-to-end: a fitting request
returns the exact length; a genuine near-end request returns the available
audio (rc=0) and is reported as truncated.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Ethanfel
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