recover_timestamps() left Length null for events consisting of only an
mp4 plus a snapshot.jpg, because the mp4 branch parsed ffprobe's stderr
Duration: line and produced a bogus value when the regex did not match.
Length is decimal(10,2) NOT NULL, so the recovered row failed to insert.
Add mp4_duration() which asks ffprobe for the machine-readable
format=duration, falling back to the human-readable Duration: line, and
always set Length via sprintf('%.2f', ...) defaulting to 0 on failure.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
5e3b0e8524