normalize_segments repairs what Whisper actually emits: an end timestamp of
-1 when the closing token is never predicted (usually the trailing chunk),
out-of-bounds and inverted spans, and blank text. Left alone these produce
malformed subtitles.
It also warns when chunk starts are non-monotonic, which is the cheap signal
that start_ts is window-relative rather than absolute -- that would misplace
every cue past 0:30, and it should surface as a log line rather than a user
report.
Timestamps convert to integer milliseconds before splitting into fields;
formatting the seconds field directly renders 3599.9996 as "00:59:60.000".
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
