FA-77922 / Subtitle cue timing / Member archive
Subtitle frame-rate retiming: rational rate parsing · case 02
NTSC-rate sources written as 30000/1001 retime as if they were exactly 29 fps.
Case contract
Cue times authored against a src frame rate are rescaled for playback at dst by t*src/dst, rounded half up to integer ms. Rates are "N", "N/D", or the aliases "23.976"/"29.97" meaning (N+1)*1000/1001. The end is rounded independently; an end that does not exceed the start becomes start+1.
Why this case matters
Subtitle timing defects shift, hide or overlap captions that viewers depend on for comprehension and accessibility.
One recorded failure
Sample boundary fixtureThis sample comes from the broken implementation of a controlled reproducer.
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| regression: rational rate parsing | [[1, 969]] | [[1, 1001]] | Failed |
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