How frame rate conversion works
Every cue timestamp is multiplied by target fps ÷ source fps. For 23.976 → 25 that's a factor of ≈ 1.0427: a cue at 1:00:00 becomes 1:02:34, and the drift that accumulated over the film disappears.
Common conversion pairs
- 23.976 → 25 (NTSC film / web rips → PAL broadcast)
- 25 → 23.976 (PAL → NTSC)
- 23.976 → 24 or 24 → 25 (cinema masters, YouTube exports)
- 29.97 → 23.976 (NTSC camcorder footage → film-rate release)
Diagnose: shift or frame rate?
- Subtitles are equally early/late throughout → use a constant time shift
- Subtitles are in sync at the start, worse at the end → frame rate conversion (this tool)
- Subtitles are in sync in the middle, off at both ends → rare, usually a different cut of the film; look for a different subtitle release