How to fix subtitles that are out of sync
Updated
First work out whether the drift is constant or growing. If the captions are out by the same amount at the start and the end, shift every cue by that amount — one number, one edit. If the gap grows as the video plays, the subtitles were made for a different frame rate or a different cut, and shifting will not fix it.
Diagnose it first: constant or growing?
Play the first spoken line and note how far off the caption is. Then jump near the end and do the same. Those two numbers tell you which problem you have, and they call for completely different fixes.
- Same offset at both ends — a constant offset. Shift everything. This is the common case.
- Larger offset at the end — a rate mismatch, usually 23.976 against 25 frames per second, or a different cut of the video.
- Correct at the start, wrong only after a certain point — the video was edited after the captions were made.
Fixing a constant offset
This is the one that takes ten seconds. In this tool, the Shift every caption control takes a number of seconds: negative moves the captions earlier, positive moves them later. Enter the offset you measured and apply it.
To get the number precisely rather than by feel, scrub to the exact frame where a line begins and read the playhead, then compare it with that cue's own start time. The waveform makes this easy — the start of speech is visible as the point where the trace jumps out of the quiet.
Cues pushed before zero by a negative shift are dropped rather than piled up at 00:00, and a cue straddling zero is clamped so the part still on screen survives.
Fixing a growing offset
A growing gap means the timings and the video disagree about how fast time passes, which a shift cannot repair — correcting the start makes the end worse. The usual cause is a film transferred between 23.976 and 25 frames per second, which drifts by about four per cent, or roughly two and a half seconds per minute.
The honest fix is to retime against the actual audio. For a short clip it is often quickest to transcribe it again from the video you actually have: the timings then come from that file rather than from a different one. This tool will do that without uploading anything, and you can keep your existing text where the transcription is worse.
Why subtitles drift in the first place
Captions carry timestamps, not a link to the footage, so anything that changes the footage's timeline invalidates them. A different cut, an added intro, a trimmed head, a frame rate conversion, a re-export with different padding — all of them move the speech without moving the timestamps.
That is also why a caption generated against the file you are publishing is reliable in a way a downloaded subtitle file is not.