How to Fix Out-of-Sync Subtitles
Every out-of-sync subtitle file is one of three patients, and the treatment only works if the diagnosis is right. The good news: telling them apart takes two observations and thirty seconds.
Quick answer: Note how wrong the timing is at two points. Same error everywhere → constant offset, shift everything. Error grows → drift, resync with two sync points. Off by a steady ratio (4% = PAL speedup) → frame-rate conversion.
Step 1 — take two notes
Pick a line near the start and one near the end. At each, write how far the subtitle is off and in which direction. “2 seconds late at minute 2, 2 seconds late at minute 80” is a different patient from “1 second late at minute 2, 8 seconds late at minute 80”.
Case A — same error everywhere: shift
A uniform delay means the subtitle was timed for a version of the video with a different beginning — a streaming bumper, a shortened intro, a different region's cut. Apply a constant offset (negative to make subtitles earlier, positive to delay them) and the file is fixed everywhere at once.
Case B — growing error: two-point resync
When the error grows, the subtitle's clock runs at the wrong rate. Two sync points — “this line appears at X, it should appear at Y” twice — define a linear mapping that shifts and stretches every timestamp to match. Beyond the second point the mapping extrapolates, which is exactly what you want for the rest of the film.
Case C — a steady ratio: frame rate
A subtitle that drifts by about 4.166% was timed for 23.976 fps film and is playing with 25 fps PAL-speedup video (or the reverse). Direct frame-rate conversion compresses or stretches every time by the exact ratio — the classic fix, and more reliable than eyeballing two points.
Confirm before saving
- Preview the first, middle and last cues with their new times
- Direction check: making subtitles earlier means subtracting from every time
- After the fix, spot-check the same two notes you took in step 1