Subtitles that start in sync and drift further off: stretch them to fit
If the subtitles match at the beginning of a film but are a few seconds off by the middle and worse by the end, a single shift will not fix them. The file runs at a slightly different speed from your video. Tell the tool the correct start time of an early line and a late line, and every line is moved proportionally between them. Jobs with up to 3,000 lines are free in full; bigger jobs are $5, paid once.
- Two points: a line number and its correct start time, early and late in the file
- Every other line moved on the same straight line, before, between and after
- Late line left empty means the last line of the file
- Refused if the points imply speeding up or slowing down by more than double or less than half
- One file at a time; returned in its own format
Why subtitles drift
Drift means the subtitle file and the video run at slightly different speeds. The most common cause is frame rate: films are made at 24 frames per second, but releases for European TV and many European DVDs play them at 25, which makes the whole film about 4 percent shorter. Subtitles timed to one of those versions fall behind or run ahead on the other by a few more seconds every minute. Smaller drifts come from subtitles timed to a different encode or edit of the same film.
Whatever the cause, if the error grows steadily, it is a straight-line problem: each time needs to be scaled, not just shifted. Two correct points define that line.
How to pick the two points
- Open the subtitle file on screen after upload or in a text editor and pick a clear line of dialogue near the start, for example line 12. Note its number.
- Play the video, find that line being spoken, and note the time in your player, for example 00:01:48,200.
- Do the same for a line near the end, for example line 1350, spoken at 01:41:05,600. The further apart the two lines, the more accurate the result.
- Enter both numbers and times. Leave the second line number empty to use the last line of the file.
When stretch is not the right tool
If you already know the subtitles were made for 25 fps and your video is 23.976, choose the frame rate option instead; it applies the exact ratio without any checking. If the error does not grow but jumps at one point, for example after an ad break, use shift with "only lines after". If a release has several scenes cut or added, the drift is not a straight line, and each part needs its own shift.
The tool also refuses points that would speed the file up or slow it down by more than double or less than half; that almost always means a wrong line number. Stretch works on one file at a time, because two points from one film do not fit another episode.
How the tool works, what it costs and how your files are handled is on the Fix Subtitle Sync page; prices for every tool are on the pricing page.
Last updated
Questions and answers
Can ChatGPT fix subtitles that drift out of sync?
It can explain the formula, and on a short file it may apply it correctly. On a full film, scaling and retyping every time by hand tends to produce approximations, skipped lines or a reply that stops partway. This tool computes each new time exactly from your two points.
Why can I not just shift the subtitles?
A shift moves every line by the same amount. If the error grows over the film, any single shift fixes one part and leaves the rest wrong.
Do the two lines have to be the first and last?
No. Any early and late line works, and lines before the first or after the second point are moved on the same line. Points far apart give the best result.
What does it cost?
Jobs with up to 3,000 lines are free in full, which covers most single films. A longer file is $5, paid once, for up to 50,000 lines.
Can I stretch a whole season at once?
No, stretch works on one file at a time. For a season with the same frame rate problem in every episode, the frame rate option handles a ZIP in one job.