Fix subtitles that drift out of sync
When the delay grows through the film, set the right time of one line near the start and one near the end, and every line in between is stretched to match.
workbench · no file open
.srt .vtt .ass .ssa .sbv
Drop a subtitle file here
Drop the video too to preview the lines over it and to set each start and end by its sound. Nothing is uploaded. No subtitle yet? Make one from the audio with transcribe.tools.
Formats it reads and writes
| Format | Timecode | Kept when saved here |
|---|---|---|
| SRT.srt | 00:01:23,450 | Italic, bold, underline, font tags |
| WebVTT.vtt | 00:01:23.450 | Italic, bold, underline |
| ASS.ass .ssa | 0:01:23.45 | Styles, actors, {\an8} and {\pos} when the file was ASS |
| SBV.sbv | 0:01:23.450 | Text only |
Reading speed and timing limits
The presets of the checker: Netflix English. Every number can be changed.
| Limit | Adult | Children’s |
|---|---|---|
| Characters per line | 42 | 42 |
| Lines per subtitle | 2 | 2 |
| Reading speed, CPS | 20 | 17 |
| Shortest on screen | 833 ms | 833 ms |
| Longest on screen | 7 s | 7 s |
| Gap between lines (2 frames at 24 fps) | 83 ms | 83 ms |
Source: Netflix Partner Help Center, English (USA) Timed Text Style Guide; Netflix Partner Help Center, Timed Text Style Guide: General Requirements; Netflix Partner Help Center, Timed Text Style Guide: Subtitle Timing Guidelines, opened .
Check a file against these limitsHow to use the fix subtitle sync
- 00:01
Mark an early line
Pick a line in the first minutes and set the time you actually hear it.
- 00:02
Mark a late line
Do the same near the end. The panel shows the stretch and offset it will apply.
- 00:03
Resync and check
Apply, play a few lines in the middle, and download. Undo if a point was off.
Why do subtitles start in sync and drift later?
The two usual causes are a different frame rate and a different edit. A subtitle timed for a 23.976 fps release played over a 25 fps release runs about 4% slow, so it falls a little further behind every minute; on a two-hour film that is close to five minutes by the end. A different edit (an extra scene, a shorter intro) gives a delay that jumps at one point instead of growing.
How does two-point sync work?
Pick a line near the start and note when it is actually heard in your video, then do the same for a line near the end. The editor draws a straight line through the two corrections: every time in the file is moved and stretched along it. That fixes a constant delay and a steady drift together, and the panel shows the stretch factor and the offset before you apply it.
When should I use the frame-rate change instead?
When you know both rates, for example from the file names (a “25fps” or “PAL” release against a 23.976 subtitle). Choose the rate the subtitle was made for and the rate of your video, and every time is scaled by the ratio. 23.976 and 29.97 are used as the exact NTSC values, 24000/1001 and 30000/1001, so there is no rounding drift over a long film.
The drift is fixed but a few lines are still off. What now?
That usually means the edit differs at one point. Find the first line that is off and shift only the lines from that time on. If lines now overlap or touch, the Fix panel closes overlaps to a gap you choose; Netflix’s timing guide, for example, asks for a minimum of 2 frames between subtitles.
Questions
How precise do the two points need to be?
Choose lines far apart, one in the first minutes and one near the end, and set each start where the first syllable is heard. An error of a tenth of a second on points an hour apart gives a stretch error too small to see.
Can I take the times straight from the video?
Yes. Load the video, pause where a line is heard, and press Video time next to that point. Selected line fills the time in the file from the line you picked in the list.
Which frame rates are listed?
23.976, 24, 25, 29.97, 30, 50, 59.94 and 60 frames per second, which cover film, PAL, NTSC and most web video.
Will two-point sync fix subtitles from a different cut?
Only if the difference is a steady drift. Missing or extra scenes need a shift from the point where the scenes differ; you can combine both in the same session.
Can I undo a resync?
Yes. Undo restores the file as it was before the resync, so you can try another pair of points.
More subtitle tools
- Subtitle editorEdit lines over your video, then save as SRT, VTT, ASS or SBV.
- SRT to VTTWebVTT for HTML5 players, with header and timestamps rewritten.
- Shift timingMove every line earlier or later, or only from a point on.
- ASS to SRTPlain SRT from ASS or SSA, with italics and line breaks kept.
- Merge and splitJoin two parts, combine two languages, or cut a file in two.
- Line length and CPSCharacters per line, reading speed and timing against your limits.
Sources
- Timed Text Style Guide: Subtitle Timing Guidelines
Subtitles must have a minimum of 2 frames between them, at any frame rate; gaps should be either 2 frames or half a second or more.
Netflix Partner Help Center. Opened on .
Style limits differ between broadcasters, languages and clients; the presets are one published guide, and every limit can be changed. Your files never leave your browser.