Subtitle Timing Shifter
Shift subtitle timings by a fixed offset or stretch them to correct a frame rate mismatch, and see which cues become invalid as a result.
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Two different desync problems
Subtitles that are wrong by a constant amount throughout need a fixed offset: every cue moves the same number of seconds. Subtitles that start correct and drift progressively worse need a stretch, because the two files were made at different frame rates. Applying an offset to a drift problem fixes the beginning and makes the end worse, which is why it is worth watching both the first and last cue before deciding.
The frame rate ratios are specific
The common conversions come from film and broadcast standards. Film at 23.976 frames per second against PAL at 25 gives a ratio of about 1.0427, which is why a subtitle file from a film release runs progressively ahead of a PAL video. NTSC at 29.97 against 30 gives the 1000/1001 pulldown ratio. These are not arbitrary numbers, and matching the right pair is what turns a progressive drift into a perfect match rather than an approximation.
Two point sync is more reliable than guessing
If you can identify the correct time for one line near the start and another near the end, the offset and the stretch factor both follow arithmetically. This handles any combination of the two problems at once, including cases where the file was both shifted and made at a different frame rate, and it does not require knowing which frame rates were involved.
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Frequently Asked Questions
Should I use an offset or a stretch?
An offset if the error is constant throughout, and a stretch if it grows as the file progresses. Check the first and last cue against the video: if both are wrong by the same amount, offset; if the last is worse, stretch.
What are the common frame rate ratios?
23.976 to 25 is a factor of about 1.0427 and is the usual film to PAL conversion. 25 to 23.976 is its inverse. 29.97 to 30 and 30 to 29.97 use the 1000/1001 NTSC pulldown ratio. Matching the right pair gives an exact fix rather than an approximation.
How does two point sync work?
Give the correct time for one line near the start and another near the end. The stretch factor is the ratio of the intervals and the offset follows from it. This corrects an offset and a drift together without needing to know the frame rates.
What happens to cues that go negative?
A negative start time is invalid in both SRT and WebVTT, and most players reject the file or skip the cue. The tool reports how many would go negative and clamps them to zero so the file stays valid.
Does shifting affect the video?
No. Subtitle files are separate from the video and contain only text and timings. Changing them cannot affect playback of the video itself, so this is always safe to experiment with.
Privacy & Security
Everything runs in your browser; nothing is uploaded.
How to Use
Paste your subtitles and set an offset or a frame rate conversion to correct the sync.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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