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About this tool
Shift, scale, and correct subtitle timings with range targeting, QA checks, and export-ready SRT output.
The Subtitle Timing Adjuster re-times an SRT file by applying a millisecond offset, a percentage speed scale, or a frame-rate ratio such as 23.976 to 25 fps, to every cue or only to a chosen cue range. It parses standard hh:mm:ss,mmm timecodes, recalculates them, and rewrites a clean, renumbered SRT you can paste straight back into your player or editor. Editors and fansubbers use it when captions drift or arrive out of sync with a re-encoded video.
Open Subtitle Timing Adjuster on AltFTool — it loads instantly in your browser.
Upload or drag in the file you want to work with.
Adjust the settings and preview the result.
Download the finished file to your device.
A percentage scale and a source-to-target fps ratio stretch or compress the whole timeline, which is what progressive desync actually needs.
Start and end cue numbers confine the shift, so one bad section can be corrected without disturbing timings that are already right.
It counts overlapping cues, cues shorter than 0.7 seconds and lines exceeding 20 characters per second, so readability problems surface before delivery.
Enter a positive offset in milliseconds to push every cue later, and a negative one to pull them earlier — 2 seconds is 2000. A constant offset is the right fix only when the gap stays the same from the first line to the last.
That is a frame-rate mismatch, usually a file timed for 23.976 fps played against 25 fps or the reverse. Timecodes are rescaled by the source-over-target ratio, which corrects the drift proportionally instead of moving everything by a fixed amount.
The QA panel flags any cue above 20 characters per second, along with cues that last under 0.7 seconds. Broadcast guidelines typically sit in the 17–20 cps range for adult programming, and lower for children's content.
Yes. With overlap removal on, any cue that would start before the previous one ends is pushed back to leave a minimum gap, 20 ms by default, and cue numbering is rebuilt sequentially on export.