Subtitle drift calculator
For subtitles that start in sync and slowly drift. Two sync points give you the speed and offset, a corrected .srt and a check that one fix is enough.
How it works
A plain offset only fixes subtitles that are late by the same amount everywhere. When they are fine at the start and seconds off by the end, the speed is wrong too — usually a different frame rate (25 vs 23.976 fps) or a different cut of the video.
How to use it: pick a line near the start and one near the end. Write the time shown in the SRT and the time the line is really spoken in the video (pause your player). Open or paste the SRT and press Calculate and fix. Download the fixed file.
Add a third point from the middle to test the fix. If it is more than 0.2 seconds off, one straight-line correction cannot fix the file: the video was edited, or has ad breaks, and needs retiming section by section.
FAQ
Is my file uploaded?
No. It is calculated in your browser.
Can it tell the original frame rate?
No. An SRT has no frame rate. If the speed ratio matches a common pair such as 25 → 23.976 fps, it says so as a likely cause.
Will it fix every file?
Only files with a steady drift. Edited videos need section-by-section work.