How to Use This Tool
Downloaded subtitles are out of sync more often than they are right, and the fix depends entirely on which of two problems you have. Getting that diagnosis wrong is why people spend an hour nudging an offset that was never going to work.
Diagnosing it in ten seconds
Play the film and note how far off the subtitles are near the start. Skip to near the end and check again. If the gap is the same, you have a constant offset — use the first tab. If the gap has grown, you have frame-rate drift, and no amount of shifting will fix it because the error is proportional rather than fixed.
Fixing a constant offset
Load or paste your file, then enter the offset in seconds. Negative makes subtitles appear
earlier, which is the direction people get backwards most often. If the subtitle for a line shows
up two seconds before the actor speaks, you want -2. The quick buttons cover the common
amounts, and the before-and-after panel shows the first few lines so you can confirm the direction before
downloading anything.
Fixing frame-rate drift
Switch to the second tab and pick the rate the subtitles were made for and the rate your video actually runs at. Every timestamp is multiplied by the ratio between them. The two rates you will meet most are 25 fps, which is the European broadcast and DVD standard, and 23.976 fps, which is what film transfers use. Converting between them is a 4.3% error — imperceptible in the first minute and five minutes adrift by the end of a feature.
If the subtitles are both drifting and starting at the wrong point, fix the drift first, then re-run the result through the offset tab. Doing it the other way round means recalculating the offset after the rescale changes it.
Formats and what gets preserved
The tool reads SRT and WebVTT and writes either. The difference is small but real: SRT separates seconds
from milliseconds with a comma, WebVTT uses a full stop and adds a WEBVTT header. Feeding one
to a parser expecting the other usually fails silently with no subtitles at all rather than an error.
Formatting tags, positioning and line breaks pass through untouched — only the timestamps change.
Timestamps that would go negative are clamped to zero rather than dropped, so a large negative shift will pile the first few lines at 00:00:00 instead of losing them. That is deliberate: silently deleting someone's subtitle lines is worse than showing them slightly wrong.
