Uploaded subtitles are out of sync or drift - causes and fixes
Uploaded SRT/VTT subtitles drift when the timestamps don't match the actual frame timing of the file the player is using. Re-time the captions against the player file (not against the original cut) and re-upload; many editors let you shift the subtitle track by a fixed offset.
Check these first
- Confirm the uploaded video is the exact file the subtitles were authored against (frame rate, cuts, re-encodes).
- Check whether the subtitles file is valid SRT or VTT (run it through the Caption QA tool).
- Compare subtitle timing at start, middle, and end of the file; drift usually grows over time.
Likely causes
- Subtitles authored against a different cut
If the video was trimmed or re-rendered after authoring, the subtitle timestamps no longer match.
- Frame rate mismatch between editor and player
A 30 fps editor exporting 29.97 fps creates drift of ~1 frame per second.
- Invalid SRT / VTT format
Some platforms silently reject malformed subtitle files; nothing appears.
Fix it
- Re-time the captions against the exact file
Open the exact upload file in your editor, place cues by ear, export SRT/VTT.
Re-time the captions against the exact file - Validate the subtitle file before upload
Use Caption QA to detect timestamp / overlap / duration issues before uploading.
Validate the subtitle file before upload
Prepare a copy in Koldflux, review its output and check the current destination requirements before publishing.
Automate this in Koldflux