Renumber and repair a subtitle file
Clean up a subtitle file that editing has broken: renumber from one, sort by start time, close overlaps, drop empty and duplicated cues, and see what problems are left.
How subtitle files break
Hand editing leaves gaps and duplicates in the numbering, cues that overlap in time, cues with no text at all and lines repeated twice. Some players stop rendering partway through a file like that.
What gets fixed automatically
The file is sorted by start time and renumbered from one, and a cue that runs into the next one has its end trimmed back. Empty cues, duplicates that repeat the previous line while overlapping it, and cues shorter than your minimum can all be dropped.
Reading the report
Problems that remain are listed cue by cue. Readability limits — under half a second on screen, a line over 42 characters, more than two lines — are reported rather than changed, because fixing them means rewriting the text.
Frequently asked questions
Does broken numbering actually matter?
Most players tolerate it, but several editors and authoring tools reject a file with duplicated or missing numbers. Renumbering before you hand the file over avoids the argument.
How are overlaps closed?
The end of the earlier cue is trimmed to just before the next cue starts (one millisecond by default). Start times are never moved, so nothing drifts out of sync with the audio.
Are my files uploaded to a server?
No. Everything runs as JavaScript inside your browser and the file contents never leave your machine, which makes it safe for unreleased scripts and confidential recordings.
Is it free? Do I need to sign up?
It is free, needs no account and nothing to install, and there are no usage limits.