Structural errors
Malformed timestamps, reversed times, overlapping cues, blank cues, and broken sequence numbers.
Caption files can break in transit. An edit can shift one timestamp past the next cue, a re-export can duplicate sequence numbers, or a translation can leave an empty cue. Players respond to these faults in different ways. Some skip one cue, while others drop the later cues. A file can therefore work in one player and fail in another.
The validator separates faults by severity. Errors are things a player may refuse: unparseable timing lines, cues that end before they start, overlaps, blanks. Warnings are things a viewer will feel: a cue flashed for 400 milliseconds, a 60-character line that wraps unpredictably, three-line cues that cover the picture.
Automatic fixing is conservative. It renumbers, re-orders by start time, swaps reversed timestamps, trims overlaps, extends short cues into available gaps, and removes empty cues. Each repair is mechanical and has one correct outcome. The tool keeps cue text unchanged because shortening a long line is an editorial decision.
After a fix, the tool validates the file again and reports the remaining wording warnings for human review. Download the corrected file and finish those items in your caption editor.