Find where your SRT or VTT timing breaks

First work out which kind of problem it is. If every line is early or late by the same amount, shift all timestamps by that offset. If the captions start fine and get worse over time, the timing needs rescaling or realigning to the audio, usually because of a frame-rate change or an edit. Checking the file here catches problems inside it, such as overlaps and lines that read too fast, but a text check cannot tell whether the file lines up with your video. With a free account you can upload the media and download a repaired, audio-aligned SRT or VTT.

The most common causes are a re-edit after the captions were made (a trimmed intro shifts everything), a frame-rate mismatch such as 23.976 vs 25 fps (the drift grows through the file), a format conversion that rounded timestamps, and machine-translated subtitles whose lines no longer fit the original timing.

Both are plain-text caption files with numbered cues and start and end times. SRT uses a comma before the milliseconds (00:00:01,000) and has no header. WebVTT starts with a WEBVTT line, uses a period (00:00:01.000), and supports styling and positioning. Most video platforms accept both; browsers use VTT for HTML5 video.

It analyzes your SRT or VTT caption file for timing issues — overlapping cues, cues that read too fast, suspiciously long gaps, and duration outliers. The free preview shows how many cues have issues, the top issues, and the first 5 cues. It reads only the caption file, so it cannot tell whether the captions match your audio: a file that is late by the same amount everywhere, or stretched by a frame-rate mismatch, passes cleanly. Audio-aligned repair (the actual fix) requires a free signup so we can match cues to your media's real word timings.

A real fix needs your audio or video so we can align cues against the actual word timings — not just heuristics. The signed-in flow lets you upload media, and we produce a repaired SRT/VTT you can download. The preview here catches problems inside the file itself; whether it is in sync with your media can only be measured against the media.

Up to 1 MB of SRT or VTT text in the free preview — that covers most full-length episodes and movies. Larger files work after signup.

Yes, the diagnostic preview is stored for 30 days so you can continue from where you left off after signup.

Yes. The diagnostics work on caption files in any language. The audio-aligned repair (after signup) matches the captions to the spoken audio, so the caption file normally needs to be in the same language as the audio.