Sync
When downloaded or generated subtitles start too early, too late or drift progressively because of a framerate mismatch, Sync realigns them automatically with the offline ffsubsync engine. It is the one tool in Tools that needs a license.
What you need
Install FFmpeg and FFsubsync in Settings → Dependencies. Open Tools → Sync and add one subtitle file.
Choosing what to sync against
Sync against offers two references:
- The video — the app uses the video with a matching name beside the subtitle, or you choose the video it belongs to. Pick which audio track to listen to. It is slow — minutes.
- A subtitle file already in sync, or a subtitle track from the video. It is fast — seconds.
Matching listens for when speech happens, not what is said, so a translated subtitle syncs against audio in the original language. When a video contains the very subtitle you are fixing, the app deliberately listens to the audio track, so it does not find a perfect match with itself and change nothing. If there is nothing to sync against, the screen says so.
Options
- Max offset — how far subtitles may move: 30 seconds, 1 minute (the default), 2, 5 or 10 minutes. An offset right at the limit is treated as a failed search and refused, not applied.
- Skip framerate correction — keeps the timing scale and only shifts.
- Use golden-section search — a slower, more precise alignment.
- Use auditok voice detection — for low-quality audio (video sync only).
Running it and saving
Click Sync; it shows progress and has a Stop button. The result is previewed against the original, and Save or Save as… writes it. Subtitles that are blank or would start before 0:00 are dropped by the sync; the app moves any other dropped cues by the same shift, so your subtitles stay matched to the dialogue.