Resync Subtitles
Automatically detect and fix out-of-sync subtitle timing against your video's audio
Drop your subtitle file here
or click to browse (multiple files supported)
Supported: SRT, VTT, ASS, SSA, SBV, SUB, SMI, SAMI, LRC, TTML, ITT, DFXP
Drop the matching video or audio file
or click to browse (multiple files supported)
Supported: MP4, MOV, MKV, WEBM, AVI, MP3, WAV, M4A, AAC, OGG
Drop a subtitle file to detect its sync.
About Resync Subtitles
Resync Subtitles automatically detects and fixes subtitle timing drift by analyzing your video or audio file's speech and comparing it against your subtitle file's cue timing, no manual guesswork, no typing an offset by hand.
What is automatic subtitle sync?
When a subtitle file doesn't match its video release exactly (a different cut, a re-encode, or a PAL/NTSC framerate mismatch) every line runs early or late by a consistent amount. Resync Subtitles listens for speech in your media file and correlates it against your subtitle's cue timing to detect that offset (and, when relevant, a small framerate correction) automatically.
When to use this tool
- Downloaded a subtitle file that runs a few seconds ahead or behind your video
- A subtitle was made for a different release (theatrical cut vs. extended, PAL vs. NTSC)
- You don't know the exact offset and don't want to guess with manual shifting
- You want a quick spot-check against real playback before trusting the fix
How the detection works
Resync Subtitles runs voice-activity detection on your media's audio track entirely in your browser, builds a simple speech-timing signal, and cross-correlates it against your subtitle's cue timing to find the best-matching constant offset, checking a few common framerate ratios along the way. A confidence score tells you how sure the detection is; low-confidence results are flagged so you're never silently handed a bad guess.
What this tool fixes (and what it doesn't, yet)
v1 detects a constant time offset, optionally combined with a common framerate mismatch (like 24 vs 23.976 fps). It does not yet handle subtitles that drift non-uniformly across a file (for example, scenes cut for a different release), for that, adjust manually with Shift Subtitles once you've isolated the affected range.
Common use cases
Downloaded subtitles
Fix subtitles grabbed from a different release than your video file.
Framerate mismatches
Correct PAL/NTSC-style timing drift automatically.
Re-encoded videos
Re-align subtitles after a video has been trimmed or re-encoded.
Frequently Asked Questions
How does automatic subtitle sync work?
SubtitleKit detects speech in your video or audio file using voice-activity detection, then compares that timing against your subtitle file's cue timing to find the offset that best lines them up, all inside your browser, nothing uploaded.
Is my video uploaded anywhere?
No: detection runs entirely client-side in your browser. Your video, audio, and subtitle files never leave your device.
What if the detected sync looks wrong?
You can adjust the offset manually before downloading, or use the dedicated Shift Subtitles tool if you know the exact correction you need, it can also preview the shift against your own video.
Does this fix subtitles that drift throughout the file, not just a constant offset?
Not yet: v1 handles a constant offset and common framerate mismatches. Subtitles that drift non-uniformly (for example, from scene cuts) aren't corrected automatically.
What file formats are supported?
Any timed subtitle format SubtitleKit already supports (SRT, VTT, ASS/SSA, and more) alongside common video and audio formats.
Tips
Use the exact video or audio file the subtitle was meant for, if you have it, a trailer or a clip won't have enough matching speech.
If detection comes back uncertain, try Shift Subtitles with a manually-measured offset instead.
Always spot-check a couple of points before downloading, the preview player lets you jump straight to them.
