How to use the Audio–Video Sync Fixer
- Choose the video.
- Enter how far to shift the audio in milliseconds: positive moves it later, negative earlier.
- Click Fix sync and check the result.
- Adjust and repeat until it matches.
Finding the right amount
Watch a moment with a clear sound, like a clap or a "p" sound. If you hear the sound before you see it, the audio is early: enter a positive number, such as 200. If you hear it after, enter a negative number. Most sync problems are between 50 and 500 ms.
Lossless
Both tracks are copied without re-encoding; only their timing changes.
Good to know
Shifting works by changing the audio timestamps; neither the picture nor the sound is re-encoded, so you can repeat the fix as many times as you like without losing quality.
Supported files
MP4, MOV, MKV, WEBM, AVI, WMV, FLV, M4V, 3GP, 3G2, MPEG, MPG, TS, MTS, M2TS, VOB, OGV, MXF, ASF, DIVX, F4V, SWF, DV, MOD, TOD, WTV, RM and RMVB video, with H.264, HEVC, VP8, VP9, MPEG-4, MPEG-2, WMV, Theora and other codecs. AV1 videos cannot be read in the browser yet. Files up to 1 GB each.
Frequently asked questions
The audio drifts more and more over time
That is a frame-rate or sample-rate mismatch, not a fixed delay. Converting the video to MP4 with the Video Converter often fixes drift.
Do I have to pay or sign up to use the Audio–Video Sync Fixer?
No. There is no account, no payment and no watermark. The only limit is 1 GB per file, set by what browsers can handle.
Do you keep a copy of my files?
We never receive them. All processing happens on your device, so there is nothing for us to store or delete.
Can I use it on my phone?
Yes. Open the page in your phone's browser and choose a file. Phones have less memory than computers, so very large files are better converted on a laptop or desktop.