100% local & free

Fix Audio Sync in Video — Free

Fix videos where the sound is out of sync with the picture, right in your browser. Only the audio track's timing information is rewritten, so neither video nor audio is re-encoded — completely lossless. Adjust in 10-millisecond steps while checking the result by ear. No upload, everything runs in your browser.

Drop a video / tap to select
Supports MP4 & MOV (H.264 / HEVC, AAC audio) ・ Free, unlimited
Nothing is uploaded — everything is processed in your browser

📖How to use

1

Choose a video

Drag & drop or tap to select the out-of-sync video (MP4/MOV).

2

Play and check the desync

Play the preview and check whether the sound comes earlier or later than the picture. Scenes with lip movement or sharp sound effects make it easy to tell.

3

Match it with the slider

If the sound is early, go +; if late, go −. Adjust in 10 ms steps — the preview switches to the corrected timing instantly, even during playback. Use "Compare with original" for a before/after check.

4

Export and download

Once it's spot on, hit "Export with this correction". Since nothing is re-encoded, exporting takes just a moment. On iPhone, use the share sheet's "Save to Files".

Want to remove the sound? A sister tool in the same series

Otokeshi — Remove Audio from Video, Free

Mute all or part of a video's audio, or beep it out — free, in-browser, no upload

Try Otokeshi

Just want the audio? A sister tool in the same series

Ototori — Extract Audio from Video, Free

Extract a video's audio losslessly — free, in-browser, no upload

Try Ototori

Video facing the wrong way? A sister tool in the same series

Yokotate — Rotate Video Losslessly, Free

Rotate sideways videos without re-encoding — free, in-browser, no upload

Try Yokotate

Video file too big? A sister tool in the same series

Chidimeru — Compress Video, Free

Shrink video file sizes — free, in-browser, no upload

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❓FAQ

Is it really free?
Yes, completely free. No account needed.
Are my videos uploaded to a server?
No. All processing happens in your browser, so your video never leaves your device and your privacy is protected.
Does the picture or sound quality degrade?
No. Otoawase re-encodes neither video nor audio — it only rewrites the audio track's timing information (timestamps). Picture and sound quality lose not a single byte. Video editors re-render everything on export, which degrades quality; Otoawase never touches the actual data.
How does it fix the desync?
Inside a video file, picture and sound live in separate tracks, each with its own timing information saying when to play. Otoawase shifts only the audio track's timing by the amount you choose, so the timing changes without the data being processed at all.
How precisely can I adjust?
In 10-millisecond (0.01 s) steps, up to ±3 seconds. People generally start noticing desync at around 50 ms, so 10 ms steps are plenty to nail it.
If I advance the audio (−), what happens to the beginning?
When you advance the audio, the part that would stick out before the start of the video (at most the correction amount — e.g. the first 0.2 s at −200 ms) is trimmed. It's only the very beginning, so it usually goes unnoticed.
Does it work with .mov files from iPhone?
Yes. iPhone .mov (H.264/HEVC) is supported. Portrait-orientation metadata is carried over, so the exported video keeps its orientation.
Which video formats are supported?
MP4/MOV (ISOBMFF) with H.264 or HEVC video and AAC audio. Phone recordings, screen captures and gameplay videos are almost always in this format.
Can it fix videos where the desync grows over time?
Otoawase fixes constant desync, where the whole track is shifted by a fixed amount. Progressive drift that widens as playback continues (typically caused by mismatched sampling rates during recording) cannot be fixed by a timing shift alone and is not supported.
I want to remove the audio / extract just the audio.
To remove a video's audio, use our sister tool Otokeshi (mute/beep video audio). To extract just the audio, use Ototori (extract audio from video). Both are in-browser and lossless, just like Otoawase.

📚What to know about fixing audio sync

No re-encoding — video and audio stay lossless

Fixing audio sync in a video editor re-encodes the whole video on export, degrading quality every time. Otoawase never touches the video or audio data — it only rewrites the audio track's timestamps. That's why exporting takes a moment and quality stays exactly as it was.

Why does audio go out of sync?

In screen recordings and gameplay captures, picture and sound are recorded through separate paths, so a tiny difference in start timing can remain as a fixed desync. Other causes include Bluetooth earphone latency baked into a recording, editor export settings, and recording on an overloaded phone. Videos with this kind of constant shift can be fixed perfectly with a timing correction.

Plus or minus — which way should I go?

If you hear the voice before the lips move, or an effect before you see it, the audio is early — go + to delay it. If the voice arrives after the lips move, the audio is late — go − to advance it. Unsure? Move about 200 ms in one direction and play: if the desync gets worse, go the other way.

Tune it by ear, live

Otoawase's preview switches to the corrected timing the instant you move the slider. No more export-and-check-again loops. The "Compare with original" button lets you A/B the before and after to hear exactly how much better it got.

In-browser means private

Your video is never sent to a server. Everything runs inside your browser, so even confidential meeting recordings or family videos are safe to work with. No account, no installation.