Fix Video Audio Sync
Pick a video and a shift — its audio is nudged earlier or later in your browser while the picture stays untouched. Nothing is uploaded.
Fix audio that's out of sync with the video
Pick a video, tell it how far to nudge the audio relative to the picture, and get the same clip back with the two lined up. The picture is stream-copied (not re-encoded), so it stays byte-for-byte identical and processing is fast; only the audio track is re-encoded, because its timeline is being rewritten. Everything runs in your browser; nothing is uploaded.
Which way do I shift it?
Watch a moment where a mouth moves or something makes a sharp sound, then pick a direction with the Offset value:
- Sound arrives before the picture (voices are ahead of the lips) → the
audio is early, so delay it with a positive offset (e.g.
200). - Sound arrives after the picture (lips move, then you hear it) → the audio
lags, so advance it with a negative offset (e.g.
-200).
Set the amount in milliseconds (the default) or seconds with the
Unit control — 200 ms is the same as 0.2 s. The range is ±60000 ms
(±60 s); 0 is rejected because it wouldn't change anything.
Worked example: a Bluetooth-mic recording where the voice trails the lips by
about a fifth of a second. Load talk.mp4, set Offset to -200 with
Unit = Milliseconds, and you get talk-synced.mp4 — same video, audio
pulled 200 ms earlier so it matches the lips.
How the shift is done
- A positive offset pads silence at the front of the audio (
adelay), so everything you hear plays that much later. - A negative offset trims that much off the head of the audio and resets its timestamps, so everything plays earlier.
- The video stream is always copied losslessly; the picture never moves or re-encodes.
Notes and limits
- The output keeps the same container (mp4 → mp4, webm → webm). WebM audio is re-encoded to Opus, everything else to AAC.
- This applies one constant offset to the whole clip. If the drift grows over the length of the video (audio slowly sliding out), a fixed shift can't fix it — that needs time-stretching, a different tool.
- Input and output are each capped at 25 MB (the file is processed in your browser's memory).
FAQ
Is my video uploaded to a server?
No — ffmpeg runs inside your browser tab, so the file never leaves your device.
Should I use a positive or a negative offset?
If the sound comes before the picture (you hear the word before the lips
move), the audio is early — delay it with a positive value. If the
sound comes after the picture (lips move, then you hear it), the audio
lags — advance it with a negative value. A few frames is often enough:
one frame at 25 fps is about 40 ms.
What's a typical offset to try?
Bluetooth headphones and speakers commonly add about -150 to -250 ms of
audio lag, so -200 ms is a good first guess. For most other drift, start near
100–200 ms in whichever direction lines the sound up, then fine-tune.
Will nudging the audio hurt the video quality?
No. Only the audio is changed; the picture is stream-copied without re-encoding, so the video quality is identical to the original.
The sync drifts more and more over the clip — will this fix it?
No. This tool applies a single constant shift to the whole clip, which fixes audio that's uniformly early or late. Drift that grows over time means the audio plays at a slightly wrong speed and needs time-stretching instead — a constant offset can't correct it.
Which video formats can I use, and how big can the file be?
Anything ffmpeg can read — mp4, mov, mkv and webm are the common cases. The
output keeps the input's container and is named after the original with a
-synced suffix (e.g. clip.mp4 → clip-synced.mp4). The input and output are
each capped at 25 MB.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool video-audio-sync-offset 'url=https://example.com/input' 'offset=200' 'unit=ms'New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/video-audio-sync-offset/?url=https://example.com/input&offset=200&unit=msMachine-readable descriptor: tool.json — title + parameters JSON Schema for agents.