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Open the video, find how far the sound is ahead or behind, check it in slow motion and save a new file with the picture untouched. Nothing is uploaded.
When audio and video are out of sync, first check whether the fault is in the file or in the way it is being played. If the same video is out of step on your phone, your laptop and in another app, the file itself is wrong: open it here, move the sound until the words meet the lips, and save a corrected copy. If it is only wrong on one TV, soundbar, pair of headphones or app, the file is fine and that playback chain is adding delay, which is fixed in that device’s settings.
For a file, the tool above does the fiddly part. Detect automatically looks for sharp sounds and the moments in the picture that made them, and the clap method lets you pick the exact frame by eye. You then nudge the sound Earlier or Later in 10 ms or 1 ms steps, watch the result at ¼ speed, and press Export video. The picture is copied as it is, and when only the timing changes the sound is copied too, so nothing is re-encoded.
For playback problems, the audio delay test puts a number on the lag, and the guides below show where that number goes on a TV or soundbar, with Bluetooth headphones, in VLC or in OBS. Sound that starts in sync and slowly slips away is a different fault called drift, covered on fix audio drift.
Fix audio sync
These steps fix the file itself, so it plays correctly everywhere. If the video is only wrong on one device, start with the audio delay test instead.
Drop the clip onto Drop a video to fix its sound, or press Choose a video (Ctrl/⌘+O). MP4, MOV, MKV and WebM open directly; AVI and camcorder files are converted on your device first.
Press Detect automatically (A) and, if the result looks right, Use this. If there is a clap or a hit, press Jump to the clap (C), step to the frame of contact with , and . and press This frame is the clap (K).
Play a moment where someone speaks clearly. Press Earlier or Later ([ and ]) to move the sound 10 ms at a time, add Shift for 1 ms, or type the number of milliseconds. Replay around here (L) and the ½× and ¼× speeds make small gaps obvious.
Press Export video (Ctrl/⌘+Enter), then Download video. On a phone, use Share to save the new copy to your photos.
This ten-second check saves a lot of wasted effort. Play the same file on a second device, ideally with its own speakers rather than headphones. The answer tells you where to look.
| What you notice | Most likely cause | Where to fix it |
|---|---|---|
| Out of sync on every device and in every app | The file: a camera, an export or a recording app wrote the sound at the wrong time | Here, with the tool above |
| Starts in sync, worse after a few minutes | Drift: two clocks running at slightly different speeds, or a variable frame rate | Fix audio drift |
| Only with wireless headphones or speakers | Bluetooth buffering, typically a tenth to a third of a second | Bluetooth audio delay |
| Only on one TV, soundbar or receiver | Picture processing in the TV, or decoding in the soundbar | TV and soundbar delay |
| Only in one streaming app | The app, the stream or the audio format it sends | Streaming apps |
| Only in your own recordings from OBS | A webcam or capture card that delivers its picture late | OBS audio delay |
| Subtitles out of step, not the sound | Subtitles made for a different cut or frame rate | Subtitle sync |
It is easy to get this backwards, so think about what you hear. If you hear a word before the mouth makes it, the sound is early and needs to play later. If the mouth moves first and the word follows, the sound is late and needs to play earlier. In the tool, a positive number plays the sound later and a negative one plays it earlier, and the badge on the preview says it in words, such as “Sound 120 ms earlier”.
Moving the sound is the usual fix, because the picture holds key frames that can only start in certain places, while sound can start anywhere. Shifting the sound by a value is exactly equivalent to shifting the picture the other way, so you lose nothing by always moving the sound.
People are more forgiving of sound that arrives slightly late than slightly early, because in real life light reaches us before sound. In practice a sound that leads the lips by a couple of frames already looks wrong, while one that trails by a little longer can pass. When you fix a file, aim for the offset that looks right on close-ups of speech, and check it on a hard consonant such as a “p” or a “b”, or on a clap.
A constant offset is one number for the whole video. If the gap grows as the video goes on, it is drift, and a single number won’t cure it: set two sync points with Set point A and Set point B under Sound drifts over time, as fix audio drift explains.
Video files store a time for every frame and every slice of sound. Fixing an offset only changes the sound’s times, so the new file holds the original compressed picture and, by default, the original compressed sound, with the shift recorded in the file’s edit list. Players such as browsers, QuickTime, VLC and phone galleries read that list.
If you only need a number for a player rather than a new file, Copy ms puts the current offset on your clipboard, ready to type into VLC, OBS or an editor.
Either the file stores the sound at the wrong time (a camera, a recording app or an export put it there), or something in the playback chain delays it: Bluetooth headphones, a soundbar, a TV’s picture processing or a struggling app. Playing the file on a second device tells you which.
Move the audio. It gives exactly the same result as moving the picture the other way, and sound can start at any moment, while a video’s picture can only start cleanly on certain frames.
Let Detect automatically suggest a number, or use a clap: Jump to the clap, step to the frame where the hands meet and press This frame is the clap. Then confirm by eye on clear speech, nudging in 10 ms steps.
No. The picture is copied, never re-encoded, and with Copy (lossless) the sound is copied too. Only drift correction or Rebuild encode the sound again, at a high bitrate.
Nothing in the file. The TV or the speaker connected to it is adding delay. Measure it with the audio delay test and enter the number in the TV’s or soundbar’s audio sync setting.
Yes, in a recent Safari or Chrome. The timeline, the nudge buttons and slow motion all work by touch, and Share saves the result to your photos.
No. Your browser opens, analyses and writes the file on your device. Nothing about it is sent anywhere.