When the sound comes before or after the picture, lips move out of step with words and a door slams before it closes. This page moves the sound to where it belongs, by as little as a millisecond, and lets you hear the result as you change it. A plain shift saves by changing only the sound's timestamps: the picture and the sound are copied exactly as they were, so nothing is lost and even a long video saves in moments. It is free to use, with no account and no upload limit, and it runs entirely in your browser: nothing is uploaded, and while the page stays open, a feature you have already used keeps working offline.
Phones record at a variable frame rate to save power, and some editors and players assume a fixed one, so the picture slowly slides against the sound. Screen recordings made with OBS or a game recorder can start the sound late when the audio device takes a moment to open, or drift when the computer is busy. Bluetooth headphones add their own delay of 100 to 300 ms, so a video can sound out of step on them but fine on speakers; check on speakers before fixing the file. Converting or downloading a video can also drop the information that held the sound back, and a camera and a separate sound recorder each run on their own clock, which drifts apart over a long take.
- Does fixing the sync lower the video's quality?
- Not for a plain shift. The picture and the sound are copied from the file as they are; only the time the sound starts at is changed. A drift fix or a separate recording needs new sound, so the sound is encoded again (AAC, or Opus in a WebM), while the picture is still copied untouched.
- Should I move the sound earlier or later?
- If you hear things after you see them, the sound is late: move it earlier, which is a negative number. If you hear a clap before the hands meet, move it later. Small amounts matter: most people notice the sound being 45 ms early or 125 ms late.
- The sound is in step at the start but not at the end. What do I do?
- That is drift. Set the amount that is right at the start, tick "The sound drifts", then go near the end and set the amount that is right there. The sound is stretched or squeezed very slightly, usually by well under one percent, so it moves steadily from one to the other; at that size the change in pitch cannot be heard. Drift fixes work on videos up to half an hour long.
- How does lining up a separate recording work?
- The page looks for the moments where sounds start, such as words, claps and footsteps, in both the camera's sound and the recording, and finds the position where the two patterns match best, to the millisecond. A clap at the start of the take makes it surer. The recording then replaces the camera's sound in the saved video. It needs the camera's own sound to compare with, and works for videos up to half an hour long.
- Will the fixed video stay in sync in every player?
- Yes. In MP4 and MOV a sound that starts after the picture is held back by an edit list, which every common player follows; in MKV and WebM each piece of sound carries its own time. A video with its sound moved earlier simply loses the part that would come before the picture starts.
- Is my video uploaded anywhere?
- No. The video is read and saved by your browser, on your computer; nothing is sent anywhere, so there is no upload to wait for either. Only the main picture and sound tracks are kept in the saved file.