The video starts fine, but later the lips move and the sound arrives half a second late, or the whole video's audio is slightly behind. This page explains the most common causes and how to deal with each.
Two cases: a constant offset, or drifting
- The whole video is off by the same small amount: usually the audio was recorded separately, or something shifted in the edit. Easy to fix: move the whole audio track a little earlier or later.
- Fine at the start, worse and worse later: this is variable frame rate, and the most common case. Explained below.
What variable frame rate is
A normal video has a fixed 30 frames every second. Some recording methods save resources by recording fewer frames when the picture is simple and more when it's complex; that's variable frame rate. The audio is continuous, but the frame count fluctuates, and editing software lays the frames out at a fixed rate, so the drift grows. It's most common in:
- Screen recordings on computers and phones
- Recordings from Zoom, Google Meet, Teams and other video calls
- Some Android camera apps and some dashcams
- Saved livestreams
What you can do yourself
- Convert to constant frame rate first: open the file in the free tool HandBrake, set the frame rate to Constant Framerate, choose 30, and export. Then edit the converted file; most of the time it lines up.
- Align manually in the edit: find a distinct sound (a clap, a door), and line the audio waveform up with the picture. Enough for a constant offset.
- Avoid it when recording: use the phone's built-in camera app; in screen recording software, turn on the constant frame rate option if there is one.
When to get help
If the video is long, comes from many sources (several phones plus a recorder), or still won't sync after conversion, it's faster to hand it to an editor. When we edit, we convert all footage to a consistent frame rate before starting. If the file won't open, stops halfway, or has sound but no picture, that's file damage, not a sync problem: send it to the video repair site for assessment.
Frequently asked questions
It's in sync on my phone but not on the computer. Why?
Typical of variable frame rate. The phone's player corrects it on the fly; desktop editing software doesn't. Convert to constant frame rate and it's fine.
We filmed with two phones. How do we sync the audio?
Clap once at the start where both phones can see it, and align on the clap in the edit. More multi-camera tips in filming tips that make editing easier.
Should we convert before sending you the footage?
No, send the originals. Conversion loses quality; we'd rather handle it from the original files.
