Audio goes out of sync when the video and sound are recorded or processed at different speeds. To prevent it, use constant frame rates, record sound the same way throughout, make a clear sync mark at each take, and keep clip lengths manageable.
Why Sync Problems Happen
There are several common causes. Variable frame rate files, often from phones and screen recorders, confuse editing software. A separate audio recorder runs on its own clock, which can drift slightly over a long take. A mismatch between the project settings and the footage, such as a project set to a different frame rate, can also create gradual drift. Wireless microphones can add a small delay as well.
Prevention Steps During Recording
- Use a fixed frame rate such as 24, 25 or 30 frames per second, and keep the same rate for the whole project.
- Set the shutter speed and other options before recording, rather than switching modes mid-take.
- If you use an external recorder, record a scratch track on the camera too, even if it is poor quality. This gives your editor a guide for matching.
- Make a sync mark: a clap, a slate or a snap of the fingers at the beginning of each take, visible and audible on both devices.
- Match the audio sample rate across devices, typically 48 kHz for video work.
- Use fully charged batteries and plenty of storage space, since some cameras split files when they hit a size limit and may drop frames.
- Keep clips shorter where possible, as drift grows with duration.
Fixing Problems in Editing
| Situation | Approach |
|---|---|
| Constant offset | Slide the audio until the clap lines up |
| Gradual drift | Match both ends of the clip and adjust speed slightly |
| Variable frame rate video | Convert to constant frame rate before editing |
| Multiple devices | Use the editor’s automatic waveform sync |
Good Habits
- Wireless microphone delay is usually small, so test before an important shoot and note the offset.
- Name files clearly so you can match video and audio quickly.
- Do a short test recording and play it back on a computer, not only on the camera screen.
When you plan a long shoot, schedule short breaks to check files on a computer. Look at the waveform of the camera audio against the external recording to see whether the two still line up. Catching a drift early lets you change settings or batteries before the whole session is affected, and it costs only a few minutes.
FAQ
Why does the sync drift later in a long clip?
Devices use slightly different clocks. Over long takes the difference adds up, so shorter takes and a fresh clap before each take help.
Do I need timecode?
Not for simple projects. Timecode helps with multiple cameras and recorders, but a clap and waveform sync is enough for most small productions.
The Short Version
Use constant frame rates, match sample rates, record a scratch track, clap at every take and keep clips short. Convert variable frame rate files and sync by waveform in editing if needed.
