Why won't my footage sync by audio?

Usually because the clips share no sound: the camera mic was off or on the wrong channel, nothing else was recording, or two lav mics each only heard their own wearer. Very short, quiet or noisy clips also fail to match.

Why does my audio drift out of sync over a long take?

Each device's clock runs at a slightly different speed, so long takes slowly drift apart. Mismatched frame rates (23.976 against 24) or sample rates (44.1 kHz against 48 kHz) cause bigger drift. Sync at the middle of the take or cut it into shorter pieces.

Why doesn't my timecode line up?

Devices that weren't jammed, or were jammed only once in a long day, drift apart. Record-run timecode only counts while recording, so it never matches other devices. Use time-of-day timecode and re-jam after breaks.

Footage won't sync? Common causes and fixes

There's no shared sound

Sound sync can only match clips that heard the same thing at the same time.

The camera mic was off, muted or turned right down. Check the clip actually has audio. Some cameras put scratch audio on channel 2 only, or record silence on a channel.
Nothing else was recording. A clip shot while no other camera or recorder was rolling has nothing to match. Place it by its timecode or recording time instead.
Two lav mics on two people. Each mostly hears its own wearer, so they barely match each other. A camera rolling at the same time links them.

The sound is too short, quiet or noisy

Clips of a second or two rarely have enough sound to match with confidence.
Wind, generator hum or a loud room can swamp the scratch track. Clips with clear speech or a clap sync best.
A camera across a big room hears a lot of echo. It'll usually still sync, but with less confidence.

It syncs at the start and slips later (drift)

Every recorder's clock runs at a slightly different speed. Over a long take (20 minutes or more) two devices can drift apart by a frame or more.

Sync at the middle of the take so the error is split, or cut long takes into shorter pieces.
Check frame rates match: 23.976 footage conformed to 24 (or 29.97 to 30) drifts by about 3.6 seconds an hour.
Check the sample rate is what you think: a 44.1 kHz file treated as 48 kHz plays fast.

Phone or screen-recorded footage

Phones record a variable frame rate, which editors handle differently, so their footage can drift or sit slightly off. Converting it to a constant frame rate before editing helps.

Timecode doesn't line up

Not jammed, or jammed only in the morning: devices drift apart over the day. Re-jam after breaks.
Record-run timecode: it only counts while recording, so it doesn't match other devices at all. Use time-of-day (free-run) timecode for syncing.
Drop-frame against non-drop-frame, or a 50p camera recording 25 fps timecode: make sure your software reads them correctly.

Clips are out by a tiny amount

Some cameras' AAC audio has a few milliseconds of padding at the start that editors treat differently, which can leave clips 20 ms or so out.
Cameras can only start on a whole frame, so a camera clip can be up to half a frame from the exact sound position. Recorder audio can be placed to the sample in most editors.

A file won't open at all

It may be damaged, or still copying from the card. Copy it again from the card if you can, and check it plays in another app.

How Clam Sync helps

Clam Sync tells you what happened to every clip instead of leaving you to spot it: synced clips in green, drifting clips flagged, clips placed by timecode or recording time marked, and anything it couldn't place parked at the end of the timeline with the reason in a report. See troubleshooting Clam Sync.

Try Clam Sync free

Footage won't sync?