Sync drift
Also known as: multicam drift, camera clock drift
Two cameras recording the same event gradually diverging, so clips aligned at the start of a session no longer line up by the end.
Updated
What it means
Sync drift is a divergence between devices rather than within one clip. Each camera runs on its own clock, and clocks that differ by a fraction of a percent separate steadily across a long session.
It is distinct from Audio drift, where sound and picture inside a single recording come apart. Here each clip is internally fine and the cameras simply disagree with each other.
The effect compounds with session length. A few frames apart after ten minutes becomes a visible offset after an hour, which is exactly when multi camera coverage matters most.
How it works in practice
A shared reference at the start is the standard remedy. A clap, a flash or anything visible to every camera gives a point to align all of them against afterwards.
Repeating the reference periodically is what catches drift rather than merely offset. Two points an hour apart reveal the rate, which is the information needed to correct it properly.
Where cameras support it, setting them from one source before filming reduces the starting error, though Timecode is rarely available on consumer action bodies. Setting the clocks by hand from one phone is the realistic substitute.
What to watch out for
Aligning on a single point hides the problem instead of fixing it. The start matches, the end does not, and the mismatch is blamed on the edit rather than on the clocks.
Dropped frames make it worse and harder to diagnose, since a camera that lost frames is also short rather than merely offset, which Dropped frames explains and a simple shift cannot fix.
Correcting by stretching a clip changes its frame timing, so doing it after any cutting means the marks no longer sit where somebody put them. Sync work belongs before a Rough cut rather than after one.
How RawClip handles it
Clips are aligned by their own timestamps and analysed individually rather than assumed to share a clock, so cameras that drifted apart still contribute. Multi camera coverage of one moment is grouped by content as well as by time, which is what stops two angles of the same trick being read as two separate events.