Audio drift is a synchronization error that changes progressively as playback continues. Sound and picture may start aligned, then separate over minutes, unlike a fixed offset that stays approximately constant. Different effective clock rates, incorrect timestamp interpretation, resampling problems or stream discontinuities can contribute. The term describes the changing relationship rather than proving a particular cause. Restarting playback or seeking may temporarily restore alignment if the player re-establishes timing, but that observation is evidence for diagnosis rather than a permanent correction of the underlying problem.
Two timelines must remain aligned
Audio samples and video frames have timestamps and are presented against a playback clock. Small rate differences accumulate if they are not corrected. A mismatch that seems negligible for a short clip can become obvious during a long programme. Proper playback must manage timing continually rather than synchronising the first sound and picture and then treating the streams independently.
An offset cannot correct a slope
Moving audio by a fixed number of milliseconds can align one moment while leaving later moments wrong if the error keeps growing. Likewise, a subtitle offset is unrelated to audio-clock stability. Distinguish smooth progressive drift from an abrupt jump after an advertisement or damaged segment; the latter suggests a discontinuity or transition problem rather than a constant rate mismatch.
Record behaviour over time
Note whether alignment changes after several minutes and whether pausing, seeking or switching outputs resets it. Compare another long item and, where available, another supported playback engine without changing several variables together. If every source drifts only on one output path, investigate that route. If only one recording drifts across players, inspect its timing and production history.
An illustrative example
A long interview begins in sync, but the voice is noticeably late after half an hour. Seeking briefly restores alignment before the error grows again. A fixed audio offset can improve one point but cannot hold the whole interview aligned, making a timing-rate investigation more useful than repeated manual adjustments.
Practical actions
- Measure alignment at several playback times.
- Record whether seeking resets the error.
- Compare a second long programme and another supported output path.