Sync audio and video tracks
Motion lets you determine how to handle the playback of audio when audio tracks are not in sync with the video. You can skip video frames to resync with the audio, or pause audio playback to avoid skipping frames if the video is out of sync.
Set audio sync preferences
Choose Motion > Preferences, then open the Time pane.
In the Playback Control section, select one of the following:
Skip video frames: Video frames are dropped to enable an uninterrupted flow of audio, for as close to real-time playback as possible.
Pause audio playback: Audio playback pauses when video and audio are out of sync, then begins when audio catches up on the next loop. This enables an uninterrupted flow of video frames (at the expense of playback slowing down) to evaluate the look of your composition.