Definition: lip sync
The synchronization of people's lips to their mouths. Maintaining the same rate of speed to synchronize audio and video tracks is always an issue in movie and video production. However, the processing required to upconvert a DVD in a DVD player may delay the video a few milliseconds behind the audio. In addition, the video cable to a ceiling-mounted projector may be considerably long, introducing delay. A/V receivers therefore often have a "LipSync," "A/V Sync" or similar function that delays the audio a variable number of milliseconds to synchronize with the delayed video.