Audio-to-video synchronization

Audio-to-video synchronization (AV synchronization, also known as lip sync, or by the lack of it: lip-sync error, lip flap) refers to the relative timing of audio (sound) and video (image) parts during creation, post-production (mixing), transmission, reception and play-back processing. AV synchronization can be an issue in television, videoconferencing, or film.

In industry terminology, the lip-sync error is expressed as the amount of time the audio departs from perfect synchronization with the video where a positive time number indicates the audio leads the video and a negative number indicates the audio lags the video.^[1] This terminology and standardization of the numeric lip-sync error is utilized in the professional broadcast industry as evidenced by the various professional papers,^[2] standards such as ITU-R BT.1359-1, and other references below.

Digital or analog audio video streams or video files usually contain some sort of synchronization mechanism, either in the form of interleaved video and audio data or by explicit relative timestamping of data.

^ "ITU-R BT.1359-1, Relative Timing of Sound and Vision for Broadcasting" (PDF). ITU. 1998. Retrieved 30 May 2015.
^ Patrick Waddell; Graham Jones; Adam Goldberg. "Audio/Video Standards and Solutions A Status Report" (PDF). ATSC. Archived from the original (PDF) on 17 February 2016. Retrieved 4 April 2012.

[BT1359-1] "ITU-R BT.1359-1, Relative Timing of Sound and Vision for Broadcasting" (PDF). ITU. 1998. Retrieved 30 May 2015.

[2] Patrick Waddell; Graham Jones; Adam Goldberg. "Audio/Video Standards and Solutions A Status Report" (PDF). ATSC. Archived from the original (PDF) on 17 February 2016. Retrieved 4 April 2012.

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