charge-coupled device (CCD) and CMOS image sensors) can delay the video signal by one or more frames. A video camera should have some sort of explicit AV-sync timing put into the video and audio streams. A video camera with built-in microphones or line-in may not delay sound and video paths by the same number of milliseconds.The AV-sync delay is static but can vary with the individual clip.Įxamples of transmission ( broadcasting), reception and playback that can get the AV-sync incorrectly synchronized: During mixing of video clips normally either the audio or video needs to be delayed so they are synchronized.The AV-sync delay increases with distance. If the sound source is 340 meters from the microphone, then the sound arrives approximately 1 second later than the light. External AV-sync error: If a microphone is placed far away from the sound source, the audio will be out of sync because the speed of sound is much lower than the speed of light.Internal AV-sync error: Different signal processing delays between image and sound in video camera and microphone.During creation AV-sync errors happen because of.There are different ways in which the AV-sync can get incorrectly synchronized: 3 Viewer experience of incorrectly synchronized AV-sync.If the processing does not respect the AV-sync error, it will increase whenever data gets lost because of transmission errors or because of missing or mistimed processing. stretching between or interpolation of received data. The processing of data must respect the relative data timing by e.g. This terminology and standardization of the numeric lip-sync error is utilized in the professional broadcast industry as evidenced by the various professional papers, standards such as ITU-R BT.1359-1, and other references below.ĭigital 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. In industry terminology, the lip-sync error is expressed as an 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. AV synchronization can be an issue in television, videoconferencing, or film. 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.
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