Audio To Video Synchronization - Effect of No Explicit AV-sync Timing

Effect of No Explicit AV-sync Timing

When a digital or analog audio video stream does not have some sort of explicit AV-sync timing these effects will cause the stream to become out of sync:

• In film movies these timing errors are most commonly caused by worn films skipping over the movie projector sprockets because the film has torn sprocket holes.
• Errors can also be caused by the projectionist misthreading the film in the projector, although this is rare with competent projectionists.
• Audio to Video Synchronization is commonly corrected and maintained with an audio synchronizer. Television industry standards organizations have established acceptable amounts of audio and video timing errors and suggested practices related to maintaining acceptable timing.
• A/V sync errors are becoming a significant problem in the digital television industry because of the use of large amounts of video signal processing in television production, television broadcasting and pixelated television displays such as LCD, DLP and plasma displays.
• In the television field, audio video sync problems are commonly caused when significant amounts of video processing is performed on the video part of the television program.
• Typical sources of significant video delays in the television field include video synchronizers and video compression encoders and decoders. Particularly troublesome encoders and decoders are used in MPEG compression systems utilized for broadcasting digital television and storing television programs on consumer and professional recording and playback devices.
• A source of significant video delay is found in pixelated television displays (LCD, Plasma display, DLP) which utilize complex video signal processing to convert the resolution of the incoming video signal to the native resolution of the pixelated display, for example converting standard definition video to be displayed on a high definition display. "Lip-flap" may exceed 200 ms at times.
• In broadcast television, it is not unusual for lip-sync error to vary by over 100 ms (several video frames) from time to time.
• The EBU Recommendation R37 “The relative timing of the sound and vision components of a television signal” states that end-to-end audio/video sync should be within +40ms and -60ms (audio before / after video, respectively) and that each stage should be within +5ms and -15ms.