sentences:  This effect is commonly referred to as A/V sync or lip sync error and can cause serious problems related to the viewer's enjoyment of the program.To correct audio video sync problems, the video processing circuitry outputs a DDO (digital delay output) signal, which carries information about the amount of delay the video signal experiences due to the video processing.The DDO may, for example, be provided by equipment which adheres to the SMPTE  Audio to Video Synchronization Standard.