sentences:  Presentation time stamps (PTS) are embedded in MPEG transport streams to precisely signal when each audio and video segment is to be presented, to avoid AV-sync errors.However, these timestamps are often added after the video undergoes frame synchronization, format conversion and preprocessing, and thus the lip sync errors created by these operations will not be corrected by the addition and use of timestamps.The Real-time Transport Protocol clocks media using origination timestamps on an arbitrary timeline.