The Presentation Time Stamp (PTS) indicates the instant at which an access unit should be removed from the receiver buffer, instantaneously decoded, and  presented for display.  Any delay in a practical decoding or display process can be compensated for if it is fixed.  Therefore, if a practical decoder has a variable delay, it must include buffering to restore a constant delay at the output.  Note that the display itself may include a delay, for example, the time for the vertical scanning of a CRT to reach the middle of the picture.

PTS (or DTS) is entered in the bitstream at intervals not exceeding 700 mS.  ATSC further constrains PTS (or DTS) to be inserted at the beginning of each access unit.

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