Mpeg decoding system adjusting the presentation in a predetermined

Abstract

A Motion Picture Experts Group (MPEG) multiplexed data bitstream includes encoded video and audio data units, which are prefixed with headers including Presentation Time Stamps (PTS) indicating desired presentation times for the respective data units. The data units are decoded, and presented at a fixed time after decoding, such that the fixed time can be subtracted from the PTS to provide a desired decoding time. The bitstream is parsed, the video and audio headers are stored in video and audio header memories, and the associated video and audio data units are stored in video and audio channel memories respectively. A first interrupt is generated each time a header is stored, and a host microcontroller responds by storing the PTS from the header and the starting address of the corresponding data unit in the channel memory as an entry in a list. A second interrupt is generated each time a data unit is decoded, and the host microcontroller responds by accessing the list using the starting address of the data unit to obtain the corresponding PTS, and thereby the desired decoding time. Decoding and presentation are synchronized by comparing the desired decoding time with a system clock time. If the desired decoding time is later than the system clock time by more than one presentation (frame) time period for the data unit, presentation of the data unit is skipped. If the desired decoding time is earlier than the system clock time by more than the presentation time period, presentation of the data unit is repeated.