The only tool the play back system has for approximating the correct byte position is the requested play back time stamp and the bit rate of the MPEG stream. MPEG streams do not encode their play back time. To approximate an intermediate position in a variable bit rate stream, the play back system must grope around near the end of the stream to calculate the playback time, and assume the stream is approximately constant bit rate. The groping around for the correct position can take several seconds. This is not appropriate for an interactive presentation or game.
Audio streams are always fixed bit rate.
A hypothetical decoder that is conceptually connected to the output of the encoder. This postulates the existence of a buffer in the receiver and a prediction mechanism in the encoder. 361-372, Dec. 1992. A series of one or more pictures.