The basic principle of MPEG System coding is the use of time stamps which specify the decoding and display time of audio and video and the time of reception of the multiplexed coded data at the decoder, all in terms of a single 90KHz system clock. This method allows a great deal of flexibility in such areas as decoder design, the number of streams, multiplex packet lengths, video picture rates, audio sample rates, coded data rates, digital storage medium or network performance. It also provides flexibility in selecting which entity is the master time base, while guaranteeing that synchronization and buffer management are maintained. Variable data rate operation is supported. A reference model of a decoder system is specified which provides limits for the ranges of parameters available to encoders and provides requirements for decoders.