The MPEG system committee completed and approved for release the technical specification for combining a plurality of coded audio and video streams into a single data stream. The specification provides a fully synchronised audio and video and facilitates the storage in and the possible further transmission of the combined information through a variety of digital media.
This systems coding includes necessary and sufficient information in the bit stream to provide the system-level functions of synchronization of decoded audio and video, initial and continuous management of coded data buffers to prevent overflow and underflow, random access start-up, and absolute time identification. The coding layer specifies a multiplex data format that allows multiplexing of multiple simultaneous audio and video streams as well as privately defined data streams.
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.
Some optional sets of constraints provide a framework for common industry acceptance of certain key parameters for use by decoder designs and information providers. While the MPEG Systems specification is included in the current work item of MPEG, it is designed for compatibility with future extensions to audio, video and hypermedia coding, and a wide variety of bitrates.