MPEG-1 Development – Systems

MPEG-1 Development – Systems

The development of the Systems part of the standard was done using yet another methodology. The Systems group, a most diversified collection of engineers from multiple industries, after determining the requirements the Systems layer had to satisfy, decided that they did not need a CfP, because the requirements were so specific that they felt they could simply design the standard by themselves in a collaborative fashion. The initial impetus was provided by Juan Piñeda, then with Apple Computer, at the Porto meeting in July 1990, when he proposed the first packet-based multiplexer. Eventually Sandy MacInnis of IBM became the chairman of that group after Allen Simon’s resignation. 

One of the issues the group had to deal with was “byte alignment”, a typical requirement from the computer world that the telco world, because of its “serial” approach to bitstreams, did not value. This can be seen, e.g., from the not byte-aligned H.261 bitstream. Byte alignment was eventually supported in MPEG-1 Systems because the system decoding of a byte-aligned 150 kbyte/s stream was already feasible using the CPUs of that time. In the process, the MPEG-1 Video syntax, too, was made byte aligned. 

Another issue was the choice between constant and variable packet size. One could have thought that, because the main target of MPEG-1 was Digital Storage Media where disk formats have a fixed block size, a fixed packet length should have been selected. Eventually, however, this did not happen, a consequence of the fact that the physical format of the disc is, in OSI terminology, a layer 2 issue, while packet multiplexing is a higher-layer issue that did not necessarily have to relate with the former. In conclusion MPEG-1 Systems turned out to be a very robust and flexible specification capable of supporting the transfer of tightly synchronised video and audio streams across an arbitrary error-free delivery system. 

The second MPEG London meeting in November 1992 put the seal on MPEG-1, with the approval of the first three parts of the standard: Systems, Video and Audio. Since then the standard has been very stable: in spite of its complexity, very few corrigenda were published after that date: two for Systems, three for Video and one for Audio. The MPEG-1 work did not stop at that meeting, though, because work on conformance and reference software continued well into 1994. 

One thought on “MPEG-1 Development – Systems

  1. Pingback: The Roadmap | Riding the Media Bits