There are a number of applications in which it is cost effective to shift more of the computational burden to the encoder. For example, in multimedia applications where a video sequence is stored on a CD-ROM, the decompression will be performed many times and has to be performed in real time.
However, the compression is performed only once, and there is no need for it to be in real time. Thus, the encoding algorithms can be significantly more complex. A similar situation arises in broadcast applications, where for each transmitter there might be thousands of receivers. In this section we will look at the standards developed for such asymmetric applications.
These standards have been developed by a joint committee of the International Standards Organization (ISO) and the International Electrotechnical Society (IEC), which is best known as MPEG (Moving Picture Experts Group). MPEG was initially set up in 1988 to develop a set of standard algorithms, at different rates, for applications that required storage of video and audio on digital storage media. Originally, the committee had three work items, nicknamed MPEG-1, MPEG-2, and MPEG-3, targeted at rates of 1.5, 10, and 40 Mbits per second, respectively.
Later, it became clear that the algorithms developed for MPEG-2 would accommodate the MPEG-3 rates, and the third work item was dropped . The MPEG-1 work item resulted in a set of standards, ISO/IEC IS 11172, “Information Technology—Coding of Moving Pictures and Associated Audio for Digital Storage Media Up to about 1.5 Mbit/s” .
During the development of the standard, the committee felt that the restriction to digital storage media was not necessary, and the set of standards developed under the second work item, ISO/IEC 13818 or MPEG-2, has been issued under the title “Information Technology—Generic Coding of Moving Pictures and Associated Audio Information” . In July of 1993 the MPEG committee began working on MPEG-4, the third and most ambitious of its standards. The goal of MPEG-4 was to provide an object-oriented framework for the encoding of multimedia. It took two years for the committee to arrive at a satisfactory definition of the scope of MPEG-4, and the call for proposals was finally issued in 1996. The standard ISO/IEC 14496 was finalized in 1998 and approved as an international standard in 1999. We have examined the audio standard in Chapter 16. In this section we briefly look at the video standards.