Fundamentals and Evolution of MPEG-2 Systems: Paving the MPEG Road

5Motivation for a Systems Standard

Why an MPEG systems standard is needed to packetize video and audio and what kind of problems such a standard is required to meet.

The need for systems technology for audiovisual applications arises from the wish to combine multiple elementary audio and/or video streams into a single system stream in a manner independent of the transport medium. Though it is possible to provide audio and video as parallel streams, it is in many situations far more practical to provide a single stream that contains audio and video. For example:

• from optical disc a single serial data stream is delivered;
• a digital broadcast stream is a single serial data stream;
• for movie playback from hard disc, it is easier to deliver a single data stream that contains both audio and video than reading data from two files, one containing compressed video and the other compressed audio, as for the latter option the reading device has to jump regularly between physical hard disc positions in both files.

Therefore MPEG decided to address combining audio and video into a single system stream. A simple example of combining an audio stream and a video stream into a system stream is presented in Figure 5.1.

Figure 5.1 Example of combining audio and video into a system stream

In Figure 5.1, the audio and video streams are depicted as byte streams. In the system stream there are ...