MPEG-2 Standard

Moving Picture Experts Group (MPEG), one of the working groups chartered by International Standards Organization (ISO), released the MPEG-2 standard initially in 1994. The current MPEG-2 standard [26] has 9 parts, of which the first three parts are widely adopted by the DTV industry:

• Part 1 -- Systems: deals with audio, video and general data transmission.
• Part 2 -- Video: deals with video compression.
• Part 3 -- Audio: deals with audio compression.

Among these three parts, Part 1 -- Systems is of special importance to datacast because it is the basis for transmitting DTV programs and general data on the DTV channel. Concretely, Part 1 specifies the following four basic functionalities: (1) how to multiplex the audio/video streams and general data into a single MPEG-2 packet stream that is necessary for transmission; (2) how to synchronize the different streams in the single stream, e.g., synchronize the audio and video streams; (3) how to organize related streams into groups (or virtual channels); and (4) how to provide Program Specific Information (PSI), a guide for the decoders to extract different streams in the single stream. The lowest level packet encapsulation defined in Part 1 is called the ``Transport Stream (TS)'' packet, which has fixed length of 188 bytes. All higher level packets are finally carried in the TS packets. To facilitate the synchronization of the audio and video streams, Part 1 also defines a higher level packet encapsulation called ``Packet Elementary Stream (PES)'' packet, which is used to carry an individual audio or video stream.