IBM SG24-4817-00 manual MPEG-2 Data Streams, Multiplexing and Synchronization

This soft copy for use by IBM employees only.

quality, low bandwidth, and low resolution standard with fixed limited rates. MPEG-2 expands upon MPEG-1 in all directions:

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Higher quality (at the expense of higher bandwidth requirements)

Higher resolutions (up to HDTV levels)

Tremendous flexibility in compression rates.

MPEG-2 provides the standard for high-quality motion video compression. It is accepted by all segments of the entertainment, broadcasting, and video editing industry.

4.6.1.1 MPEG-2 Data Streams

MPEG-2 allows for the multiplexing of many independent audio and video streams (called Elementary Streams) into a System Stream, with synchronization information and audio/video correlation information.

There are two types of system stream:

1. Program data stream

This is suitable in environments where reliable storage is ensured.

2. Transport data stream

This is designed to transmit audiovisual content over networks.

The MPEG-2 transport data stream carries video and audio in the same data stream within separate fields. All video and audio material is stamped with presentation time stamps at the time of encoding. These time stamps are synchronized during the decoding process. This ensures synchronization of data without perceivable jitter.

4.6.1.2 Multiplexing and Synchronization

MPEG-2 defines a system layer that provides the ability to multiplex and synchronize multiple video and audio streams, and other private data. The system layer includes clocking information between the encoder and decoder. Even when an MPEG-2 stream is stored, the decoder may read the clock values to accurately recreate the motion picture.

The system layer also removes storage and transmission dependencies from MPEG-2. Since the system layer is self-clocking, MPEG-2 does not require synchronized transmission lines. Error checking fields add robustness to the transmission layer.

In comparison, there is no standardized system layer for M-JPEG. Therefore, it must record and transmit video and audio separately. The lack of a standard prevents M-JPEG encoded material from being freely exchanged. It cannot be recorded for future playback due to the absence of built-in timing information. M-JPEG requires a synchronous transmission line, that is, a more expensive communications network.

Chapter 4. IBM 8285 ATM Modules 49