MPEG

MPEG refers to a group of digital video and audio compression standards and file formats commonly used to store and play back movies, video clips, and audio—a universal means of efficiently and compactly coding digital video and audio signals for consumer use.

MPEG takes its name from its creators, the Moving Picture Experts Group, who developed the original set of standards under the direction of Leonardo Chiariglione (CSELT) and Hiroshi Yasuda (JVC Corporation). Originally convened in 1988 under the direction of the International Standards Organization (ISO) and the International Electro-Technical Commission (IEC), the group sought to address the concern of “interoperatability” for audio and video playback—the ability to operate across software or hardware produced by different manufacturers. The result was a set of universal standards, proposed in 1991, defining the encoding and decoding of full-motion video and associated audio, commonly referred to as MPEG. It is noteworthy that about the same time that the Moving Picture Experts Group convened, another compression method, Digital Video Interactive (DVI), was being developed by a research group at Princeton University. It was eventually bought by Intel, where it continues to be developed.

The first phase of the MPEG standard, named MPEG-1, is what is typically thought of when full-motion digital video is discussed as an MPEG file or format. MPEG-1 consisted of four sets of standards, [Page 326]including those related to the synchronization of video and audio, video compression, audio compression, and the compliance testing of each. The goal of the MPEG-1 standard was to introduce guidelines that would be independent of a particular application, allowing the user to determine how it is used. The standard determines an encoding procedure, and by default a decoding procedure, and the user decides how to apply it. Common applications of the MPEG-1 standard include products such as video CDs and MP3s.

MP3, a popular format for storing digital audio that is increasingly used to distribute music online, gets its name from MPEG-1 Layer 3, which outlines audio compression standards. MP3 files are commonly downloaded from a site and require a special player to be heard. As with any compressed file, the MP3 player decompresses and decodes the file, resulting in sound.

MPEG-1 encoding takes advantage of redundancies in the information being stored in order to represent it efficiently; as a rough estimate of its efficiency, an hour of video encoded in this format uses approximately one gigabyte of storage space. The encoding process used by MPEG-1 is somewhat analogous to the individual frames found on film, except for one major difference. A high video compression rate is produced not by encoding all of the information for each frame as traditional film does; rather, it encodes only the changes from frame-to-frame, through a technique called DCT. Although this process inevitably results in a loss of information, it is hardly noticeable to the naked eye, and the video quality that it produces approximates that of the typical home VCR.

MPEG-1 specifications also determine how full-motion video is decoded. MPEG-1 video viewing on, for instance, a personal computer requires an MPEG decoder, which can be in the form of hardware, software, or a combination of the two. The decoder communicates with the software programs used to view the video through its drivers, which determine the procedures needed to translate the information into what is seen on the monitor as full-motion video.

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