THE WHATIS.COM WORD-OF-THE-DAY   
December 27, 2001

MPEG standards 
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TODAY'S WORD: MPEG standards 

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The MPEG standards are an evolving set of standards for video and
audio compression and for multimedia delivery developed by the Moving
Picture Experts Group (MPEG). 

MPEG-1 was designed for coding progressive video at a transmission
rate of about 1.5 million bits per second. It was designed
specifically for Video-CD and CD-i media. MPEG-1 audio layer-3 (MP3)
has also evolved from early MPEG work. 

MPEG-2 was designed for coding interlaced images at transmission
rates above 4 million bits per second. MPEG-2 is used for digital TV
broadcast and DVD. An MPEG-2 player can handle MPEG-1 data as well. 

MPEG-1 and -2 define techniques for compressing digital video by
factors varying from 25:1 to 50:1. The compression is achieved using
five different compression techniques: 

- The use of a frequency-based transform called Discrete Cosine
Transform (DCT). 
- Quantization, a technique for losing selective information
(sometimes known as lossy compression) that can be acceptably lost 
from visual information. 
- Huffman coding, a technique of lossless compression that uses code
tables based on statistics about the encoded data. 
- Motion compensated predictive coding, in which the differences in
what has changed between an image and its preceding image are
calculated and only the differences are encoded. 
- Bi-directional prediction, in which some images are predicted from
the pictures immediately preceding and following the image. 

The first three techniques are also used in JPEG file compression. 

A proposed MPEG-3 standard, intended for High Definition TV (HDTV),
was merged with the MPEG-2 standard when it became apparent that the
MPEG-2 standard met the HDTV requirements. 

MPEG-4 is a much more ambitious standard and addresses speech and
video synthesis, fractal geometry, computer visualization, and an
artificial intelligence (AI) approach to reconstructing images.
MPEG-4 addresses a standard way for authors to create and define the
media objects in a multimedia presentation, how these can be
synchronized and related to each other in transmission, and how users
are to be able to interact with the media objects. 

MPEG-21 provides a larger, architectural framework for the creation
and delivery of multimedia. It defines seven key elements: 


Digital item declaration 
Digital item identification and declaration 
Content handling and usage 
Intellectual property management and protection 
Terminals and networks 
Content representation 
Event reporting 

The details of various parts of the MPEG-21 framework are in various
draft stages. 

RELATED TERMS:

compression 
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Moving Picture Experts Group 
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CD-i 
http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci503661,00.html

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SELECTED LINKS

For additional information, see the official MPEG Committee Web site.
http://mpeg.telecomitalialab.com/

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