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.
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