MPEG is a working group of experts that was formed by ISO and
IEC to set standards for audio and video compression and transmission. It was
established in 1988 by the initiative of Hiroshi Yasuda (Nippon Telegraph and
Telephone) and Leonardo Chiariglione, group Chair since its inception.
The MPEG compression methodology is
asymmetric as the encoder is more complex than the decoder. The encoder needs
to be algorithmic or adaptive whereas the decoder is 'dumb' and carries out
fixed actions. This is advantageous in applications such as broadcasting where
the number of expensive complex encoders is small but the number of simple
inexpensive decoders is large. The MPEG's approach to standardization is novel,
because it is not the encoder that is standardized, but the way a decoder
interprets the bitstream. A decoder that can interpret the bitstream is said to
be “compliant”. The advantage of standardizing the decoder is that over time
encoding algorithms can improve, yet compliant decoders continue to function
with them.
The MPEG standards give very little
information regarding structure and operation of the encoder and implementers
can supply encoders using proprietary algorithms. This gives scope for
competition between different encoder designs, which means better designs can
evolve and users have greater choice, because encoders of different levels of
cost and complexity can exist, yet a compliant decoder operates with all of
them.
MPEG also standardizes the protocol and
syntax under which it is possible to combine or multiplex audio data with video
data to produce a digital equivalent of a television program. Many such
programs can be multiplexed and MPEG defines the way such multiplexes can be
created and transported. The definitions include the metadata used by decoders
to demultiplex correctly
Standards
The MPEG standards consist of different
Parts. Each part covers a certain aspect of the whole specification. The
standards also specify Profiles and Levels. Profiles are intended to define a
set of tools that are available, and Levels define the range of appropriate
values for the properties associated with them. Some of the approved MPEG
standards were revised by later amendments and/or new editions. MPEG has
standardized the following compression formats and ancillary standards:
- MPEG-1 (1993):
Coding of moving pictures and associated audio for digital storage media
at up to about 1.5 Mbit/s (ISO/IEC 11172). The first MPEG compression
standard for audio and video. It is commonly limited to about 1.5 Mbit/s
although the specification is capable of much higher bit rates.
- MPEG-2 (1995):
Generic coding of moving pictures and associated audio information
(ISO/IEC 13818). Transport, video and audio standards for
broadcast-quality television. MPEG-2 standard was considerably broader in
scope and of wider appeal – supporting interlacing and high definition.
- MPEG-3: MPEG-3 dealt
with standardizing scalable and multi-resolution compression and was
intended for HDTV compression but was found to be redundant and was merged
with MPEG-2, as a result there is no MPEG-3 standard. MPEG-3 is not to be
confused with MP3, which is MPEG-1 Audio Layer III.
- MPEG-4 (1998):
Coding of audio-visual objects. (ISO/IEC 14496) MPEG-4 uses further coding
tools with additional complexity to achieve higher compression factors
than MPEG-2. In addition to more efficient coding of video, MPEG-4 moves
closer to computer graphics applications. In more complex profiles, the
MPEG-4 decoder effectively becomes a rendering processor and the
compressed bitstream describes three-dimensional shapes and surface
texture. Several new higher-efficiency video standards (newer than MPEG-2
Video) are included, notably:
- MPEG-4 Part 2 (or Simple and Advanced Simple
Profile) and
- MPEG-4 AVC (or MPEG-4 Part 10 or H.264).
MPEG-4 AVC may be used on HD DVD and Blu-ray Discs, along with VC-1 and
MPEG-2.
- MPEG-4 has been chosen as the compression
scheme for over-the-air in Brazil (ISDB-TB), based on original digital
television from Japan (ISDB-T).
In addition, the following standards,
while not sequential advances to the video encoding standard as with MPEG-1
through MPEG-4, are referred to by similar notation:
- MPEG-7 (2002):
Multimedia content description interface. (ISO/IEC 15938)
- MPEG-21 (2001):
Multimedia framework (MPEG-21). (ISO/IEC 21000) MPEG describes this
standard as a multimedia framework and provides for intellectual property
management and protection.
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