The Moving Picture Experts Group (MPEG) is a working group under ISO/IEC
in charge of the development of international standards for compression,
decompression, processing and coded representation of moving pictures,
audio and their combination. So far MPEG has produced
MPEG ususally holds three meetings a year. These comprise plenary
meetings and subgroup meetings on Requirements, Systems, Video,
Audio, SNHC, Test, Implementation, DSM and Liason. MPEG meetings
are attended by some 300 experts from some 20 countries.
Within the MPEG video group the video coding standards are developed
based on a Verification Model (or Test Model) and an associated "Core
Experiment" process.
The purpose of a Verification Model (VM) within MPEG is to describe
completely defined encoding and decoding "Common Core" algorithms,
such that collaborative experiments performed by multiple independent parties
can produce identical results and will allow the conduction of "Core
Experiments" under controlled conditions in a common environment.
A Verification Model (in MPEG-2 phase this was called "Test Model")
is established at the beginning of a standardization phase based on the
assesment of individual proposals submitted to the MPEG video group. It
specifies the input and output formats for the uncoded data and the format
of the bitstream containing the coded data. It specifies the algorithm
for encoding and decoding, including the support for one or more functionalities.
For the development of a MPEG Video standard the MPEG Video group establishes
a number of "Core Experiments" to improve the efficiency of the
MPEG-4 VM between meetings with respect to the functionalities already
supported - and to identify new coding techniques that allow provisions
for functionalities not yet supported by the VM. A Core Experiment is defined
with respect to the Verification Model, which is considered as the Common
Core algorithm. A Core Experiment proposal describes a potential algorithmic
improvement to the VM, i.e. a motion compensation technique different to
the one defined by the VM. Furthermore the full description of encoder
and decoder implementation of the algorithm and the specification of experimental
conditions (bit rates, test sequences, etc.) to compare the proposed Core
Experiment technique against the performance of the VM are provided. A
Core Experiment is being established by the MPEG Video group if two independent
parties are committed to perform the experiment. If a Core Experiment is
successful in improving on techniques described in the VM - i.e. in terms
of coding efficiency, provisions for functionalities not supported by the
VM and implementation complexity - the successful technique will be incorporated
into the newest version of the VM. The technique will either replace an
existing technique or supplement the algorithms supported by the VM.
Core Experiments are being performed between two MPEG Video group meetings.
At each MPEG Video group meeting the results of the Core Experiments
are being reviewed and the VM is updated depending on the outcome
of the experiment and a new version of the VM is being released.
Thus the VM progresses from one meeting to the next. The last version
of the MPEG-2 Verification Model was Test Model 5 (TM 5) which formed
the basis for the MPEG-2 video standard.
In 1988 the Moving Picture Experts Group (MPEG) was founded under ISO/SC2 with
the charter to standardize a video coding algorithm targeted for
digital storage media and bit rates at up to about 1.5 Mbits/s.
Its official denotation is now ISO/IEC/JTC1/SC29/WG11. The first
Draft Iinternational Standard (DIS) released by the committee, ISO
11172 (MPEG-1), was drafted in 1991 and finally issued as IS in
1992. MPEG-1 is intended to be generic (although the initial target
applications envisaged and applications parameters defined were
constrained to digital storage media). Generic means, that the standard
is independent of a particular application and therefore comprises
mainly a toolbox. It is up to the user to decide, which tools to
select to suit the particular applications envisaged. This implies,
that only the coding syntax is defined and therefore mainly the
decoding scheme is standardized. MPEG-1 defines a hybrid DCT/DPCM
coding scheme with motion compensation similar to the H.261 and
CCIR Rec. 723 coding standards. Further refinements in prediction
and subsequent processing were introduced to provide the functionality
required for random access in digital storage media.
Studies on MPEG-2 started in 1990 with the initial target to issue a
standard for coding of TV-pictures with CCIR Rec. 601 resolution at data
rates below 10 Mbit/s. In 1992 the scope of MPEG-2 was enlarged to suit
coding of HDTV - thus making an initially planned MPEG-3 phase superfluous.
The DIS for MPEG-2 video was issued in early 1994.
The video coding scheme used in MPEG-2 is again generic and similar
to the one of MPEG-1, however with further refinements and special consideration
of interlaced sources. Furthermore many functionalities such as "scalability"
were introduced. In order to keep implementation complexity low for products
not requiring the full video input formats supported by the standard (e.g.
SIF to HDTV resolutions), so called "Profiles", describing functionalities,
and "Levels", describing resolutions, were introduced to provide
separate MPEG-2 conformance levels.
The MPEG-4 Video Coding Standard
Anticipating the rapid convergence of telecommunications
industries, computer and TV/film industries, the MPEG group officially
initiated a new MPEG-4 standardization phase in 1994 - with the mandate
to standardize algorithms and tools for coding and flexible representation
of audio-visual data to meet the challenges of future Multimedia applications
and applications requirements. In particular MPEG-4 addresses the need for
- Universal accessibility and robustness in error prone
environments - Multimedia audio-visual data need to be transmitted
and accessed in heterogeneous network environments, possibly under severe
error conditions (e.g. mobile channels). Although the MPEG-4 standards
will be network (physical-layer) independent in nature, the algorithms
and tools for coding audio-visual data need to be designed with awareness
of network peculiarities.
- High interactive functionality - Future Multimedia
applications will call for extended interactive functionalities to assist
the user's needs. In particular the flexible, highly interactive access
to and manipulation of audio-visual data will be of prime importance. It
is envisioned that - in addition to conventional playback of audio and
video sequences - the user need to access "content" of audio-visual
data to present and manipulate/store the data in a highly flexible way.
- Coding of natural and synthetic data - Next generation
graphics processors will enable Multimedia terminals to present both pixel
based audio and video data together with synthetic audio/speech and video
in a highly flexible way. MPEG-4 will assist the efficient and flexible
coding and representation of both natural (pixel based) as well as synthetic
data.
- Compression efficiency - For the storage and transmission
of audio-visual data a high coding efficiency, meaning a good quality of
the reconstructed data, is required. Improved coding efficiency, in particular
at very low bit rates below 64 kbits/s, continues to be an important functionality
to be supported by the MPEG-4 video standard.
Bit rates targeted for the MPEG-4 video standard are between
5-64 kbits/s for mobile or PSTN video applications and up to 2 Mbits/s
for TV/film applications. Seven new (with respect to existing or emerging
standards) key video coding functionalities have been defined which support
the MPEG-4 focus and which provide the main requirements for the work in
the MPEG video group. The requirements cover the main topics related to
"Content-Based Interactivity? "Compression?and "Universal
Access? The release of the MPEG-4 International Standard is targeted for
July 1998.
More on MPEG-4 Video
J.L.Mitchell, W.B.Pennebaker, C.E.Fogg and D.J.LeGall, "MPEG Video
Compression Standard", in Digital Multimedia Standards Series,Chapman
& Hall, New York, NY, 1997.
D.J. Le Gall, "The MPEG Video Compression Algorithm", Signal Processing:
Image Communication 4, No. 2, pp. 129-140, 1992
J.L.Mitchell, W.B.Pennebaker, C.E.Fogg and D.J.LeGall, "MPEG Video
Compression Standard", in Digital Multimedia Standards Series,Chapman
& Hall, New York, NY, 1997.
B. G. Haskell, A. Puri and A. N. Netravali, "Digital Video:
An Introduction to MPEG-2," ISBN: 0-412-08411-2, Chapman & Hall,
1997.
Multifunctional Ad hoc Group, "Core experiments Description,"
ISO/IEC JTC1/SC29/WG11 N1266, March 1996.
Stereoscopic Video Coding
A. Puri, R. V. Kollarits and B. G. Haskell, "Basics of Stereo
scopic Video, New Compression Results with MPEG-2 and a Proposal
for MPEG-4," accepted for pub, Signal Processing: Image Communications.
A. Puri, R. V. Kollarits and B. G. Haskell, "Stereoscopic
Video Compression Using Temporal Scalability," Proc. SPIE
Visual Communications and Image Processing'95, Taiwan, May 1995.
A. Shigenaga and T. Homma, "Experimental Results of Coding of
Stereo Sequences with Temporal Scalability," ISO/IEC JTC1/SC29/WG11
Doc. MPEG95/254, July 1995.
A. Puri and B. G. Haskell, "A Revised Proposal for Multiview Coding and
Multiview Profile" ISO/IEC JTC1/SC29/WG11 MPEG95/249, July 1995.
A. Luthra and X. Chen, "MPEG-2 Multiview Profile for MPEG-2," to appear Proc.
SPIE/IS&T Multimedia Hardware Architectures, EI'97, Feb. 1997.
L.Chiariglione, "MPEG and Multimedia Communications",
IEEE Trans. CSVT, Vol.7, No.1, Feb.1997.
T.Sikora, "The MPEG-4 Video Standard Verification Model", IEEE Trans.
CSVT, Vol.7, No.1, Feb.1997.
T.Sikora, "MPEG-4 Very Low Bit Rate Video ", Proc. IEEE ISCAS Conference,
Hongkong, June 1997.
