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标 题: MPEG and multimedia communications
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MPEG and multimedia communications
Leonardo Chiariglione
CSELT - Torino - Italy
Number of visitors to this Page since 19 August 1996
Abstract
Digital Television is a reality today but Multimedia Communications, after
years of hype, is still a catchword. Lack of suitable multi-industry standards
supporting it is one reason for the unfulfilled promise.
The MPEG committee which originated the MPEG-1 and MPEG-2
standards that made Digital Television possible, is currently developing
MPEG-4 with wide industry participation. This paper describes how the
MPEG-4 standard, with its network-independent nature and
application-level features is poised to become the enabling technology for
multimedia communications and will therefore contribute to solve the
problems that are hindering Multimedia Communications.
Table of content
1. Introduction
2. About Multimedia
3. Multimedia and standardisation
4. The MPEG approach to standardisation
4.1 Stick to the deadline
4.2 A-priori standardisation
4.3 Not systems but tools
4.4 Specify the minimum
4.5 One functionality - one tool
4.6 Relocation of tools
4.7 Verification of standard
5. A guided tour to MPEG-1 and MPEG-2
5.1 MPEG-1
5.2 MPEG-2
5.3 Other MPEG-2 functionalities
5.4. Other MPEG-2 work
6. MPEG-2 or Digital Television
7. MPEG-4, or Multimedia Communications
8. The MPEG-4 standard
8.1 MPEG-4 architecture
8.2 Multiplexer
8.3 Video
8.4 Audio
8.5 SNHC
8.6 Flexibility
8.7 Software implementation of the standard
9. Is this all that we need to make multimedia
communications?
9.1 IPR management
9.2 Security
9.3 Content search
9.4 Transport protocol
10. Conclusions
11. Acknowledgements
12. References
1. Introduction
After 10 years since the word "multimedia" has entered the
techno-vocabulary, 5 years of "convergence" hype and 2 � years of digital
video, we are still struggling to make multimedia communications happen.
The reasons of this stalemate are manifold. Here are some of them.
The terms of the convergence issue are not well posed. It is not the
businesses of telecommunications, entertainment and computer that
are going to converge, but the traditional barriers inherited by the
three business in the content production and packing, information
transport and processing, and user equipment domains that are going
to disappear. It makes technical and business sense if the content,
transport and equipment industries converge, less if the mentioned
businesses do. The sooner these traditional barriers are removed, the
sooner multimedia communications will happen.
Digital television is a technology for better exploitation of
bandwidth when used to transmit television signals. The current usage
of MPEG-1 and MPEG-2 is restricted to digital television. The few
openings towards multimedia communications that were embedded in
the standard have been emasculated by the all-out hijacking of the
technology by a particular industry.
There is an antithesis created by the traditional, slow, bottom-up,
generic, broadband, network service-driven model proper of
telecommunication operators and the swift, pragmatic, specific,
narrowband, application-driven approach proper of the Internet.
video, we are still struggling to make multimedia communications happen.
The reasons of this stalemate are manifold. Here are some of them.
The terms of the convergence issue are not well posed. It is not the
businesses of telecommunications, entertainment and computer that
are going to converge, but the traditional barriers inherited by the
three business in the content production and packing, information
transport and processing, and user equipment domains that are going
to disappear. It makes technical and business sense if the content,
transport and equipment industries converge, less if the mentioned
businesses do. The sooner these traditional barriers are removed, the
sooner multimedia communications will happen.
Digital television is a technology for better exploitation of
bandwidth when used to transmit television signals. The current usage
of MPEG-1 and MPEG-2 is restricted to digital television. The few
openings towards multimedia communications that were embedded in
the standard have been emasculated by the all-out hijacking of the
technology by a particular industry.
There is an antithesis created by the traditional, slow, bottom-up,
generic, broadband, network service-driven model proper of
telecommunication operators and the swift, pragmatic, specific,
narrowband, application-driven approach proper of the Internet.
The bit-transportation industry has invested in the former but the
latter seems to provide many of the applications that were intended
to be supported by the former.
Communications mean standards but producing standards for multimedia
communications is beset by the problem that the many industries having a
stake in it have radically different approaches to standardisation.
A solution to this problem is offered by MPEG with its successful
development of the multi-industry MPEG-1 and MPEG-2 standards, even
though it is recognised that the new task is vastly more complex than that of
the previous two standards. Such MPEG-established standardisation
principles as "not systems but tools", "one functionality - one tool",
"relocatability of tools", "specify the minimum", "a priori standardisation",
"stick to the deadline" etc. if not adopted in practice by other standards
bodies, are at least becoming widely known, discussed and their positive
implications are gradually being appreciated in the standards world. The
profile/level approach that complements the principles above combines the
need of generic technology specifications with the application-specific needs
of different industries.
MPEG-4, the current standardisation project of MPEG, combines some of
The bit-transportation industry has invested in the former but the
latter seems to provide many of the applications that were intended
to be supported by the former.
Communications mean standards but producing standards for multimedia
communications is beset by the problem that the many industries having a
stake in it have radically different approaches to standardisation.
A solution to this problem is offered by MPEG with its successful
development of the multi-industry MPEG-1 and MPEG-2 standards, even
though it is recognised that the new task is vastly more complex than that of
the previous two standards. Such MPEG-established standardisation
principles as "not systems but tools", "one functionality - one tool",
"relocatability of tools", "specify the minimum", "a priori standardisation",
"stick to the deadline" etc. if not adopted in practice by other standards
bodies, are at least becoming widely known, discussed and their positive
implications are gradually being appreciated in the standards world. The
profile/level approach that complements the principles above combines the
need of generic technology specifications with the application-specific needs
of different industries.
MPEG-4, the current standardisation project of MPEG, combines some of
lists the additional features that MPEG-4 will need to avoid some of the
problems encoutered with the customisation of MPEG-2 made by specific
industries.
2. About Multimedia
After years of multimedia hype, there is no sign that multimedia
communications will happen in the way media gurus had anticipated, i.e. by
convergence of telecommunications, entertainment and computers, all
adopting digital technology. This is not happening as much as the
professions of barber, butcher and cobbler have not moved a single inch to
a convergence point through the millennia in spite of all sharing the common
"knife" technology. What is happening is movie makers buying broadcasting
companies, telcos buying CATV companies, consumer electronics
companies buying movie makers etc. To do this digital technology
convergence is redundant, you need fat wallets, complacent boards of
directors and patient shareholders.
Digital technologies have many benefits but the real plus is the possibility to
replicate in a more economic and compact way the different system
components that technologies specific of a field have made possible so far.
Some examples:
The vinyl disc, including its predecessors the hard disc and the and
the phonograph cylinder, has existed for over 100 years but now the
compact disc is used by hundreds of million people;
Analogue speech has existed for almost 100 years but now A-law/
m-law PCM is used in the network by billions of people;
Analogue satellite television has been in operation for 2 decades but
now digital satellite television is being watched by millions of people.
Now, try and ask the layman to tell you the difference between the analogue
and the digital version! People buy benefits, even if only perceived, and not
features.
I am not an unbeliever in convergence, which is part of life as much as
divergence, but certainly not of the mentioned businesses. The first thing we
must do if we want to have any chance of understanding, forecasting and, if
possible, shaping what is going to happen, is to acknowledge that the three
industries of entertainment, telecommunications and computers do not
provide the right dimensions to study the phenomenon. "Entertainment"
usually represents a vertical business such as terrestrial broadcasting that
produces content and takes care of its delivery up to the customers' homes.
"Telecommunications" is another vertical business spanning all
communication layers. "Computer" is an inextricable mixture of hardware
and software, an underlying technology that is used everywhere, in the
telecommunication system as well as in the user devices.
Better axes are provided by "Content", "Transport" and "Equipment".
"Content" - the message - is what matters to the user who foots the entire
bill and therefore justifies the existence of the entire system, "Transport" is
what is needed to deliver "Content" to people who want it and "Equipment"
- the user device - is what is needed to enable the human user to interact
with the system and to convert "Content" into human-consumable form.
There are different types of "Content": movies, TV programs, news,
telephone call and many ways to pack content in a way that makes users
more prone to consume; different types of "Transport": radio channel, cable,
twisted pair, at the physical level and emerging ones as middleware; and an
almost infinite variety of "Equipment".
The many businesses ("industries") that play a role in making the system
work are present in one or more of the three domains, e.g. the broadcasting
industry typically integrates content and transport, the CATV industry
transport and equipment and the video games industry content and
equipment.
Table 1 below gives some examples, possibly different from an environment
to another, of how the different industries (first column) integrate within
themselves the content, transport and equipment components.
Tab. 1 - Examples of integration of industries
Content
Transport
Equipment
Terrestrial TV
X
X
CATV
X
X
Satellite TV
X
X
Telecommunications
X
X
Movies
X
X
Consumer Electronics
X
X
Video games
X
X
The convergence case can be made, even though I do not personally think
the businesses will converge, nor that there is a cogent need for it. But this
will not happen because the industries will decide to abandon the
technologies proper to their businesses and convert to digital technologies,
something they have been doing since a long time (see the examples above)
while in search of rationalising their way of doing business, but because they
will decide to do the conversion in such a way that the communication
standards of one industry will be compatible with those of the other
industries.
And this is a monumental task, seeing the diverging attitudes of the different
industries towards standardisation that are described in the next paragraph.
3. Multimedia and standardisation
Communications require standards that define the meaning and the syntax
given to information at the source when it reaches the destination. Starting
from the Morse alphabet communication standards have become
increasingly more sophisticated and the different industries that have been
created in the process have developed considerably diverging attitudes.
The telecommunications industry bases its standards on the original
consideration that impedance mismatches in passing from the wires of
one telephone company to another is not the right way to promote
communications, i.e. the telephone companies' business. Even the
famous A-law/mu-law (digital speech) dichotomy can be justified, if
not praised for its farsightedness, considering that at the time (the
sixties) digital speech was just a means to optimise transmission in the
network, not something to be offered as an end-to-end service to
customers.
The movie industry has settled on a small number of film formats
each characterised by different audio-visual performance levels. The
hardware and software motion picture industry agreed that having the
possibility to project a movie everywhere in the world was good for
everybody's business.
The radio industry took the commendable approach of defining
standards of world-wide reach but its daughter, the television
industry has defined its standards in such a way that users can only
watch programs coming from a certain source. Notwithstanding a
good 405 lines at 50 Hz television system having been deployed in
the UK in the late '30s, in the early '40s the United States established
their 525/60 system that improved on the UK system by some 20%
and a few years later Europe established its own 625/50 television
system that did not improve bandwidth over NTSC at all
(625x25~=525x30). With the addition of colour to the monochrome
signal the number of "national paths" to television increased
dramatically with NTSC, PAL, SECAM and their almost countless
variants.
The CATV industry, sitting in between television and
telecommunications and by definition a local business, has a
schizophrenic attitude towards standards depending on the country in
which it operates.
The consumer electronics industry (mostly recording) has taken the
most straightforward application of the definition of standards: a
freely entered agreement between a manufacturer and a user to
sell/buy a certain piece of equipment with which users can play back
audio or video from media that are specific of the type of equipment
purchased ("format") from a third party that agrees to produce
content in that format.
The computer industry takes an attitude very similar to consumer
electronics', but considerably more articulated. The purchase of a
computer is a freely entered agreement between a manufacturer and
a user to provide hardware and some layers of software on top of it
so that high-level applications can be developed or purchased from
the manufacturer or a third party.
In the electronic games industry the purchase of an electronic game
is a freely entered agreement between a manufacturer and a user to
sell/buy hardware and software (the latter possibly from a third party)
that runs exclusively on the hardware.
So far the different industries have been diverging but Multimedia
Communications necessarily need some convergence zone that can only be
achieved by standardisation in key areas. Putting every stakeholder together
and producing communication standards accepted by all is a big task. Still
MPEG succeeded in doing that for its first-generation standards MPEG-1
and MPEG-2, particularly the latter which from now on will be used to
indicate both.
4. The MPEG approach to standardisation
With MPEG-2, MPEG has produced common audio-visual coding
standards that can be used by all industries mentioned in paragraph 3. This
has enabled sharing of cost, acceleration of digital audio-visual technology
development and, more fundamentally for users, flow of content unrestricted
by built-in technical barriers. If convergence will happen it will be because
all industries will be willing to adopt this kind of single representation of
information, shared by all industries.
It is worth looking at the way in which MPEG has operated in its 8 years of
activity and try to rationalise what has been a successful approach to
standardisation serving the needs of multiple industries for the general
multimedia communication case.
4.1 Stick to the deadline
No business can survive if work is done living day by day. This is,
unfortunately, the practice of some standards committees. They are in
charge of producing something (the something being often itself loosely
defined) without a date attached for delivering an output (the standard) or
with a date that is just a reference. It would be as if a company promised its
customers to deliver something sometime.
Standards are the goods standards that committees sell their customers. As
for a company the goods have of course to be of high quality, have to be
according to the specification issued by the customers but, foremost, they
have to be delivered by the agreed date.
Standards are not novels, standards are the technology that enables
companies to make products (those sold to end users). If a company makes
a plan to go to the market by a certain date with a certain product that
requires a certain technology, and makes the necessary investments for it,
the company - the buyer vis-�-vis the standards committee - is not going to
be happy if the standards committee - the supplier vis-�-vis the company -
at the due date reports that they are "behind schedule".
MPEG has a strict workplan that specifies, for all parts of a standard, the
times when the levels of Working Draft, Committee Draft, Draft
International Standards and International Standards are reached. So far
there have been occasional minor slips at intermediate steps but no delay
in reaching International Standard status compared to the planned dates.
4.2 A-priori standardisation
Everybody agrees that standards should be issued by standards bodies for
which making standards is the raison d'阾re, however, the inability of many
standards committees to deliver on time, has forced companies to take
shortcuts, so-called "industry standards". These private specifications,
possibly endorsed by a few other companies, are often submitted to a
standards committee for ratification.
The main problem with such an approach is that the standards committee
then becomes a place where discussions cease to be technical, i.e. definition
of a technology, to become commercial. The issues discussed are no longer
those aimed at making a good technical standard but definition of terms of
exploitation, fitness of the technology to the current plans of companies etc.
Of course there is nothing wrong with technology deals between companies,
but this is wrong if it is done in a standards committee. MPEG instead takes
a very clear attitude:
1.Before industries make commitments the maturity of a technology for
standardisation is identified;
2.A Call for Proposals, to which interested companies are free to
respond, is usually produced;
3.In all cases the technology is standardised by MPEG experts.
So far MPEG has successfully applied this principle. Standardisation items
have been identified well in advance so that it can be claimed that no MPEG
standard has endorsed an "industry standard". It must be borne in mind that
MPEG standards do not specify complete systems. It is therefore possible
that "industry standards" are needed alongside with MPEG standards to
make complete products.
4.3 Not systems but tools
The principles described above, applicable to standardisation in general,
require further ingenuity when they are to be applied to the production of
standards that serve multiple industries.
Industries, by definition, need to make vertically integrated specifications in
order to make products that satisfy some needs. Audio-visual decoding
may well be a piece of technology that can be shared with other
communities but in the event industries need to sell a satellite receiver or a
Video CD player, and these require an integrated standard. But if different
industries need the same standard, quite likely they will have different end
systems in mind. Therefore only the components of a standard, the "tools",
as they are called in MPEG, can be specified in a joint effort.
The implementation of this principle requires the change of the nature of
standards from "system" standards to "component" standards. Industries will
assemble the tool specification from the standards body and build their own
product specification.
If "tools" are the object of standardisation, a new process must be devised
to produce meaningful standards. The following sequence of steps has been
found to be practically implementable and to produce the desired result:
1.select a number of target applications for which the generic
technology is intended to be specified;
2.list the functionalities needed by each application;
3.break down the functionalities into components of sufficiently
reduced complexity so that they can be identified in the different
applications;
4.identify the functionality components that are common across the
systems of interest;
5.specify the tools that support the identified functionality components,
particularly those common to different application;
6.verify that the tools specified can actually be used to assemble the
target systems and provide the desired functionalities.
Still industry needs some guidance. It is therefore advisable that certain
major combinations of tools be specified as normative, making sure that
these are not application-specific, but functionality-specific. These
standardised sets of tools have been called "profiles" in MPEG-2 Video.
4.4 Specify the minimum
In some environments it is very convenient to add to a standard those nice
little things that bring a standard nearer to a product specification. This is,
for instance, the case of industry standards or when standards are used to
enforce the concept of "guaranteed quality" so dear to broadcasters and
telecommunication operators because of their "public service" nature.
This practice must be abandoned when a standard is to be used by multiple
industries. Only the minimum that is necessary for interoperability can be
specified. Going beyond this border line requires a separate agreement
involving all participating industries.
4.5 One functionality - one tool
A standard is an agreement to do certain things in a definite way and in
abstract terms everybody agrees that tools should be unique. Unfortunately,
when people working for a company are in a standards committee the
determination dwindles, if they see competing technologies to their
company's prevail in the favours of the committee. The usual outcome of a
dialectic battle lasting anywhere from an hour to three years is
compromising the intellectually accepted principle of one functionality - one
tool and, voil�, "options" come in. Because of too many signalling options it
took 10 years for European ISDN to achieve a decent level of
interoperability between different telecommunications operators and, within
the same operator, between equipment of different manufacturers. Because
of too many options many standards were stillborn because the critical mass
that would have justified the necessary investments by the industry could not
be reached.
What constitutes a tool, however, is not always obvious. Single channel and
multichannel audio or conventional television and HDTV are components
needed in many systems. Defining a single "tool" that does the job of coding
both single channel and multichannel audio or conventional television and
HDTV may be impractical because the technology has to be designed and
manufactured to do things to an extent that in some cases are not needed.
The "profile/level" philosophy successfully implemented by MPEG provides
a solution: within a single tool one may define different "grades", called
"levels" in MPEG.
4.6 Relocation of tools
When a standard is defined by a single type of industry there is generally
agreement on where a certain functionality resides in the system. In a
multi-industry environment this is not possible. Take the case of encryption.
Depending on which is your role in the audio-visual distribution chain you
will like to have the encryption function located where it serves your place in
the chain best, because encryption is an important value-added function. If
the standard endorses your business model you will adopt the standard, if it
does not you will antagonise it.
Not only must the technology be defined in a generic way, but also in such a
way that the technology can be located at different points in the system.
4.7 Verification of standard
Once the work is nearing completion it is important to make sure that the
work done does indeed satisfy the requirements ("product specification")
originally set. MPEG does that through a process called "Verification Tests"
with the scope of ascertaining how well the standard produced meets the
specification.
5. A guided tour to MPEG-1 and MPEG-2
The Moving Picture Coding Experts Group (MPEG) was established in
January 1988 with the mandate to develop standards for coded
representation of moving pictures, audio and their combination. It operates
in the framework of the Joint ISO/IEC Technical Committee (JTC 1) on
Information Technology and is formally WG11 of SC29.
5.1 MPEG-1
The first standard developed by the group, nicknamed MPEG-1, was the
coding of the combined audio-visual signal at a bitrate around 1.5 Mbit/s.
This was motivated by the prospect that was becoming apparent in 1988 to
store video signals on a compact disc with a quality comparable to VHS
cassettes'.
In 1988 coding of video at such low bitrates had become possible thanks to
decades of research in video coding algorithms. These algorithms, however,
had to be applied to subsampled pictures - a single field from a frame and
only � of samples in a line - to show their effectiveness. Also coding of
audio, as separate from speech, could rely on R&D work that allowed
reduction by 1/6 of the PCM bitrate, typically 256 kbit/s for a stereo
source, with virtual transparency. Encoded audio and video streams, with
the constraint of having a common time base, were combined into a single
stream by the MPEG system layer.
MPEG-1, formally known as ISO/IEC 11172, is a standard in 5 parts. The
first three parts are Systems, Video and Audio, in that order. Two more
parts complete the suite of MPEG-1 standards: Conformance Testing,
which specifies the methodology for verifying claims of conformance to the
standard by manufacturers of equipment and producers of bitstreams, and
Software Simulation, a full C-language implementation of the MPEG-1
standard (encoder and decoder).
Manifold have been the implementations of the MPEG-1 standard: from
software implementations running on a PC in real time, to single boards for
PCs, to the so-called Video CD etc. The last product has become a market
success in some countries: in China alone 2 million Video CD decoders
were sold this year and the number is expected to double next year.
5.2 MPEG-2
The second standard developed by MPEG, nicknamed MPEG-2, has the
title "Generic coding of moving pictures and associated audio". Work on
this standard could commence as early as July 1990 because:
at that time the technical foundations of MPEG-1 had already been
laid down
extrapolations from the results of MPEG-1 promised a quality
comparable to composite TV at about 4 times the typical MPEG-1
bitrate and
there were expectations that VLSI technology would be ready to
implement a video decoder handling full-size pictures at bitrates up to
10 Mbit/s.
Unlike MPEG-1, basically a standard to store moving pictures on a disk at
low bitrates, the much larger number of applications of the MPEG-2
standard forced MPEG to develop and implement the "toolkit approach"
described above for MPEG-2 Video. Different coding "tools" serving
different purposes were developed and standardised. Different assemblies
of tools - called "profiles" - were also standardised and could be used to
serve different needs. Each profiles had in general different "levels" for some
parameters (e.g. picture size). Tab. 2 below gives the current situation of
MPEG-2 Video Profiles and Levels.
Fig. 2 - MPEG-2 Profile/Level table
Simple
Profile
Main
Profile
SNR
Scalable
Profile
Spatially
Scalable
Profile
High
Profile
4:2:2
Profile
High Level
X
X
High-1440
Level
X
X
X
Main
Level
X
X
X
X
X
Low Level
X
X
MPEG-2 Audio is an extension of MPEG-1 Audio to the multichannel
case. This means that an MPEG-1 Audio decoder can decode two
channels of the MPEG-2 stream and an MPEG-2 Audio decoder can
decode an MPEG-1 Audio stream as if it were an MPEG-1 Audio
decoder.
As for MPEG-1 the systems part of the MPEG-2 standard addresses the
combination of one or more elementary streams of video and audio as well
as other data into single or multiple streams which are suitable for storage or
transmission. Two such combinations are specified: Program Stream and
Transport Stream.
The Program Stream is analogous to MPEG-1 Systems Multiplex. It results
from combining one or more Packetised Elementary Streams (PES), which
have a common time base, into a single stream. The Program Stream is
designed for use in relatively error-free environments and is suitable for
applications which may involve software processing.
The Transport Stream combines one or more PESs with one or more
independent time bases into a single stream. Elementary streams sharing a
common timebase form a program. The Transport Stream is designed for
use in environments where errors are likely, such as storage or transmission
in lossy or noisy media.
MPEG-2, formally known as ISO/IEC 13818, is also a multi-part standard.
The first 5 parts have the same function as the corresponding parts of
MPEG-1.
MPEG-2 has been a very successful standard, pieces of equipment that
claim conformance to it have been produced by the millions, receivers for
digital satellite broadcasting being the most popular. More application
domains are anticipated, such as digital receivers for CATV or DVD, a new
generation of compact disc capable of playing back MPEG-2 bitstreams at
a higher and variable bitrate and for a longer time than standard CDs.
ITU-T has collaborated with MPEG in the development of MPEG-2
Systems and Video which have become ITU-T Recommendations for the
purpose of broadband visual communications. This means that the same
physical document has the value of ISO standard and ITU-T
Recommendation.
5.3 Other MPEG-2 functionalities
MPEG-2 provides support to a number of technical features, the most
important of which are support to content addressing, encryption and
copyright identification.
The MPEG-2 Systems Transport Stream has been designed so that
it can be used to carry a large number of television programs. For
this reason it provides support to signal the content of the programs
by means of tables that describe which program can be found where.
This specification has been extended by regional initiatives to identify
more features, such as the nature of the program, the scheduled time,
the interval between starting times etc.
Copyright protection and management are important features that a
system designed to carry audio-visual information must support.
MPEG-2 Systems defines two special streams called ECM and
EMM that carry information that can be used to decrypt information
carried by the MPEG-2 Transport Stream, if this has been
encrypted. The encryption system itself is not specified by MPEG.
MPEG-2 Systems provides support for the management of
audio-visual works copyrighting. This is done by means of a
copyright descriptor that identifies the society that manages the rights
of that particular audio-visual work followed by a field that gives the
identification number of the work, as assigned by the society. This
information enables, for instance, the monitoring of the flow of
copyrighted work through a network.
5.4 Other parts of MPEG-2
MPEG-2, as described above, provides the enabling technology for a
variety of television-based applications, such as satellite broadcasting and
CATV, which can now send an average of 5 times more programs on the
same delivery medium if this is MPEG-2 encoded programs are carried on
top of medium-specific modulation schemes.
Other applications, however, require a standardised terminal-to-server
protocol to provide a complete working system. This is for instance the
case when the user needs to interact with the source to select the content he
or she wishes to see and hear, such as in Video on Demand and Home
Shopping.
Part 6 of MPEG-2, titled Digital Storage Media Command and Control
(DSM-CC), an International Standard since July 1996, is the specification
of a set of protocols which provide the control functions and operations
specific to managing MPEG bitstreams. These protocols may be used to
support applications in both stand-alone and heterogeneous network
environments. In the DSM-CC model, a stream is sourced by a Server and
delivered to a Client, both considered to be Users of the DSM-CC
network. DSM-CC defines a logical entity called the Session and Resource
Manager (SRM) which provides a logically centralised management of the
DSM-CC Sessions and Resources.
Part 7 of MPEG-2 is the so-called Non-Backwards Compatible Audio
Coding standard. The need for such a standard arose from the
consideration that the backwards compatibility built in MPEG-2 Audio is an
important service feature for many applications, such as television
broadcasting. This compatibility, however, entails a degree of quality
penalty that other applications need not pay. Work in this area has
produced the first specification (Committee Draft) that is being balloted with
the National Bodies. International Standard status will be reached in April
1997.
Part 8 of MPEG-2 was originally planned to be coding of video when input
samples are 10 bits, to provide room for post-processing. Work on this
part was discontinued when the professional video industry that had
requested the standard eventually shifted its interests to other domains.
Part 9 of MPEG-2, titled Real-time Interface (RTI), an International
Standard since July 1996, provides a specification for a real-time interface
to Transport Stream decoders which may be utilised for adaptation to all
appropriate networks carrying Transport Streams. RTI can be used to
achieve equipment-level interoperability in consumer electronic, computer,
and other domains because it enables the building of network adaptation
layers which are guaranteed to provide the required performance, and
simultaneously it enables the building of decoders which are guaranteed to
have appropriate behaviour of buffers and timing recovery mechanisms.
Part 10 of MPEG-2 is the Conformance Testing of DSM-CC and is still
under development.
Other current MPEG activities concern the definition of other MPEG-2
Video Profiles. The 4:2:2 Profile, completed in January 1996, provides a
response to users of professional video equipment and services who were
keen to exploit the existing consumer-electronics MPEG-2 Video
technology for professional applications. The Multiview Profile, to be
completed in October 1996, uses existing video coding tools for the
purpose of providing an efficient way to encode two slightly different
pictures such as those obtained from two slightly separated cameras
shooting the same scene.
6. MPEG-2, or Digital Television
A broadcast TV program is sometimes a simple piece of linear audio and
video, basically the output of a microphone and a video camera shooting an
outdoor scene, but sometimes it is much more than that. Imagine your
favourite evening TV news: you see a computer graphics animation with,
say, a rotating globe, an animated "Evening News" text moving along a
curve on the screen, the station's logo blinking at the bottom etc. Then you
see a snapshot of the studio, a zoom to the announcer and then a window
containing the bulleted textual summary of the main news items opens and
lasts on the screen for a few seconds. Then the announcer presents the first
news item with, say, an on-site report and an interview in the original
language with subtitles of the interpreted interview at the bottom of the
screen and an inserted small moving picture of the announcer. This is in turn
followed by a photograph of the individual the news is about with some
biographical details, lasting for a few seconds and so on�
What is the difference between this evening news program and an
interactive multimedia application from your PC or a Web page? In terms of
richness of multimedia presentation the TV program is by and large
superior. However, you cannot do the most natural thing you do when you
are shown the table of content of a Web page: choose the item you want. In
a TV program you have to watch and listen to the first item and, if you find
something of interest, you have no chance of being shown a button with the
indication "click here for more detail", nor can you click on a part of the
screen that is sensitive to your mouse.
Does this matter? Depending on whom you are talking to you will be told
that couch potatoes do not like interactivity but, oh well, something of it
would be a nice addition or that every day millions of people surf the net in
search of content that, today, contains a high degree of interactivity but no
video, the addition of which would be a great complement to the existing
media offered by the Web.
MPEG-2 by itself cannot provide interactivity to a broadcast environment,
but it is not a big deal to exploit some "hooks" and enhance the "multimedia
look" that will provide some elements that can be perceived as interactivity:
multiplexing more than one audio channel in a program can be used
to offer users the possibility to, say, switch original/interpreted
language;
multiplexing more that one video stream can be used to, say, switch
on/off the face of the announcer from a video reportage;
sending character streams as "other data" in the MPEG multiplex
gives the possibility to the user to choose subtitles in the preferred
language;
sending graphics files and animate them to enhance the multimedia
look;
sending the same program at staggered starting times decreasing the
time a user has to wait to see the preferred program.
There are many technical ways to do the things listed above. Therefore a
standard is needed if all TV receivers are expected to render the different
standard is needed if all TV receivers are expected to render the different
media correctly.
Now we are at a bifurcation point which is exactly at the same point we
heard the two differing views on interactivity. Do we want to define this
"multimedia embellishment" specification for a broadcast-only environment
or do we want to define it in such a way that the broadcast-only
environment is the zero-return channel case of a more general interactivity?
In other words, do we want convergence of broadcasting,
telecommunication and computer technologies or not?
If we do not want convergence then the multimedia look can be
implemented by exploiting some simple hooks in MPEG-2 Systems that let
you multiplex "other data" such as characters, graphic files etc. with their
time and space information along with audio and video. The approach is to
treat all additional information sources as supplementary to the audio-visual
information, e.g.
A full graphic page will be transmitted as an MPEG-2 I-frame (a
mode of MPEG-2 Video to code pictures without dependence on
past or future information);
The temporal and spatial information of rectangles containing graphic
information superimposed on top of a natural TV picture will be
transmitted by hooks present in MPEG-2 Systems;
The temporal and spatial information of moving graphics will be
transmitted extending the hooks present in MPEG-2 Systems;
The attributes of the text displayed on the screen will be encoded
using some ad-hoc method.
It is clear that no representative of the computer world is ever going to take
this solution and extend it to the non-zero return channel case. They have
been working for years starting from the other end of the spectrum, building
multimedia inch by inch as text + graphics + still pictures + � with the
intention of including eventually audio and video as the last step to full
multimedia.
In the mind of the author who launched and implemented the idea of the
Digital Audio-Visual Council (DAVIC) at the beginning of 1994 DAVIC
should have provided the neutral solution acceptable to the broadcasting,
telecommunications and computer worlds. Regrettably he failed. It was not
possible to convince DAVIC people to address the problem in a rational
way. Those of broadcast background were unable or unwilling to think of it
without making reference to "subtitling". They further aggravated the
problem with their inability to agree on a compression scheme for 2-D
arrays of pixels representing graphic information, because they kept on
saying that none of the one hundred or so graphic formats developed by the
computer world suited their needs. They invented a new text coding scheme
when a very small subset of HTML, the number of pages of which in the
world numbers tens of millions, would have amply sufficed. Those of
computer background stuck to their "application downloading" paradigm,
an impossible marriage with broadcasting. DAVIC people of
telecommunication background gathered around the MHEG standard
because it fitted their idea of multimedia information representation, that
would obviously require a standardised coded representation. In the event
DAVIC settled with a double solution, one that contrasts the
one-functionality - one tool principle: use of MPEG-2 hooks and MHEG.
This is convergence of entertainment, telecommunications and computers at
work!
Having so created a dividing line between the technology needed to make
interactive and non interactive multimedia communication, DAVIC has
automatically raised the entry threshold for the former. Interactive
multimedia communication will happen, but it will not be via an extension of
the current information consumption paradigm that is supported by
broadcasting. Interactive multimedia communication will have to wait for a
new approach that overcomes the current broadcasting/interactive
antithesis.
7. MPEG-4, or multimedia communications
With their convergence frenzy multimedia gurus have forgotten to respond
to a simpler, but basic question: what is multimedia communications? Let me
try to give my definition.
Multimedia communication is the possibility to communicate audio-visual
information that
1.is natural, synthetic or both;
2.is real time and non real time;
3.supports different functionalities responding to user's needs;
4.flows to and from different sources simultaneously;
5.does not require the user to bother with the specifics of the
communication channel, but uses a technology that is aware of it.
6.gives users the possibility to interact with the different information
elements;
7.lets the user present the result of his interaction with content in the
way suiting his needs;
MPEG-4 is the current MPEG project that is being developed to provide enabling technology for the 7 items above. Started in July 1993, it will reach
Working Draft level in November 1996, Committee Draft level in
November 1997 and International Standard level in November 1998.
Even though the MPEG-4 project predates the Internet frenzy, the
motivations at the basis of the project bear a high degree of similarity with
some of the topics that make headlines today.
Physical network independence. In spite of the word "net" Internet
has nothing to do with "network", at least not in the traditional sense
of physical-layer telecommunications infrastructure. As soon as a
communication link is digitised you can start using the Internet
Protocol (IP) and on top of it TCP or UDP and on top of these
protocols the suite of Internet Protocols, such as SMTP for mail,
HTTP for the Web, FTP for file transfer etc.
Internet has smashed vertically-integrated communications: an end
user needs not be concerned with the physical nature of the bit pipe,
if it is twisted pair, cable, optical fibre or microwave (of course the
Internet Access Provider and the Core Network Operator do care).
TCP/IP can be considered as a part of the communication socket.
Already in MPEG-1 and MPEG-2 physical-layer independence has
always been assumed and in MPEG-4 this is just confirmed. Of
course independence does not mean unawareness of network
peculiarities, the standard must be capable of coping with them.
Interactivity. The Web phenomenon has shown that the capability
to search ("surf") the net and interacting with content found in it is
indeed a feature users are keen to have. What the Web has not been
able to provide is real-time moving pictures and audio. MPEG is the
expert body in moving pictures and audio and MPEG-4 must be
capable of providing audio and video with the kind of interactivity
users have grown accustomed with the Web.
Interactivity, however, is at the level of visual objects that are of
arbitrary shapes rather than imposing the "video window" paradigm.
MPEG-4 will deliver not only multiple arbitrary shaped video
objects, but also individual audio channels associated with objects.
Once there is explicit segmentation of objects, there is far greater
scope for content developers to produce applications with hitherto
unattainable levels of interactivity.
Decoding downloadability. The success of Internet has prompted
the obvious question: if Internet is ubiquitous and the bandwidth
available to the user is constantly expanding, why should I have my
PC loaded with Mbytes of software, most of which I seldom use? Is
it not just more effective to download the software I need on
demand? Much before the network computer hype MPEG has come
to realise that in many applications a programmable decoder where
decoding tools are downloaded is a preferable solution. MPEG-4
must therefore support downloadability.
8. The MPEG-4 standard
Let us see in more detail some of the features of the MPEG-4 standard.
8.1 MPEG-4 architecture
In the MPEG-4 architecture one or more AV objects, including their
spatio-temporal relationships, if any, are transmitted from a source to an
MPEG-4 decoder, as illustrated in Figure 1. At the source, the AV objects
are error protected if necessary, multiplexed, and transmitted downstream.
The transmission may occur across multiple channels offering various
qualities of service. At the decoder, the AV objects are demultiplexed,
error corrected if necessary, decompressed, composited, and presented to
the end user. The end user may like to interact with the presentation.
Interaction information can be processed locally, or can be transmitted
upstream to the encoder for action.
Before the AV objects are transmitted, the source and the decoder must
exchange configuration information. The source determines which classes of
algorithms, tools, and other objects are needed by the decoder to process
the AV objects. Each class of objects can be defined by a data structure
plus executable code. The definitions of any missing classes are
downloaded to the decoder, where they supplement or override existing
class definitions installed or pre-defined at the decoder. As the decoder
executes, new class definitions may be needed in response to user
interaction. The decoder can request that the source download specific
additional class definitions, possibly in parallel with the transmitted data.
Fig. 1 - General MPEG-4 architecture
8.2 Multiplexer
The multiplexer performs the function of combining all the elementary data
streams into one output data stream. The demultiplexer defines
functionalities needed to recover a system time base, synchronise multiple
compressed data streams on decoding, interleave multiple compressed
streams into a single stream and initialise and continuously manage the
decoder buffers (Fig. 2).
Fig. 2 - MPEG-4 multiplexer
Some MPEG-4 applications do not involve the serialisation function but the
stream-synchronisation-related functions still apply.
8.3 Video
In MPEG-1 and MPEG-2 the video information is assumed to be
rectangular of fixed size displayed at fixed interval. In MPEG-4 the concept
of Video Object (VO), Video Object Layer (VOL) and Video Object
Plane (VOP) have been introduced (Fig. 3). VOP represents instances of a
given VO. VO and VOP correspond to entities in the bitstream that a user
can access and manipulate (with e.g. cut and paste operations). The VOP
can have arbitrary shape. At the encoder side, together with the VOP,
composition information is sent to indicate where and when each VOP is to
be displayed. At the decoder side the user may be allowed to change the
composition of the scene displayed by interacting on the composition
information.
Figure 3 - MPEG-4 Video Encoder and Decoder Structure
Video Objects overcome the limitation of such standards as JPEG and
MPEG where images, still and moving, have been represented as
rectangular matrices and compressed with this format, e.g. in MP@ML of
MPEG2 video is represented as moving frames each of size e.g. 720x576
pixels. This way of representation destroys the capability to distinguish
different elements or objects that make up the picture. For the applications
that do not require content/object level interactivity, this type of
representation, and coding based on that, has proven to be very efficient.
However, it does not provide a convenient way of adding object level
interactivity. For example, if one wants to point at a particular person in a
scene and get more information about him/her (this is sometimes also called
creation of "hot regions" in a scene), it becomes necessary to represent a
scene as separate parts called objects. An object does not have to be a
person, it can be as broad as foreground or background or a local region
containing an advertisement inside a picture.
This type of representation requires that the compression scheme be able to
handle arbitrary shapes and also that the receivers not only have the
capability to decompress the compressed information but also be able to
put them together (composition). Therefore, an additional information need
to be sent to the receiver telling it how to compose, or put together, the
scene. This additional information is called Alpha Channel.
In a simple case the Alpha Channel information can be just an on or off (1
or 0) information for a given pixel. In this case different objects completely
hide the information behind them. However, in general, the Alpha Channel
can easily consist of 8 bits/pixel/frame to allow for various levels of the
transparency. As rge transmission ofsuch an information in uncompressed
form can require several Mbits/s of bandwidth it is not practical in many
situations. Thus, for this representation and object level interactivity to be
successful, a successful scheme is required to compress the Alpha Channel.
Driven by these applications in mind, the MPEG-4 Video part will provide
efficient compression of objects/parts of a scene and Alpha Channel
describing how to put those parts together.
One of the task of the System Layer (MSDL), therefore, is to allow the
capability to send (or multiplex) the additional information for different
objects and bind (or synchronize) it with the objects and/or to be able to
retrieve additional information about the selected objects with in a scene. It
should be noted that MPEG-4's field of view is not limited to allow this type
of capability for only the natural scenes but also for computer generated
information.
Amongst the main functionalities supported are spatial and temporal
scalability and error robustness at VOL and VOP level. Scalability is an
important feature when the same audio-visual objects are to be made
available through channels of different bandwidth, receivers of different
processing capability or to respond to different user requests. Robustness to
errors is also an important feature, as audio-visual communications on radio
channels is foreseen to be an important application of MPEG-4.
8.4 Audio
The NBC standard (part 7 of MPEG-2) is bringing down to 64 kbit/s
virtual transparency of single channel music which MPEG-1 Audio had set
at 128 kbit/s. It is expected that interesting performance will be obtained
even at lower bitrates than 64 kbit/s. NBC is therefore already providing
part of the MPEG-4 Audio standard. More work, however, needs to be
done in the bitrate range much lower than 64 kbit/s. This is an area where
there is a need for a generic technology serving such different applications
as satellite and cellular communications, Internet, UMTS, etc. Fig. 4 gives a
synthesis of the different bitrates, audio bandwidths, application and coding
techniques currently considered.
Fig. 4 - Bitrates, applications and techniques considered
Fig. 5 gives a block diagram that is believed to be capable to handle the
requirements of the application scenario of Fig. 4.
Fig. 5 - General block diagram of MPEG-4 Audio
8.5 SNHC
So far the communication world has treated synthetically generated contents
as subset of natural contents, e.g graphics has been communicated by
sending as a video. Therefore, there has been no standard for representing
and compressing that information separately.
SNHC stands for "Synthetic-Natural Hybrid Coding". SNHC's aim is to
treat the synthetically generated contents as another NEW data type from
the communication point of view and to standardize how to represent and
compress it. As this is the first attempt by a standards committee to do so,
it
is expected that MPEG-4 will get some initial key work done in this area
and more needs will arise that can possibly be taken care of in future phase
s
of MPEG-4 or other standards.
An initial area of focus has been to extend the models available in VRML.
In VRML it is relatively easy to create models of things that are not live,
like
table, chair etc. However, it is virtually impossible to create a good model
of human face and body. For next generation of multimedia communications
that is a very important piece missing in VRML.
MPEG-4 is first working on developing the capability to create
representations and models for human faces and bodies. It is working on
developing the standardised set of parameters required to model a human
face and to also synchronise the facial expression and lip movements with
audio. This in addition to VRML or VRML like language can allow to
create realistic scenes. After successful completion of this effort the focus
will be on developing standardised techniques and/or parameter sets for
texture mapping.
On the audio side, the initial focus is to standardize the parameter set to
allow interoperable Text To Speech conversion.
8.6 Flexibility
A decoder with all the features described may be unnecessarily expensive.
Some decoders may have been designed to support only a subset of all
coding tools (e.g. a mobile videophone) or be flexible enough to acquire the
particular subset of the tools when it decodes content from one source (e.g.
a movie) and acquire a different subset to decode content from another
source (e.g. a video game).
This is becoming possible thanks to the progress of VLSI technology that is
producing powerful programmable processors at an accelerated rate. As an
example today I can perform real-time decoding of MPEG-1
Audio-Video-System bitstreams at 1.4 Mbit/s on my 133 MHz Pentium.
The possibility will even materialise one day when coding tools, not
belonging to the standardised set, can be downloaded on fully
programmable processors.
MPEG-4 defines three capabilities of decoder programmability that support
flexibility and extensibility.
Flex_0 (non-programmable) is a finite set of standardised algorithms
of Audio, Video, System decoders made up of standardised Audio,
Video, System tools.
Flex_1 (flexible) consists of a finite set of standardised Audio,
Video, and System tools and their standardised interfaces, which
may be flexibly configured into arbitrary algorithms.
Flex_2 (extensible) is a standardised mechanism to describe
arbitrary algorithms made of arbitrary tools. It should be clear,
however, that currently no Flex_2 specification is attempted and may
be included only at a later date.
The Flex_0 case is conceptually similar to the MPEG-2 Profile/Level
arrangement. To implement Flex_1 MPEG has started the definition of tool
API (Application Programming Interface). The language selected for this
purpose is the Java language, which is also used for the purpose of linking
the tools together and providing a complete decoder. No commitment is
made at this time, however, that Java will be the language eventually
retained for these purposes.
Fig. 6 below describes how the standardised tool set can be used to
assemble algorithms and profiles.
Fig. 6 - MPEG-4 tools, algorithms and profiles
8.7 Software implementation of the standard
In MPEG-1 and MPEG-2 extensive use was already made of simulation
programs written in C language to implement the Simulation Models of
MPEG-1 and the Test Models of MPEG-2. Parts 5 of both standards give
a software implementation of both encoder and decoder. In MPEG-4 a
substantial innovation has been made with the definition of a Reference
Implementation of the MPEG-4 Audio, Video and System Verification
Model (VM), written in C or C++, recognising the benefits of reference
programs implementing the VMs as a means to improve collaboration,
speed up development, reduce unnecessary duplication of efforts and
promote eventual acceptance of the standard in the market place.
At the same time MPEG is aware of the possibility that such reference
programs become the de facto MPEG-4 standard specification. From the
ISO viewpoint a situation in which the copyright of the reference programs
are not owned by the ISO would not be acceptable. The alternatives are
either not to allow the existence of a reference VM, losing the mentioned
benefits or to define a set of rules that avoid the mentioned risks. The latter
solution has been chosen and is currently being addressed as follows:
1.All MPEG members are free to use any of the VM modules,
provided by whomever from MPEG for the purposes of executing
core experiments.
2.VM modules are written in well-documented machine-independent C
or C++. The use of other languages for the system layer VM may be
agreed in the future;
3.The copyright of decoder source code modules representing
normative elements is released to ISO. Any patent needed to
implement the VM in either hardware or software still applies;
4.ISO gives users of the standard free licence to use the normative
elements of the VM decoder software or modifications thereof for
use in hardware or software products claiming conformance to the
standard;
5.Source code donators are relieved of any liability caused by third
party use of their code in an implementation;
6.Extension of clause 3. and 4. above to include non-normative
elements of the decoder software and/or encoder software is being
considered.
9. Is this all that we need to make
multimedia communications?
MPEG-4 will provide a generic technology for multimedia communications
applications and services. In the list of issues considered above some more
elements, not currently included in the MPEG-4 considerations, are needed
to complete the picture. These are: Intellectual Property Right (IPR)
management, security, search of content, transport protocol.
9.1 IPR management
No matter what is the different consumption paradigm brought about by the
Internet and the WWW in particular, the role of content as the engine that
drives authors to produce it and users to consume it will remain intact, but
the nature of IPR will not necessarily be the same as today.
In MPEG-2 IPR management is a transposition to the digital world of what
is being done today, because of the very superficial role played by the
coding algorithm. The fact that content is digital and can be "stamped" with
the copyright descriptor gives the advantage that more effective IPR
management by automatic processing in the delivery chain becomes
possible.
Three important new elements can be discerned in an MPEG-4 scenario:
In MPEG-4 the way content is represented goes deeper into the
semantics of the information itself. There is an obvious IPR on the
elementary components (say, a VOP) and on the way they are
composited at the source, but then the user can himself make a
different compositing and presentation, using information of natural
and synthetic origin, real-time and non-real time, from one or more
different sources.
A second element of difference lies in the nature of the coding
algorithms. In MPEG-2 the algorithm is fixed, while in MPEG-4 it
may be assembled by the author. Even though every single tool may
have one or more pieces of IPR associated with it, what is the nature
of the assembly of tools used by a particular author?
In MPEG-2 a decoder is a fixed piece of silicon capable of
performing only certain operations. This case will still exist in
MPEG-4 but alongside with it there will be a range of alternative
cases culminating with the extreme case of a generic programmable
processor whose decoding software will downloaded with the
content itself. In this case "algorithm IPR" can no longer be
associated with the decoder hardware but with the content itself.
Watermarking is a widely used technology today in the analogue
domain. Watermarking is also possible in the digital domain and may
depend on the technical features of the coding algorithm. Appropriate
hooks may have to be put in place to allow an effective watermarking
of content.
There is a need to provide a solid IPR management mechanism in
MPEG-4. This will have to be done through the involvement of the content
world.
9.2 Security
Support for security in the form of encryption (ECM and EMM messages)
was already present in MPEG-2. Unfortunately the MPEG-2 specification
fell too short of the goal of enabling transparency of the encryption
technology to the user. This is becoming a major hindrance to the wide
deployment of MPEG-2 services. Moreover MPEG-2 security was
designed to provide mostly scrambling functions for a service provider in a
broadcasting environment.
These limitations should be avoided in MPEG-4. Security is an essential
feature of a communication standard that has several dimensions, scrambling
being just one of them.
9.3 Content search
MPEG-1 and MPEG-2 have been designed and are widely used to encode
content that has a clear identity such as a movie, a documentary etc. In the
current usage of MPEG-2 the so-called "Service Information" describes
each piece of content according to well-identified categories, so as to
enable search by a user.
This solution serves well the purpose for which it has been designed: to find
information of interest in a large but still manageable number of programs. It
would be awkward, as an example, to extend the solution for use in content
search in the Web. This is, however, the paradigm, if not exactly the
environment, in which MPEG-4 will mostly be used.
The lack of suitable search technologies is one of the reason why, in spite of
the explosive growth of the Web, many are questioning its business value.
The problem is exacerbated by the fact that HTML was just designed as a
language to encode text and links without any consideration for the
information searching function.
That this limitation should be avoided in MPEG-4 has been clearly identified
and a new project is about to start with the nickname MPEG-7. This will
address, among others:
the requirements from different application domains when a need for
a certain piece of MPEG-4 encoded information must be searched;
the definition of appropriate support within the MPEG-4 syntax for
search functions and
the specification of generic tools for search engines for MPEG-4
encoded information.
9.4 Transport protocol
Every age has its religion war and the one that is raging now has two camps
called ATM and Internet. In summary the technical terms of the debate are
the following.
ATM has been designed as digital broadband network capable of
carrying all sort of information. Applications should use the network
services provided by ATM via an appropriate AAL (ATM
Adaptation Layer).
Internet has already developed and deployed a suite of protocols that
provide all services that are needed by a range of (narrow band)
applications. They sit on the Internet Protocol (IP) which can sit or
not on ATM.
MPEG-4 needs not take side in this debate. As much as MPEG-2 can be
carried directly on a digital stream at the physical layer, or over ATM or
over TCP/IP, so MPEG-4 shall be usable in all three cases.
10. Conclusions
This paper has addressed the decade-old problem of multimedia
communications, recognising the unfulfilled promises of this new
communication domain and clearly separating the technical issues from the
"convergence" hype of the early nineties.
The multi-industry nature of multimedia communications calls for
cross-industry standards. The difficulty to deal with industries having so
different approaches to standardisation has then been recognised but the
successful recipe adopted by MPEG in its MPEG-1 and MPEG-2
standards can be applied again to the new standardisation project
MPEG-4, which promises to become the enabling technology for
multimedia communications.
11. Acknowledgements
The Author would like to thank Olivier Avaro (FT/CNET), Phil Chou
(Xerox), Touradj Ebrahimi (EPFL), Paul Fellows (ST), Ajay Luthra (GI),
Geoff Morrison (BTLabs), Pentti Haikonen (Nokia) Rob Koenen (KPN),
Kevin O'Connel (Motorola), Sakae Okubo (GCL), Pete Schirling (IBM),
Ali Tabatabai (Tektronix) for their careful reading of the manuscript and
their valuable comments.
12. References
1. Sakae Okubo, Ken McCann, Andrew Lippman,
1. Sakae Okubo, Ken McCann, Andrew Lippman,
"MPEG-2 requirements, profiles and performance verification - Framework
for developing a generic video coding standard",
Signal Processing: Image Communication, Vol. 7, pp.201-209, 1995.
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