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Introduction to MPEG
1. What is MPEG ?
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.
Starting from its first meeting in May 1988 when 25 experts participated,
MPEG has grown to an unusually large committee. Usually some 350 experts from
some 200 companies and organisations from about 20 countries take part in MPEG
meetings. As a rule, MPEG meets three times a year (in March, July and November)
but meets more frequently when the workload so demands. In 1998 it will hold 5
meetings, all lasting 5 days.
A large part of the MPEG membership is made of individuals operating in research
and academia. Even though the MPEG environment looks rather informal, it has
to be borne in mind standards can be of high strategic relevance. It should
be no surprise that operation of ISO standards committees is carefully regulated
by "Directives" issued by ISO/IEC and "Procedures for the Technical Work" issued
by JTC1.
MPEG exists to produce standards. Those currently produced by ISO are indicated
by 5 digits (the ISO number for MPEG-1 is 11172 and for MPEG-2 is 13818). Published
standards are the last stage of a long process that starts with the proposal
of new work within a committee. These proposals of work (NP = New Proposal)
are approved at Subcommittee and then at the Technical Committee level (SC29
and JTC1 respectively, in the case of MPEG).
- MPEG-1 Target: VHS quality on a CD-ROM (320 x 240 + CD audio @ 1.5
Mbits/sec)
- Standard had three parts:
- Video: based on H.261 and JPEG
- Audio: based on MUSICAM technology
- System: control interleaving of streams
2. MPEG Video
- Recall H.261 dependencies:
- Problem: many macroblocks need information not in the reference
frame.
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3. Differences from H.261
- Larger gaps between I and P frames, so expand motion vector search
range.
- To get better encoding, allow motion vectors to be specified to
fraction of a pixel (1/2 pixels).
- Bitstream syntax must allow random access, forward/backward play,
etc.
- Added notion of slice for synchronization after loss/corrupt
data. Example: picture with 7 slices:
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- B frame macroblocks can specify two motion vectors (one to past and
one to future), indicating result is to be averaged.
Compression performance of MPEG 1 ------------------------------
Type Size Compression
------------------------------
I 18 KB 7:1
P 6 KB 20:1
B 2.5 KB 50:1
Avg 4.8 KB 27:1
------------------------------ |
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4. MPEG Video Bitstream
- Public domain tool
mpeg_stat and
mpeg_bits will analyze a bitstream.
- Sequence Information
- Video Params include width, height, aspect ratio of pixels,
picture rate.
- Bitstream Params are bit rate, buffer size, and constrained
parameters flag (means bitstream can be decoded by most hardware)
- Two types of QTs: one for intra-coded blocks (I-frames) and one for
inter-coded blocks (P-frames).
- Group of Pictures (GOP) information
- Time code: bit field with SMPTE time code (hours, minutes,
seconds, frame).
- GOP Params are bits describing structure of GOP. Is GOP
closed? Does it have a dangling pointer broken?
- Picture Information
- Type: I, P, or B-frame?
- Buffer Params indicate how full decoder's buffer should be
before starting decode.
- Encode Params indicate whether half pixel motion vectors
are used.
- Slice information
- Vert Pos: what line does this slice start on?
- QScale: How is the quantization table scaled in this slice?
- Macroblock information
- Addr Incr: number of MBs to skip.
- Type: Does this MB use a motion vector? What type?
- QScale: How is the quantization table scaled in this MB?
- Coded Block Pattern (CBP): bitmap indicating which blocks
are coded.
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5. Decoding MPEG
Video in Software |
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6. MPEG-2, MPEG-3, and MPEG-4
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MPEG Resources on the Web.
Video Teleconferencing Standards (Table
I.)
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Narrow-band
VTC
(H.320) |
Low Bitrate
VTC
(H.324) |
Iso-Ethernet
VTC
(H.322) |
Ethernet
VTC
(H.323) |
ATM
VTC
(H.321) |
High Res
ATM
VTC
(H.310) |
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Videoconferencing Picture
Format:
---
Sub-QCIF - 128 x 96 Pixels;
--- QCIF - 176 x 144 Pixels;
--- CIF -
352 x 288 Pixels;
--- 4CIF - 702 x 576 Pixels;
--- 16CIF - 1408 x
1152 Pixels;
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| Video |
H.261 |
H.261
H.263 |
H.261 |
H.261
H.263 |
H.261 |
MPEG-2
H.261 |
| Audio |
G.711
G.722
G.728 |
G.723 |
G.711
G.722
G.723
G.728 |
G.711
G.722
G.723
G.728
G.729 |
G.711
G.722
G.728 |
MPEG-1
MPEG-2
G.7xx |
| Data |
T.120 |
T.120
T.434
T.84
Others |
T.120 |
T.120 |
T.120
H.281
(H.224) |
T.120 |
| Multiplex |
H.221 |
H.223 |
H.221 |
H.22z |
H.221 |
H.222.1
H.221 |
| Signalling |
H.230
H.242 |
H.245 |
H.230
H.242 |
H.230
H.245 |
H.230
H.242 |
H.245 |
| Multipoint |
H.243 |
N/A |
H.243 |
N/A |
H.243 |
N/A |
| Encryption |
(In draft
revision)
H.233
H.234 |
H.233
(adapted in
H.324)
H.234 |
(By reference to H.320) |
TBD |
H.233
H.234 |
N/A |
H.Series
- H.100 - Recommendation
H.100 (11/88) - Visual telephone systems.
- H.110 - Recommendation
H.110 (11/88) - Hypothetical reference connections for videoconferencing using
primary digital group transmission.
- H.120 - Recommendation
H.120 (03/93) - Codecs for videoconferencing using primary digital group
transmission.
- H.130 - Recommendation
H.130 (11/88) - Frame structures for use in the international interconnection
of digital codecs for videoconferencing or visual telephony.
- H.140 - Recommendation
H.140 (11/88) - A multipoint international videoconference system.
- H.200 - Recommendation
H.200 (03/93) - Framework for Recommendations for audiovisual services.
- H.221 - The Consultative Committee on
International Telephone and Telegraph (CCITT) recommendation on frame structure for a 64 to 1920 Kbit/s channel in audiovisual
teleservices.
- The framing protocol
- How bits are structures into streams
- and how they should be multiplexed over ISDN.
- H.222 - Recommendation
H.222.0 (07/95) - Information technology - Generic coding of moving pictures
and associated audio information: Systems.
- H.222.0 Corr. 1 -
Corrigendum 1 (02/98) Recommendation H.222.0 - Information technology -
Generic coding of moving pictures and associated audio information: Systems
Technical Corrigendum 1.
- H.222.0 Amd1-2 - Amendments 1 and 2 (11/96)
to Recommendation H.222.0 - Information Technology - Generic coding of moving
pictures and associated audio information: Systems.
- H.222.0 Amd.3 -
Amendment 3 (02/98) Recommendation H.222.0 - Information technology - Generic
coding of moving pictures and associated audio information: Systems Amendment
3.
- H.222.0 Amd.4 - Amendment 4 (02/98)
Recommendation H.222.0 - Information technology - Generic coding of moving
pictures and associated audio information: Systems Amendment 4.
- H.222.1 - Recommendation
H.222.1 (03/96) - Multimedia multiplex and synchronization for audiovisual
communication in ATM environments.
- H.223 - Multiplexer, designed for low
bitrate communications
- H.224 - A Real Time Control protocol for
simplex applications using the H.221 LSD/HSD/MLP channels
- H.225 - Specifies Messages for call control
including signaling, registration and admissions, and
packetization/synchronization of media stream.
- H.230 - The Consultative Committee on International Telephone and Telegraph
(CCITT) recommendation on frame-synchronous control and
indication signals for audiovisual systems
- Same as H.221 but for none audio/video data
- H.231 - ITU-T MCU recommendation for multipoint control
units for audiovisual systems using digital channels up to 2 Mbit/s
- Multipoint Control Units (MCUs)
- How bridges and mixers should work
- H.233 - Confidentiality system for
audiovisual services
- Encryption of data and distribution of keys
- H.235 - (was H.Secure). Secure operations
thru firewalls
- H.242 - The Consultative Committee on International Telephone and Telegraph
(CCITT) recommendation on a system for establishing
communication between audio-visual terminals using digital channels up to 2
Mbit/s (How to make a connection )
- H.243 - ITU-T recommendation procedures for establishing
communication between three or more audiovisual terminals using digital
channels up to 2 Mbit/s
- H.245 - ITU-T recommendation; control protocol for media
communication. Specifies messages for opening and closing
channels for media streams, and other commands, requests and indications.
- H.246 - (was H.24i and H.Interworking).
Gateway
- H.261 -1)
The Consultative Committee on International Telephone and Telegraph's
(CCITT's) standard for digitally compressed video. 2) ITU-T codec
Recommendation regarding a video codec for audiovisual services at p x 64
Kbps. Regrettably, motion compensation and field sub-sampling (loop filter)
are implementation optional in the standard. Users considering an ITU-T codec
for operation at bit rates of 384 Kbps or below should ensure that the
manufacturer has implemented these options.
- Three picture components:
- Y:C:C with 4:1:1 subsampling
- QCIF and optional CIF
- 30 frames/s. Frame types are CCIR 601 CIF (352x288) and
QCIF (176x144) images with 4:2:0 subsampling. Two frame
types: Intraframes (I-frames) and Interframes (P-frames) .
I-frames provide us with an accessing point and use basically JPEG. P-frames
use "pseudo-differences" from previous frame ("predicted"), so frames
depend on each other.
- Compression: DPCM. Predicted frames based on only previous
frames (like P-frames). No B-frames. DCT.
- Quantization is linear in contrast to MPEG that uses a
table
- Entropy encoding
- H.261 Annex D - TU-T codec Recommendation for simultaneous graphics
transmission in the North American region. Other administrations may use JPEG
.
- H.263 - ITU-T Recommendation, Video Coding for Low Bitrate Communication;
regarding a video codec for audiovisual services. Considerably broadens H.261
capabilities, extending from low- resolution, credit card-size images, to
high-quality, exceptional detail images, for applications such as
telemedicine. Backward compatibility to H.320 QCIF (Quarter Common
Intermediate Format) and, optionally, to CIF and SQCIF (Sub-QCIF) is provided.
Specifies a new video CODEC for video POTS. (Extension of
H.261 ).
- Supports higher resolutions
- Up to 16CIF (1408x1152)
- Can compete with MPEG
- Better optimization
- H.281 - A Far End Camera Control protocol
for Videoconferencing using
- H.310 - For native ATM/B-ISDN
networksI
- H.320 - TU-T codec Recommendation bringing together other recommendations to
produce an overall "visual telephony" system specification. Narrow-band visual telephone systems and terminal equipment. The H.320-series
governs the basic video-telephony concepts of audio, video and graphical communications
by specifying requirements for processing audio and video information, providing
common formats for compatible audio/video inputs and outputs, and protocols
that allow a multimedia terminal to utilize the communications links and synchronization
of audio and video signals. Like the other multimedia teleconferencing standards,
H.320 applies to multipoint and point-to-point sessions. The H.320 suite addresses
videoconferencing over circuit switched services like ISDN or Switched-56.
- H.321 - ITU-T recommendation
describing ATM-based LANs.
- H.322 - ITU-T recommendation
describing visual telephone systems and terminal equipment for local area
networks which provide a guaranteed quality of service [guaranteed bandwidth].
This standard makes direct reference to the Draft the Institute of Electrical
and Electronic Engineers (IEEE) P802.9a (which see . These standards describe
LANs which provide low latency, suitable for video conferencing.
- H.323 - ITU-T recommendation describing visual telephone systems
and terminal equipment for local area networks which provide a non- guaranteed
quality of service. (Packet Based Multimedia Conferencing
Systems).
- H.324/I - H.324 via ISDN
- H.324/M - H.324 via mobile (cellular) systems
- H.324 - ITU-T recommendation describing a terminal for low bitrate
multimedia communication; includes various recommendations including video
codec, for low-speed connections using single or dual V.34 connected to analog
POTS, plus ISDN, ATM and probably mobile, bringing together other recommendations
to produce an overall "visual telephony" system specification. Some compatibility
with H.320, network transcoding and exceptionally good multipoint support
and continuous presence are also provided. High Quality Video and Audio Compression over POTS modem connections
- H.331 - Broadcasting type audiovisual
multipoint systems and terminal equipment
- H.332 - (was H.Loosely-Coupled). Extends
H.323 to large scale conferences (thousands)
- H.450.X - Supplementary Services for H.323.
Call Forwarding and Call Transfer
-
- CIF - (Full) Common Intermediate Format. When using
ITU-T Rec. H.261 and H.263 coding methods (for videoconferencing), describes
the type of coded video frame transmitted. The CIF is 352H x 288V pixels at
video frame rates of 7.5, 10, 15 and 30 fps. Note that a codec which
provides capabilities of no greater than 7.5 fps is compliant with the
recommendation. If better motion-handling is needed, look for a numerically
greater fps specification. The table 1 gives all the possible image
resolutions under these coding methods: and SQCIF (Sub-QCIF) as well. The
table 1 provides the range of resolutions possible under H.324.
- QCIF - H.263 coding methods. (See Quarter Common
Intermediate Format. Describes a subset of the type of coded video signals
transmitted when using ITU-T Rec. H.261 and CIF). - (Full) Common Intermediate Format. When using ITU-T Rec. H.261 and
H.263 coding methods (for videoconferencing), describes the type of coded
video frame
- ITU-T-Compatible Codec - H.320. In order to be A video
codec which meets all the minimum requirements as set out in ITU-T
Recommendations H.221, H.230, H.242, H.261 and compatible with the ITU-T
Multipoint Control Unit (MCU), codecs also need to generate and receive
commands as set out in H.231 and H.243. T.120 support is also desirable.
- JPEG - Joint Photographic Expert Group". Voted
as international standard in 1992. Works with color and grayscale images,
e.g., satellite, medical, ...
- MPEG - "Motion Picture Expert Group", established
circa 1990 to create standard for delivery of audio and video MPEG-1 Target:
VHS quality on a CD-ROM (320 x 240 + CD audio @ 1.5 Mbit/sec)
- MPEG2 - Scalable and provides for predictive
(interpretive) frames when used above 2 Mbps.
- Huffman Coding - A lossless, statistically-based entropy
coding technique used to compress data in which the most frequently occurring
code groups are represented by shorter codes, and rarely occurring code groups
are represented by longer codes. Used in H.320 and other
video conferencing codecs, Group 3 facsimile and JPEG.
G.Series
A series of standards defined by the ITU-TS
covering transmission facilities. They are: G.703 2.048Mbit/s transmission
facilities running at 2.048Mbit/s that use the ITU-TS recommended physical and
electrical interface specified in G.703; G.703 641K likewise for transmission
facilities running at 64Kbits/s; G.703 the ITU-TS standard 1984 current version
for the physical and logical traits of transmissions over digital circuits.
G.703 now includes specifications for the US 1.544Mbit/s as well as the European
2.048Mbit/s, and circuits with larger bandwidths on both continents. G.703 is
still generally used to refer to the standard for 2.048Mbit/s; G.821 ITU-TS
Recommendation that specifies performance criteria for digital circuits for
ISDN.
T.Series
- T.35 - Procedure for the Allocation of CCITT
Defined Codes for Non-Standard Facilities
- T.38 - ITU-T Recommendation T.38 -
Procedures for real time Group 3 facsimile communication over IP
networks
- T.120 - An ITU-T overview recommendation describing
transmission protocols for data; including multilayer protocols which considerably
enhance media, MCU and codec control capabilities, permitting greater MCU
operational sophistication beyond that described in H.231 and H.243.
Standards address Real Time Data Conferencing (Audio graphics)
- T.120 LITE - Same as T.120
w/o T.126 and T.128
- T.121 - Generic Application Template (GAT)
- T.122 - Multipoint Communications Services
(MCS)
- T.123 - Network-Specific Transport Protocols
- T.124 - Generic Conference Control (GCC)
- T.125 - Multipoint Communications Services
(MCS)
- T.126 - Still Image Exchange (White Board)
- T.127 - Multipoint File Transfer
- T.128 - Application Sharing
- T.130 - Audio-visual Control (AVC) For Multimedia
Conferencing. ITU-T recommendation describing real-time architecture for multimedia
conferencing. This suite of standards introduces such concepts as virtual
networks, virtual and distributed MCUs and many more innovative new network
architecture approaches for voice, video, graphics, data etc. Fully supports
T.120 suite and a variety of coding and transmission methods. Note that the
numbering and content of the T.130 suite specifications is subject to change
during this formative period. This glossary will be updated as this important
standards suite develops.
- T.131 - Network-Specific Mappings (NSM)
- T.133 - ITU-T recommendation describing
audio-video control applications protocol.
- T.132 - AVC services and protocols.
- T.134 - old T.CHAT.
- T.140 - old V.CHAT.
V.Series Modems
A group of ITU-TS recommendations governing data transmission
over telephone lines.
- V.34 - is one of the latest
standards in modem protocols. It is capable of transmitting data up to 33.6k
bps. V.Fast Class (V.FC) was a de facto standard implemented from Rockwell
while waiting for the V.34 protocol's approval. Both are capable of doing
33.6k bps but they cannot communicate with each other unless the modem manufacturers'
have specifically designed this functionality into each modem. Until recently,
most of the vendors had adopted the chip from Rockwell and it has been fairly
popular among modems on the market. The V.FC modems should have an upgrade
option to V.34. The 'V.Fast' class is a generic name modem vendors give to
their 33.6k bps modem description. It could either refer to V.FC or V.34 modems.
V.34 model modems are necessary for connections with the V.34 Internet Services.
- V.35 - The International Consultative
Committee for Telephone and Telegraph (CCITT) standard for data transmission
at 48K-bps using 60-180KHz wideband circuits.
- V.70
- V.80 (for H.324)
Governmental
Standards
American National Standard
Institute
- ANSI T1.306-1990, Digital Processing of Audio Signals -
Algorithm and Line Format for Transmission of 7-kHz Audio Signals at 64/56
Kbit/s
- ANSI T1.314-1991, Digital Processing of Video Signals - Video
Coder/Decoder for Audiovisual Services at 56 to 1536 Kbit/s
European Telecommunications Standards
Institute
- ETS 300-142, Video CODEC for Audiovisual Services At p*64
Kbit/s
- ETS 300-143, Inband Signaling Procedures for Audiovisual
Terminals using Digital Channels up to 2048 Kbit/s
- ETS 300-144, Frame Structure For a 64 to 1920 Kbit/s Channel
and Associated Syntax for Inband Signaling
- ETS 300-145, Video telephone Systems and Terminal Equipment
Operating on One or Two 64 Kbit/s Channels
- ETS 300-146, Frame synchronous control and indication signals
for audiovisual systems, March 1991
The ITU, headquartered in Geneva, Switzerland
is an international organization within which governments and the private sector
coordinate global telecom networks and services.
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