mpeg compression standards

PROJECT REPORT

MPEG COMPRESSION STANDARDS

by

AJAY KHATRI

Submitted: December 25th, 2014

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Table of Contents

Table of Figures ............................................................................................................................ 2

Glossary of Terms ......................................................................................................................... 3

1 Compression ............................................................................................................................. 4

1.1 Introduction ........................................................................................................................... 4

1.2 History of MPEG .................................................................................................................. 4

2 MPEG-4 .................................................................................................................................... 7

2.1 Introduction ........................................................................................................................... 7

2.2 Parts....................................................................................................................................... 7

2.3 Working steps ....................................................................................................................... 7

2.3.1 Reduction of resolution. .................................................................................................. 7

2.3.2 Motion compensation...................................................................................................... 8

2.3.3 DCT............................................................................................................................... 10

2.3.4 Quantization. ................................................................................................................. 11

2.3.5 Entropy encoding. ......................................................................................................... 11

2.4 Applications. ......................................................................................................................... 12

3 MPEG-7 .................................................................................................................................. 14

3.1 Introduction ......................................................................................................................... 14

3.2 Applications ........................................................................................................................ 14

4 MPEG-21. ............................................................................................................................... 15

4.1 Introduction. ....................................................................................................................... 15

4.2 Applications.. ..................................................................................................................... 16

5 Summary ................................................................................................................................. 17

References .................................................................................................................................. 18

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Table of figures

Figure 1: Codec and MPEG standards .......................................................................................... 4

Figure 2: Sub sampling of colors .................................................................................................. 6

Figure 3: VOP vs. frame based coding ......................................................................................... 7

Figure 4: Forward and backward frames ...................................................................................... 8

Figure 5: Arbitrary shape of VOP ................................................................................................. 9

Figure 6: Zigzag tracing of AC & DC components .................................................................... 10

Figure 7 4x4 block for coding ..................................................................................................... 10

Figure 8: Relation between tool and elaboration process ........................................................... 12

Figure 9: MPEG-21 timeline ...................................................................................................... 12

Figure 10: Interaction of users. ................................................................................................... 13

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Glossary of terms

MPEG: Motion Pictures Expert Group

ISO: International Standardization Organization.

ITU: International Telecommunication Union.

IEC: International Electro-Technical Commission.

JTC: Joint Technical Committee.

VOP: Video Object Plane

VO: Video Objects

DCT: Discrete Cosine Transform.

IDCT: Inverse Discrete Cosine Transform.

AV: Audio-Video.

XML: Extensible Markup Language.

AVC: Advanced Video Coding.

AAC: Advanced Audio Coding.

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1 Compression

1.1 Introduction

Compression means to store and transfer a given piece of information(audio, video or an image)

using fewer number of bits. Raw data is fed to an encoder, compressed data flows through the

network or medium, and is decompressed at receiver end using a decoder. Few of the advantages

that data compression offers can be:

Reduced bandwidth usage.

Less storage space required.

Lower communication cost(Infrastructure).

Data compression is either lossy or lossless in nature. In lossless compression technique there is

a variation of information received from actual data being sent. But these variations are not

easily detected by human eyes and ears. Lossless compression method is used for files, text

documents, etc. where the accuracy of content is given utmost importance. Out of these, lossy

compression has got wider range of applications. The two famous groups responsible for setting

audio-video standards are JPEG and MPEG. JPEG basically accounts for still images, and

MPEG is responsible mainly for moving frames i.e. videos. One can find a lot of similarities in

the workflow of standards set by these groups.

1.2 History of MPEG

MPEG stands for Motion Picture Experts Group. It is basically a group of authorities that was

established by a combined effort of ISO(International Standardization Organization) and

IEC(International Electro-technical Commission). The main role is to set standards for

compression of audio, video and related data. The first joint meeting was held in the year 1988 in

Ottawa, Canada. This group helps the industry to make better use of digital media. The

designation is denoted by ISO/IEC JTC1/SC29 WG11- Coding of moving pictures and audio.

The main sub groups can be named as:

Requirements.

System.

Video.

Audio.

3D Graphics.

Test.

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Communication.

This sub groups often collaborates with other groups such as Joint Video Team (JVT) and Joint

Collaborative Team on Video Coding(JCT-VC). There is a dedicated standardization process

involving multiple stages like Preliminary Work Item(PWI), Working Draft(WD), Committee

Draft(CD), Draft International Standard(DIS), Proof of a new International Standard(PRF),

International Standard(IS).

Wide range of MPEG standards have already been approved and used in the industry. Some of

the worth mentioning compression standards are:

1) MPEG-1: This standard was established in the year 1992. It defines production of reasonable

quality images and low bit rate sounds. It achieved great success due to low space requirement,

but the acceptance went down with evolution of further standards. MPEG-1 Audio layer III

forms MP3 which is based on a lossy compression technique.

Figure 1: Codec and mpeg standards[1]

2) MPEG-2: Designated to produce higher quality images at higher bit rates. It was established in

the year 1994. Also known as ITU-T H.261.

3) MPEG- 3: This standard should not be confused with audio MP3. The sole purpose of this

standard was HDTV, providing sampling rates between 20-40 Mbits/Sec. Later on it was merged

to MPEG-2 only.

4) MPEG-4: This is still the most widely accepted MPEG standard, introduced in the year 1998.

It defines the compression of audio-video data for web, Compact discs, voice and broadcast

applications.

5) MPEG-7: It is basically a description standard for multimedia. In other words it can be called

as Multimedia Content Description Interface. For example: Lyrics synchronization, etc.

6) MPEG-21: The core term of importance in MPEG-21 to talk about is Digital Item. Its main

objective is to define a standard to manage restrictions on digital content usage. License

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information can be considered as a good example of MPEG 21. Some researchers consider it as

an extension of MPEG-2.

There is a thin line of difference between mpg and MPEG-1. The above picture shows the type

of data containers, codec and MPEG compression standards. There is still a lot of research going

on in the field of video compression techniques. Each MPEG standard consists of different parts

which are further subdivided into Profiles and Levels. Profiles are meant to describe available

tools and levels are related to defining values for properties associated with them.

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2. MPEG- 4

2.1 Introduction

MPEG-4 is formally known as ISO/IEC 14496. The traditional features of older compression

techniques like MPEG-1 and MPEG-2 have been carried along with addition of some new

features like object oriented composite files, 3D rendering and various interactive features. For

multimedia producers, MPEG4 offers a better reusability feature and copyright protection. It

uses object based coding method. MPEG-4 offers the following features:

Greater efficiency as compared with MPEG-2.

Encoding of mixed data(audio, video, speech).

Interaction of audio-visual scene at receiver.

MPEG-4 has got a large number of parts and is still considered as an evolving standard. Some of

the corporate tech giants promoting the capability of this standard never specify which part of

MPEG-4 the product actually supports. Uses of MPEG 4 includes TV broadcasting, mobile

entertainment, internet video, conferencing, etc.

2.2 MPEG4 Parts

MPEG-4 consists of several different closely related standards which are known as "parts".

Total of 30 parts are there, out of which the fundamentals of MPEG4 are described by:

Part 1: ISO/IEC 14496-1: Systems

Part 2: ISO/IEC 14496-2: Visual

Part 3: ISO/IEC 14496-3: Audio

Part 10: ISO-IEC 14496-10: Advanced video coding. This is technically similar to H.264.

2.3 Working steps

MPEG-4 is an inclusive superset of mpeg-1 and mpeg-2 standards. This means the core

compression algorithm remains the same except the fact that it has got so many additional

features like re-scalability and user interactivity. These features are defined with the help of

further sub parts of MPEG-4. MPEG-4 also offers improvements over audio video codec's with

introduction of AVC, AAC. Starting with reduction of resolution, it ends with quantization

using run length or Huffman encoding. The 5 basic steps can be described in detail below:

1) Reduction of resolution: For a human eye, it is not easy to differentiate between almost same

colors. Eyes are comparatively more sensitive to dark-bright contrasts. This serves as the base for

conversion of available RGB color space to YUV color components. The U and V components

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are responsible for chrominance whereas Y is responsible for luminance. Here, U and V

components are sub sampled to nearly half of the total pixels horizontal direction(4:2:2). Also it

can be done in both horizontal and vertical directions(4:2:0) as shown in the picture below:

Figure 2: Sub sampling of colors[2]

Mathematically we have,

|Y |=|U |=|V |

Thus we can see that sub sampling reduces the total data volume by 50% when both horizontal

and vertical technique techniques are utilized. Coming down to audio compression, a similar

technique is observed. But at this point, only video compression is of importance to us.

2) Motion Compensation: Sometimes this process is also referred to as Motion Estimation. The

main aim of this algorithm is to get a motion vector that describes the transformation between

objects. MPEG-1 and MPEG-2 use block based or frame based compensation. MPEG-4 uses an

entirely new concept called as video object plane. The technique is known as VOP coding. The

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basic difference between frame based and object based encoding techniques can be explained

with the help of a diagram shown below:

Figure 3: VOP Vs frame based coding[3]

I VOPs: Intra frame coded VOPs.

P VOPs: Inter frame coded VOPs for forward direction.

B VOPs: Inter frame coded VOPs for bidirectional direction.

Figure 4: Forward and backward frames[4]

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While doing motion compensation technique for VOPs, the arbitrary shape of VOPs while

carrying out further process should be considered. For this process, there is shape coding. This

involves assigning values '0' and '1. This forms a type of binary map. Also the opacity and

transparency of the object plane is determined using this bitmap values.

Figure 5: Arbitrary shape of VOP[5]

3) Discrete Cosine Transform: This transform technique converts still VOP object blocks into

their equivalent frequency domains. Each 8x8 or 16x16 VOP block is represented in its

frequency domain with the given formula:

Here f(x,y) represents the position of pixel at coordinate (x,y). In order to reconstrcut the pixel

values at decoder end, inverse discrete transofrm is used. The equivalent equation can be given

as:

Here F(u,v) represents the transform value matrix at [u,v]. The reults obtained after carrying out

IDCT are exactly the same as before DCT.

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4) Quantization: During this process, the DCT terms are divided by a quantization matrix. The

main logic behind quantization is to exploit human visual perception. Thus, this accounts for the

major loss as well. Higher frequencies end up with a zero after quantization.

FQ= F(u, v) DIV Q(u, v)

Here Q is the quantization matrix. Selection of Q determines the final compression and quality as

well. This process creates a separation between AC and DC terms. AC terms are stored in a

zigzag path in increasing order of frequencies.

Figure 6: Zigzag tracing of AC and DC components[6]

5) Entropy Encoding:

The entropy coding converts a vector X made up of integers into binary set Y. Its main role is to

exploit redundancies in the dataset in order to reduce the size of outcome set Y. There are variety

of techniques used for MPEG-4 which can be listed as:

Context adaptive binary arithmetic coding.

Context adaptive variable length coding.

Out of above three techniques, CAVLC is mostly preferred as it offers good compression rates. It

is used to transform zigzag order blocks of transformation coefficients. CAVLC[7]

is preferred

over CABAC as it offers comparatively easier decoding and can be explained as:

For example: 0,3,0,1,-1,-1,0,1,0…

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Figure 7: 4X4 block for coding[8]

Total coefficients= 5( High to low frequency) Number of zero= 3 Total number of one=3

Element Value Code

coeff_token TotalCoeffs=5, T1s=3 0000100

T1 sign (4) + 0

T1 sign (3) - 1

T1 sign (2) - 1

Level (1) +1 (use Level_VLC0) 1

Level (0) +3 (use Level_VLC1) 0010

TotalZeros 3 111

run_before(4) ZerosLeft=3; run_before=1 10




The bit stream finally obtained for this block is 000010001110010111101101. This is finally the

last process to understand when it comes to MPEG-4 standard.

2.4 Applications

MPEg4 is the most widely used standard till date. It has got a very large range of applications,

few of them are described in points below.

IP based television distribution: Due to the easy availability of DSL and broadband

connections, IP based television is the replacement for satellite or cable television. It is

entirely based on MPEG-4 part 10 AVC as it offers highest efficiency.

Portable gaming: Gaming accessories manufacturer like SONY use MPEG-4 for viewing

videos stored in the device memory or on external memory cards. The play station

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portable also uses this MPEG-4 for playing videos. For audio purposes, it uses Advanced

audio coding(MPEG4 part 7).

Mobile entertainment: The introduction of 3G mobile standards for mobile phones in the

year 2001 revolutionized the video access feature in mobiles. Nowadays the video calling

features over 3G network is based on MPEG-4 standard. Also the music download

services rely on MPEG 4 AAC.

Internet streaming: This is one of the most important applications of MPEG-4. Apple's

QuickTime platform uses MPEG-4 simple profile. The recent quicktime 7 is based on

recently developed MPEG-4 AVC.

Video conferencing: MPEG4 part 10 advanced video coding forms the base of video

conferencing. It offers comparatively better video than H261 and H263.

Surveillance cameras: Video security firms these days have started to use MPEG-4 at D1

resolution with 30 frames per second. This reduces the storage cost. Also the

interoperability feature allows the usage of equipments from different manufacturers with

their system.

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3 MPEG-7

3.1 Introduction

Formally known as ISO/IEC 15938. It is basically a description standard, contains no algorithm

like MPEG-1, MPEG-2 and MPEG-4. The purpose of this standard is to allow easy searching of

content by the user over the internet. It has nothing to do with encoding and decoding of data. It

uses XML to store data and can be attached with a timestamp in stream of data. The main idea

was to standardize:

a set of description schemes(DS) and descriptors(D).

a description language for above descriptors(DDL).

a scheme for including the description into mainstream data(system tools).

Figure 8: Relation between tools and elaboration process[9]

A basic feature of MPEG-7 is that the audio visual content must be different from the

description. On the other hand, there must be a relation between description and content. So it

means both must be multiplexed. .

3.2 Applications

MPEG-7 standard is still under testing phase. But it will prove to be useful for multimedia

directory services such as yellow pages, etc. Another use is in library such as musical dictionary.

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4 MPEG 21

4.1 Introduction

Formally known as ISO/IEC 21000. The main motive behind introduction of this standard is

related to multimedia applications. It is based on 2 concepts:

Definition of a digital item.

User interaction with those digital items.

A digital item is a structured object having a well defined representation and metadata located

inside a MPEG-21 framework. This digital item has an identification factor as well. In practical

usage, digital item has resources, metadata and structure. Structure represents relation between

resource and metadata. Movie compilation can be considered as an example of digital item

which includes movie, photos, interviews with actors, ratings, etc. The current progress of

MPEG-21 is shown below:

Figure 7: MPEG-21 Timeline[10]

A user basically interacts with digital items. Here user can be a organization, community or

software agents. In simple words, a user interacts with other user through Digital item. The

figure below shows two different users interacting with each other. MPEG-21 considers a

resource provider and a user equal to each other. But it is interesting to note that the users can

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protect their rights and responsibilities while interacting with other user. This is shown in the

diagram below:

Figure 8: Interaction of users[11]

4.2 Applications

MPEG-21 is still under development phase. Researchers are looking to implement this standard

for information systems management sources like digital libraries. The concept of digital rights

management is a very wide topic for delivering quality of services using MPEG-21. One other

area of application research for MPEG-21 is digital TV broadcasting.

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5 SUMMARY

Due to the wide scope of multimedia applications, need for up gradation of technology standards

is always there. This project mainly focused on MPEG4 video compression standard, which is

the most widely used standard till date. It involved discussion of basic steps in encoding process

followed by various applications. After this, a brief introduction to the most recent developments

in the form of MPEG-7 and MPEG-21 was observed. The upcoming standards don't define a

new encoding-decoding process, instead new functionalities are being added to the basic

algorithm.

Concluding, MPEG-4 is still the most efficient and effective standard for compression of moving

objects such as video files.

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REFERENCES

General:

Explanation of video compression sequences.

http://www.axis.com/files/whitepaper/wp_videocompression_33085_en_0809_lo.pdf

MPEG-4 video compression.

http://www.cs.cf.ac.uk/Dave/Multimedia_CM0340/PDF/12_CM340_MPEG4_VIDEO.pdf

MPEG-4: An object-based multimedia coding standard supporting mobile applications. Atul Puri

and Alexandros Eleftheriadis. 2004.

Fundamentals of multimedia, Chapter 12. Li & Drew Prentice Hall 2003.

http://www.cs.rutgers.edu/~elgammal/classes/cs334/slide12_short.pdf

Understanding MPEG4, MPEG industry forum. Whitepaper.

https://www1.ethz.ch/replay/docs/whitepaper_mpegif.pdf

MPEG Video compression technique.

https://vsr.informatik.tu-chemnitz.de/~jan/MPEG/HTML/mpeg_tech.html

Citations:

[1] Djordje Mitrovic, "Video Compression", University of Edinburgh. Slide 1.

http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/AV0506/s0561282.pdf



[3] Prifysgol Caerdydd, "Multimedia CMOS 540", Cardiff University. Slide 515.

http://www.cs.cf.ac.uk/Dave/Multimedia_CM0340/PDF/12_CM340_MPEG4_VIDEO.pdf

[4] Per Trane and Joakim Welin, "A new method for Motion Compensation in MPEG using

Hierarchical Mean Calculation", December 1995.

[5] Graham R Martin, "Block matching motion compensation", The university of warwick.

http://www.dcs.warwick.ac.uk/research/mcg/bmmc/



[7]Context adaptive variable length coding. http://en.wikipedia.org/wiki/Context-

adaptive_variable-length_coding

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[8] 4x4 block for CAVLC. http://en.wikipedia.org/wiki/Context-adaptive_variable-

length_coding#mediaviewer/File:4x4CAVLC.svg

[9] MPEG-7.

http://upload.wikimedia.org/wikipedia/commons/thumb/f/fa/Mpeg7image2.svg/350px-

Mpeg7image2.svg.png

[10] Information Technology- MPEG 21 multimedia framework. http://mpeg-21.itec.uni-

klu.ac.at/cocoon/mpeg21/

[11] Information technology- MPEG 21 multimedia framework. http://mpeg-21.itec.uni-

klu.ac.at/cocoon/mpeg21/

mpeg compression standards

Engineering

history of mpeg

ajay khatri

working steps

reduction of resolution

motion compensation

entropy encoding

glossary of terms