Multimedia Compression Technologies - Google Sites

An Introduction to Lossy Multimedia Compression Technologies Vinay M K Co-founder and Sr DSP architect PathPartner Technologies

Contents

Video compression basics and tools Trends in video compression Standards for lossy video compression References

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Vinay M K PathPartner Technologies

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Video compression basics and tools

Video compression exploits : Spatial redundancies – Intra frame coding Temporal redundancies – Inter frame coding

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Encoder overview

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Intra frame coding

Processed on each macroblocks Coding methodology very similar to JPEG

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Need for inter-frame encoding

In each subsequent frames most of the objects are fixed excepts for few Exploit this basic premise

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Motion compensation - MC

For every MB in target frame search corresponding best matching MB in reference frame On finding code the difference and transmit as MV

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Inter frame coding – P frames

Motion can be at fractional sample distances as well - various standards support different sample resolutions and interpolation logic 2/1/2008


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Search problem

Cost function for best match is SAD – Mean 2/1/2008 M K PathPartner Technologies 10 absolute error Vinay function

Inter frame coding – B frames

Uses both past and future reference frames

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Typical compression ratios Type

Size

Compression

I

18KB

7:1

P

6KB

20:1

B

2.5KB

50:1

Avg

4.8KB

27:1

Figures are for MPEG-1 codec Better performance expected in later standards

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Advanced features

Unrestricted motion vectors Prediction of motion vectors from neighbouring blocks Quarter pixel interpolation Intra-prediction 4x4 sub-block processing DC/AC coefficient prediction Inloop deblocking filter module 2/1/2008


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Standards comparison chart Body

Standard

Bit-rate

Application

ITU-T

H.261

192Kbps

ISDN-Phone

ISO

MPEG-1

1.5Mbps

CD-ROM

ISO

MPEG-2

4-8Mbps

SDTV, HDTV

ITU-T

H.263

2 Mbps

PSTN-Phone

ISO

MPEG-4

1 Mbps

Streaming, IP

ITU-T /ISO

H.264

< 1Mbps

MMS, cellular systems, IP

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References

ITU-T SG16, Gary Sullivan, ed., “Draft text of Recommendation H.263 Version 2 (“H.263+”) for Decision,” January, 1998. ITU-T Recommendation H.261: “Video codec for audiovisual services at p x 64 kbit/s,” Geneva, 1990, revised at Helsinki, March 1993. ITU-T Recommendation H.263: “Video coding for low bitrate communication,” March 1996. ITU-R Recommendation BT.601-4: “Encoding parameters of digital; television for studios.”

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