CHAPTER-VIDEO COMPRESSION STANDARDS

1

Contents

What is Video Compression? Why Video compression? Video Compression Standards Evaluation of Video standards H.26X (X=1,3,4)Video Standards Comparison of H.261 with MPEG Comparison of H.26X Question –Answer References

Storing video in less bit is known video compression.Video Compression follow lossy method .Video compression use modern coding

techniques to reduce redundancy in video data.Video compression focus on reduction of

Spatial and Temporal redundancy.Major role played by Temporal redundancy in

video compression.

3

What is Video Compression ?

640 x 480 resolution, 8 bit color, 24 Fps un compressed video contains-

307.2 Kbytes per image (frame) 7.37 Mbytes per second 442 Mbytes per minute 26.5 G-Bytes per hours

4

Why Video Compression ?

640 x 480 resolution, 24 bit colors, 30 fps uncompressed video contains- 921.6 Kbytes per image (frame) 27.6 Mbytes per second 1.66 G-bytes per minute 99.5 G-bytes per hour � 100 Gigabyte disk (100 x 109 bytes), can

store about 1- 4 hours of high quality video �5

Continue………………

Raw video contains vast amount of data. Sending these video through communication

channel required very high bandwidth andstorage capacity.Without compression communication of video

take huge time and very high cost.20 Mb/s HDTV channel bandwidth require

compression by factor 70.

6

Continue……………

7

Data compression Methods

Loss of information is acceptable in a picture of video.The reason is that our eyes and ears cannot

distinguish subtle changes.Loss of information is not acceptable in a text

file or a program file.Examples of lossy method- Joint photographic experts group (JPEG) Motion picture experts group (MPEG)

8

Lossy Compression Methods

H.261/H.262/H.263/H.263+/H.263++/H.264/H.265 Video MPEG-1, MPEG-2, MPEG-4, etc. AVI�Cinepak �Sorensen �Indeo Real

9

Video Compression Standards

Evaluation of Video Standards

10

Evaluation of Video Standards

11

Symmetric compressionRequires same time for encoding anddecoding Used for dialog mode applications(teleconference).�Asymmetric compression

Performed once when enough time is available(Two Pass Encoding used for retrieval modeapplications) Asymmetric compression does notacquire same time for encoding and decoding.

12

Types of Compression

H.261 is a video coding standard adopted by by the ITU(CCITT) in 1990.

It is the most widely used international video compression standard for video coding.

H.261 is usually used in conjunction with other control and framing standards.

13

H.261 Video Compression Standard

CIF(Common Intermediate format)-This ismainly used for high bit rate application.

QCIF(Quarter CIF)- This is one quarter of CIFand it is mainly used for low-bit rate application.

(Aspect ratio, Temporal rates, Interlacing aresame in CIF and QCIF but they differ inChroma(U,V) and number of active pels/lineLum(Y) )

H.261 Input Image Formats

14

H.261 have mainly two compression mode-

1.Intra Mode- The intra Mode is similar to JPEG still image compression which is based on block by block DCT Coding technique.

2.Inter Mode- In this mode Temporal prediction is employed with or without motion compensation. Then the interframe prediction error is DCT encoded.

H.261 Compression mode

15

The H.261 standard describes the videocoding/decoding methods for the video portion ofan audio visual service.

Designed for data rates of p*64 kbps, where p is inthe range 1-30.

Targeted for circuit-switched networks (ISDN wasthe communication channel considered within theframework of the standard)

16

H.261 Features-

Defines two picture formats:i) CIF (352x288) ii)QCIF(176x144)

The H.621 encoding algorithm is a combination of: inter-picture prediction (to remove temporal

redundancy) transform coding (to remove spatial redundancy) motion vectors (for motion compensation)

17

Continue……..

It provide maximum coding delay of 150 msec(because it is mainly intended for bidirectionalvideo communication)

It provide low cost VLSI implementationwhich is well suited for commercialization ofvideophone and teleconferencing equipment.MPEG 1 part 2 design is heavily influenced

by H.261

Continue……….

18

-

19

H.261 Coding Process

H.261 Encoder-E

DCT-1

Q-1

ME

MC

Codingcontrol

VLCQDCT

Framebuffer

-

+

Video in

Intra/interMode

Qp

Video out

MV

H.261 Decoder

D

MC FrameMemory

+

IDCT

Q-1VLCDecoderBufferError

Correction

Input data

Decoded data

Intra/inter

Motion Vector

Step size

H.261 Summary

Used in video/teleconferencingTwo dimensional (2-D) 8 X 8 DCT to remove intra-frame

correlationZig-zag order to scan the transform coefficientsRun Length coding for zero-valued coefficients after

quantizationMotion estimation is applied to video sequence to improve

the prediction between successive frames

Continue……….

Transmission rates control in the range of p X 64 KbpsError resilience including synchronization and

concealment technique required in transmission code, to cover up channel errorsCommon Intermediate Format (CIF) and Quarter

CIF (QCIF) for a single solution to different video formats (NTSC / PAL)

H.261Based on JPEGEncodes video only Lossy algorithm with compression in space and timeUses I and P-framesUses DCT on 8x8 blocksBest for video with little motion (eg. video conferencing) Optimized for bandwidth efficiency and low delay

24

Comparison of H.261 with MPEG

25

MPEG Based on H.261 and JPEG Encodes audio & video Lossy algorithm with compression

in space and time Uses I, P, and B-frames Uses DCT on 8x8 blocks Designed to handle moving picture

components Less bandwidth efficient

Video conferencing productsMS Windows NetMeeting Audio VisionIntel Video Phone Internet PhoneH.261 is currently used in teleconferencing standards

H.320, H.323 and H.324

26

Application of H.261

Internet Phone

27

Intel Video Phone

28

Intel video Phone S/w

29

Intel Video Phone Upgrade Kit

30

ITU- International Telecommunication UnionCIF - Common Intermediate Format

DPCM – Differential Pulse Code Modulation

DCT – Discrete Cosine Transform

ISDN – Integrated Services Digital Network

Key Word Used in H.261

31

Spatial Redundancy Temporal Redundancy Motion Compensation

Continue…….

32

Initially created for videoconferencing and video on internet, this codec was a major step towards the standardization of video compression.

In this capability for progressive scan is better than H.261

It was primarily used as a starting point for the development of MPEG ( that is optimized for higher data rates).

MPEG 4 part 2 similar to H.263

H. 263

33

It is now used to compress video in Flash format.Its disadvantages is that makes a fairly

intensive CPU use and may not be successful in lower-end machines.

Continue……………….

34

This codec provides high quality encoding and decoding for streaming video applications in real time, at rates ranging from one quarter to half the file size of previous video formats.

The file size achieved is 3 times smaller than those achieved with MPEG-2 codec’s

Good quality images achieved both high and low ratios as better picture quality than MPEG-2, MPEG-4 or H.263.

MPEG 4 part 10 and H.264 are technically identical

H.264

35

H.264

36

H.264 Picture Quality

37

It is twice more efficient than MPEG-4. It is easy to integrate and covers a wide range of image Its disadvantages are that requires more time

to coding and licensing agreements are complicated

Continue………

38

Comparison of H.26X Standards

39

Refrences:-1.Murat Tekalp “ Digital video processing’’ Prentice Hall Signal Processing series publication, ISBN: 0-13-190075-7 (alk paper) published Year 1995.2.AL Bovik, “The Essential Guide to Video Processing” Academic Press is an imprint of Elsevier publication, ISBN: 978-0-12-374456-2 published Year 2009.3.Video codec for audiovisual services at p x 64 kbit/s ITU-T (International Telecommunication Union – Telecommunication Standardization Sector) Recommendation H.261, 19934.Stephen J. Solari, Digital Video and Audio Compression, McGraw-Hill Professional; (March 1, 1997) 5.K. Rijkse, “H.261 : Video Coding for Low-Bit-Rate Communication”, IEEE Communications Magazine, pp. 42 – 456.H.261 Video Coding , http://www-mobile.ecs.soton.ac.uk/peter/h261/h261.html7. www.itglitz.in/ICT/unit2/unit%203/H261.PPT