Chosun Univ. Multimedia ASIC Lab. 1

http://vlsi.chosun.ac.kr

3. H.261 Video Codec for A/V Services at px64 kbits

1998. 02. 18.

/ß¿�� ÃOÔ³t�´�» MEDALMultimedia Engineering & Design ASIC Lab.

3 Ô Ãkhrhee@vlsi.chosun.ac.kr

http://vlsi.chosun.ac.kr

Chosun Univ. Multimedia ASIC Lab. 2

http://vlsi.chosun.ac.kr

Outline

• H.261 Video Coding Basic• H.261 Video Coding Algorithm• H.261 Video Multipex Coder• H.261 Transmission Coder• Reference

Chosun Univ. Multimedia ASIC Lab. 3

http://vlsi.chosun.ac.kr

H.261 Video Coding Basic

• H.261 System Block Diagram• H.261 System Feature• H.261 Encoder/Decoder• H.261 Data Structure• Video Signal Format• Samples of Luma & Chroma

Chosun Univ. Multimedia ASIC Lab. 4

http://vlsi.chosun.ac.kr

H.261 System Block Diagram

Chosun Univ. Multimedia ASIC Lab. 5

http://vlsi.chosun.ac.kr

H.261 System Feature

• Audiovisual ÀèH: ¥eù9$Üø• ¨EÌ: px64kbps, p=1,2,...,30•  8¤e: Y��¸X• ¥e�Ü: NTSC(525 lines;480), PAL (625 lines;576)• ¥e ��d ù9

• INTER L�: ME& MC• INTRA L�: DCT• Yh L�: VLC

• ��d ��: 4 hÙ �µø• t�ÀX: BCH(511,493)

Chosun Univ. Multimedia ASIC Lab. 6

http://vlsi.chosun.ac.kr

H.261 Encoder

Chosun Univ. Multimedia ASIC Lab. 7

http://vlsi.chosun.ac.kr

H.261 Decoder

Chosun Univ. Multimedia ASIC Lab. 8

http://vlsi.chosun.ac.kr

H.261 Data Structure

Chosun Univ. Multimedia ASIC Lab. 9

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Video Signal Format

Chosun Univ. Multimedia ASIC Lab. 10

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H.261 Video Multiplex Coder

• H.261 Stream 4 hÙ��• Picture Layer• GOB layer• Macroblock Layer• Block Layer• Multipoint Functions

Chosun Univ. Multimedia ASIC Lab. 11

http://vlsi.chosun.ac.kr

H.261 Stream 4 �ô +/

GOB dataPictureHeader ... GOB data

GOBHeader ...MB data MB data

...MBHeader

block datablock data

... EOBTCOEF TCOEF

PictureLayer

Group ofBlock Layer

MacroBlockLayer

BlockLayer

Chosun Univ. Multimedia ASIC Lab. 12

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Picture Layer

PSC(20)

TR(5)

PTYPE(6)

PEI(1)

PSPARE(0/8/16...)

PEI(1)

GOB data(...)

• PSC(Picture Start Code) : 20 bits; “0000 0000 0000 0001 0000”

• TR(Temporal Reference) : 5 bits• PTYPE( Type Information) : 6 bits

bit 1 : Split screen indicator; off(0)/on(1) bit 2 : Document camera indocator; off(0)/on(1) bit 3 : Freeze picture release; off(0)/on(1) bit 4 : Source format; QCIF(0)/ CIF(1) bit 5 : Optional still image mode HI_RES; on(0)/off(1) bit 6 : Spare

• PEI(Extra Insertion Information for picture) : 1 bit; 0 setting

• PSPARE(Spare Information for picture) : 0/8/16 ... bits PEI=‘1’ ðp �P�; ITU-T future backward compatible addition

Chosun Univ. Multimedia ASIC Lab. 13

http://vlsi.chosun.ac.kr

GOB Layer

GBSC(16)

GN(4)

GQUANT(5)

GEI(1)

GSPARE(0/8/16...)

GEI(1)

MB data(...)

• GOBt MB¤ jXh ¥ GOB�ø8 ¨��• � á<ü GOBÀÀ:

CIF(352x288)

QCIF(176x144)

1

3

5

7

9

11

8

10

12

1

3

5

2

4

6

A GOB of Y

176 pels/line

24lines/GOB

A GOBof CB, CR

88 pels/line

48lines/GOB

Chosun Univ. Multimedia ASIC Lab. 14

http://vlsi.chosun.ac.kr

GOB Layer

• GBSC(GOB Start Code) : 16 bits; “0000 0000 0000 0001”

• GN(Group Number) : 4 bitsGN=0: PSC; GN=13,14,15: reserved

• GQUANT(Quantization Info for GOB) : 5 bits; [1 , 31] overridden by any subsequent MQUANT

• GEI(Extra Insertion Info for GOB) : 1 bit; 0 setting

• GSPARE(Spare Info for GOB) : 0/8/16 ... bitsGEI=‘1’ ðp �P�; ITU-T future backword compatible addition

• GOBXü MB,Ü(1 GOB = 33 MBs)MB,ܤ ¨EÀÀ(

1

12

23

2

13

24

3

14

25

4

15

26

5

16

27

6

17

28

7

18

29

8

19

30

9

20

31

10

21

32

11

22

33

MB of Y

16 pels/line

16lines/MB

8

8

MB of CB, CR

Chosun Univ. Multimedia ASIC Lab. 15

http://vlsi.chosun.ac.kr

Macroblock Layer

• MBA(Macroblock address)– GOBXü MB¨üt ¤� VLC(Table 1 Ü�)– O,� ¨E¼8 MBA8 MBü ¬¤  0; �ð$Ô8 �¨¨E� MB ,Üä $¶è ¨E

• MTYPE(Type Info fro MB)– MBt ¤� ¹�ä �Pü8 ��d80 <dh(Table 2 Ü�)

• MQUANT(Quantizer) : 5 bits; [1 , 31]– MTYPEà� MQUANT�P <dh– �ð MQUANT¤ Ðððd ¨P GOBtÀ PM

MBA MTYPE MQUANT(5)

MVD CBP Block data

CBP

MVD

MBA stuffing

Chosun Univ. Multimedia ASIC Lab. 16

http://vlsi.chosun.ac.kr

Block Layer

TCOEFF EOB

1 2

3 4

5

Y(16x16) CB(8x8) CR(8x8)

6

• MBXü ¸� ,Ü; ¨E ÀÀ

Chosun Univ. Multimedia ASIC Lab. 17

http://vlsi.chosun.ac.kr

Block Layer

• TCOEFF(Transform Coefficients)– INTRA ð L� ¸�t �P; ��8 MTYPE, CBPt Ô �P– Zig-zag scanning– INTRA-coded DC: FLC(8 bits)– INTRA-coded & INTER-coded AC: (Table 5Ü�) 2-D Huffman Coding: [zero run, QC(i,j)]; sign bit: ‘s’; positive(0)/negative(1)– Remaining combination of [zero run, QC(i,j)] : 20 bits Escape(6) + Run(6) + Level(8): (Table 6,7 Ü�) black:’0001 0000’/white:’110 1011’ not used level: ‘0000 0000’,

‘1000 0000’(REC Level 1024 coded ‘1111 1111’)– Reconstruction level(REC): [-2048, 2047] : (Table 8 Ü�) REC of INTRA DC: (Table 9 Ü�)

• EOB(End of Block)– ¸�ü ldm ø�: ’10’

Chosun Univ. Multimedia ASIC Lab. 18

http://vlsi.chosun.ac.kr

H.261 Transmission Coder

• Video Data Buffering• Video Coding Delay• Forward Error Correction• Still Image Transmission

Chosun Univ. Multimedia ASIC Lab. 19

http://vlsi.chosun.ac.kr

Video Data Buffering

• $ÜÔü @É H\`: HRDü 8�P�t �0 ÀX– $Üø¼8 � átü �¤ è\H\`: 256kbits(CIF), 64 kbits(QCIF) PSC and all other data,PSPARE,GSPARE,MBA stuffing ��; error corection framming bits, fill indicator(Fi), fill bits/error correction parity infoÀ�– Hypothetical Reference Decoder(HRD) HRD ¼�( : (B+256 kbits)

t

t

R (t )d t

B

b

n+1

n

n

n+ 1

d

n+1

t n n+1t

b

n+ 1 n

H RD buffe roccu pa ncy(bit)

T im e(C IF in te rva l)

N O T E – T im e (t – t ) is a n in teger nu m b er o f C IF pic tu re pe rio d s (1 /2 9 .97 , 2 /2 9 .9 7 , 3 /2 9 .9 7 , ...) .

ÁÑ= ³±¸

ìà÷

­¸¶

ã á Ñ ó ãó Áí í

ó

ó

í

í

+ ≥ + −+∫°

°

§ ¨

Chosun Univ. Multimedia ASIC Lab. 20

http://vlsi.chosun.ac.kr

Video Coding Delay• è¸È $ÜÔä �ÜÔü d�:

– È¸È d� �e– lip synchronization

• Codec delay measurement method:– depend on implementation, picture format(CIF/QCIF) and data rate– measuring points:

videocoder

videodecoderA C

B

input video sequence: more than 100 sec.typical moving scene consistentmin coded picture rate: 7.5 Hzvisible ID mark a): átü O¸�t 97 ¨¬(  Ô� õ/Õè dø �Xless than 10% stuffing

encoder delay: A´ü vidible ID dø¤ B´tÀ $@Äððd �¨decoder delay: B´ü vidible ID dø¤ C´tÀ $@Äððd �¨

Chosun Univ. Multimedia ASIC Lab. 21

http://vlsi.chosun.ac.kr

Forward Error Correction• BCH(511,493) forward error correction code• General polynomial: g(x)=(x9+x4+1)(x9+x6+x4+x3+1)• Error Correction Framing(ECF):

• Relock Time of ECF– 3 ECF(24 bits) ¤ frame lock¨t ¼�¼X �– �ÜÔ8 ECF dø ¨ 34kbitsXt frame lockè Pȹüh� Èh� �

Chosun Univ. Multimedia ASIC Lab. 22

http://vlsi.chosun.ac.kr

Still Image Transmission

• High quality image ¨E:normal video resolutionü 4Ô– progressive, hierarchical ¨E– �ÈP�: H.261ü �0dø, hÍ ua,øl  ¨E1hü Ä�Õ– QCIF--->CIF, CIF(352x288)--->4CIF(704x576)– still image ¼m/¼eà� 2:1 sub-samplingü� è¸È �� ¨E sub-sampling pattern: 0 3 0 3 0 3 0 3

1 2 1 2 1 2 1 2 0 3 0 3 0 3 0 3 1 2 1 2 1 2 1 2 0 3 0 3 0 3 0 3 1 2 1 2 1 2 1 2

– PTYPEü HI_RES=‘0’, TR=‘000xx’, xx= sub-images 0,1,2,3

• Multipoint �ÈP�– broadcasting of still image– for this capability H.230 define MCV/Cancel-MCV TerminaltÀ MCUt MCV �X � è¸È broadcast¼h� ü�, Cancel-MCV �X �¨L�� �d �X *MCV: Multipoint Command Visualization-forcing MCU: Multipoint Control Unit

Chosun Univ. Multimedia ASIC Lab. 23

http://vlsi.chosun.ac.kr

Reference

• ITU-T Recommendation H.261, Video Codec for AudiovisualServices at px64 kbits, Mar, 1993

• ¨¤¨(KT), H.261}øe$Üø ÔÄ,À\¤ýô ¼hX�}��0üh¹0, 1996

• J.J.Hwang and B.R.Lee, Chapter 10. ITU-T Recomm. H261 Coder-Decoder of Digital Consumer Electronis Handbook, 1997

• Andy C. Hung, PVRG-P64 CODEC 1.1, Nov. 17, 1993

Chosun Univ. Multimedia ASIC Lab. 24

http://vlsi.chosun.ac.kr

4. H.263 Video Codec for Low Bitrate Communcations