1. Introduction to JPEG, MPEG 1/2, and H.261/H.263 Chuan-Yu Cho

2. Outline Video/Image Compression Still Image Compression –JPEG/ JPEG 2000 'Joint Photographic Experts Group ‘ Video Compression –H.261, H.263, H.263+, MPEG-1, MPEG-2, MPEG-4, MPEG-7, MPEG-21.

3. Still Image Coding JPEG, JPEG2000

4. Image/Video Redundancy Spatial redundancy 253 255 A B

5. Transform coding Encoder Decoder TQ Entropy coding Entropy coding Q -1 T -1 Image block Transform Coefficients Zigzag Scan (2D->1D) Bitstream Inverse Zigzag Scan (1D->2D) Reconstructed Transform Coefficients Reconstructed Image block

6. Block-Based Coding Why divide to blocks? Image->Blocks

7. 52 55 61 66 70 61 64 73 63 59 66 90 109 85 69 72 62 59 68 113 144 104 66 73 63 58 71 122 154 106 70 69 67 61 68 104 126 88 68 70 79 65 60 70 77 68 58 75 85 71 64 59 55 61 65 83 87 79 69 68 65 76 78 94 -26 -3 -6 2 2 0 0 0 1 -2 -4 0 0 0 0 0 -3 1 5 -1 -1 0 0 0 -4 1 2 -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -26 -3 -6 2 2 0 0 0 1 -2 -4 0 0 0 0 0 -3 1 5 -1 -1 0 0 0 -4 1 2 -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -26 –3 1 –3 2 –6 2 –4 1 –4 1 1 5 0 2 0 0 –1 2 0 0 0 0 0 –1 –1 EOB 2D->1D Number->binary -26 –3 1 –3 2 –6 2 –4 1 –4 1 1 5 0 2 0 0 –1 2 0 0 0 0 0 –1 –1 EOB 1010110 0100 001 0100 0101 100001 0110 100011 001 100011 001 001 100101 11100110 110110 0110 11110100 000 1010 -415 -29 -62 25 55 -20 -1 3 7 -21 -62 9 11 -7 -6 6 -46 8 77 -25 -30 10 7 -5 -50 13 35 -15 -9 6 0 3 11 -8 -13 -2 -1 1 -4 1 -10 1 3 -3 -1 0 2 -1 -4 -1 2 -1 2 -3 1 -2 -1 -1 -1 -2 -1 -1 0 -1 16 11 10 16 24 40 51 61 12 12 14 19 26 58 60 55 14 13 16 24 40 57 69 56 14 17 22 29 51 87 80 62 18 22 37 56 68 109 103 77 24 35 55 64 81 104 113 92 49 64 78 87 103 121 120 101 72 92 95 98 112 100 103 99 -415/16 = -26 Example of JPEG Coding(Encoder) Transform coding(DCT) Quantization Zigzag Scan Entropy Coding (bit stream)

8. -26 -3 -6 2 2 0 0 0 1 -2 -4 0 0 0 0 0 -3 1 5 -1 -1 0 0 0 -4 1 2 -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -26 –3 1 –3 2 –6 2 –4 1 –4 1 1 5 0 2 0 0 –1 2 0 0 0 0 0 –1 –1 EOB 1D->2D Binary->number 1010110 0100 001 0100 0101 100001 0110 100011 001 100011 001 001 100101 11100110 110110 0110 11110100 000 1010 -26 –3 1 –3 2 –6 2 –4 1 –4 1 1 5 0 2 0 0 –1 2 0 0 0 0 0 –1 –1 EOB -416 -33 -60 32 48 0 0 0 12 -24 -56 0 0 0 0 0 -42 13 80 -24 -40 0 0 0 -56 17 44 -29 0 0 0 0 18 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 58 64 67 64 59 62 70 78 56 55 67 89 98 88 74 69 60 50 70 119 141 116 80 64 69 51 71 128 149 115 77 68 74 53 64 105 115 84 65 72 76 57 56 74 75 57 57 74 83 69 59 60 61 61 67 83 93 81 67 62 69 80 84 84 Example of JPEG Coding(decoder) Inverse Entropy Coding (bit stream) Inverse Zigzag Scan Inverse Quantization Inverse Transform coding(DCT)

9. Transform coding Encoder Decoder TQ Entropy coding Entropy coding Q -1 T -1 Image block Transform Coefficients Zigzag Scan (2D->1D) Bitstream Inverse Zigzag Scan (1D->2D) Reconstructed Transform Coefficients Reconstructed Image block

10. Transform (0,1) (1,0) (-1,1)(1,1) (0.2,1.8) = 0.2(1,0)+1.8(0,1) = 1(1,1)+0.8(-1,1)

11. Basis of Transform Basis vectors{v 1,v 2, …,v n } Orthogonal : (v i ) · (v j ) = 0 if i!=j Normalized : (v i ) · (v i ) = 1 Orthonormal : orthogonal and normalized –eg. orthonormal : {(0,1),(1,0)} Orthogonal : {(1,1),(-1,1)}

12. Why DCT is used for image compressing KLT(Karhunen-Loeve transform): –Statistically optimal transform: minimal MSE for any specific bandwidth reduction –KLT depends on the type of signal statistics –No fast algorithm DCT approaches KLT for highly correlated signals: –sample values typically vary slowly from point to point across an image =>Highly correlated signals –Fast algorithm(but not optimal)

13. DCT-basis

14. DCT :Discrete Cosine Transform Frequency DomainSpatial Domain [8,8,8,8,8,8,8,8] [8,8,8,8,8,8,8,9] [8,8,10,9,7,8,8,9] [8,90,-100,3,4,-10,2,80] DCT [44,0,0,0,0,0,0,0] [44,-2,0,-2,0,-2,0,-2] [46,-2,-2,-4,-2,2,0,-2] [48,-56,146,6,74,-148,-158,-136]

15. DCT 52 55 61 66 70 61 64 73 63 59 66 90 109 85 69 72 62 59 68 113 144 104 66 73 63 58 71 122 154 106 70 69 67 61 68 104 126 88 68 70 79 65 60 70 77 68 58 75 85 71 64 59 55 61 65 83 87 79 69 68 65 76 78 94 -415 -29 -62 25 55 -20 -1 3 7 -21 -62 9 11 -7 -6 6 -46 8 77 -25 -30 10 7 -5 -50 13 35 -15 -9 6 0 3 11 -8 -13 -2 -1 1 -4 1 -10 1 3 -3 -1 0 2 -1 -4 -1 2 -1 2 -3 1 -2 -1 -1 -1 -2 -1 -1 0 -1 Example of JPEG Coding(Encoder)

16. Transform coding Encoder Decoder TQ Entropy coding Entropy coding Q -1 T -1 Image block Transform Coefficients Zigzag Scan (2D->1D) Bitstream Inverse Zigzag Scan (1D->2D) Reconstructed Transform Coefficients Reconstructed Image block

17. Quantization 目的：提高壓縮倍率 缺點：還原後的值會有誤差 原則：希望還原後的值，與原值差距較小 再經過較佳的 IQ 1 1 1 4 4 4 7 7 7 10 10 10 再直接乘以 3 ( 一般的 IQ) 0 0 0 3 3 3 6 6 6 9 9 9 經過 Q( 整除以 3) 0 0 0 1 1 1 2 2 2 3 3 3 原值 0 1 2 3 4 5 6 7 8 9 10 11

18. Quantization(con ’ t) DC term ： Uniform quantization AC terms 1 2 369 BACK

19. -415 -29 -62 25 55 -20 -1 3 7 -21 -62 9 11 -7 -6 6 -46 8 77 -25 -30 10 7 -5 -50 13 35 -15 -9 6 0 3 11 -8 -13 -2 -1 1 -4 1 -10 1 3 -3 -1 0 2 -1 -4 -1 2 -1 2 -3 1 -2 -1 -1 -1 -2 -1 -1 0 -1 16 11 10 16 24 40 51 61 12 12 14 19 26 58 60 55 14 13 16 24 40 57 69 56 14 17 22 29 51 87 80 62 18 22 37 56 68 109 103 77 24 35 55 64 81 104 113 92 49 64 78 87 103 121 120 101 72 92 95 98 112 100 103 99 -415/16 = -26 Example of JPEG Coding(Encoder)

20. -26 -3 -6 2 2 0 0 0 1 -2 -4 0 0 0 0 0 -3 1 5 -1 -1 0 0 0 -4 1 2 -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -415 -29 -62 25 55 -20 -1 3 7 -21 -62 9 11 -7 -6 6 -46 8 77 -25 -30 10 7 -5 -50 13 35 -15 -9 6 0 3 11 -8 -13 -2 -1 1 -4 1 -10 1 3 -3 -1 0 2 -1 -4 -1 2 -1 2 -3 1 -2 -1 -1 -1 -2 -1 -1 0 -1 Example of JPEG Coding(Encoder)

21. Transform coding Encoder Decoder TQ Entropy coding Entropy coding Q -1 T -1 Image block Transform Coefficients Zigzag Scan (2D->1D) Bitstream Inverse Zigzag Scan (1D->2D) Reconstructed Transform Coefficients Reconstructed Image block

22. Zigzag Scan 2D->1D DC term AC term BACK

23. -26 -3 -6 2 2 0 0 0 1 -2 -4 0 0 0 0 0 -3 1 5 -1 -1 0 0 0 -4 1 2 -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -26 –3 1 –3 2 –6 2 –4 1 –4 1 1 5 0 2 0 0 –1 2 0 0 0 0 0 –1 –1 EOB 2D->1D Example of JPEG Coding(Encoder) Transform coding(DCT) Quantization Zigzag Scan Zigzag Scan Entropy Coding (bit stream)

24. Transform coding Encoder Decoder TQ Entropy coding Entropy coding Q -1 T -1 Image block Transform Coefficients Zigzag Scan (2D->1D) Bitstream Inverse Zigzag Scan (1D->2D) Reconstructed Transform Coefficients Reconstructed Image block

25. Entropy Coding (Variable-Length Coding) Huffman coding Run-length coding Arithmetic coding

26. Huffman Coding 設法讓 ” 出現次數最多 ” 的字 (word) ，使用 最短的代碼 (code) 111110100Variable- Length Code 11100100Fixed- Length Code 1/24 1/63/4 出現機率 ‘D’‘C’‘B’‘A’ 範例 1*(3/4)+2*(1/6)+3*(1/24)+3 *(1/24) = 1.333 2*(3/4)+2*(1/6)+2*(1/24)+2 *(1/24) = 2 平均長度

27. DPCM : Differential PCM 若連續出現重複字 (word) 或相近字的機率 很高，則 coding ” 差值 ” 會比個別 coding 每個 字效果好 例如 ‘ AAFFFFFCCC ’ –PCM => ’ 65,65,70,70,70,70,70,67,67,67 ’ or ‘ 0,0,5,5,5,5,5,2,2,2 ’ –DPCM => ’ 0,0,5,0,0,0,0,-3,0,0 ’

28. Run-Length Coding 0 0 0 –1 6 0 3 EOB ^^^^^^^ ^ ^^^ (3,1) (0,6) (1,3) 001111 001000010 001001010 10 BACK 3 1 0011 1s 3 2 0010 0100 s 0 5 0010 0110 s 0 6 0010 0001 s 1 2 0001 10s 1 3 0010 0101 s

29. Video Coding MPEG I/II, H.261/H.263

30. Main Ideas of Still Image Coding (Intra Coding) Block-based coding Transform coding (DCT) Quantization Zagzig scan DPCM (Differential PCM) Entropy coding (Variable-length coding) –Huffman coding –Run-length coding –Arithmetic coding

31. Main Ideas of Video Coding (Inter Coding) Intra coding –Block-based coding, transform coding, quantization, zagzig scan, DPCM, entropy coding Inter coding –Intra coding for residual –Motion estimation/compensation

32. Image/Video Redundancy Spatial redundancy Temporal redundancy 253 255 A B A Frame N-1 B Frame N Use A to code B

33. Video Compression Encoder For Still Image TQ Entropy coding Image block Transform Coefficients Zigzag Scan (2D->1D) Bitstream Encoder For Video Sequence Q -1 T -1 Reconstructed Transform Coefficients Reconstructed Image block MC -

34. Results of DCT Coding JPEG PSNR (Peak Singal-to-Noise Ratio) MSE (Mean Square Error)

35. Temporal Redundancy Frame #1Frame #2

36. Residual Image Frame #2 – Frame #1 =

37. Results of Motion Compensation Coding PSNR = 22.68 dB, MSE=6.50, MAE=25 Bits for motion vector = 1002 bits Residual Image Coded Image DCT Coding PSNR = 43.35 dB Bit Rate = 21957 bits/frame Compression ration= = (256 * 256 * 8) / 21957 = 23.9

38. ITU-T Recommendation H.261 (Previously “ CCITT Recommendation ” ) Video Codec for Audiovisual Services at p × 64 kbit/s Geneva, 1990: revised at helsinki, 1993

39. H.261 v.s. p × 64 The Recommendation H.261 describes the video coding and decoding methods for the moving picture component of audiovisual services(videophone, videoconference, etc.) at the rates of p × 64 kbit/s, where p is in the range 1 to 30. => p × 64 (called p times sixty four) coder

40. H.261 v.s. MPEG The H.261 specification is already implemented in several manufacturers. Its target is telecommunications at a rate as low as 64 kbits. MPEG is defined for higher bit rate – 0.9 Mbits to 1.5 Mbits and consequently for higher quality.

41. H.261 Video codec for audiovisual services –ISDN Videophone and video conferencing –Low bit rates, low delay 1984: at m × 384 kbits/s ( m = 1, …, 5) 1988-90: at p × 64 kbits/s ( p = 1, …, 30)

42. H.261 Coder DCTQ Inverse DCT Motion Compensation Loop Filter Video in

43. Motion Estimation For each 16*16 superblock(SB), ME searches the best match in the referenced frame, and returns a motion vector MV = (X,Y). Both X and Y have integer value not exceeding ±15. Only the difference (residual) between the SB and the best match is DCT encoded

44. Motion Estimation (32,16) (-10,4) (22,20) Referenced frame Current frame

45. Coding of Motion Vectors Differential coding VLC for MV difference Example: MVDCode… -7&250000 0111 -6&260000 1001 -5&270000 1011 -4&280000 111 -3&290001 1 -2&300011 -1011 01 1010 2&-300010 3&-290001 0 4&-280000 110 5&-270000 1010 6&-260000 1000 7&-250000 0110… 1514 -13 12 … -1 -27 25 … 011 00001010 00000111 …

46. Motion Compensation(MC) & Motion Estimation (ME) MC is optional for each MB. (MTYPE => MB based) Only one MV for each MB. The ME compares a 16x16 superblock in the luminance block (Y) throughout a small search area of the previously transmitted image. Both horizontal and vertical components of these motion vectors have integer values not exceeding ±15. The MV is used for all 4 Y blocks. The MV for both Cb and Cr is derived by halving the component values of the MB MV. [NOT in H.261] The displacement with the smallest absolute superblock difference, determined by the sum of the absolute values of the pel-to-pel difference throughout the block, is considered the MV for the particular MB

47. Quantization # of quantizers is 1 for INTRA dc coefficient and 31 for all other coefficients. Within a MB, the same quantizer is used for all coefficient excepts the INTRA dc one. The equations for the quantizer can be written in terms of the MB quantization factor, Q sometimes termed MQUANT: –C(u,v) = F(u,v) / 2Q if Q is odd –C(u,v) = (F(u,v) ±1)Q 1 if Q is even (F>0 => +-, F -+ Quantization for INTRA dc term: –C = (F+4) / 8 with inverse F = 8C. ±

48. Loop Filter (FIL) The filter is separable into one-dimensional horizontal and vertical functions. The function is non-recursive with coefficients of ¼, ½, ¼ except at block edges. The function has coefficients of 0, 1, 0 at block edges. The filter is switched on/off for all 6 blocks in a MB according to MTYPE. ×¼×¼ ×½×½ ×¼×¼

49. H.261 Decoder Inverse DCT Motion Compensation Loop Filter Intra Inter

50. Decoder Source format –Pictures are coded as luminance and two colour difference components (Y, Cb, and Cr). CIF (Common Intermediate Format) –Y: 352 × 288 –Cb, Cr: 176 × 144

51. Decoder QCIF (Quarter-CIF) –Y: 176 × 144 –Cb, Cr: 88 × 72 CIF for NTSC (National Television System Committee) input (MPEG SIF 525) –Y: 352 × 240 –Cb, Cr: 176 × 120 All codecs must be able to operate using QCIF. Some codecs can also operate with CIF.

52. H.261 Video Formats Video Format Luminance (Y)Chrominance(Cb, Cr) pixels/linelines/framepixels/linelines/frame CIF352288176144 QCIF1761448872 Y pixel Cb, Cr pixel Block boundary

53. Arrangement of H.261 12 34 56 78 910 1112 176 352 48 288 1 3 5 176 48 QCIF CIF

54. Arrangements of data structure in H.261 1 2 3 176 144 QCIF picture 1234567891011 1213141516171819202122 2324252627282930313233 176 48 GOB (Group Of Block) Y1Y2 Y3Y4 UV 8 8 8 8 16 MB (Macro Block)

55. Positioning of luminance and chrominance smaples Y pixel Cb, Cr pixel Block boundary

56. Data Structure of Compressed Bitstream in H.261 Picture HeaderGOB data … Picture Layer GOB HeaderMB data … GOB Layer MB Header Block data … MB Layer TCOEFF … Block data Block Layer Fixed Length Code Variable Length Code

57. Structure of picture layer Picture start code (PSC) (20 bits) 0000 0000 0000 0001 0000 Temporal reference (TR) (5 bits) It is formed by incrementing its value in the previously transmitted picture header by one plus the number of non-transmitted pictures since that last transmitted one. (Only the five LSBs used) PSCTRPTYPEPEIPSPARE … PEI … GOB data

58. Structure of picture layer Type information (PTYPE) (6 bits) Bit 1 Split screen indicator Bit 2 Document camera indicator, “ 0 ” off, “ 1 ” on; Bit 3 Freeze picture release, “ 0 ” off, “ 1 ” on; Bit 4 Source format, “ 0 ” QCIF, “ 1 ” CIF; Bit 5 Optional still image model HI_RES, “ 0 ” on, “ 1 ” off Bit 6 Spare where Bit 1 is MSB Extra insertion information (PEI) (1 bit) “ 1 ” signals the presence of the following optional data field. PSCTRPTYPEPEIPSPARE … PEI … GOB data

59. GOB Layer Group of blocks start code (GBSC) (16 bits) –0000 0000 0000 0001 (if “ 0000 ” followed, then it is treated as a PSC) Group number (GN) (4 bits) –GN indicates the position of the group of blocks. 13, 14 and 15 are reserved for future use. 0 (0000) is used in the PSC. GBSCGNGQUANTGEIGSPARE … GEI … MB data

60. GOB Layer Quantizer information (GQUANT) (5 bits) –The quantizer to be used in the GOB until overridden by any subsequent MQUENT. Extra insertion information (GEI) (1 bit) –“ 1 ” signals the presence of the following optional data field. Spare information (GSPARE) (0/8/16 … bits) –If PEI = “ 1 ”, then the following 8-bits data is GSPARE. GBSCGNGQUANTGEIGSPARE … GEI … MB data

61. MB Layer Macroblock address(MBA) (Variable length: TABLE 1) –MBA indicates the position of a MB within a GOB. It is the difference between the absolute addresses of the MB and the last transmitted MB. Type information (MTYPE) (Variable length: TABLE 2) MBAMTYPEMQUANTMVDCBPBlock data

62. MB Layer Quantizer (MQUANT) (5 bits) –MQUANT is present only if so indicated by MTYPE (1, 3, 6, 9). MBAMTYPEMQUANTMVDCBPBlock data

63. MB Layer Motion vector data (MVD) (Variable length: TABLE 3) –MVD is obtained from the MV (for the MB) by subtracting the vector of the preceding MB. The vector of the preceding MB is regarded as zero in the following three situations: 1) evaluating MVD for MB 1, 12, 23. 2)evaluating MVD for MBs in which MBA does not represent a difference of 1 3) MTYPE of the previous MB was not MC. –Only one of the pair will yield a MV falling within the permitted range. MBAMTYPEMQUANTMVDCBPBlock data

64. MB Layer Coded block pattern (CBP) (Variable length: TABLE 4) –CBP is present if indicated by MTYPE (2, 3, 5, 6, 8, 9). The codeword gives a pattern number signifying those blocks in the MB for which at least one transform coefficient is transmitted. –CBP = 32P 1 + 16P 2 + 8P 3 + 4P 4 + 2P 5 + P 6 where P n = 1 if any coefficient is present for block n, else 0. MBAMTYPEMQUANTMVDCBPBlock data 12 34 56 Y CbCb CrCr

65. Block Layer Transform coefficients (TCOEFF) (Variable length: TABLE 5) –TCOEFF is always present for all six blocks in a MB when MTYPE indicates INTRA. In other cases MTYPE and CBP signal which blocks have coefficient data transmitted for them. –The most commonly occurring combination of successive zeros (RUN) and the following value (LEVEL) are encoded with variable length codes in TABLE 5. Other combinations of (RUN, LEVEL) are encoded with a 20-bit word consisting of 6 bits ESCAPE, 6 bits RUN and 8 bits LEVEL.

66. Block Layer There are two code tables in TABLE 5: –1) Being used for the first transmitted LEVEL in INTER, INTER+MC, and INTER+MC+FIL blocks. (EOB is not included). –2) Being used for all other LEVELs (EOB is included) except the first one in INTRA blocks which is fixed length coded with 8 bits. Coefficients after the last non-zero one are not transmitted. EOB is always the last item in blocks for which coefficients are transmitted.

67. Structure of H.261 Bitstream PSCTRPTYPEPEIPSPARE … PEI … GOB data GBSCGNGQUANTGEIGSPARE … GEI … MB data MBAMTYPEMQUANTMVDCBPBlock data … …

68. Coding of H.261 Bitstream PSCTRPTYPEPEIPSPARE GOB Layer GBSCGNGQUANTGEIGSPARE MB Layer Picture Layer GOB Layer

69. Coding of H.261 Bitstream MBA MTYPE MQUANT MB Layer MVDCBPBlock Layer CBP MVD MBA stuffing TCOEFF EOB Fixed length Variable length

70. H.263  H.263 = (H.261) + (MPEG-like features)  Compared to H.261 –More allowable picture formats –Half-pixel motion estimation, no loop filter –Different VLC tables at macroblock and block levels –Four negotiable options  3~4 dB better PSNR than H.261 at <64 kbps

71. H.263 Video Formats Sub-CIFQCIFCIF4CIF16CIF Pels/line1281763527041408 Lines961442885761152

72. Four Negotiable Options  Unrestricted Motion Vector: motion vectors can point outside the picture, -31.5 to 31.5 instead of –16 to 15.5  Advanced Prediction Mode: 8  8 motion vectors, overlapped block motion compensation, and motion vectors can point outside the picture  Syntax-based Arithmetic Coding (about 5% decreasing in bit-rate)  PB-frame

73. H.263+ 12 Optional Modes  Annex D: New Unrestricted Motion Vector (mv range up to +/- 256)  Annex I: Advanced Intra Coding  Annex J: Deblocking Filter  Annex M: Improved PB-Frame  Annex O: Temporal, Spatial, and SNR Scalability  Annex P: Reference Picture Resampling  Annex Q: Reduced Resolution Update

74. H.263+ Optional Modes  Annex S: Alternative Inter VLC  Annex I: Modified Quantization Error Resilience  Annex K: Slice Structured  Annex R: Independent Segment Decoding  Annex N: Reference Picture Selection

75. Codec Implementation Issues  Fast algorithm for motion estimation  Fast algorithm for DCT/IDCT  Huffman table implementation  Program design –Program diagram –Memory assess (frame stores) –Register assignment –Program redundancy

76. Supplemental Enhancement Information  Enhanced features Picture freeze and release Tagging information  Snapshot  Video segment start/end  Progressive refinement start/end Chroma key  Can be discarded by decoders that do not understand

77. H.263++ and H.263L  H.263++ (year 2000) Backward compatible to H.263 and H.263+ Technical proposals on  Error resilience  4 4 motion compensation and transform  Adaptive quantization  Long-term/background memory  De-blocking and de-ringing filters  …  H.263++ (year 2002) Not necessarily Backward compatible to H.263- type encoders

78. Conclusion Basic ideas of Video Coding H.261/(H.262)/H.263/H.263+ MPEG1/MPEG2/MPEG4/MPEG7/MPEG21 Key concepts in H.26x –Transform base coding –Motion Estimation