5. Video coding techniques for Teleconferencing(1)

Transcription

1 5. Video coding techniques for Teleconferencing(1) /ß ÃOÔ³tŸ» MEDAL Multimedia Engineering & Design ASIC Lab. 3 Ô Ã khrhee@vlsi.chosun.ac.kr Chosun Univ. Multimedia ASIC Lab. 1 Digital A/V Service System Camera ADC Video Encoder Mic ADC Audio Encoder Mux Channel Encoder Timing & Control Data Transmission Channel Monitor DAC Video Encoder Speaker DAC Audio Encoder De Mux Channel Decoder Timing & Control Data Chosun Univ. Multimedia ASIC Lab. 2

2 ITU-T Standards for Video Teleconferencing System Narrowband Low Bitrate Iso-Ethernet Ethernet ATM High Res. ATM VTC (H.320) VTC (H.324) VTC (H.322) VTC (H.323V2) VTC (H.321) VTC (H.310) Video H.261 H.263 H.261 H.261 H.261 H.263 H.261 H.261 H.262 Audio G.711 G.722 G.728 H.200/AV.253 G G.711 G.722 G.723 G.728 G.711 G.722 G.723 G.728 G.729 G.711 G.728 MPEG-1 MPEG-2 G.7xx Data T.129 H.200/AV.270 T.120 T.434 T.84 Others T.120 T.120 T.120 T.120 Multiplex H.221 H.230 H.223 H.221 H H.221 H H.221 Control & Signalling H.230 H.242 H.243 H.245 H.230 H.242 H.245 H (Call Control & RAS, Q.931) H.242 H.230 H.221 Q.2931 H.242/H.230 H.245 Q.2931 Multipoint Encrytion H.231 N/A H.243 H.24I H.Loose-Multipoint H.MediaMIB H.233 H.234 H.233 H.234 (By reference to H.320) H.Packet- Encryption H.243 N/A H.233 H.234 N/A Chosun Univ. Multimedia ASIC Lab. 3 Standards for VTC H.320 Narrow-band visual telephone systems and terminal equipment(03/96) H.324 Terminal for low bit rate multimedia communications(03/96) H.323V2 Visual telephone systems and equipment for Local Area Network which provide a non-guaranteed Quality of Services(02/97) Chosun Univ. Multimedia ASIC Lab. 4

3 Video Conferencing(ISDN) Chosun Univ. Multimedia ASIC Lab. 5 Typical H.320 Add-In Board Chosun Univ. Multimedia ASIC Lab. 6

4 Video Conferencing(GSTN) Chosun Univ. Multimedia ASIC Lab. 7 Typical H.324 Add-In Board Chosun Univ. Multimedia ASIC Lab. 8

5 Video Conferencing(LAN) Chosun Univ. Multimedia ASIC Lab. 9 H.323 Protocol Stack Control Data Audio Video A/V Cntl Control H.225 H.245 T T T T.124 T.122 T.125 X.224 G.7xx H.26x RTP RTCP Gate Keeper Reg and Status TPKT/TCP TCP UDP IP Chosun Univ. Multimedia ASIC Lab. 10

6 Interoperability of Terminals Chosun Univ. Multimedia ASIC Lab. 11 Video Coding Standards VJPEG(ISO/IEC 10918), ITU-T T.81 digital compression and coding of continuous-tone still image VITU-T H.261 video codec for audiovisual services at p x 64 Kbps VMPEG-1(ISO/IEC 11172) coding of moving pictures and associated audio at up to about 1.5 Mbps VMPEG-2(ISO/IEC 13818), ITU-T H.262 generic coding of moving pictures and associated audio VMPEG-4(ISO/IEC 14496), ITU-T H.263 coding of audiovisual objects VMPEG-7: Multimedia content description interface Chosun Univ. Multimedia ASIC Lab. 12

7 Video Coding Standards,Û Ã` Ÿ»hC; JPEG (still image) H.261 (slow motion) MPEG-1 (moving picture) MPEG-2 (H.262) MPEG-4 (H.263) FCC GA, ATSC (HDTV, DTV) CMTT (digital TV) 10 20:1 Image Storage, Compressed TX p x 64 Kbps Video Videophone, Videoconference Mbps Video/audio Storage (DSM), Storage 100 Mbps Video/audio Transmission DVD (DTV, HDTV) 4 Mbps Video/audio Videophone, ( 64 Kbps) Mobile, Internet 100 Mbps Video/audio HDTV, DTV 10 Mbps Video DTV Chosun Univ. Multimedia ASIC Lab. 13 What s Video Compression? Orange Juice Analogy Orange H 2 O Concentrate: Shipped, Stored and Sold OJ - + H 2 O Water is the redundant element Tastes Like Fresh-Squeezed Fresh-Squeezed In video compression, the encoder removes spatial and temporal redundany; the decoder puts it back in. Chosun Univ. Multimedia ASIC Lab. 14

8 Video compression basis Remove spatial and temporal redundancy that exist in natural video imagery - correlation itself can be removed in a lossless fashion - important for medical applications -only realizes about 2:1 compression efficiency Exploit limitations in Human Visual System(HVS) - limited luminance and very limited color response - reduced sensitivity to noise in high frequencies (e.g., edges of objects, high detailed areas) - reduced sensitivity to noise in brighter areas - goal is to throw away bits in a psychovisually lossless manner - can realize 50:1 or more compression efficiency Chosun Univ. Multimedia ASIC Lab. 15 À Ÿ TïT ÔœtP: e Üü µ Õ(redundant information)è 0/À 4ˆ$Üø(Lossy Coding)-- ü ]Õ M - ¹ µ Õ µ Õ Yh µ Õ ¼ M 1¼8ø ü ÄPÕè M ø e Õè 0ø ÄP dh (ü d ü ÄPÕ M d e h 0ø ù( M m è\¼ ( MPEGtÀ M de( e Å$Üø DCT ³ õ 54ø, DCT h¼, de(eô ü Å$Üø VLC (Variable Length Coding) source from Ho Yo Seong from K-JIST Chosun Univ. Multimedia ASIC Lab. 16

9 Video compression basis Max (8 bpp) Redundancy reduction by entropy coding (e.g., Huffman coding) Entropy of an image Irrelevancy reduction by exploiting HVS (e.g., DCT/DPCM coding) Compression lower bound? Min (0 bpp) Chosun Univ. Multimedia ASIC Lab. 17 Quantization Analog image/ audio Sampling, Nyquist rate Quantization uniform/ nonuniform Source coder Uniform & nonuniform Symmetric & nonsymmetric midtreader & midriser Quantization results in compression Chosun Univ. Multimedia ASIC Lab. 18