Audio Video coding Standard of (AVS) China Submitted by, Swaminathan Sridhar EE 5359 Multimedia Processing Project

Video coding standards [5]

Video coding standards [4], [5] MPEG-2 (DVD, MPEG-2 (DVD, SDTV, HDTV) More than 10 years old Compression efficiency 4.7GB DVD – 2 hours movie (5.3Mbps) 18GB – 2 hours high definition movie (20Mbps) MPEG-4 AVC/H.264 (Multimedia applications) Advanced coding techniques Multiple-reference frame prediction Context-based adaptive binary arithmetic coding High compression efficiency 1.5~2Mbps for SD, 6~8Mbps for HD Save storage space, channel bandwidth, and frequency spectrum

Development stages of AVS [3] December 2003 In the 7th AVS meeting, AVS-video (part-2) and AVS-system (part-1) was finalized. December 2004 In the 11th AVS meeting, AVS-M (part-7) was finalized March 2005 Authentication of ‘AVS101’ – high definition decoding chip May 2005 AVS Industry Alliance was set up. June 2005 Joint AVS/ISMA workshop on IPTV standard and industry forum February 2006 AVS part-2 was announced as a national standard.

Parts of AVS [3]

Applications of the commonly used parts of AVS China [3] AVS Part-2: HD/SD video Jizhun Profile & Zengqiang Profile HD broadcasting High density storage media Video surveillances Video on demand AVS Part-7: Mobility video Jiben Profile Record and local playback on mobile devices Multimedia Message Service (MMS) Streaming and broadcasting Real-time video conversation

Major and Minor coding tools used in AVS part 2 [1] Major tools Interlace handling: Picture-level adaptive frame/field coding (PAFF) Macroblock-level adaptive frame/field coding (MBAFF) Intra prediction: 5 modes for luma and 4 modes for chroma Motion compensation: 16x16/16x8/8x16/8x8 block size Resolution of MV: 1/4-pel, 4-tap interpolation filter Transform: 16bit-implemented 8x8 integer cosine transform Quantization and scaling: scaling only in encoder Entropy coding: 2D-VLC and Arithmetic Coding In-loop deblocking filter Minor tools Motion vector prediction Adaptive scan

AVS encoder structure [1]

Different picture types [2] Three types of picture are defined by AVS namely Intra pictures (I) Predicted pictures (P)- At most two reference frames (P or I) Interpolated pictures (B)- two reference frames (I or P or both)

MB level Adaptive frame coding [2] MB-level adaptive frame/field coding (MBAFF) The frame/field encoding decision is made independently for each vertical pair of macro blocks in a frame. A frame consisting of both moving and non-moving regions is coded more efficiently by: frame mode for the non-moving regions field mode for the moving regions MBAFF is much more complicated than PAFF – zig-zag scanning – motion vector prediction – intra prediction – deblocking – context modeling in entropy coding The advantage compared with the MBAFF in H.264 – A field-coded MB belonging to the bottom field CAN use the top field of the same frame as a reference for motion prediction

Intra Prediction [2] Five different modes for luma is as shown below

Luma Intra Prediction difference between AVS and H.264 [6] AVS Block size: 8x8 5 modes Reference pixels low pass filtered Advantages: low complexity with less modes H.264 Block size: 4x4 or 16x16 9 modes for 4x4 and 4 modes for 16x16 Advantage: better prediction Disadvantage: more complex

Intra prediction modes for Chroma [2] 4 Prediction modes for Chroma

Inter Prediction and Motion Compensation [1] At most 2 frames can be stored as reference for motion prediction. Block size of motion prediction and compensation – 16x16, 16x8, 8x16 and 8x8 In each MB, the number of MV pairs can be 1, 2 or 4, depending on the block size of MC. MVD, the difference between the predicted MV and the real MV, is coded. Resolution of MV – 1/4-pixel for luma – 1/8-pixel for chroma Motion prediction modes – Forward – Backward (only applicable for B frame) – Bi-directional (only applicable for B frame) Skip Direct Symmetric

Reference Frame [1] At most 2 reference frames are used. No matter PAFF or MBAFF is used, – if the current MB is frame-coded, 2 frames can be used as reference for motion prediction. – if the current MB is field-coded, 4 fields can be used. Reference index should be coded with every MC block to indicate which reference picture is used

Reference Index [1]

Motion Vector Prediction [3]

Use A, B, C, D’s MV (MVA, MVB, MVC and MVD) to predict E’s MV (PredMVE) Reason: reduce the bits for coding MV Method: Geometrical median of MVA, MVB, MVC VAB = Dist(MVA, MVB) VBC = Dist(MVB, MVC) VCA = Dist(MVC, MVA) FMV = Median(VAB, VBC, VCA) where Dist(MV1, MV2)=|x1-x2|+|y1-y2|. Determine PredMVE If FMV equals VAB, PredMVE=MVC. If FMV equals VBC, PredMVE=MVA. If FMV equals VCA, PredMVE=MVB.

Interpolation for Luma [3] Resolution – Quarter-pixel Filter – Half-pixel Blue: [-1, 5, 5, -1] – Quarter-pixel White: [1, 7, 7, 1] Red: bilinear

Interpolation for Luma [3]

Interpolation for Chroma [3]

Bilinear predMatrix[x,y] = [(8–dx)×(8–dy)×A + dx×(8dy)×B + (8–dx)×dy×C + dx×dy×D]/64

Forward and Backward Prediction [1] Forward prediction MV pointing only to the previous frame Get reference block only from the previous frame Backward prediction MV pointing only to the backward frame Get reference block only from the backward frame

Forward and Backward Prediction [1]

Bi-directional Prediction [1] Skip mode Block size of MC: 16x16 No transform coefficient is coded, since they all equal zeros. No MV is coded, since they can be calculated. Direct mode Block size of MC: 16x16 or 8x8 Transform coefficients are not all zeros, so they had to be coded. No MV is coded, since they can be calculated the same way for skip mode. Symmetric mode Block size of MC: 16x16, 16x8, 8x16, 8x8. Transform coefficients are not all zeros, so they had to be coded. Only forward MV is coded, and the backward MV can be calculated by using the forward one.

MV Derivation for Skip and Direct Mode [1]

MV Derivation for Symmetric Mode [1]

Pre-scale Transform [3]

AVS 8×8 ICT Matrix [3]

Context-based Adaptive 2D Variable Length Coding (CA-2D-VLC) [1] (level, run) pair mapping to CodeNum using VLC tables level>0: CodeNum is the number in VLC tables directly level<0: CodeNum is number+1 in VLC tables. Example level= 2, run=1, CodeNum=11; level= −2, run=1, CodeNum=12 CodeNum mapping to bit string using Exp-Colomb coding

Context-based Adaptive 2D Variable Length Coding (CA-2D-VLC) [1]

Deblocking Filter [3] 8x8 block Three steps Choose boundary strength (BS), according to Prediction modes MV Decide whether to filter according to Quantization Parameter (QP) BS – Apply filter to the boundary

Deblocking Filter [3]

AVS Part-2 vs H.264/AVC [4], [6]

AVS Part-2 performance [1], [A]

Container.qcif sequence [A]

Decoded frame [A]

Claire.qcif sequence [A]

Decoded frame [A]

News.qcif sequence [A]

Decoded frame [A]

References 1] L. Yu et al. “An Overview of AVS-Video: tools, performance and complexity”, Visual Communications and Image Processing 2005, Proc. of SPIE, vol. 5960, pp , July 31, ] L. Yu et al. “An area-efficient VLSI architecture for AVS intra frame encoder” Visual Communications and Image Processing 2007, Proc. of SPIE-IS & T Electronic Imaging, SPIE vol. 6508, pp , Jan. 29, ] W. Gao et al. “AVS - The Chinese Next-Generation Video Coding Standard” NAB, Las Vegas, ] T. Wiegand et al. “Overview of the H.264/AVC Coding Standard” IEEE Trans. Circuits Syst. Video Technol., vol.13, pp , July ] J. Wang et al. “An AVS-to-MPEG2 Transcoding System” China Proceedings of 2004 International Symposium on Intelligent Multimedia, Video and Speech Processing, Hong Kong, pp , October 20-22, ] X. Wang et.al “Performance comparison of AVS and H.264/AVC video coding standards” J. Comput. Sci. & Technol., Vol.21, No.3, pp J, May ] Bo Tang et al. “ AVS Encoder Performance and Complexity Analysis Based on Mobile Video Communication”, WRI International conference on Communications and Mobile Computing, CMC ‘09, volume 3, pp , 6-8 Jan

Web References: AVS China software A] ftp:// /public/avs_doc/avs_softwareftp:// /public/avs_doc/avs_software