Windows Media Video 9Introduction 1Introduction 2Introduction 3The Block Diagram :-Block Transforms(Integer DCT)8x8 Integer DCT MatricesKey features of the TransformsQuantizationLoop FilteringMotion Estimation and CompensationAdvanced entropy codingInterlaced codingAdvanced B frame codingOverlap smoothingLow rate tools (<100 Kbps)Fading compensationReferencesAVS China’s next generation video coding standardIntroductionData FormatsStructureStructureSlide 24Block Diagram (Encoder)Block Diagram (Decoder)BuffersWindows Media Video 9Tarun Bhatia [email protected] Processing LabUniversity Of Texas at Arlington11/05/04Introduction 1Introduction 2Introduction 3•Latest video codec which gives state-of-art video quality from very low bit rates (160x120 at 10 Kbps for modem) to very high bit rates (1920x1080 for HDTV)•8-bit , 4:2:0 format•Uses block based transform and motion compensation with quantization and entropy coding.The Block Diagram :-Block Transforms(Integer DCT)•8x8 blocks can be encoded using 1_8x8 2_8x4 2_4x8 4_4x4 -Frame / Macroblock/Block signaling-Block level for coarse and fine level specification -Frame level for overhead reduction -Only 8x8 used for I frames8x8 Integer DCT Matrices•WMV 9•H.264 HPKey features of the Transforms•The norms of vectors of the ratio 288:289:299•The variation in the norm accounted for in the encoder itself•At the decoder inverse transform(rows) -> rounding-> inverse transform (columns) ->rounding (to operate in the 16 bit range)Quantization•Same rule applied to all block sizes•Both types with (bit savings at low bit rates) and without dead zone ( available•Type used signaled at the frame level to the decoder•At the encoder side automatic switch from uniform quantization to dead zone quantization as Q – parameter increases•Other factors like noise and rate control can be used to control this switchLoop Filtering•Done to remove blocky artifacts and thus quality of current frame for future prediction•Operates on pixels on the border of blocks•The process involves a discontinuity measurement •Checks are computationally expensive so done only for one set of pixel per boundaryMotion Estimation and Compensation•Max resolution of ¼ pixel (i.e. ¼, ½, ¾) allowed •16x 16 motion vectors used by default but 8x8 allowed•Bicubic filter with 4 taps/ Bilinear filters with 2 taps to generate subpixel precision.•4 combined modes 1.Mixed block size (16x16 and 8x8), ¼ p ,bicubic 2.16x16, ¼ p, bicubic 3.16x16, ½ p, bicubic 4.16x16, ½ p, bilinear•Bilinear filters for chroma componentsAdvanced entropy coding•Simple VLC codes•Multiple code tables for encoding each particular alphabet out •A possible set of code tables is chosen (based on frame level quantization parameter) and signaled in the bitstream•Additional information e.g. motion vectors resolution coded using bitplane codingInterlaced coding•Supports field and frame codingAdvanced B frame coding•B frames:- employ bi-directional prediction•Fractional position definition with respect to the reference frames for better scaling of motion vectors•Intra coded B frames for scene changes•Allow inter field referenceOverlap smoothing•The deblocking filter smoothens out the block as well as true edges and it may be disabled in less complex profiles•A lapped transform (input spans to pixels from other blocks as well) is used at the edges•Used in spatial domain as pre and post processing•Used only at low bit rates where blocking artifacts are higher•Signaled at macroblock level so can be turned off in smooth regionsLow rate tools (<100 Kbps)•Code frames at multiple resolutions (both in X and Y direction) •A frame can be downscaled at the encoder and then upscaled at the decoder for LBR transmission•The downscaling factor needs to remain same from the start of 1 I frame to the start of next I frame.•The frame must be upscaled prior to display (upscaling out of scope of the standard).Fading compensation•Large amount of bits required for scenes having effects like fade-to-black ,fade-from-black•Not possible to predict motion using normally used techniques.•Effective fading detection (original refrence image- current video image>threshold=fading)•If detected then encoder computes fading parameters which specify a pixel-wise first order linear transform for the reference image. •Also signaled to the decoderReferences•Windows Media Video 9: overview and applications Sridhar Srinivasan, Pohsiang (John) Hsu, TomHolcom b, Kunal Mukerjee, Shankar L. Regunathan, Bruce Lin, Jie Liang, Ming-Chieh Lee, Jordi Ribas-Corbera Windows Digital Media Division, Microsoft Corporation, Redmond, WA 98052, USA available online at www.sciencedirect.comAVS China’s next generation video coding standardIntroduction•Streamlined video coder dedicated to coding HDTV content (1920x1080 in 4:2:0 and 4:2:2)•4 levels are defined Level 4.0 : Standard Definition 4:2:0 Level 4.2 : Standard Definition 4:2:2 Level 6.0 : HD 4:2:0 Level 6.2 : HD 4:2:2 (HD: High Definition)•Designed to provide near optimum performance and considerable reduction in complexity (low cost implementation)•Applications include broadcast TV,HD-DVD and broadband video networkingData Formats•Progressive scan results in significantly less coding complexity •Interlaced scanStructureHavestart codesStructure SliceStructure4:2:04:2:2Block Diagram (Encoder)Block Diagram (Decoder)Buffers•The rate buffer at the encoder side helps in converting variable data rate produced by encoder to fixed data rate by controlling quantization using feedback•The rate buffer at the decoder side gets the fixed rate data and stores it and then passes on to the decoder at a rate demanded by decoding of each macroblock and
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