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Mikemage@CMLab, 2004 NTU CSIE 1 Ch.6 H.264/AVC Part2 (pp.200~222) Chun-Wei Hsieh

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Mikemage@CMLab, 2004 NTU CSIE 2 Outline 6.4.13.2 CAVLC Main profile –B slices, weighted prediction, CABAC Extended profile –SP & SI slices Transport of H.264

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Mikemage@CMLab, 2004 NTU CSIE 3 CAVLC Context-Based Adaptive Variable Length Coding Characteristics: –Run-level coding to compact zero string –Trailing ones (+1, -1 after 0) –Number of nonzero coefficient in neighboring blocks is correlated –Choice VLC lookup table for level parameter for level magnitude

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Mikemage@CMLab, 2004 NTU CSIE 4 CAVLC Encoding process 1. Encode the number of coefficients and trailing ones (coeff token) –TotalCoeffs : 0 ~ 16 –TrailingOnes : 0 ~ 3 if more than tree TrailingOnes, only last three are treated as ‘ special cases ’ –Four look up table Three variable-length, one fixed-length Choice depend on neighboring blocks

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Mikemage@CMLab, 2004 NTU CSIE 5 CAVLC Encoding process(2) 2. Encode the sign of each TrailingOne –In reverse order 3. Encode the levels of the remaining nonzero coefficients –level_prefix, level_suffix

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Mikemage@CMLab, 2004 NTU CSIE 6 CAVLC Encoding process(3) 4.Encode the total number of zeros before the last coefficient –Zero-runs at start of the array need not to be encoded 5. Encode each run of zeros If less then 3 TrailingOnes, the first nonzero coefficient is adjusted

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Mikemage@CMLab, 2004 NTU CSIE 7 Main profile

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Mikemage@CMLab, 2004 NTU CSIE 8 Main profile(2) Suitable application: –broadcast media –applications such as digital television and stored digital video

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Mikemage@CMLab, 2004 NTU CSIE 9 B slices May be predicted from one or two reference pictures, before or after the current in temporal order. List 0 –The closest past picture, followed by any other past pictures, followed by any future pictures List 1 –The closest future picture, followed by any other future picture followed by any past picture

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Mikemage@CMLab, 2004 NTU CSIE 10 B slices(2) Prediction options

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Mikemage@CMLab, 2004 NTU CSIE 11 B slices: Bi-direction prediction Each sample of the prediction block is calculated as an average of the list 0 and list 1 prediction sample pred(i,j) = (pred0(i,j) + pred1(i,j) + 1) >> 1

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Mikemage@CMLab, 2004 NTU CSIE 12 B slices: Direction prediction(2) No motion vector is transmitted Spatial direct mode –Using the process described in 6.4.5.4 Temporal direct mode

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Mikemage@CMLab, 2004 NTU CSIE 13 Weighted prediction 1. P slice macroblock, ‘ explicit ’ weighted prediction; 2. B slice macroblock, ‘ explicit ’ weighted prediction; 3. B slice macroblock, ‘ implicit ’ weighted prediction. Explicit: weighting factor are transmitted Implicit: weighting factor are calculated based on reference picture

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Mikemage@CMLab, 2004 NTU CSIE 14 Interlaced video In macroblock-adaptive frame/field (MB-AFF) coding mode, the choice of field or frame coding may be specified at the macroblock level –16 luminance samples wide and 32 luminance samples high

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Mikemage@CMLab, 2004 NTU CSIE 15 Interlaced video(2)

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Mikemage@CMLab, 2004 NTU CSIE 16 Interlaced video(3)

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Mikemage@CMLab, 2004 NTU CSIE 17 CABAC Context-based Adaptive Binary Arithmetic Coding –Selecting probability models for each syntax element according to the element ’ s context –Adapting probability estimates based on local statistics –Using arithmetic coding rather than variable-length coding

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Mikemage@CMLab, 2004 NTU CSIE 18 CABAC(2) Binarisation Context model selection –Context model is a probability model for one or more bins of binarised symbol Arithmetic encoding Probability update

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Mikemage@CMLab, 2004 NTU CSIE 19 Extended profile

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Mikemage@CMLab, 2004 NTU CSIE 20 SP & SI slices SP and SI slices are specially-coded slices that enable efficient switching between video streams and efficient random access for video decoders SP-slices are designed to support switching between similar coded sequences without the increased bitrate penalty of I-slices SI-slice may be used to switch from one sequence to a completely different sequence

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Mikemage@CMLab, 2004 NTU CSIE 21 SP slices

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Mikemage@CMLab, 2004 NTU CSIE 22 SI slice Prediction is formed using the 4 × 4 Intra Prediction modes (see Section 6.4.6.1) from previously-decoded samples of the reconstructed frame

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Mikemage@CMLab, 2004 NTU CSIE 23 Data partitioned slices The coded data that makes up a slice is placed in three separate Data Partitions (A, B and C) Partition A contains the slice header and header data for each macroblock in the slice Partition B contains coded residual data for Intra and SI slice macroblocks Partition C contains coded residual data for inter coded macroblocks (forward and bi-directional)

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Mikemage@CMLab, 2004 NTU CSIE 24 Transport of H.264 A coded H.264 video sequence consists of a series of NAL units, each containing an RBSP

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Mikemage@CMLab, 2004 NTU CSIE 25 RBSP type

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Mikemage@CMLab, 2004 NTU CSIE 26 Parameter set sequence parameter set contains parameters to be applied to a complete video sequence picture parameter set contains parameters which are applied to one or more decoded pictures within a sequence

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Mikemage@CMLab, 2004 NTU CSIE 27 Thank You!!

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