H.264 MV 学习笔记1：Inter Prediction 基本流程

The process will output 1 16x16 luma sample array and 2  8x8 chroma sample array(for mainprofile with chroma_format_idc = 1).

Notice, the inter prediction is executed partition by partition, for main profile all partition will be involved except for 8x8

(1)   The derivation of Partwidth&partHeight

   For Luma:

ü        Not 8x8 partition: = MbpartWidth()

       (Such as 8x16,16x8,)

ü        8x8 with subpartition: = SubMbPartWidth

              (P_8x8, P_8x8ref0, B_8x8 without B_Direct_8x8)

ü        8x8 without subpartition: = 4, since the smallest partition is 8x8

              (B_Skip or B_Direct_16x16, even B_8x8 with B_Direct_8x8 )

For Chroma:

       When chroma_format_idc is not equal to 0 (monochrome)

       partWidthC = partWidth / SubWidthC

       partHeightC = partHeight / SubHeightC

(2)   The Inter Prediction for each partition

Ø        Step1 (important): get MV and REF list information, refer to (3)

In:

      mbpartIdx, subMbpartIdx

out:

      mvL0,mvL1, subMvCnt

       refIdxL0,refIdxL1 with predFlagL0,predFlagL1

Ø        Step2:

MVcnt += subMcCnt

 

Ø        Step3: (important) refer to (5)

 

(mbpartIdx, subMbpartIdx, partWidth, partHeight

mvL0,mvL1, subMvCnt,

refIdxL0,refIdxL1 with predFlagL0,predFlagL1 )

->Inter prediction samples (partWidth x partHeight)

 

Ø        Step4: (store result for next decoding process)

MvL0[ mbPartIdx ][ subMbPartIdx ] =  mvL0

MvL1[ mbPartIdx ][ subMbPartIdx ] =  mvL1

RefIdxL0[ mbPartIdx ]  =  refIdxL0

RefIdxL1[ mbPartIdx ]  =  refIdxL1

PredFlagL0[ mbPartIdx ] =  predFlagL0

PredFlagL1[ mbPartIdx ] =  predFlagL1

 

Ø        Step5:

Derivation of partition location: (xP,yP) relative to macroblock

Derivation of subpartition location: (xS,yS) relative to macroblock partition

Pred[xP+xS+x,yP+yS+y] = predPart[x,y]

 

(3)   process of derivation of motion vector an reference indices

P_skip: refer to 8.4.1.1for refIdxL0 of mvL0 and set predflagL0 ‘1’

B_skip, B_Direct_16x16,B_direct_8x8: refer to 8.4.1.2

Other B,P:

ü        step1:

get refIdxLX from parsed semantics , and set predFlagLX

ü        step2:

       subMvCnt = predFlagL0+predFlagL1

MvCnt += subMvCnt

(4)   derivation of motion vector prediction mvpLX[] (main algoritm)

   The process is related with neighbor MB

 

( Note: reference to below function:

prepare_direct_params(dec_picture, img, mb_nr, pmvl0, pmvl1, &l0_rFrame, &l1_rFrame) in JM )

 

(5)   Derivation of MvLX[], RefIdxLX[], PredFlagLX[] for partition or subpartition

       Horizon:

              MvLX[mbPartIdx ][subMbPartIdx ][0]=

                                   mvpLX[0] + mvd_IX[mbpartIdx][subMbpartIdx][0]

       Vertical:

              MvLX[mbPartIdx ][subMbPartIdx ] [1] =

                                   mvpLX[1] + mvd_IX[mbpartIdx][subMbpartIdx][1]

       (p: prediction, d: delta or data)

       RefIdxL0[ mbPartIdx ] = refIdxL0

       RefIdxL1[ mbPartIdx ] = refIdxL1

       PredFlagL0[ mbPartIdx ] = predFlagL0

       PredFlagL1[ mbPartIdx ] = predFlagL1

 

(6)   Decoding of PredPartl and Predpartc (inter prediction samples )

 

( predPart(x,y) = predPartl(x,y) or predPartc(x,y) )

The predL[ xP + xS + x, yP + yS + y ]  =  predPartL[ x, y ]

predC[ xP / SubWidthC + xS / SubWidthC + x, yP / SubHeightC + yS / SubHeightC + y ]  =  predPartC[ x, y ]

 24/02/08 Created by Shuguang

 03/06/08 Modified by Shuguang

 

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