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OpenH264 是一个开源的 H.264 编码和解码器#xff0c;由思科系统开发并维护。它专为实时应用程序如 WebRTC 设计#xff0c;提供了从基础到高级特性的广泛支持。OpenH264 的编码器支持从 Constrained Baseline Profile 到 5.2 级别#xff0c;允许任意分辨率的编…openh264
OpenH264 是一个开源的 H.264 编码和解码器由思科系统开发并维护。它专为实时应用程序如 WebRTC 设计提供了从基础到高级特性的广泛支持。OpenH264 的编码器支持从 Constrained Baseline Profile 到 5.2 级别允许任意分辨率的编码不限于 16x16 的倍数并且具有自适应量化或恒定量化的速率控制、多切片选项、多线程自动用于多切片等特性。此外它还支持高达 4 层的时序可伸缩性、单一输入的 4 种空间分辨率的 Spatial Simulcast、长期参考帧LTR、内存管理控制操作MMCO等功能。
帧间预测编码
视频帧间预测编码Inter-frame prediction coding是视频压缩技术中的一种关键方法主要用于减少视频序列中时间维度上的冗余。这种编码方式依赖于视频帧之间的空间相关性通过预测和补偿来减少数据量从而实现高效的视频压缩。
帧间预测编码是视频编码中非常有效的技术广泛应用于各种视频编码标准如H.264/AVC、H.265/HEVC、VP9和AV1等。通过减少时间冗余帧间预测编码显著提高了视频数据的压缩率同时保持了视频质量。
帧间预测的核心技术主要包括以下几个方面 运动估计Motion Estimation, ME: 运动估计是指在参考帧中搜索与当前块最匹配的区域以确定最佳匹配块的位置。 运动补偿Motion Compensation, MC: 运动补偿使用运动估计得到的运动向量来预测当前块通过补偿先前图像的抽样点来生成当前图像块的预测值。 宏块Macroblock, MB和子宏块Sub-Macroblock的树状结构分块: H.264 支持多种宏块分割方式如16x16、16x8、8x16和8x8以及更细致的子宏块分割如8x8、8x4、4x8和4x4。 多参考帧预测: 特别是在B帧中可以使用两个方向的参考帧List0和List1进行双向预测。 亚像素精度的运动估计: 除了整像素精度外H.264还支持1/2像素和1/4像素的亚像素插值以提高预测精度。 快速搜索算法: 为了减少计算复杂度使用快速搜索算法来确定最佳匹配块。 运动向量的编码: 运动向量的编码通常涉及编码运动向量与预测值的差值MVD而不是直接编码运动向量本身。 预测模式的选择: H.264定义了多种预测模式包括直接模式、双向模式、List0和List1模式等。 参考帧管理: 管理参考帧以确保解码器能够正确地重建预测图像。 变换/量化编码和熵编码: 这些步骤与帧内编码相同或相似用于进一步压缩预测残差。 帧间预测通过这些技术有效地减少了视频序列中的时间冗余提高了压缩效率。 openh264 帧间预测编码过程
帧间预测过程函数关系图 关键模块说明 通过API 函数EncodeFrame完成具体的编码过程可执行程序封装该函数进行编码通过二维数组g_pWelsSliceCoding[2][2]来完成具体的I 帧、P 帧以及变化片数和非变化片数编码在非变化片数帧间编码过程中在WelsMdInterMbLoop函数中循环处理每个宏块在变化片数帧间编码过程中在 WelsMdInterMbLoopOverDynamicSlice函数中循环处理每个宏块pfInterMd函数指针指向具体的增强层WelsMdInterMbEnhancelayer或基本层WelsMdInterMb帧间预测过程在基本层预测过程中WelsMdInterSecondaryModesEnc函数完成二级帧间预测过程编码在增强层预测过程中WelsMdSpatialelInterMbIlfmdNoilp函数完成具体的预测过程编码 帧间预测过程核心函数介绍
WelsMdInterMbLoopOverDynamicSlice 函数 用于动态切片的宏块编码过程循环处理每个 MB // Only for inter dynamic slicing
int32_t WelsMdInterMbLoopOverDynamicSlice (sWelsEncCtx* pEncCtx, SSlice* pSlice, void* pWelsMd,const int32_t kiSliceFirstMbXY) {SWelsMD* pMd (SWelsMD*)pWelsMd;SBitStringAux* pBs pSlice-pSliceBsa;SDqLayer* pCurLayer pEncCtx-pCurDqLayer;SSliceCtx* pSliceCtx pCurLayer-sSliceEncCtx;SMbCache* pMbCache pSlice-sMbCacheInfo;SMB* pMbList pCurLayer-sMbDataP;SMB* pCurMb NULL;int32_t iNumMbCoded 0;const int32_t kiTotalNumMb pCurLayer-iMbWidth * pCurLayer-iMbHeight;int32_t iNextMbIdx kiSliceFirstMbXY;int32_t iCurMbIdx -1;const int32_t kiMvdInterTableStride pEncCtx-iMvdCostTableStride;uint16_t* pMvdCostTable pEncCtx-pMvdCostTable[pEncCtx-iMvdCostTableSize];const int32_t kiSliceIdx pSlice-iSliceIdx;const int32_t kiPartitionId (kiSliceIdx % pEncCtx-iActiveThreadsNum);const uint8_t kuiChromaQpIndexOffset pCurLayer-sLayerInfo.pPpsP-uiChromaQpIndexOffset;int32_t iEncReturn ENC_RETURN_SUCCESS;SDynamicSlicingStack sDss;if (pEncCtx-pSvcParam-iEntropyCodingModeFlag) {WelsInitSliceCabac (pEncCtx, pSlice);sDss.iStartPos sDss.iCurrentPos 0;sDss.pRestoreBuffer pEncCtx-pDynamicBsBuffer[kiPartitionId];} else {sDss.iStartPos BsGetBitsPos (pBs);}pSlice-iMbSkipRun 0;for (;;) {//DYNAMIC_SLICING_ONE_THREAD - MultiD//stack pBs pointerpEncCtx-pFuncList-pfStashMBStatus (sDss, pSlice, pSlice-iMbSkipRun);//point to current pMbiCurMbIdx iNextMbIdx;pCurMb pMbList[ iCurMbIdx ];//step(1): set QP for the current MBpEncCtx-pFuncList-pfRc.pfWelsRcMbInit (pEncCtx, pCurMb, pSlice);// if already reaches the largest number of slices, set QPs to the upper boundif (pSlice-bDynamicSlicingSliceSizeCtrlFlag) {//a clearer logic may be://if there is no need from size control from the pSlice size, the QP will be decided by RC; else it will be set to the max QP// however, there are some parameter updating in the rc_mb_init() function, so it cannot be skipped?pCurMb-uiLumaQp pEncCtx-pWelsSvcRc[pEncCtx-uiDependencyId].iMaxQp;pCurMb-uiChromaQp g_kuiChromaQpTable[CLIP3_QP_0_51 (pCurMb-uiLumaQp kuiChromaQpIndexOffset)];}//step (2). save some vale for future use, initial pWelsMdWelsMdIntraInit (pEncCtx, pCurMb, pMbCache, kiSliceFirstMbXY);WelsMdInterInit (pEncCtx, pSlice, pCurMb, kiSliceFirstMbXY);TRY_REENCODING:WelsInitInterMDStruc (pCurMb, pMvdCostTable, kiMvdInterTableStride, pMd);pEncCtx-pFuncList-pfInterMd (pEncCtx, pMd, pSlice, pCurMb, pMbCache);//mb_qp//step (4): save from the MD process from future useWelsMdInterSaveSadAndRefMbType ((pCurLayer-pDecPic-uiRefMbType), pMbCache, pCurMb, pMd);pEncCtx-pFuncList-pfMdBackgroundInfoUpdate (pCurLayer, pCurMb, pMbCache-bCollocatedPredFlag,pEncCtx-pRefPic-iPictureType);//step (5): update cacheUpdateNonZeroCountCache (pCurMb, pMbCache);//step (6): begin to write bit stream; if the pSlice size is controlled, the writing may be skippediEncReturn pEncCtx-pFuncList-pfWelsSpatialWriteMbSyn (pEncCtx, pSlice, pCurMb);if (iEncReturn ENC_RETURN_VLCOVERFLOWFOUND (pCurMb-uiLumaQp 50)) {pSlice-iMbSkipRun pEncCtx-pFuncList-pfStashPopMBStatus (sDss, pSlice);UpdateQpForOverflow (pCurMb, kuiChromaQpIndexOffset);goto TRY_REENCODING;}if (ENC_RETURN_SUCCESS ! iEncReturn)return iEncReturn;//DYNAMIC_SLICING_ONE_THREAD - MultiDsDss.iCurrentPos pEncCtx-pFuncList-pfGetBsPosition (pSlice);if (DynSlcJudgeSliceBoundaryStepBack (pEncCtx, pSlice, pSliceCtx, pCurMb, sDss)) {pSlice-iMbSkipRun pEncCtx-pFuncList-pfStashPopMBStatus (sDss, pSlice);pCurLayer-LastCodedMbIdxOfPartition[kiPartitionId] iCurMbIdx -1; // update LastCodedMbIdxOfPartition, need to -1 due to stepping back pCurLayer-NumSliceCodedOfPartition[kiPartitionId];break;}//step (7): reconstruct current MBpCurMb-uiSliceIdc kiSliceIdx;OutputPMbWithoutConstructCsRsNoCopy (pEncCtx, pCurLayer, pSlice, pCurMb);#if defined(MB_TYPES_CHECK)WelsCountMbType (pEncCtx-sPerInfo.iMbCount, P_SLICE, pCurMb);
#endif//MB_TYPES_CHECK//step (8): update status and other parameterspEncCtx-pFuncList-pfRc.pfWelsRcMbInfoUpdate (pEncCtx, pCurMb, pMd-iCostLuma, pSlice);/*judge if all pMb in cur pSlice has been encoded*/ iNumMbCoded;iNextMbIdx WelsGetNextMbOfSlice (pCurLayer, iCurMbIdx);//whether all of MB in current pSlice encoded or notif (iNextMbIdx -1 || iNextMbIdx kiTotalNumMb || iNumMbCoded kiTotalNumMb) {pCurLayer-LastCodedMbIdxOfPartition[kiPartitionId] iCurMbIdx; pCurLayer-NumSliceCodedOfPartition[kiPartitionId];break;}}if (pSlice-iMbSkipRun) {BsWriteUE (pBs, pSlice-iMbSkipRun);}return iEncReturn;
}}//namespace WelsEnc
WelsMdInterMbLoop函数 用于固定切片的宏块编码过程循环处理每个 MB // for inter non-dynamic pSlice
int32_t WelsMdInterMbLoop (sWelsEncCtx* pEncCtx, SSlice* pSlice, void* pWelsMd, const int32_t kiSliceFirstMbXY) {SWelsMD* pMd (SWelsMD*)pWelsMd;SBitStringAux* pBs pSlice-pSliceBsa;SDqLayer* pCurLayer pEncCtx-pCurDqLayer;SMbCache* pMbCache pSlice-sMbCacheInfo;SMB* pMbList pCurLayer-sMbDataP;SMB* pCurMb NULL;int32_t iNumMbCoded 0;int32_t iNextMbIdx kiSliceFirstMbXY;int32_t iCurMbIdx -1;const int32_t kiTotalNumMb pCurLayer-iMbWidth * pCurLayer-iMbHeight;const int32_t kiMvdInterTableStride pEncCtx-iMvdCostTableStride;uint16_t* pMvdCostTable pEncCtx-pMvdCostTable[pEncCtx-iMvdCostTableSize];const int32_t kiSliceIdx pSlice-iSliceIdx;const uint8_t kuiChromaQpIndexOffset pCurLayer-sLayerInfo.pPpsP-uiChromaQpIndexOffset;int32_t iEncReturn ENC_RETURN_SUCCESS;SDynamicSlicingStack sDss;if (pEncCtx-pSvcParam-iEntropyCodingModeFlag) {WelsInitSliceCabac (pEncCtx, pSlice);sDss.pRestoreBuffer NULL;sDss.iStartPos sDss.iCurrentPos 0;}pSlice-iMbSkipRun 0;for (;;) {if (!pEncCtx-pSvcParam-iEntropyCodingModeFlag)pEncCtx-pFuncList-pfStashMBStatus (sDss, pSlice, pSlice-iMbSkipRun);//point to current pMbiCurMbIdx iNextMbIdx;pCurMb pMbList[ iCurMbIdx ];//step(1): set QP for the current MBpEncCtx-pFuncList-pfRc.pfWelsRcMbInit (pEncCtx, pCurMb, pSlice);//step (2). save some vale for future use, initial pWelsMdWelsMdIntraInit (pEncCtx, pCurMb, pMbCache, kiSliceFirstMbXY);WelsMdInterInit (pEncCtx, pSlice, pCurMb, kiSliceFirstMbXY);TRY_REENCODING:WelsInitInterMDStruc (pCurMb, pMvdCostTable, kiMvdInterTableStride, pMd);pEncCtx-pFuncList-pfInterMd (pEncCtx, pMd, pSlice, pCurMb, pMbCache);//mb_qp//step (4): save from the MD process from future useWelsMdInterSaveSadAndRefMbType ((pCurLayer-pDecPic-uiRefMbType), pMbCache, pCurMb, pMd);pEncCtx-pFuncList-pfMdBackgroundInfoUpdate (pCurLayer, pCurMb, pMbCache-bCollocatedPredFlag,pEncCtx-pRefPic-iPictureType);//step (5): update cacheUpdateNonZeroCountCache (pCurMb, pMbCache);//step (6): begin to write bit stream; if the pSlice size is controlled, the writing may be skippediEncReturn pEncCtx-pFuncList-pfWelsSpatialWriteMbSyn (pEncCtx, pSlice, pCurMb);if (!pEncCtx-pSvcParam-iEntropyCodingModeFlag) {if (iEncReturn ENC_RETURN_VLCOVERFLOWFOUND (pCurMb-uiLumaQp 50)) {pSlice-iMbSkipRun pEncCtx-pFuncList-pfStashPopMBStatus (sDss, pSlice);UpdateQpForOverflow (pCurMb, kuiChromaQpIndexOffset);goto TRY_REENCODING;}}if (ENC_RETURN_SUCCESS ! iEncReturn)return iEncReturn;//step (7): reconstruct current MBpCurMb-uiSliceIdc kiSliceIdx;OutputPMbWithoutConstructCsRsNoCopy (pEncCtx, pCurLayer, pSlice, pCurMb);#if defined(MB_TYPES_CHECK)WelsCountMbType (pEncCtx-sPerInfo.iMbCount, P_SLICE, pCurMb);
#endif//MB_TYPES_CHECK//step (8): update status and other parameterspEncCtx-pFuncList-pfRc.pfWelsRcMbInfoUpdate (pEncCtx, pCurMb, pMd-iCostLuma, pSlice);/*judge if all pMb in cur pSlice has been encoded*/ iNumMbCoded;iNextMbIdx WelsGetNextMbOfSlice (pCurLayer, iCurMbIdx);//whether all of MB in current pSlice encoded or notif (iNextMbIdx -1 || iNextMbIdx kiTotalNumMb || iNumMbCoded kiTotalNumMb) {break;}}if (pSlice-iMbSkipRun) {BsWriteUE (pBs, pSlice-iMbSkipRun);}return iEncReturn;
}
WelsMdInterMb函数 基本层的预测编码的核心实现函数主要用模式决策等过程 void WelsMdInterMb (sWelsEncCtx* pEncCtx, SWelsMD* pWelsMd, SSlice* pSlice, SMB* pCurMb, SMbCache* pUnused) {SDqLayer* pCurDqLayer pEncCtx-pCurDqLayer;SMbCache* pMbCache pSlice-sMbCacheInfo;const uint32_t kuiNeighborAvail pCurMb-uiNeighborAvail;const int32_t kiMbWidth pCurDqLayer-iMbWidth;const SMB* top_mb pCurMb - kiMbWidth;const bool bMbLeftAvailPskip ((kuiNeighborAvail LEFT_MB_POS) ? IS_SKIP ((pCurMb - 1)-uiMbType) : false);const bool bMbTopAvailPskip ((kuiNeighborAvail TOP_MB_POS) ? IS_SKIP (top_mb-uiMbType) : false);const bool bMbTopLeftAvailPskip ((kuiNeighborAvail TOPLEFT_MB_POS) ? IS_SKIP ((top_mb - 1)-uiMbType) : false);const bool bMbTopRightAvailPskip ((kuiNeighborAvail TOPRIGHT_MB_POS) ? IS_SKIP ((top_mb 1)-uiMbType) : false);bool bTrySkip bMbLeftAvailPskip || bMbTopAvailPskip || bMbTopLeftAvailPskip || bMbTopRightAvailPskip;bool bKeepSkip bMbLeftAvailPskip bMbTopAvailPskip bMbTopRightAvailPskip;bool bSkip false;//try BGD skipif (pEncCtx-pFuncList-pfInterMdBackgroundDecision (pEncCtx, pWelsMd, pSlice, pCurMb, pMbCache, bKeepSkip)) {return;}//try static or scrolled Pskipif (pEncCtx-pFuncList-pfSCDPSkipDecision (pEncCtx, pWelsMd, pSlice, pCurMb, pMbCache)) {return;}//step 1: try SKIPbSkip WelsMdInterJudgePskip (pEncCtx, pWelsMd, pSlice, pCurMb, pMbCache, bTrySkip);if (bSkip) {if (bKeepSkip) {WelsMdInterDecidedPskip (pEncCtx, pSlice, pCurMb, pMbCache);return;}} else {PredictSad (pMbCache-sMvComponents.iRefIndexCache, pMbCache-iSadCost, 0, pWelsMd-iSadPredMb);//step 2: P_16x16pWelsMd-iCostLuma WelsMdP16x16 (pEncCtx-pFuncList, pCurDqLayer, pWelsMd, pSlice, pCurMb);pCurMb-uiMbType MB_TYPE_16x16;}WelsMdInterSecondaryModesEnc (pEncCtx, pWelsMd, pSlice, pCurMb, pMbCache, bSkip);
}WelsMdInterSecondaryModesEnc函数 基本层帧间二级模式的编码实现函数主要用与判断出了 skip 和 p16x16 块类型之外的模式决策 void WelsMdInterSecondaryModesEnc (sWelsEncCtx* pEncCtx, SWelsMD* pWelsMd, SSlice* pSlice, SMB* pCurMb,SMbCache* pMbCache, const bool bSkip) {//step 2: Intraconst bool kbTrySkip pEncCtx-pFuncList-pfFirstIntraMode (pEncCtx, pWelsMd, pCurMb, pMbCache);if (kbTrySkip)return;if (bSkip) {WelsMdInterDecidedPskip (pEncCtx, pSlice, pCurMb, pMbCache);} else {//Step 3: SubP16 MDpEncCtx-pFuncList-pfSetScrollingMv (pEncCtx-pVaa, pWelsMd); //SCCpEncCtx-pFuncList-pfInterFineMd (pEncCtx, pWelsMd, pSlice, pCurMb, pWelsMd-iCostLuma);//refinement for inter typeWelsMdInterMbRefinement (pEncCtx, pWelsMd, pCurMb, pMbCache);//step 7: invoke encodingWelsMdInterEncode (pEncCtx, pSlice, pCurMb, pMbCache);//step 8: double check PskipWelsMdInterDoubleCheckPskip (pCurMb, pMbCache);}
}WelsMdSpatialelInterMbIlfmdNoilp函数 增强层的预测编码的核心实现函数主要用模式决策等过程 //
// MD for enhancement layers
//
void WelsMdSpatialelInterMbIlfmdNoilp (sWelsEncCtx* pEncCtx, SWelsMD* pWelsMd, SSlice* pSlice,SMB* pCurMb, const Mb_Type kuiRefMbType) {SDqLayer* pCurDqLayer pEncCtx-pCurDqLayer;SMbCache* pMbCache pSlice-sMbCacheInfo;const uint32_t kuiNeighborAvail pCurMb-uiNeighborAvail;const int32_t kiMbWidth pCurDqLayer-iMbWidth;const SMB* kpTopMb pCurMb - kiMbWidth;const bool kbMbLeftAvailPskip ((kuiNeighborAvail LEFT_MB_POS) ? IS_SKIP ((pCurMb - 1)-uiMbType) : false);const bool kbMbTopAvailPskip ((kuiNeighborAvail TOP_MB_POS) ? IS_SKIP (kpTopMb-uiMbType) : false);const bool kbMbTopLeftAvailPskip ((kuiNeighborAvail TOPLEFT_MB_POS) ? IS_SKIP ((kpTopMb - 1)-uiMbType) : false);const bool kbMbTopRightAvailPskip ((kuiNeighborAvail TOPRIGHT_MB_POS) ? IS_SKIP ((kpTopMb 1)-uiMbType) : false);bool bTrySkip kbMbLeftAvailPskip | kbMbTopAvailPskip | kbMbTopLeftAvailPskip | kbMbTopRightAvailPskip;bool bKeepSkip kbMbLeftAvailPskip kbMbTopAvailPskip kbMbTopRightAvailPskip;bool bSkip false;if (pEncCtx-pFuncList-pfInterMdBackgroundDecision (pEncCtx, pWelsMd, pSlice, pCurMb, pMbCache, bKeepSkip)) {return;}//step 1: try SKIPbSkip WelsMdInterJudgePskip (pEncCtx, pWelsMd, pSlice, pCurMb, pMbCache, bTrySkip);if (bSkip bKeepSkip) {WelsMdInterDecidedPskip (pEncCtx, pSlice, pCurMb, pMbCache);return;}if (! IS_SVC_INTRA (kuiRefMbType)) {if (!bSkip) {PredictSad (pMbCache-sMvComponents.iRefIndexCache, pMbCache-iSadCost, 0, pWelsMd-iSadPredMb);//step 2: P_16x16pWelsMd-iCostLuma WelsMdP16x16 (pEncCtx-pFuncList, pCurDqLayer, pWelsMd, pSlice, pCurMb);pCurMb-uiMbType MB_TYPE_16x16;}WelsMdInterSecondaryModesEnc (pEncCtx, pWelsMd, pSlice, pCurMb, pMbCache, bSkip);} else { //BLMODE SVC_INTRA//initial prediction memory for I_16x16const int32_t kiCostI16x16 WelsMdI16x16 (pEncCtx-pFuncList, pEncCtx-pCurDqLayer, pMbCache, pWelsMd-iLambda);if (bSkip (pWelsMd-iCostLuma kiCostI16x16)) {WelsMdInterDecidedPskip (pEncCtx, pSlice, pCurMb, pMbCache);} else {pWelsMd-iCostLuma kiCostI16x16;pCurMb-uiMbType MB_TYPE_INTRA16x16;WelsMdIntraSecondaryModesEnc (pEncCtx, pWelsMd, pCurMb, pMbCache);}}
}
