openh264解码h264视频帧主流程
一 解析一帧的入口
int32_t WelsDecodeSlice (PWelsDecoderContext pCtx, bool bFirstSliceInLayer, PNalUnit pNalCur) {
// 解码slice
PDqLayer pCurDqLayer = pCtx->pCurDqLayer;
PFmo pFmo = pCtx->pFmo;
int32_t iRet;
int32_t iNextMbXyIndex, iSliceIdc;
PSlice pSlice = &pCurDqLayer->sLayerInfo.sSliceInLayer;
PSliceHeaderExt pSliceHeaderExt = &pSlice->sSliceHeaderExt;
PSliceHeader pSliceHeader = &pSliceHeaderExt->sSliceHeader;
int32_t iMbX, iMbY;
const int32_t kiCountNumMb = pSliceHeader->pSps->uiTotalMbCount; //need to be correct when fmo or multi slice
uint32_t uiEosFlag = 0;
PWelsDecMbFunc pDecMbFunc;
pSlice->iTotalMbInCurSlice = 0; //initialize at the starting of slice decoding.
if (pCtx->pPps->bEntropyCodingModeFlag) { //cabac 熵编码
if (pSlice->sSliceHeaderExt.bAdaptiveMotionPredFlag ||
pSlice->sSliceHeaderExt.bAdaptiveBaseModeFlag ||
pSlice->sSliceHeaderExt.bAdaptiveResidualPredFlag) {
WelsLog (& (pCtx->sLogCtx), WELS_LOG_ERROR,
"WelsDecodeSlice()::::ILP flag exist, not supported with CABAC enabled!");
pCtx->iErrorCode |= dsBitstreamError;
return dsBitstreamError;
}
if (P_SLICE == pSliceHeader->eSliceType) //P Slice帧解析
pDecMbFunc = WelsDecodeMbCabacPSlice;
else if (B_SLICE == pSliceHeader->eSliceType) // B slice解析
pDecMbFunc = WelsDecodeMbCabacBSlice;
else //I_SLICE. B_SLICE is being supported
pDecMbFunc = WelsDecodeMbCabacISlice; // I Slice解析
} else { //
if (P_SLICE == pSliceHeader->eSliceType) {
pDecMbFunc = WelsDecodeMbCavlcPSlice;
} else if (B_SLICE == pSliceHeader->eSliceType) {
pDecMbFunc = WelsDecodeMbCavlcBSlice;
} else { //I_SLICE
pDecMbFunc = WelsDecodeMbCavlcISlice;
}
}
二 解析P slice函数
int32_t WelsDecodeMbCabacPSlice (PWelsDecoderContext pCtx, PNalUnit pNalCur, uint32_t& uiEosFlag) {
PDqLayer pCurDqLayer = pCtx->pCurDqLayer; //当前解码上下文
PSlice pSlice = &pCurDqLayer->sLayerInfo.sSliceInLayer; // slice上下文
PSliceHeader pSliceHeader = &pSlice->sSliceHeaderExt.sSliceHeader; // slice header
PPicture* ppRefPic = pCtx->sRefPic.pRefList[LIST_0]; //参考帧上下文
uint32_t uiCode;
int32_t iMbXy = pCurDqLayer->iMbXyIndex;
int32_t i;
SWelsNeighAvail uiNeighAvail;
pCurDqLayer->pCbp[iMbXy] = 0; //code block parttern信息
pCurDqLayer->pCbfDc[iMbXy] = 0;
pCurDqLayer->pChromaPredMode[iMbXy] = C_PRED_DC;
pCurDqLayer->pNoSubMbPartSizeLessThan8x8Flag[iMbXy] = true;
pCurDqLayer->pTransformSize8x8Flag[iMbXy] = false;
GetNeighborAvailMbType (&uiNeighAvail, pCurDqLayer); //填充邻居mb_type 为当前宏块解码做准备
WELS_READ_VERIFY (ParseSkipFlagCabac (pCtx, &uiNeighAvail, uiCode)); //解析是否为skip块
if (uiCode) {
int16_t pMv[2] = {0};
pCurDqLayer->pDec->pMbType[iMbXy] = MB_TYPE_SKIP;
ST32 (&pCurDqLayer->pNzc[iMbXy][0], 0);
ST32 (&pCurDqLayer->pNzc[iMbXy][4], 0);
ST32 (&pCurDqLayer->pNzc[iMbXy][8], 0);
ST32 (&pCurDqLayer->pNzc[iMbXy][12], 0);
ST32 (&pCurDqLayer->pNzc[iMbXy][16], 0);
ST32 (&pCurDqLayer->pNzc[iMbXy][20], 0);
pCurDqLayer->pInterPredictionDoneFlag[iMbXy] = 0;
memset (pCurDqLayer->pDec->pRefIndex[0][iMbXy], 0, sizeof (int8_t) * 16);
bool bIsPending = GetThreadCount (pCtx) > 1;
pCtx->bMbRefConcealed = pCtx->bRPLRError || pCtx->bMbRefConcealed || ! (ppRefPic[0] && (ppRefPic[0]->bIsComplete
|| bIsPending));
//predict mv
PredPSkipMvFromNeighbor (pCurDqLayer, pMv); //通过周围块的信息，计算得到当前块的mvp
for (i = 0; i < 16; i++) {
ST32 (pCurDqLayer->pDec->pMv[0][iMbXy][i], * (uint32_t*)pMv);
ST32 (pCurDqLayer->pMvd[0][iMbXy][i], 0);
}
//if (!pSlice->sSliceHeaderExt.bDefaultResidualPredFlag) {
// memset (pCurDqLayer->pScaledTCoeff[iMbXy], 0, 384 * sizeof (int16_t));
//}
//reset rS
pCurDqLayer->pLumaQp[iMbXy] = pSlice->iLastMbQp; //??????????????? dqaunt of previous mb 前一个qp，当前
//解码得到 delta + 这里的qp就是实际qp
for (i = 0; i < 2; i++) {
pCurDqLayer->pChromaQp[iMbXy][i] = g_kuiChromaQpTable[WELS_CLIP3 (pCurDqLayer->pLumaQp[iMbXy] +
pSliceHeader->pPps->iChromaQpIndexOffset[i], 0, 51)];
//计算得到chromaqp，和lumaqp有对应关系
}
//for neighboring CABAC usage
pSlice->iLastDeltaQp = 0;
WELS_READ_VERIFY (ParseEndOfSliceCabac (pCtx, uiEosFlag));
return ERR_NONE;
}
WELS_READ_VERIFY (WelsDecodeMbCabacPSliceBaseMode0 (pCtx, &uiNeighAvail, uiEosFlag)); //实际解析slice 中MB列表
return ERR_NONE;
三 解析Bslice过程
int32_t WelsDecodeMbCabacBSlice (PWelsDecoderContext pCtx, PNalUnit pNalCur, uint32_t& uiEosFlag) {
//解析B slice
PDqLayer pCurDqLayer = pCtx->pCurDqLayer; //当前帧上下文
PSlice pSlice = &pCurDqLayer->sLayerInfo.sSliceInLayer; //Slice指针
PSliceHeader pSliceHeader = &pSlice->sSliceHeaderExt.sSliceHeader; //当前slice头指着
PPicture* ppRefPicL0 = pCtx->sRefPic.pRefList[LIST_0]; //前向参考列表
PPicture* ppRefPicL1 = pCtx->sRefPic.pRefList[LIST_1]; //后向参考列表
uint32_t uiCode; //
int32_t iMbXy = pCurDqLayer->iMbXyIndex;
int32_t i;
SWelsNeighAvail uiNeighAvail;
pCurDqLayer->pCbp[iMbXy] = 0; //
pCurDqLayer->pCbfDc[iMbXy] = 0;
pCurDqLayer->pChromaPredMode[iMbXy] = C_PRED_DC;
pCurDqLayer->pNoSubMbPartSizeLessThan8x8Flag[iMbXy] = true;
pCurDqLayer->pTransformSize8x8Flag[iMbXy] = false;
GetNeighborAvailMbType (&uiNeighAvail, pCurDqLayer); //填充周围宏块信息
WELS_READ_VERIFY (ParseSkipFlagCabac (pCtx, &uiNeighAvail, uiCode)); //解析 skip标记
memset (pCurDqLayer->pDirect[iMbXy], 0, sizeof (int8_t) * 16);
bool bIsPending = GetThreadCount (pCtx) > 1;
if (uiCode) {
int16_t pMv[LIST_A][2] = { {0, 0}, { 0, 0 } };
int8_t ref[LIST_A] = { 0 };
pCurDqLayer->pDec->pMbType[iMbXy] = MB_TYPE_SKIP | MB_TYPE_DIRECT;
ST32 (&pCurDqLayer->pNzc[iMbXy][0], 0);
ST32 (&pCurDqLayer->pNzc[iMbXy][4], 0);
ST32 (&pCurDqLayer->pNzc[iMbXy][8], 0);
ST32 (&pCurDqLayer->pNzc[iMbXy][12], 0);
ST32 (&pCurDqLayer->pNzc[iMbXy][16], 0);
ST32 (&pCurDqLayer->pNzc[iMbXy][20], 0);
pCurDqLayer->pInterPredictionDoneFlag[iMbXy] = 0;
memset (pCurDqLayer->pDec->pRefIndex[LIST_0][iMbXy], 0, sizeof (int8_t) * 16);
memset (pCurDqLayer->pDec->pRefIndex[LIST_1][iMbXy], 0, sizeof (int8_t) * 16);
pCtx->bMbRefConcealed = pCtx->bRPLRError || pCtx->bMbRefConcealed || ! (ppRefPicL0[0] && (ppRefPicL0[0]->bIsComplete
|| bIsPending)) || ! (ppRefPicL1[0] && (ppRefPicL1[0]->bIsComplete || bIsPending));
if (pCtx->bMbRefConcealed) {
SLogContext* pLogCtx = & (pCtx->sLogCtx);
WelsLog (pLogCtx, WELS_LOG_ERROR, "Ref Picture for B-Slice is lost, B-Slice decoding cannot be continued!");
return GENERATE_ERROR_NO (ERR_LEVEL_SLICE_DATA, ERR_INFO_REFERENCE_PIC_LOST);
}
SubMbType subMbType;
if (pSliceHeader->iDirectSpatialMvPredFlag) { //Direct 块类型判断
//predict direct spatial mv
int32_t ret = PredMvBDirectSpatial (pCtx, pMv, ref, subMbType);
if (ret != ERR_NONE) {
return ret;
}
} else {
//temporal direct mode
int32_t ret = PredBDirectTemporal (pCtx, pMv, ref, subMbType);
if (ret != ERR_NONE) {
return ret;
}
}
//reset rS
pCurDqLayer->pLumaQp[iMbXy] = pSlice->iLastMbQp; //??????????????? dqaunt of previous mb
for (i = 0; i < 2; i++) {
pCurDqLayer->pChromaQp[iMbXy][i] = g_kuiChromaQpTable[WELS_CLIP3 (pCurDqLayer->pLumaQp[iMbXy] +
pSliceHeader->pPps->iChromaQpIndexOffset[i], 0, 51)];
}
//for neighboring CABAC usage
pSlice->iLastDeltaQp = 0;
WELS_READ_VERIFY (ParseEndOfSliceCabac (pCtx, uiEosFlag));
return ERR_NONE;
}
WELS_READ_VERIFY (WelsDecodeMbCabacBSliceBaseMode0 (pCtx, &uiNeighAvail, uiEosFlag)); //实际解析BSlice中的mb
return ERR_NONE;
}
四 解析ISlice过程
int32_t WelsDecodeMbCabacISliceBaseMode0 (PWelsDecoderContext pCtx, uint32_t& uiEosFlag) {
//解析I slice
PDqLayer pCurDqLayer = pCtx->pCurDqLayer; //当前帧解码上下文
PBitStringAux pBsAux = pCurDqLayer->pBitStringAux;
PSlice pSlice = &pCurDqLayer->sLayerInfo.sSliceInLayer; //slice上下文
PSliceHeader pSliceHeader = &pSlice->sSliceHeaderExt.sSliceHeader;
SWelsNeighAvail sNeighAvail;
int32_t iScanIdxStart = pSlice->sSliceHeaderExt.uiScanIdxStart;
int32_t iScanIdxEnd = pSlice->sSliceHeaderExt.uiScanIdxEnd;
int32_t iMbXy = pCurDqLayer->iMbXyIndex;
int32_t i;
uint32_t uiMbType = 0, uiCbp = 0, uiCbpLuma = 0, uiCbpChroma = 0;
ENFORCE_STACK_ALIGN_1D (uint8_t, pNonZeroCount, 48, 16);
pCurDqLayer->pNoSubMbPartSizeLessThan8x8Flag[iMbXy] = true;
pCurDqLayer->pTransformSize8x8Flag[iMbXy] = false;
pCurDqLayer->pInterPredictionDoneFlag[iMbXy] = 0;
pCurDqLayer->pResidualPredFlag[iMbXy] = pSlice->sSliceHeaderExt.bDefaultResidualPredFlag;
GetNeighborAvailMbType (&sNeighAvail, pCurDqLayer);
WELS_READ_VERIFY (ParseMBTypeISliceCabac (pCtx, &sNeighAvail, uiMbType)); //解析mb类型
if (uiMbType > 25) { //非法的mb类型
return GENERATE_ERROR_NO (ERR_LEVEL_MB_DATA, ERR_INFO_INVALID_MB_TYPE);
} else if (!pCtx->pSps->uiChromaFormatIdc && ((uiMbType >= 5 && uiMbType <= 12) || (uiMbType >= 17
&& uiMbType <= 24))) { //如果没有色度信息，这里mb类型不合法的类型判断
return GENERATE_ERROR_NO (ERR_LEVEL_MB_DATA, ERR_INFO_INVALID_MB_TYPE);
} else if (25 == uiMbType) { //I_PCM
WelsLog (& (pCtx->sLogCtx), WELS_LOG_DEBUG, "I_PCM mode exists in I slice!");
WELS_READ_VERIFY (ParseIPCMInfoCabac (pCtx)); //解析PCM 信息，cabac
pSlice->iLastDeltaQp = 0;
WELS_READ_VERIFY (ParseEndOfSliceCabac (pCtx, uiEosFlag));
if (uiEosFlag) {
RestoreCabacDecEngineToBS (pCtx->pCabacDecEngine, pCtx->pCurDqLayer->pBitStringAux);
}
return ERR_NONE;
} else if (0 == uiMbType) { //I4x4 16个4x4的帧内块
ENFORCE_STACK_ALIGN_1D (int8_t, pIntraPredMode, 48, 16);
pCurDqLayer->pDec->pMbType[iMbXy] = MB_TYPE_INTRA4x4;