版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/CrystalShaw/article/details/83896681
一、名词解释
计算码控时会用到如下的一些参数：
SAD (Sum of Absolute Difference)=SAE(Sum of Absolute Error)绝对误差和
SATD(Sum of Absolute Transformed Difference)即hadamard变换后再绝对值求和
SSD (Sum of Squared Difference)=SSE(Sum of Squared Error) 差值的平方和
MAD (Mean Absolute Difference)=MAE(Mean Absolute Error) 平均绝对差值
MSD (Mean Squared Difference)=MSE(Mean Squared Error) 平均平方误差
SAD绝对误差和，仅反映残差时域差异，影响PSNR值，不能有效反映码流的大小。SATD将残差经哈德曼变换的4×4块的预测残差绝对值总和，可以将其看作简单的时频变换，其值在一定程度上可以反映生成码流的大小。因此，不用率失真最优化时，可将其作为模式选择的依据。一般帧内要对所有的模式进行检测，帧内预测选用SATD的原因同上。
在做运动估计时，一般而言，离最优匹配点越远，匹配误差值SAD越大，这就是有名的单一平面假设，现有的运动估计快速算法大都利用该特性。但是，转换后SATD值并不满足该条件，如果在整象素中运用SATD搜索，容易陷入局部最优点。而在亚象素中，待搜索点不多，各点处的SAD差异相对不大，可以用SATD选择码流较少的匹配位置。
RDO（Rate–distortion optimization）率失真优化，用来确定编码模式，保证码率比特数和图像失真的最佳权衡点。
RQ模型是在上一层码率数一定的情况下用来确定下一层分配的比特数。RQ先于RDO进行。
二、码控钩子函数初始化
WelsRcInitFuncPointers函数初始化各种码控模式下的钩子函数。
三、RC_BITRATE_MODE码控函数框架
四、结构体参数
1、帧级QP参数
TagWelsRc->iInitialQp
typedef struct TagWelsRc {
int32_t iRcVaryPercentage;
int32_t iRcVaryRatio;
int32_t iInitialQp; //initial qp
int64_t iBitRate; // Note: although the max bit rate is 240000*1200 which can be represented by int32, but there are many multipler of this iBitRate in the calculation of RC, so use int64 to avoid type conversion at all such places
int32_t iPreviousBitrate;
int32_t iPreviousGopSize;
double fFrameRate;
int32_t iBitsPerFrame;
int32_t iMaxBitsPerFrame;
double dPreviousFps;
// bits allocation and status
int32_t iRemainingBits;
int32_t iBitsPerMb;
int32_t iTargetBits;
int32_t iCurrentBitsLevel;//0:normal; 1:limited; 2:exceeded.
int32_t iIdrNum;
int64_t iIntraComplexity; //255*255(MaxMbSAD)*36864(MaxFS) make the highest bit of 32-bit integer 1
int32_t iIntraMbCount;
int64_t iIntraComplxMean;
int8_t iTlOfFrames[VGOP_SIZE];
int32_t iRemainingWeights;
int32_t iFrameDqBits;
bool bGomRC;
double* pGomComplexity;
int32_t* pGomForegroundBlockNum;
int32_t* pCurrentFrameGomSad;
int32_t* pGomCost;
int32_t bEnableGomQp;
int32_t iAverageFrameQp;
int32_t iMinFrameQp;
int32_t iMaxFrameQp;
int32_t iNumberMbFrame;
int32_t iNumberMbGom;
int32_t iGomSize;
int32_t iSkipFrameNum;
int32_t iFrameCodedInVGop;
int32_t iSkipFrameInVGop;
int32_t iGopNumberInVGop;
int32_t iGopIndexInVGop;
int32_t iSkipQpValue;
int32_t iQpRangeUpperInFrame;
int32_t iQpRangeLowerInFrame;
int32_t iMinQp;
int32_t iMaxQp;
//int32_t delta_adaptive_qp;
int32_t iSkipBufferRatio;
int32_t iQStep; // *INT_MULTIPLY
int32_t iFrameDeltaQpUpper;
int32_t iFrameDeltaQpLower;
int32_t iLastCalculatedQScale;
//for skip frame and padding
int32_t iBufferSizeSkip;
int64_t iBufferFullnessSkip;
int64_t iBufferMaxBRFullness[TIME_WINDOW_TOTAL];//0: EVEN_TIME_WINDOW; 1: ODD_TIME_WINDOW
int32_t iPredFrameBit;
bool bNeedShiftWindowCheck[TIME_WINDOW_TOTAL];
int32_t iBufferSizePadding;
int32_t iBufferFullnessPadding;
int32_t iPaddingSize;
int32_t iPaddingBitrateStat;
bool bSkipFlag;
int32_t iContinualSkipFrames;
SRCTemporal* pTemporalOverRc;
//for scc
int64_t iAvgCost2Bits;
int64_t iCost2BitsIntra;
int32_t iBaseQp;
long long uiLastTimeStamp;
//for statistics and online adjustments
int32_t iActualBitRate; // TODO: to complete later
float fLatestFrameRate; // TODO: to complete later
} SWelsSvcRc;
2、Slice级QP参数
SRCSlicing->iCalculatedQpSlice
// slice level rc statistic info
typedef struct TagRCSlicing {
int32_t iComplexityIndexSlice;
int32_t iCalculatedQpSlice;
int32_t iStartMbSlice;
int32_t iEndMbSlice;
int32_t iTotalQpSlice;
int32_t iTotalMbSlice;
int32_t iTargetBitsSlice;
int32_t iBsPosSlice;
int32_t iFrameBitsSlice;
int32_t iGomBitsSlice;
int32_t iGomTargetBits;
//int32_t gom_coded_mb;
} SRCSlicing;3、宏块级QP参数
TagMB->uiLumaQp/uiChromaQp
typedef struct TagMB {
/*************************mb_layer() syntax and generated********************************/
/*mb_layer():*/
Mb_Type uiMbType; // including MB detailed partition type, number and type of reference list
uint8_t uiSubMbType[4]; // sub MB types
int32_t iMbXY; // offset position of MB top left point based
int16_t iMbX; // position of MB in horizontal axis [0..32767]
int16_t iMbY; // position of MB in vertical axis [0..32767]
uint8_t uiNeighborAvail; // avail && same_slice: LEFT_MB_POS:0x01, TOP_MB_POS:0x02, TOPRIGHT_MB_POS = 0x04 ,TOPLEFT_MB_POS = 0x08;
uint8_t uiCbp;
SMVUnitXY* sMv;
int8_t* pRefIndex;
int32_t* pSadCost; // mb sad. set to 0 for intra mb
int8_t* pIntra4x4PredMode; // [MB_BLOCK4x4_NUM]
int8_t* pNonZeroCount; // [MB_LUMA_CHROMA_BLOCK4x4_NUM]
SMVUnitXY sP16x16Mv;
uint8_t uiLumaQp; // uiLumaQp: pPps->iInitialQp + sSliceHeader->delta_qp + mb->dquant.
uint8_t uiChromaQp;
uint16_t uiSliceIdc; // 2^16=65536 > MaxFS(36864) of level 5.1; AVC: iFirstMbInSlice?; SVC: (iFirstMbInSlice << 7) | ((uiDependencyId << 4) | uiQualityId);
uint32_t uiChromPredMode;
int32_t iLumaDQp;
SMVUnitXY sMvd[MB_BLOCK4x4_NUM]; //only for CABAC writing; storage structure the same as sMv, in 4x4 scan order.
int32_t iCbpDc;
//uint8_t reserved_filling_bytes[1]; // not deleting this line for further changes of this structure. filling bytes reserved to make structure aligned with 4 bytes, higher cache hit on less structure size by 2 cache lines( 2 * 64 bytes) once hit
} SMB, *PMb;