HEVC码率控制浅析——HM代码阅读之三

续上文继续分析

m_pcRateCtrl->initRCPic( )

Void TEncRateCtrl::initRCPic( Int frameLevel ){  m_encRCPic = new TEncRCPic;  m_encRCPic->create( m_encRCSeq, m_encRCGOP, frameLevel, m_listRCPictures );}

m_encRCPic->create

Void TEncRCPic::create( TEncRCSeq* encRCSeq, TEncRCGOP* encRCGOP, Int frameLevel, list<TEncRCPic*>& listPreviousPictures ){  destroy();  m_encRCSeq = encRCSeq;  m_encRCGOP = encRCGOP;  Int targetBits    = xEstPicTargetBits( encRCSeq, encRCGOP );//!< K0103式子（9）  Int estHeaderBits = xEstPicHeaderBits( listPreviousPictures, frameLevel ); //!< header bits estimation  if ( targetBits < estHeaderBits + 100 )  {    targetBits = estHeaderBits + 100;   // at least allocate 100 bits for picture data  }  //!< 以下为RC相关参数的初始化，根据变量名很容易就能判断其用途，故不罗嗦~  m_frameLevel       = frameLevel;  m_numberOfPixel    = encRCSeq->getNumPixel();  m_numberOfLCU      = encRCSeq->getNumberOfLCU();  m_estPicLambda     = 100.0;  m_targetBits       = targetBits;  m_estHeaderBits    = estHeaderBits;  m_bitsLeft         = m_targetBits;  Int picWidth       = encRCSeq->getPicWidth();  Int picHeight      = encRCSeq->getPicHeight();  Int LCUWidth       = encRCSeq->getLCUWidth();  Int LCUHeight      = encRCSeq->getLCUHeight();  Int picWidthInLCU  = ( picWidth  % LCUWidth  ) == 0 ? picWidth  / LCUWidth  : picWidth  / LCUWidth  + 1;  Int picHeightInLCU = ( picHeight % LCUHeight ) == 0 ? picHeight / LCUHeight : picHeight / LCUHeight + 1;  m_LCULeft         = m_numberOfLCU;  m_bitsLeft       -= m_estHeaderBits; //!< 考虑header bits后的剩余比特数  m_pixelsLeft      = m_numberOfPixel;  m_LCUs           = new TRCLCU[m_numberOfLCU];  Int i, j;  Int LCUIdx;  for ( i=0; i<picWidthInLCU; i++ )  {    for ( j=0; j<picHeightInLCU; j++ )    {      LCUIdx = j*picWidthInLCU + i;      m_LCUs[LCUIdx].m_actualBits = 0;      m_LCUs[LCUIdx].m_QP         = 0;      m_LCUs[LCUIdx].m_lambda     = 0.0;      m_LCUs[LCUIdx].m_targetBits = 0;#if M0036_RC_IMPROVEMENT      m_LCUs[LCUIdx].m_bitWeight  = 1.0;#else      m_LCUs[LCUIdx].m_MAD        = 0.0;#endif      Int currWidth  = ( (i == picWidthInLCU -1) ? picWidth  - LCUWidth *(picWidthInLCU -1) : LCUWidth  );      Int currHeight = ( (j == picHeightInLCU-1) ? picHeight - LCUHeight*(picHeightInLCU-1) : LCUHeight );      m_LCUs[LCUIdx].m_numberOfPixel = currWidth * currHeight;    }  }  m_picActualHeaderBits = 0;#if !M0036_RC_IMPROVEMENT  m_totalMAD            = 0.0;#endif  m_picActualBits       = 0;  m_picQP               = 0;  m_picLambda           = 0.0;#if !M0036_RC_IMPROVEMENT  m_lastPicture = NULL;  list<TEncRCPic*>::reverse_iterator it;  for ( it = listPreviousPictures.rbegin(); it != listPreviousPictures.rend(); it++ )  {    if ( (*it)->getFrameLevel() == m_frameLevel ) //!< 保存跟当前帧同一层的前一帧    {      m_lastPicture = (*it);      break;    }  }#endif}

xEstPicTargetBits()

Int TEncRCPic::xEstPicTargetBits( TEncRCSeq* encRCSeq, TEncRCGOP* encRCGOP ){  Int targetBits        = 0;  Int GOPbitsLeft       = encRCGOP->getBitsLeft(); //!< TGOP - CodedGOP  Int i;  Int currPicPosition = encRCGOP->getNumPic()-encRCGOP->getPicLeft();  Int currPicRatio    = encRCSeq->getBitRatio( currPicPosition );//!< 当前picture的权值  Int totalPicRatio   = 0;  for ( i=currPicPosition; i<encRCGOP->getNumPic(); i++ )  {    totalPicRatio += encRCSeq->getBitRatio( i );//!< 总权值  }#if M0036_RC_IMPROVEMENT  targetBits  = Int( ((Double)GOPbitsLeft) * currPicRatio / totalPicRatio );#else  targetBits  = Int( GOPbitsLeft * currPicRatio / totalPicRatio );#endif  if ( targetBits < 100 )  {    targetBits = 100;   // at least allocate 100 bits for one picture  }  //!< 在此之前targetBits是基于K0103式子（9）计算的结果，而m_encRCGOP->getTargetBitInGOP( currPicPosition )得到的  //!< bits为NotCodedPictures=0通过式子（9）得到的  if ( m_encRCSeq->getFramesLeft() > 16 )  {    targetBits = Int( g_RCWeightPicRargetBitInBuffer * targetBits + g_RCWeightPicTargetBitInGOP * m_encRCGOP->getTargetBitInGOP( currPicPosition ) );  }  return targetBits;}

xEstPicHeaderBits()

Int TEncRCPic::xEstPicHeaderBits( list<TEncRCPic*>& listPreviousPictures, Int frameLevel ){  Int numPreviousPics   = 0;  Int totalPreviousBits = 0;  list<TEncRCPic*>::iterator it;  for ( it = listPreviousPictures.begin(); it != listPreviousPictures.end(); it++ ) //!< 求出当前帧之前所有与其在同一层的帧的header bits之和  {    if ( (*it)->getFrameLevel() == frameLevel )    {      totalPreviousBits += (*it)->getPicActualHeaderBits();      numPreviousPics++;    }  }  Int estHeaderBits = 0;  if ( numPreviousPics > 0 ) //!< 取平均值  {    estHeaderBits = totalPreviousBits / numPreviousPics;  }  return estHeaderBits;}

分析第一篇提到的compressGOP中的RC初始化代码片段：

#if RATE_CONTROL_LAMBDA_DOMAIN    Double lambda            = 0.0;    Int actualHeadBits       = 0;    Int actualTotalBits      = 0;    Int estimatedBits        = 0;    Int tmpBitsBeforeWriting = 0;    if ( m_pcCfg->getUseRateCtrl() )    {      Int frameLevel = m_pcRateCtrl->getRCSeq()->getGOPID2Level( iGOPid );      if ( pcPic->getSlice(0)->getSliceType() == I_SLICE )      {        frameLevel = 0;      }      m_pcRateCtrl->initRCPic( frameLevel ); //!< picture level 初始化      estimatedBits = m_pcRateCtrl->getRCPic()->getTargetBits(); //!< 在initRCPic中已经计算出了targetBits            Int sliceQP = m_pcCfg->getInitialQP(); //!< 对应于配置文件中的InitalQP      if ( ( pcSlice->getPOC() == 0 && m_pcCfg->getInitialQP() > 0 ) || ( frameLevel == 0 && m_pcCfg->getForceIntraQP() ) ) // QP is specified      {//!< 如果配置文件对序列第一帧指定了初始QP，则基于这个QP计算出lamda        Int    NumberBFrames = ( m_pcCfg->getGOPSize() - 1 );        Double dLambda_scale = 1.0 - Clip3( 0.0, 0.5, 0.05*(Double)NumberBFrames );        Double dQPFactor     = 0.57*dLambda_scale;        Int    SHIFT_QP      = 12;        Int    bitdepth_luma_qp_scale = 0;        Double qp_temp = (Double) sliceQP + bitdepth_luma_qp_scale - SHIFT_QP;        lambda = dQPFactor*pow( 2.0, qp_temp/3.0 );      }      else if ( frameLevel == 0 )   // intra case, but use the model      { //!< 对I slice的情况，需要做些特殊处理，如targetBits的修正等#if RATE_CONTROL_INTRA        m_pcSliceEncoder->calCostSliceI(pcPic);#endif        if ( m_pcCfg->getIntraPeriod() != 1 )   // do not refine allocated bits for all intra case        {          Int bits = m_pcRateCtrl->getRCSeq()->getLeftAverageBits();#if RATE_CONTROL_INTRA          bits = m_pcRateCtrl->getRCPic()->getRefineBitsForIntra( bits );#else          bits = m_pcRateCtrl->getRCSeq()->getRefineBitsForIntra( bits ); //!< K0103 Table 3#endif          if ( bits < 200 )          {            bits = 200;          }          m_pcRateCtrl->getRCPic()->setTargetBits( bits );        }                list<TEncRCPic*> listPreviousPicture = m_pcRateCtrl->getPicList();#if RATE_CONTROL_INTRA        m_pcRateCtrl->getRCPic()->getLCUInitTargetBits();        lambda  = m_pcRateCtrl->getRCPic()->estimatePicLambda( listPreviousPicture, pcSlice->getSliceType());#else        lambda  = m_pcRateCtrl->getRCPic()->estimatePicLambda( listPreviousPicture );#endif        sliceQP = m_pcRateCtrl->getRCPic()->estimatePicQP( lambda, listPreviousPicture );      }      else    // normal case      {        list<TEncRCPic*> listPreviousPicture = m_pcRateCtrl->getPicList();#if RATE_CONTROL_INTRA        lambda  = m_pcRateCtrl->getRCPic()->estimatePicLambda( listPreviousPicture, pcSlice->getSliceType());#else        lambda  = m_pcRateCtrl->getRCPic()->estimatePicLambda( listPreviousPicture );#endif        sliceQP = m_pcRateCtrl->getRCPic()->estimatePicQP( lambda, listPreviousPicture );      }            sliceQP = Clip3( -pcSlice->getSPS()->getQpBDOffsetY(), MAX_QP, sliceQP );      m_pcRateCtrl->getRCPic()->setPicEstQP( sliceQP );            m_pcSliceEncoder->resetQP( pcPic, sliceQP, lambda ); //!< 设置当前slice使用的QP, lambda，编码时用到    }#endif

 

#if !RATE_CONTROL_INTRAInt TEncRCSeq::getRefineBitsForIntra( Int orgBits ) //!< K0103 Table 3{  Double bpp = ( (Double)orgBits ) / m_picHeight / m_picHeight;  if ( bpp > 0.2 )  {    return orgBits * 5;  }  if ( bpp > 0.1 )  {    return orgBits * 7;  }  return orgBits * 10;}#endif

#if RATE_CONTROL_INTRADouble TEncRCPic::estimatePicLambda( list<TEncRCPic*>& listPreviousPictures, SliceType eSliceType)#elseDouble TEncRCPic::estimatePicLambda( list<TEncRCPic*>& listPreviousPictures )#endif{  Double alpha         = m_encRCSeq->getPicPara( m_frameLevel ).m_alpha;  Double beta          = m_encRCSeq->getPicPara( m_frameLevel ).m_beta;  Double bpp       = (Double)m_targetBits/(Double)m_numberOfPixel;#if RATE_CONTROL_INTRA  Double estLambda;  if (eSliceType == I_SLICE)  {    estLambda = calculateLambdaIntra(alpha, beta, pow(m_totalCostIntra/(Double)m_numberOfPixel, BETA1), bpp);   }  else  {    estLambda = alpha * pow( bpp, beta );  }#else  Double estLambda = alpha * pow( bpp, beta ); //!< K0103 式子（10）#endif      Double lastLevelLambda = -1.0;  Double lastPicLambda   = -1.0;  Double lastValidLambda = -1.0;  list<TEncRCPic*>::iterator it;  for ( it = listPreviousPictures.begin(); it != listPreviousPictures.end(); it++ )  {    if ( (*it)->getFrameLevel() == m_frameLevel )    {      lastLevelLambda = (*it)->getPicActualLambda();    }    lastPicLambda     = (*it)->getPicActualLambda();    if ( lastPicLambda > 0.0 )    {      lastValidLambda = lastPicLambda;    }  }  //!< 以下对lastLevelLambda和estLambda进行clip，范围在K0103的section 3.2中进行了定义  if ( lastLevelLambda > 0.0 )  {    lastLevelLambda = Clip3( 0.1, 10000.0, lastLevelLambda );    estLambda = Clip3( lastLevelLambda * pow( 2.0, -3.0/3.0 ), lastLevelLambda * pow( 2.0, 3.0/3.0 ), estLambda );  }  if ( lastPicLambda > 0.0 )  {    lastPicLambda = Clip3( 0.1, 2000.0, lastPicLambda );    estLambda = Clip3( lastPicLambda * pow( 2.0, -10.0/3.0 ), lastPicLambda * pow( 2.0, 10.0/3.0 ), estLambda );  }  else if ( lastValidLambda > 0.0 )  {    lastValidLambda = Clip3( 0.1, 2000.0, lastValidLambda );    estLambda = Clip3( lastValidLambda * pow(2.0, -10.0/3.0), lastValidLambda * pow(2.0, 10.0/3.0), estLambda );  }  else  {    estLambda = Clip3( 0.1, 10000.0, estLambda );  }  if ( estLambda < 0.1 )  {    estLambda = 0.1;  }  m_estPicLambda = estLambda;#if M0036_RC_IMPROVEMENT  Double totalWeight = 0.0;  // initial BU bit allocation weight  for ( Int i=0; i<m_numberOfLCU; i++ )  {#if RC_FIX    Double alphaLCU, betaLCU;    if ( m_encRCSeq->getUseLCUSeparateModel() )    {      alphaLCU = m_encRCSeq->getLCUPara( m_frameLevel, i ).m_alpha;      betaLCU  = m_encRCSeq->getLCUPara( m_frameLevel, i ).m_beta;    }    else    {      alphaLCU = m_encRCSeq->getPicPara( m_frameLevel ).m_alpha;      betaLCU  = m_encRCSeq->getPicPara( m_frameLevel ).m_beta;    }#else    Double alphaLCU = m_encRCSeq->getLCUPara( m_frameLevel, i ).m_alpha;    Double betaLCU  = m_encRCSeq->getLCUPara( m_frameLevel, i ).m_beta;#endif    m_LCUs[i].m_bitWeight =  m_LCUs[i].m_numberOfPixel * pow( estLambda/alphaLCU, 1.0/betaLCU );    if ( m_LCUs[i].m_bitWeight < 0.01 )    {      m_LCUs[i].m_bitWeight = 0.01;    }    totalWeight += m_LCUs[i].m_bitWeight;  }  for ( Int i=0; i<m_numberOfLCU; i++ )  {    Double BUTargetBits = m_targetBits * m_LCUs[i].m_bitWeight / totalWeight;    m_LCUs[i].m_bitWeight = BUTargetBits;  }#endif  return estLambda;}

 

Int TEncRCPic::estimatePicQP( Double lambda, list<TEncRCPic*>& listPreviousPictures ){  Int QP = Int( 4.2005 * log( lambda ) + 13.7122 + 0.5 ); //!< 通过lambda求QP  Int lastLevelQP = g_RCInvalidQPValue;  Int lastPicQP   = g_RCInvalidQPValue;  Int lastValidQP = g_RCInvalidQPValue;  list<TEncRCPic*>::iterator it;  for ( it = listPreviousPictures.begin(); it != listPreviousPictures.end(); it++ )  {    if ( (*it)->getFrameLevel() == m_frameLevel )    {      lastLevelQP = (*it)->getPicActualQP();    }    lastPicQP = (*it)->getPicActualQP();    if ( lastPicQP > g_RCInvalidQPValue )    {      lastValidQP = lastPicQP;    }  }  //!< 以下对QP进行clip，范围在K0103的section 3.2进行了定义  if ( lastLevelQP > g_RCInvalidQPValue )  {    QP = Clip3( lastLevelQP - 3, lastLevelQP + 3, QP );  }  if( lastPicQP > g_RCInvalidQPValue )  {    QP = Clip3( lastPicQP - 10, lastPicQP + 10, QP );  }  else if( lastValidQP > g_RCInvalidQPValue )  {    QP = Clip3( lastValidQP - 10, lastValidQP + 10, QP );  }  return QP;}