HEVC函数解析

本文介绍了HEVC编码器的设计原理,包括核心类TEncEntropyIf和TEncEntropy的功能及其实现方式,以及TEncCavlc子类的具体作用。探讨了熵编码在HEVC中的应用。

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getUseAdaptiveQP()函数:在parseConfig()函数中,根据命令读入,由成员变量m_bUseAdaptiveQP保存,默认选项为false

("AdaptiveQP,-aq",  m_bUseAdaptiveQP,   false, "QP adaptation based on a psycho-visual model")

HEVC编码主要包括两个过程:模式选择和写码流,分别对应compress()和encode()。在模式选择时要统计bit信息,写码流时往bin文件中写入码流。这两种情况下都会调用EncEntropyEncoder这个类,而统计bit和写比特操作,是通过类的多态继承来实现的。
首先是两个主要的类:TEncEntropyIf和TEncEntropy,在TEncEntropy.hpp中定义类

/// entropy encoder pure class
class TEncEntropyIf
{
public:
  virtual Void  resetEntropy          (const TComSlice *pSlice)                = 0;
  virtual SliceType determineCabacInitIdx (const TComSlice *pSlice)                = 0;
  virtual Void  setBitstream          ( TComBitIf* p )  = 0;
  virtual Void  resetBits             ()                = 0;
  virtual UInt  getNumberOfWrittenBits()                = 0;

  virtual Void  codeVPS                 ( const TComVPS* pcVPS )                                      = 0;
  virtual Void  codeSPS                 ( const TComSPS* pcSPS )                                      = 0;
  virtual Void  codePPS                 ( const TComPPS* pcPPS )                                      = 0;
  virtual Void  codeSliceHeader         ( TComSlice* pcSlice )                                  = 0;

  virtual Void  codeTilesWPPEntryPoint  ( TComSlice* pSlice )     = 0;
  virtual Void  codeTerminatingBit      ( UInt uilsLast )                                       = 0;
  virtual Void  codeSliceFinish         ()                                                      = 0;
  virtual Void  codeMVPIdx ( TComDataCU* pcCU, UInt uiAbsPartIdx, RefPicList eRefList ) = 0;

public:
  virtual Void codeCUTransquantBypassFlag( TComDataCU* pcCU, UInt uiAbsPartIdx ) = 0;
  virtual Void codeSkipFlag      ( TComDataCU* pcCU, UInt uiAbsPartIdx ) = 0;
  virtual Void codeMergeFlag     ( TComDataCU* pcCU, UInt uiAbsPartIdx ) = 0;
  virtual Void codeMergeIndex    ( TComDataCU* pcCU, UInt uiAbsPartIdx ) = 0;
  virtual Void codeSplitFlag     ( TComDataCU* pcCU, UInt uiAbsPartIdx, UInt uiDepth ) = 0;

  virtual Void codePartSize      ( TComDataCU* pcCU, UInt uiAbsPartIdx, UInt uiDepth ) = 0;
  virtual Void codePredMode      ( TComDataCU* pcCU, UInt uiAbsPartIdx ) = 0;

  virtual Void codeIPCMInfo      ( TComDataCU* pcCU, UInt uiAbsPartIdx ) = 0;

  virtual Void codeTransformSubdivFlag( UInt uiSymbol, UInt uiCtx ) = 0;
  virtual Void codeQtCbf         ( TComTU &rTu, const ComponentID compID, const Bool lowestLevel ) = 0;
  virtual Void codeQtRootCbf     ( TComDataCU* pcCU, UInt uiAbsPartIdx ) = 0;
  virtual Void codeQtCbfZero     ( TComTU &rTu, const ChannelType chType ) = 0;
  virtual Void codeQtRootCbfZero ( ) = 0;
  virtual Void codeIntraDirLumaAng( TComDataCU* pcCU, UInt uiAbsPartIdx, Bool isMultiplePU ) = 0;

  virtual Void codeIntraDirChroma( TComDataCU* pcCU, UInt uiAbsPartIdx ) = 0;
  virtual Void codeInterDir      ( TComDataCU* pcCU, UInt uiAbsPartIdx ) = 0;
  virtual Void codeRefFrmIdx     ( TComDataCU* pcCU, UInt uiAbsPartIdx, RefPicList eRefList )      = 0;
  virtual Void codeMvd           ( TComDataCU* pcCU, UInt uiAbsPartIdx, RefPicList eRefList )      = 0;

  virtual Void codeCrossComponentPrediction( TComTU &rTu, ComponentID compID ) = 0;

  virtual Void codeDeltaQP       ( TComDataCU* pcCU, UInt uiAbsPartIdx ) = 0;
  virtual Void codeChromaQpAdjustment( TComDataCU* pcCU, UInt uiAbsPartIdx ) = 0;
  virtual Void codeCoeffNxN      ( TComTU &rTu, TCoeff* pcCoef, const ComponentID compID ) = 0;
  virtual Void codeTransformSkipFlags ( TComTU &rTu, ComponentID component ) = 0;
  virtual Void codeSAOBlkParam   (SAOBlkParam& saoBlkParam, const BitDepths &bitDepths, Bool* sliceEnabled, Bool leftMergeAvail, Bool aboveMergeAvail, Bool onlyEstMergeInfo = false)    =0;
  virtual Void estBit               (estBitsSbacStruct* pcEstBitsSbac, Int width, Int height, ChannelType chType) = 0;

  virtual Void codeExplicitRdpcmMode ( TComTU &rTu, const ComponentID compID ) = 0;

  virtual ~TEncEntropyIf() {}
};

TEncEntropyIf是一个由纯虚函数定义的抽象类,其成员函数被申明为纯虚函数,具体的函数功能实现留待派生类中定义。

/// entropy encoder class
class TEncEntropy
{
public:
  Void    setEntropyCoder           ( TEncEntropyIf* e );
  Void    setBitstream              ( TComBitIf* p )          { m_pcEntropyCoderIf->setBitstream(p);  }
  Void    resetBits                 ()                        { m_pcEntropyCoderIf->resetBits();      }
  UInt    getNumberOfWrittenBits    ()                        { return m_pcEntropyCoderIf->getNumberOfWrittenBits(); }
  Void    resetEntropy              (const TComSlice *pSlice) { m_pcEntropyCoderIf->resetEntropy(pSlice);  }
  SliceType determineCabacInitIdx   (const TComSlice *pSlice) { return m_pcEntropyCoderIf->determineCabacInitIdx(pSlice); }

  Void    encodeSliceHeader         ( TComSlice* pcSlice );
  Void    encodeTilesWPPEntryPoint( TComSlice* pSlice );
  Void    encodeTerminatingBit      ( UInt uiIsLast );
  Void    encodeSliceFinish         ();
  TEncEntropyIf*      m_pcEntropyCoderIf;

public:
  Void encodeVPS               ( const TComVPS* pcVPS);
  // SPS
  Void encodeSPS               ( const TComSPS* pcSPS );
  Void encodePPS               ( const TComPPS* pcPPS );
  Void encodeSplitFlag         ( TComDataCU* pcCU, UInt uiAbsPartIdx, UInt uiDepth, Bool bRD = false );
  Void encodeCUTransquantBypassFlag( TComDataCU* pcCU, UInt uiAbsPartIdx, Bool bRD = false );
  Void encodeSkipFlag          ( TComDataCU* pcCU, UInt uiAbsPartIdx, Bool bRD = false );
  Void encodePUWise       ( TComDataCU* pcCU, UInt uiAbsPartIdx );
  Void encodeInterDirPU   ( TComDataCU* pcSubCU, UInt uiAbsPartIdx  );
  Void encodeRefFrmIdxPU  ( TComDataCU* pcSubCU, UInt uiAbsPartIdx, RefPicList eRefList );
  Void encodeMvdPU        ( TComDataCU* pcSubCU, UInt uiAbsPartIdx, RefPicList eRefList );
  Void encodeMVPIdxPU     ( TComDataCU* pcSubCU, UInt uiAbsPartIdx, RefPicList eRefList );
  Void encodeMergeFlag    ( TComDataCU* pcCU, UInt uiAbsPartIdx );
  Void encodeMergeIndex   ( TComDataCU* pcCU, UInt uiAbsPartIdx, Bool bRD = false );
  Void encodePredMode          ( TComDataCU* pcCU, UInt uiAbsPartIdx, Bool bRD = false );
  Void encodePartSize          ( TComDataCU* pcCU, UInt uiAbsPartIdx, UInt uiDepth, Bool bRD = false );
  Void encodeIPCMInfo          ( TComDataCU* pcCU, UInt uiAbsPartIdx, Bool bRD = false );
  Void encodePredInfo          ( TComDataCU* pcCU, UInt uiAbsPartIdx );
  Void encodeIntraDirModeLuma  ( TComDataCU* pcCU, UInt absPartIdx, Bool isMultiplePU = false );

  Void encodeIntraDirModeChroma( TComDataCU* pcCU, UInt uiAbsPartIdx );

  Void encodeTransformSubdivFlag( UInt uiSymbol, UInt uiCtx );
  Void encodeQtCbf             ( TComTU &rTu, const ComponentID compID, const Bool lowestLevel );

  Void encodeQtCbfZero         ( TComTU &rTu, const ChannelType chType );
  Void encodeQtRootCbfZero     ( );
  Void encodeQtRootCbf         ( TComDataCU* pcCU, UInt uiAbsPartIdx );
  Void encodeQP                ( TComDataCU* pcCU, UInt uiAbsPartIdx, Bool bRD = false );
  Void encodeChromaQpAdjustment ( TComDataCU* pcCU, UInt uiAbsPartIdx, Bool bRD = false );

  Void encodeCrossComponentPrediction( TComTU &rTu, ComponentID compID );

private:
  Void xEncodeTransform        ( Bool& bCodeDQP, Bool& codeChromaQpAdj, TComTU &rTu );

public:
  Void encodeCoeff             ( TComDataCU* pcCU, UInt uiAbsPartIdx, UInt uiDepth, Bool& bCodeDQP, Bool& codeChromaQpAdj );

  Void encodeCoeffNxN         ( TComTU &rTu, TCoeff* pcCoef, const ComponentID compID );

  Void estimateBit             ( estBitsSbacStruct* pcEstBitsSbac, Int width, Int height, ChannelType chType );

  Void encodeSAOBlkParam(SAOBlkParam& saoBlkParam, const BitDepths &bitDepths, Bool* sliceEnabled, Bool leftMergeAvail, Bool aboveMergeAvail){m_pcEntropyCoderIf->codeSAOBlkParam(saoBlkParam, bitDepths, sliceEnabled, leftMergeAvail, aboveMergeAvail, false);}

  static Int countNonZeroCoeffs( TCoeff* pcCoef, UInt uiSize );

};// END CLASS DEFINITION TEncEntropy

TEncEntropy是具体类,也是在代码中经常见到的,常作为GOPEncoder,SliceEncoder等类的成员变量:m_pcEntropyCoder
该类包含唯一的 一个成员变量,指向的抽象类的指针:m_pcEntropyCoderIf

TEncEntropyIf*      m_pcEntropyCoderIf;

这个成员变量通过set()函数被赋值

Void TEncEntropy::setEntropyCoder ( TEncEntropyIf* e )
{
  m_pcEntropyCoderIf = e;
}

同时TEncEntropy的其他进行encode函数,也都是由m_pcEntropyCoderIf来实现,例如

Void TEncEntropy::encodeSliceHeader ( TComSlice* pcSlice )
{
  m_pcEntropyCoderIf->codeSliceHeader( pcSlice );
  return;

这样关系一下子就明朗了:首先由派生类的指针或引用作为参数传递给setEntropyCoder函数,这样m_pcEntropyCoderIf成员变代表了不同的派生子类,然后具体的encode任务由不同的派生类来完成,程序对外只有唯一的一个TEncEntropy的函数定义的接口。
那么,继承了TEncEntropyIf的子类有哪些呢?
派生子类TEncCavlc

/// CAVLC encoder class
class TEncCavlc : public SyntaxElementWriter, public TEncEntropyIf
{
public:
  TEncCavlc();
  virtual ~TEncCavlc();

protected:
  Void codeShortTermRefPicSet              ( const TComReferencePictureSet* pcRPS, Bool calledFromSliceHeader, Int idx );
  Bool findMatchingLTRP ( TComSlice* pcSlice, UInt *ltrpsIndex, Int ltrpPOC, Bool usedFlag );

public:

  Void  resetEntropy          (const TComSlice *pSlice);
  SliceType determineCabacInitIdx  (const TComSlice* /*pSlice*/) { assert(0); return I_SLICE; };

  Void  setBitstream          ( TComBitIf* p )  { m_pcBitIf = p;  }
  Void  resetBits             ()                { m_pcBitIf->resetBits(); }
  UInt  getNumberOfWrittenBits()                { return  m_pcBitIf->getNumberOfWrittenBits();  }
  Void  codeVPS                 ( const TComVPS* pcVPS );
  Void  codeVUI                 ( const TComVUI *pcVUI, const TComSPS* pcSPS );
  Void  codeSPS                 ( const TComSPS* pcSPS );
  Void  codePPS                 ( const TComPPS* pcPPS );
  Void  codeSliceHeader         ( TComSlice* pcSlice );
  Void  codePTL                 ( const TComPTL* pcPTL, Bool profilePresentFlag, Int maxNumSubLayersMinus1);
  Void  codeProfileTier         ( const ProfileTierLevel* ptl, const Bool bIsSubLayer );
  Void  codeHrdParameters       ( const TComHRD *hrd, Bool commonInfPresentFlag, UInt maxNumSubLayersMinus1 );
  Void  codeTilesWPPEntryPoint( TComSlice* pSlice );
  Void  codeTerminatingBit      ( UInt uilsLast );
  Void  codeSliceFinish         ();

  Void codeMVPIdx ( TComDataCU* pcCU, UInt uiAbsPartIdx, RefPicList eRefList );
  Void codeSAOBlkParam(SAOBlkParam& /*saoBlkParam*/, const BitDepths& /*bitDepths*/, Bool* /*sliceEnabled*/, Bool /*leftMergeAvail*/, Bool /*aboveMergeAvail*/, Bool /*onlyEstMergeInfo*/ = false){printf("only supported in CABAC"); assert(0); exit(-1);}
  Void codeCUTransquantBypassFlag( TComDataCU* pcCU, UInt uiAbsPartIdx );
  Void codeSkipFlag      ( TComDataCU* pcCU, UInt uiAbsPartIdx );
  Void codeMergeFlag     ( TComDataCU* pcCU, UInt uiAbsPartIdx );
  Void codeMergeIndex    ( TComDataCU* pcCU, UInt uiAbsPartIdx );

  Void codeAlfCtrlFlag   ( ComponentID /*component*/, UInt /*code*/ ) {printf("Not supported\n"); assert(0);}
  Void codeInterModeFlag( TComDataCU* pcCU, UInt uiAbsPartIdx, UInt uiDepth, UInt uiEncMode );
  Void codeSplitFlag     ( TComDataCU* pcCU, UInt uiAbsPartIdx, UInt uiDepth );

  Void codePartSize      ( TComDataCU* pcCU, UInt uiAbsPartIdx, UInt uiDepth );
  Void codePredMode      ( TComDataCU* pcCU, UInt uiAbsPartIdx );

  Void codeIPCMInfo      ( TComDataCU* pcCU, UInt uiAbsPartIdx );

  Void codeTransformSubdivFlag( UInt uiSymbol, UInt uiCtx );
  Void codeQtCbf         ( TComTU &rTu, const ComponentID compID, const Bool lowestLevel );
  Void codeQtRootCbf     ( TComDataCU* pcCU, UInt uiAbsPartIdx );
  Void codeQtCbfZero     ( TComTU &rTu, const ChannelType chType );
  Void codeQtRootCbfZero ( );
  Void codeIntraDirLumaAng( TComDataCU* pcCU, UInt absPartIdx, Bool isMultiple);
  Void codeIntraDirChroma( TComDataCU* pcCU, UInt uiAbsPartIdx );
  Void codeInterDir      ( TComDataCU* pcCU, UInt uiAbsPartIdx );
  Void codeRefFrmIdx     ( TComDataCU* pcCU, UInt uiAbsPartIdx, RefPicList eRefList );
  Void codeMvd           ( TComDataCU* pcCU, UInt uiAbsPartIdx, RefPicList eRefList );

  Void codeCrossComponentPrediction( TComTU &rTu, ComponentID compID );

  Void codeDeltaQP       ( TComDataCU* pcCU, UInt uiAbsPartIdx );
  Void codeChromaQpAdjustment( TComDataCU* pcCU, UInt uiAbsPartIdx );

  Void codeCoeffNxN      ( TComTU &rTu, TCoeff* pcCoef, const ComponentID compID );
  Void codeTransformSkipFlags ( TComTU &rTu, ComponentID component );

  Void estBit            ( estBitsSbacStruct* pcEstBitsSbac, Int width, Int height, ChannelType chType );

  Void xCodePredWeightTable          ( TComSlice* pcSlice );

  Void codeScalingList  ( const TComScalingList &scalingList );
  Void xCodeScalingList ( const TComScalingList* scalingList, UInt sizeId, UInt listId);

  Void codeExplicitRdpcmMode( TComTU &rTu, const ComponentID compID );
};

TEncCavlc是写码流的子类,同时还多继承了父类syntaxElementWritter。TEncCavlc执行code()操作的基本单元,都是调用父类syntaxElementWriter的下面几个函数

#define WRITE_CODE( value, length, name)     xWriteCode ( value, length )
#define WRITE_UVLC( value,         name)     xWriteUvlc ( value )
#define WRITE_SVLC( value,         name)     xWriteSvlc ( value )
#define WRITE_FLAG( value,         name)     xWriteFlag ( value )
class SyntaxElementWriter
{
protected:
  TComBitIf*    m_pcBitIf;

  SyntaxElementWriter()
  :m_pcBitIf(NULL)
  {};
  virtual ~SyntaxElementWriter() {};

  Void  setBitstream          ( TComBitIf* p )  { m_pcBitIf = p;  }

  Void  xWriteCode            ( UInt uiCode, UInt uiLength );
  Void  xWriteUvlc            ( UInt uiCode );
  Void  xWriteSvlc            ( Int  iCode   );
  Void  xWriteFlag            ( UInt uiCode );
#if ENC_DEC_TRACE
  Void  xWriteCodeTr          ( UInt value, UInt  length, const TChar *pSymbolName);
  Void  xWriteUvlcTr          ( UInt value,               const TChar *pSymbolName);
  Void  xWriteSvlcTr          ( Int  value,               const TChar *pSymbolName);
  Void  xWriteFlagTr          ( UInt value,               const TChar *pSymbolName);
#endif
  Void xWriteRbspTrailingBits();

  UInt  xConvertToUInt        ( Int iValue ) {  return ( iValue <= 0) ? -iValue<<1 : (iValue<<1)-1; }
};
Void SyntaxElementWriter::xWriteCode     ( UInt uiCode, UInt uiLength )
{
  assert ( uiLength > 0 );
  m_pcBitIf->write( uiCode, uiLength );
}
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