【HEVC学习与研究】31、HM编码器的基本结构

通过解码器代码的研究，已经对HEVC的编解码技术有了一个初步的认识。现在我们就对照着编码器的代码进一步理解HEVC视频编码算法的各个技术细节。

编码器在整个HM解决方案中的工程名为TAppEncoder，入口点函数位于encmain.cpp文件中：

int main(int argc, char* argv[])
{
	TAppEncTop  cTAppEncTop;

	// print information
	fprintf( stdout, "\n" );
	fprintf( stdout, "HM software: Encoder Version [%s]", NV_VERSION );
	fprintf( stdout, NVM_ONOS );
	fprintf( stdout, NVM_COMPILEDBY );
	fprintf( stdout, NVM_BITS );
	fprintf( stdout, "\n" );

	// create application encoder class
	cTAppEncTop.create();

	// parse configuration
	try
	{
		if(!cTAppEncTop.parseCfg( argc, argv ))
		{
			cTAppEncTop.destroy();
			return 1;
		}
	}
	catch (po::ParseFailure& e)
	{
		cerr << "Error parsing option \""<< e.arg <<"\" with argument \""<< e.val <<"\"." << endl;
		return 1;
	}

	// starting time
	double dResult;
	long lBefore = clock();

	// call encoding function
	cTAppEncTop.encode();

	// ending time
	dResult = (double)(clock()-lBefore) / CLOCKS_PER_SEC;
	printf("\n Total Time: %12.3f sec.\n", dResult);

	// destroy application encoder class
	cTAppEncTop.destroy();

	return 0;
}

// call encoding function
cTAppEncTop.encode();

Void TAppEncTop::encode()
{
	fstream bitstreamFile(m_pchBitstreamFile, fstream::binary | fstream::out);
	if (!bitstreamFile)
	{
		fprintf(stderr, "\nfailed to open bitstream file `%s' for writing\n", m_pchBitstreamFile);
		exit(EXIT_FAILURE);
	}

	TComPicYuv*       pcPicYuvOrg = new TComPicYuv;
	TComPicYuv*       pcPicYuvRec = NULL;

	// initialize internal class & member variables
	xInitLibCfg();
	xCreateLib();
	xInitLib();

	// main encoder loop
	Int   iNumEncoded = 0;
	Bool  bEos = false;

	list<AccessUnit> outputAccessUnits; ///< list of access units to write out.  is populated by the encoding process

	// allocate original YUV buffer
	pcPicYuvOrg->create( m_iSourceWidth, m_iSourceHeight, m_uiMaxCUWidth, m_uiMaxCUHeight, m_uiMaxCUDepth );

	while ( !bEos )
	{
		// get buffers
		xGetBuffer(pcPicYuvRec);

		// read input YUV file
		m_cTVideoIOYuvInputFile.read( pcPicYuvOrg, m_aiPad );

		// increase number of received frames
		m_iFrameRcvd++;

		bEos = (m_iFrameRcvd == m_framesToBeEncoded);

		Bool flush = 0;
		// if end of file (which is only detected on a read failure) flush the encoder of any queued pictures
		if (m_cTVideoIOYuvInputFile.isEof())
		{
			flush = true;
			bEos = true;
			m_iFrameRcvd--;
			m_cTEncTop.setFramesToBeEncoded(m_iFrameRcvd);
		}

		// call encoding function for one frame
		m_cTEncTop.encode( bEos, flush ? 0 : pcPicYuvOrg, m_cListPicYuvRec, outputAccessUnits, iNumEncoded );

		// write bistream to file if necessary
		if ( iNumEncoded > 0 )
		{
			xWriteOutput(bitstreamFile, iNumEncoded, outputAccessUnits);
			outputAccessUnits.clear();
		}
	}

	m_cTEncTop.printSummary();

	// delete original YUV buffer
	pcPicYuvOrg->destroy();
	delete pcPicYuvOrg;
	pcPicYuvOrg = NULL;

	// delete used buffers in encoder class
	m_cTEncTop.deletePicBuffer();

	// delete buffers & classes
	xDeleteBuffer();
	xDestroyLib();

	printRateSummary();

	return;
}

该函数中首先调用pcPicYuvOrg->create( m_iSourceWidth, m_iSourceHeight, m_uiMaxCUWidth, m_uiMaxCUHeight, m_uiMaxCUDepth )分配YUV数据缓存，然后再while循环中逐帧读取YUV数据、设置当前以编码的帧数、编码当前帧、写出码流，随后做其他清理工作。核心功能实现在m_cTEncTop.encode( bEos, flush ? 0 : pcPicYuvOrg, m_cListPicYuvRec, outputAccessUnits, iNumEncoded )函数中。在该函数中调用m_cGOPEncoder.compressGOP(m_iPOCLast, m_iNumPicRcvd, m_cListPic, rcListPicYuvRecOut, accessUnitsOut)进行编码一个GOP的操作。这个函数奇长无比，用了接近1500行代码，看来实现了很多很多很多的功能。这个碉堡了的函数究竟做了些啥事儿呢？这个函数中大部分内容就是在为了编码当前slice做准备，以及编码完成之后一些辅助操作。实际编码过程的操作由以下函数m_pcSliceEncoder->compressSlice( pcPic )实现。

这又是一个碉堡了的函数，占了将近400行……代码就不贴了，会死人的……简单看下好了。

首先还是各种编码的配置，包括配置熵编码器、初始化CU编码器等。在完成了一长串的设置之后，在compressCU函数中实现对一个CU的编码：

      m_pcCuEncoder->compressCU( pcCU );