XBMC源代码分析 4：视频播放器（dvdplayer）-解码器（以ffmpeg为例）

XBMC分析系列文章：

XBMC源代码分析 1：整体结构以及编译方法

XBMC源代码分析 2：Addons（皮肤Skin）

XBMC源代码分析 3：核心部分（core）-综述

本文我们分析XBMC中视频播放器（dvdplayer）中的解码器部分。由于解码器种类很多，不可能一一分析，因此以ffmpeg解码器为例进行分析。

XBMC解码器部分文件目录如下图所示：

解码器分为音频解码器和视频解码器。在这里我们看一下视频解码器中的FFMPEG解码器。对应DVDVideoCodecFFmpeg.h和DVDVideoCodecFFmpeg.cpp。

DVDVideoCodecFFmpeg.h源代码如下所示：

/* * 雷霄骅 * [e-mail] * 中国传媒大学/数字电视技术 * */#include "DVDVideoCodec.h"#include "DVDResource.h"#include "DllAvCodec.h"#include "DllAvFormat.h"#include "DllAvUtil.h"#include "DllSwScale.h"#include "DllAvFilter.h"#include "DllPostProc.h"class CCriticalSection;//封装的FFMPEG视频解码器class CDVDVideoCodecFFmpeg : public CDVDVideoCodec{public:  class IHardwareDecoder : public IDVDResourceCounted<IHardwareDecoder>  {    public:             IHardwareDecoder() {}    virtual ~IHardwareDecoder() {};    virtual bool Open      (AVCodecContext* avctx, const enum PixelFormat, unsigned int surfaces) = 0;    virtual int  Decode    (AVCodecContext* avctx, AVFrame* frame) = 0;    virtual bool GetPicture(AVCodecContext* avctx, AVFrame* frame, DVDVideoPicture* picture) = 0;    virtual int  Check     (AVCodecContext* avctx) = 0;    virtual void Reset     () {}    virtual unsigned GetAllowedReferences() { return 0; }    virtual const std::string Name() = 0;    virtual CCriticalSection* Section() { return NULL; }  };  CDVDVideoCodecFFmpeg();  virtual ~CDVDVideoCodecFFmpeg();  virtual bool Open(CDVDStreamInfo &hints, CDVDCodecOptions &options);//打开  virtual void Dispose();//关闭  virtual int Decode(uint8_t* pData, int iSize, double dts, double pts);//解码  virtual void Reset();  bool GetPictureCommon(DVDVideoPicture* pDvdVideoPicture);  virtual bool GetPicture(DVDVideoPicture* pDvdVideoPicture);  virtual void SetDropState(bool bDrop);  virtual unsigned int SetFilters(unsigned int filters);  virtual const char* GetName() { return m_name.c_str(); }; // m_name is never changed after open  virtual unsigned GetConvergeCount();  virtual unsigned GetAllowedReferences();  bool               IsHardwareAllowed()                     { return !m_bSoftware; }  IHardwareDecoder * GetHardware()                           { return m_pHardware; };  void               SetHardware(IHardwareDecoder* hardware)   {    SAFE_RELEASE(m_pHardware);    m_pHardware = hardware;    UpdateName();  }protected:  static enum PixelFormat GetFormat(struct AVCodecContext * avctx, const PixelFormat * fmt);  int  FilterOpen(const CStdString& filters, bool scale);  void FilterClose();  int  FilterProcess(AVFrame* frame);  void UpdateName()  {    if(m_pCodecContext->codec->name)      m_name = CStdString("ff-") + m_pCodecContext->codec->name;    else      m_name = "ffmpeg";    if(m_pHardware)      m_name += "-" + m_pHardware->Name();  }  AVFrame* m_pFrame;  AVCodecContext* m_pCodecContext;  CStdString       m_filters;  CStdString       m_filters_next;  AVFilterGraph*   m_pFilterGraph;  AVFilterContext* m_pFilterIn;  AVFilterContext* m_pFilterOut;#if defined(LIBAVFILTER_AVFRAME_BASED)  AVFrame*         m_pFilterFrame;#else  AVFilterBufferRef* m_pBufferRef;#endif  int m_iPictureWidth;  int m_iPictureHeight;  int m_iScreenWidth;  int m_iScreenHeight;  int m_iOrientation;// orientation of the video in degress counter clockwise  unsigned int m_uSurfacesCount;  //封装Dll的各种类  DllAvCodec m_dllAvCodec;  DllAvUtil  m_dllAvUtil;  DllSwScale m_dllSwScale;  DllAvFilter m_dllAvFilter;  DllPostProc m_dllPostProc;  std::string m_name;  bool              m_bSoftware;  bool  m_isHi10p;  IHardwareDecoder *m_pHardware;  int m_iLastKeyframe;  double m_dts;  bool   m_started;  std::vector<PixelFormat> m_formats;};

该类中以下几个函数包含了解码器的几种功能：

  virtual bool Open(CDVDStreamInfo &hints, CDVDCodecOptions &options);//打开
  virtual void Dispose();//关闭
  virtual int Decode(uint8_t* pData, int iSize, double dts, double pts);//解码
  virtual void Reset();//复位

为了说明这一点，我们可以看一下视频解码器中的libmpeg2解码器，对应DVDVideoCodecLibMpeg2.h。可以看出这几个函数是一样的。

DVDVideoCodecLibMpeg2.h源代码如下：

/* * 雷霄骅 * [e-mail] * 中国传媒大学/数字电视技术 * */#include "DVDVideoCodec.h"#include "DllLibMpeg2.h"class CDVDVideoCodecLibMpeg2 : public CDVDVideoCodec{public:  CDVDVideoCodecLibMpeg2();  virtual ~CDVDVideoCodecLibMpeg2();  virtual bool Open(CDVDStreamInfo &hints, CDVDCodecOptions &options);  virtual void Dispose();  virtual int Decode(uint8_t* pData, int iSize, double dts, double pts);  virtual void Reset();  virtual bool GetPicture(DVDVideoPicture* pDvdVideoPicture);  virtual bool GetUserData(DVDVideoUserData* pDvdVideoUserData);  virtual void SetDropState(bool bDrop);  virtual const char* GetName() { return "libmpeg2"; }protected:  DVDVideoPicture* GetBuffer(unsigned int width, unsigned int height);  inline void ReleaseBuffer(DVDVideoPicture* pPic);  inline void DeleteBuffer(DVDVideoPicture* pPic);  static int GuessAspect(const mpeg2_sequence_t *sequence, unsigned int *pixel_width, unsigned int *pixel_height);  mpeg2dec_t* m_pHandle;  const mpeg2_info_t* m_pInfo;  DllLibMpeg2 m_dll;  unsigned int m_irffpattern;  bool m_bFilm; //Signals that we have film material  bool m_bIs422;  int m_hurry;  double m_dts;  double m_dts2;  //The buffer of pictures we need  DVDVideoPicture m_pVideoBuffer[3];  DVDVideoPicture* m_pCurrentBuffer;};

现在回到DVDVideoCodecFFmpeg.h。我们可以看一下上文所示的4个函数。

Open()

//打开bool CDVDVideoCodecFFmpeg::Open(CDVDStreamInfo &hints, CDVDCodecOptions &options){  AVCodec* pCodec;  if(!m_dllAvUtil.Load()  || !m_dllAvCodec.Load()  || !m_dllSwScale.Load()  || !m_dllPostProc.Load()  || !m_dllAvFilter.Load()  ) return false;  //注册解码器  m_dllAvCodec.avcodec_register_all();  m_dllAvFilter.avfilter_register_all();  m_bSoftware     = hints.software;  m_iOrientation  = hints.orientation;  for(std::vector<ERenderFormat>::iterator it = options.m_formats.begin(); it != options.m_formats.end(); ++it)  {    m_formats.push_back((PixelFormat)CDVDCodecUtils::PixfmtFromEFormat(*it));    if(*it == RENDER_FMT_YUV420P)      m_formats.push_back(PIX_FMT_YUVJ420P);  }  m_formats.push_back(PIX_FMT_NONE); /* always add none to get a terminated list in ffmpeg world */  pCodec = NULL;  m_pCodecContext = NULL;  if (hints.codec == AV_CODEC_ID_H264)  {    switch(hints.profile)    {      case FF_PROFILE_H264_HIGH_10:      case FF_PROFILE_H264_HIGH_10_INTRA:      case FF_PROFILE_H264_HIGH_422:      case FF_PROFILE_H264_HIGH_422_INTRA:      case FF_PROFILE_H264_HIGH_444_PREDICTIVE:      case FF_PROFILE_H264_HIGH_444_INTRA:      case FF_PROFILE_H264_CAVLC_444:      // this is needed to not open the decoders      m_bSoftware = true;      // this we need to enable multithreading for hi10p via advancedsettings      m_isHi10p = true;      break;    }  }  //查找解码器  if(pCodec == NULL)    pCodec = m_dllAvCodec.avcodec_find_decoder(hints.codec);  if(pCodec == NULL)  {    CLog::Log(LOGDEBUG,"CDVDVideoCodecFFmpeg::Open() Unable to find codec %d", hints.codec);    return false;  }  CLog::Log(LOGNOTICE,"CDVDVideoCodecFFmpeg::Open() Using codec: %s",pCodec->long_name ? pCodec->long_name : pCodec->name);  if(m_pCodecContext == NULL)    m_pCodecContext = m_dllAvCodec.avcodec_alloc_context3(pCodec);  m_pCodecContext->opaque = (void*)this;  m_pCodecContext->debug_mv = 0;  m_pCodecContext->debug = 0;  m_pCodecContext->workaround_bugs = FF_BUG_AUTODETECT;  m_pCodecContext->get_format = GetFormat;  m_pCodecContext->codec_tag = hints.codec_tag;  /* Only allow slice threading, since frame threading is more   * sensitive to changes in frame sizes, and it causes crashes   * during HW accell - so we unset it in this case.   *   * When we detect Hi10p and user did not disable hi10pmultithreading   * via advancedsettings.xml we keep the ffmpeg default thread type.   * */  if(m_isHi10p && !g_advancedSettings.m_videoDisableHi10pMultithreading)  {    CLog::Log(LOGDEBUG,"CDVDVideoCodecFFmpeg::Open() Keep default threading for Hi10p: %d",                        m_pCodecContext->thread_type);  }  else if (CSettings::Get().GetBool("videoplayer.useframemtdec"))  {    CLog::Log(LOGDEBUG,"CDVDVideoCodecFFmpeg::Open() Keep default threading %d by videoplayer.useframemtdec",                        m_pCodecContext->thread_type);  }  else    m_pCodecContext->thread_type = FF_THREAD_SLICE;#if defined(TARGET_DARWIN_IOS)  // ffmpeg with enabled neon will crash and burn if this is enabled  m_pCodecContext->flags &= CODEC_FLAG_EMU_EDGE;#else  if (pCodec->id != AV_CODEC_ID_H264 && pCodec->capabilities & CODEC_CAP_DR1      && pCodec->id != AV_CODEC_ID_VP8     )    m_pCodecContext->flags |= CODEC_FLAG_EMU_EDGE;#endif  // if we don't do this, then some codecs seem to fail.  m_pCodecContext->coded_height = hints.height;  m_pCodecContext->coded_width = hints.width;  m_pCodecContext->bits_per_coded_sample = hints.bitsperpixel;  if( hints.extradata && hints.extrasize > 0 )  {    m_pCodecContext->extradata_size = hints.extrasize;    m_pCodecContext->extradata = (uint8_t*)m_dllAvUtil.av_mallocz(hints.extrasize + FF_INPUT_BUFFER_PADDING_SIZE);    memcpy(m_pCodecContext->extradata, hints.extradata, hints.extrasize);  }  // advanced setting override for skip loop filter (see avcodec.h for valid options)  // TODO: allow per video setting?  if (g_advancedSettings.m_iSkipLoopFilter != 0)  {    m_pCodecContext->skip_loop_filter = (AVDiscard)g_advancedSettings.m_iSkipLoopFilter;  }  // set any special options  for(std::vector<CDVDCodecOption>::iterator it = options.m_keys.begin(); it != options.m_keys.end(); ++it)  {    if (it->m_name == "surfaces")      m_uSurfacesCount = std::atoi(it->m_value.c_str());    else      m_dllAvUtil.av_opt_set(m_pCodecContext, it->m_name.c_str(), it->m_value.c_str(), 0);  }  int num_threads = std::min(8 /*MAX_THREADS*/, g_cpuInfo.getCPUCount());  if( num_threads > 1 && !hints.software && m_pHardware == NULL // thumbnail extraction fails when run threaded  && ( pCodec->id == AV_CODEC_ID_H264    || pCodec->id == AV_CODEC_ID_MPEG4 ))    m_pCodecContext->thread_count = num_threads;  //打开解码器  if (m_dllAvCodec.avcodec_open2(m_pCodecContext, pCodec, NULL) < 0)  {    CLog::Log(LOGDEBUG,"CDVDVideoCodecFFmpeg::Open() Unable to open codec");    return false;  }  //初始化AVFrame  m_pFrame = m_dllAvCodec.avcodec_alloc_frame();  if (!m_pFrame) return false;#if defined(LIBAVFILTER_AVFRAME_BASED)  m_pFilterFrame = m_dllAvUtil.av_frame_alloc();  if (!m_pFilterFrame) return false;#endif  UpdateName();  return true;}

Dispose()

//关闭void CDVDVideoCodecFFmpeg::Dispose(){//释放  if (m_pFrame) m_dllAvUtil.av_free(m_pFrame);  m_pFrame = NULL;#if defined(LIBAVFILTER_AVFRAME_BASED)  m_dllAvUtil.av_frame_free(&m_pFilterFrame);#endif  if (m_pCodecContext)  {  //关闭解码器    if (m_pCodecContext->codec) m_dllAvCodec.avcodec_close(m_pCodecContext);    if (m_pCodecContext->extradata)    {      m_dllAvUtil.av_free(m_pCodecContext->extradata);      m_pCodecContext->extradata = NULL;      m_pCodecContext->extradata_size = 0;    }    m_dllAvUtil.av_free(m_pCodecContext);    m_pCodecContext = NULL;  }  SAFE_RELEASE(m_pHardware);  FilterClose();  m_dllAvCodec.Unload();  m_dllAvUtil.Unload();  m_dllAvFilter.Unload();  m_dllPostProc.Unload();}

Decode()

//解码int CDVDVideoCodecFFmpeg::Decode(uint8_t* pData, int iSize, double dts, double pts){  int iGotPicture = 0, len = 0;  if (!m_pCodecContext)    return VC_ERROR;  if(pData)    m_iLastKeyframe++;  shared_ptr<CSingleLock> lock;  if(m_pHardware)  {    CCriticalSection* section = m_pHardware->Section();    if(section)      lock = shared_ptr<CSingleLock>(new CSingleLock(*section));    int result;    if(pData)      result = m_pHardware->Check(m_pCodecContext);    else      result = m_pHardware->Decode(m_pCodecContext, NULL);    if(result)      return result;  }  if(m_pFilterGraph)  {    int result = 0;    if(pData == NULL)      result = FilterProcess(NULL);    if(result)      return result;  }  m_dts = dts;  m_pCodecContext->reordered_opaque = pts_dtoi(pts);  //初始化AVPacket  AVPacket avpkt;  m_dllAvCodec.av_init_packet(&avpkt);  avpkt.data = pData;  avpkt.size = iSize;  /* We lie, but this flag is only used by pngdec.c.   * Setting it correctly would allow CorePNG decoding. */  avpkt.flags = AV_PKT_FLAG_KEY;  //解码  len = m_dllAvCodec.avcodec_decode_video2(m_pCodecContext, m_pFrame, &iGotPicture, &avpkt);  if(m_iLastKeyframe < m_pCodecContext->has_b_frames + 2)    m_iLastKeyframe = m_pCodecContext->has_b_frames + 2;  if (len < 0)  {    CLog::Log(LOGERROR, "%s - avcodec_decode_video returned failure", __FUNCTION__);    return VC_ERROR;  }  if (!iGotPicture)    return VC_BUFFER;  if(m_pFrame->key_frame)  {    m_started = true;    m_iLastKeyframe = m_pCodecContext->has_b_frames + 2;  }  /* put a limit on convergence count to avoid huge mem usage on streams without keyframes */  if(m_iLastKeyframe > 300)    m_iLastKeyframe = 300;  /* h264 doesn't always have keyframes + won't output before first keyframe anyway */  if(m_pCodecContext->codec_id == AV_CODEC_ID_H264  || m_pCodecContext->codec_id == AV_CODEC_ID_SVQ3)    m_started = true;  if(m_pHardware == NULL)  {    bool need_scale = std::find( m_formats.begin()                               , m_formats.end()                               , m_pCodecContext->pix_fmt) == m_formats.end();    bool need_reopen  = false;    if(!m_filters.Equals(m_filters_next))      need_reopen = true;    if(m_pFilterIn)    {      if(m_pFilterIn->outputs[0]->format != m_pCodecContext->pix_fmt      || m_pFilterIn->outputs[0]->w      != m_pCodecContext->width      || m_pFilterIn->outputs[0]->h      != m_pCodecContext->height)        need_reopen = true;    }    // try to setup new filters    if (need_reopen || (need_scale && m_pFilterGraph == NULL))    {      m_filters = m_filters_next;      if(FilterOpen(m_filters, need_scale) < 0)        FilterClose();    }  }  int result;  if(m_pHardware)    result = m_pHardware->Decode(m_pCodecContext, m_pFrame);  else if(m_pFilterGraph)    result = FilterProcess(m_pFrame);  else    result = VC_PICTURE | VC_BUFFER;  if(result & VC_FLUSHED)    Reset();  return result;}

Reset()

//复位void CDVDVideoCodecFFmpeg::Reset(){  m_started = false;  m_iLastKeyframe = m_pCodecContext->has_b_frames;  m_dllAvCodec.avcodec_flush_buffers(m_pCodecContext);  if (m_pHardware)    m_pHardware->Reset();  m_filters = "";  FilterClose();}