XBMC原始碼簡析 5：視頻播放器（dvdplayer）-解複用器（以ffmpeg為例）

XBMC分析系列文章：

XBMC原始碼分析 1：整體結構以及編譯方法

XBMC原始碼分析 2：Addons（皮膚Skin）

XBMC原始碼分析 3：核心部分（core）-綜述

XBMC原始碼分析 4：視頻播放器（dvdplayer）-解碼器（以ffmpeg為例）

本文我們分析XBMC中視頻播放器（dvdplayer）中的解複用器部分。由於解複用器種類很多，不可能一一分析，因此以ffmpeg解複用器為例進行分析。

XBMC解複用器部分檔案目錄如所示：

在這裡我們看一下解複用器中的FFMPEG解複用器。對應DVDDemuxFFmpeg.h和DVDDemuxFFmpeg.cpp

之前的分析類文章在解複用器這方面已經做過詳細的分析了。在此就不多敘述了，代碼很清晰。重點的地方已經標上了注釋。

DVDDemuxFFmpeg.h原始碼如下所示：

/* * 雷霄驊 * leixiaohua1020@126.com * 中國傳媒大學/數字電視技術 * */#include "DVDDemux.h"#include "DllAvFormat.h"#include "DllAvCodec.h"#include "DllAvUtil.h"#include "threads/CriticalSection.h"#include "threads/SystemClock.h"#include <map>class CDVDDemuxFFmpeg;class CURL;class CDemuxStreamVideoFFmpeg  : public CDemuxStreamVideo{  CDVDDemuxFFmpeg *m_parent;  AVStream*        m_stream;public:  CDemuxStreamVideoFFmpeg(CDVDDemuxFFmpeg *parent, AVStream* stream)    : m_parent(parent)    , m_stream(stream)  {}  virtual void GetStreamInfo(std::string& strInfo);};class CDemuxStreamAudioFFmpeg  : public CDemuxStreamAudio{  CDVDDemuxFFmpeg *m_parent;  AVStream*        m_stream;public:  CDemuxStreamAudioFFmpeg(CDVDDemuxFFmpeg *parent, AVStream* stream)    : m_parent(parent)    , m_stream(stream)  {}  std::string m_description;  virtual void GetStreamInfo(std::string& strInfo);  virtual void GetStreamName(std::string& strInfo);};class CDemuxStreamSubtitleFFmpeg  : public CDemuxStreamSubtitle{  CDVDDemuxFFmpeg *m_parent;  AVStream*        m_stream;public:  CDemuxStreamSubtitleFFmpeg(CDVDDemuxFFmpeg *parent, AVStream* stream)    : m_parent(parent)    , m_stream(stream)  {}  std::string m_description;  virtual void GetStreamInfo(std::string& strInfo);  virtual void GetStreamName(std::string& strInfo);};#define FFMPEG_FILE_BUFFER_SIZE   32768 // default reading size for ffmpeg#define FFMPEG_DVDNAV_BUFFER_SIZE 2048  // for dvd's//FFMPEG解複用class CDVDDemuxFFmpeg : public CDVDDemux{public:  CDVDDemuxFFmpeg();  virtual ~CDVDDemuxFFmpeg();  //開啟一個流  bool Open(CDVDInputStream* pInput);  void Dispose();//關閉  void Reset();//複位  void Flush();  void Abort();  void SetSpeed(int iSpeed);  virtual std::string GetFileName();  DemuxPacket* Read();  bool SeekTime(int time, bool backwords = false, double* startpts = NULL);  bool SeekByte(int64_t pos);  int GetStreamLength();  CDemuxStream* GetStream(int iStreamId);  int GetNrOfStreams();  bool SeekChapter(int chapter, double* startpts = NULL);  int GetChapterCount();  int GetChapter();  void GetChapterName(std::string& strChapterName);  virtual void GetStreamCodecName(int iStreamId, CStdString &strName);  bool Aborted();  AVFormatContext* m_pFormatContext;  CDVDInputStream* m_pInput;protected:  friend class CDemuxStreamAudioFFmpeg;  friend class CDemuxStreamVideoFFmpeg;  friend class CDemuxStreamSubtitleFFmpeg;  int ReadFrame(AVPacket *packet);  CDemuxStream* AddStream(int iId);  void AddStream(int iId, CDemuxStream* stream);  CDemuxStream* GetStreamInternal(int iStreamId);  void CreateStreams(unsigned int program = UINT_MAX);  void DisposeStreams();  AVDictionary *GetFFMpegOptionsFromURL(const CURL &url);  double ConvertTimestamp(int64_t pts, int den, int num);  void UpdateCurrentPTS();  bool IsProgramChange();  CCriticalSection m_critSection;  std::map<int, CDemuxStream*> m_streams;  std::vector<std::map<int, CDemuxStream*>::iterator> m_stream_index;  AVIOContext* m_ioContext;  //各種封裝的Dll  DllAvFormat m_dllAvFormat;  DllAvCodec  m_dllAvCodec;  DllAvUtil   m_dllAvUtil;  double   m_iCurrentPts; // used for stream length estimation  bool     m_bMatroska;  bool     m_bAVI;  int      m_speed;  unsigned m_program;  XbmcThreads::EndTime  m_timeout;  // Due to limitations of ffmpeg, we only can detect a program change  // with a packet. This struct saves the packet for the next read and  // signals STREAMCHANGE to player  struct  {    AVPacket pkt;       // packet ffmpeg returned    int      result;    // result from av_read_packet  }m_pkt;};

該類中以下幾個函數包含瞭解複用器的幾個功能。

我們查看一下這幾個函數的原始碼。

Open()

//開啟一個流bool CDVDDemuxFFmpeg::Open(CDVDInputStream* pInput){  AVInputFormat* iformat = NULL;  std::string strFile;  m_iCurrentPts = DVD_NOPTS_VALUE;  m_speed = DVD_PLAYSPEED_NORMAL;  m_program = UINT_MAX;  const AVIOInterruptCB int_cb = { interrupt_cb, this };  if (!pInput) return false;  if (!m_dllAvUtil.Load() || !m_dllAvCodec.Load() || !m_dllAvFormat.Load())  {    CLog::Log(LOGERROR,"CDVDDemuxFFmpeg::Open - failed to load ffmpeg libraries");    return false;  }  //註冊解複用器  // register codecs  m_dllAvFormat.av_register_all();  m_pInput = pInput;  strFile = m_pInput->GetFileName();  bool streaminfo = true; /* set to true if we want to look for streams before playback*/  if( m_pInput->GetContent().length() > 0 )  {    std::string content = m_pInput->GetContent();    /* check if we can get a hint from content */    if     ( content.compare("video/x-vobsub") == 0 )      iformat = m_dllAvFormat.av_find_input_format("mpeg");    else if( content.compare("video/x-dvd-mpeg") == 0 )      iformat = m_dllAvFormat.av_find_input_format("mpeg");    else if( content.compare("video/x-mpegts") == 0 )      iformat = m_dllAvFormat.av_find_input_format("mpegts");    else if( content.compare("multipart/x-mixed-replace") == 0 )      iformat = m_dllAvFormat.av_find_input_format("mjpeg");  }  // open the demuxer  m_pFormatContext  = m_dllAvFormat.avformat_alloc_context();  m_pFormatContext->interrupt_callback = int_cb;  // try to abort after 30 seconds  m_timeout.Set(30000);  if( m_pInput->IsStreamType(DVDSTREAM_TYPE_FFMPEG) )  {    // special stream type that makes avformat handle file opening    // allows internal ffmpeg protocols to be used    CURL url = m_pInput->GetURL();    CStdString protocol = url.GetProtocol();    AVDictionary *options = GetFFMpegOptionsFromURL(url);    int result=-1;    if (protocol.Equals("mms"))    {      // try mmsh, then mmst      url.SetProtocol("mmsh");      url.SetProtocolOptions("");  //真正地開啟      result = m_dllAvFormat.avformat_open_input(&m_pFormatContext, url.Get().c_str(), iformat, &options);      if (result < 0)      {        url.SetProtocol("mmst");        strFile = url.Get();      }     }//真正地開啟    if (result < 0 && m_dllAvFormat.avformat_open_input(&m_pFormatContext, strFile.c_str(), iformat, &options) < 0 )    {      CLog::Log(LOGDEBUG, "Error, could not open file %s", CURL::GetRedacted(strFile).c_str());      Dispose();      m_dllAvUtil.av_dict_free(&options);      return false;    }    m_dllAvUtil.av_dict_free(&options);  }  else  {    unsigned char* buffer = (unsigned char*)m_dllAvUtil.av_malloc(FFMPEG_FILE_BUFFER_SIZE);    m_ioContext = m_dllAvFormat.avio_alloc_context(buffer, FFMPEG_FILE_BUFFER_SIZE, 0, this, dvd_file_read, NULL, dvd_file_seek);    m_ioContext->max_packet_size = m_pInput->GetBlockSize();    if(m_ioContext->max_packet_size)      m_ioContext->max_packet_size *= FFMPEG_FILE_BUFFER_SIZE / m_ioContext->max_packet_size;    if(m_pInput->Seek(0, SEEK_POSSIBLE) == 0)      m_ioContext->seekable = 0;    if( iformat == NULL )    {      // let ffmpeg decide which demuxer we have to open      bool trySPDIFonly = (m_pInput->GetContent() == "audio/x-spdif-compressed");      if (!trySPDIFonly)        m_dllAvFormat.av_probe_input_buffer(m_ioContext, &iformat, strFile.c_str(), NULL, 0, 0);      // Use the more low-level code in case we have been built against an old      // FFmpeg without the above av_probe_input_buffer(), or in case we only      // want to probe for spdif (DTS or IEC 61937) compressed audio      // specifically, or in case the file is a wav which may contain DTS or      // IEC 61937 (e.g. ac3-in-wav) and we want to check for those formats.      if (trySPDIFonly || (iformat && strcmp(iformat->name, "wav") == 0))      {        AVProbeData pd;        uint8_t probe_buffer[FFMPEG_FILE_BUFFER_SIZE + AVPROBE_PADDING_SIZE];        // init probe data        pd.buf = probe_buffer;        pd.filename = strFile.c_str();        // read data using avformat's buffers        pd.buf_size = m_dllAvFormat.avio_read(m_ioContext, pd.buf, m_ioContext->max_packet_size ? m_ioContext->max_packet_size : m_ioContext->buffer_size);        if (pd.buf_size <= 0)        {          CLog::Log(LOGERROR, "%s - error reading from input stream, %s", __FUNCTION__, CURL::GetRedacted(strFile).c_str());          return false;        }        memset(pd.buf+pd.buf_size, 0, AVPROBE_PADDING_SIZE);        // restore position again        m_dllAvFormat.avio_seek(m_ioContext , 0, SEEK_SET);        // the advancedsetting is for allowing the user to force outputting the        // 44.1 kHz DTS wav file as PCM, so that an A/V receiver can decode        // it (this is temporary until we handle 44.1 kHz passthrough properly)        if (trySPDIFonly || (iformat && strcmp(iformat->name, "wav") == 0 && !g_advancedSettings.m_dvdplayerIgnoreDTSinWAV))        {          // check for spdif and dts          // This is used with wav files and audio CDs that may contain          // a DTS or AC3 track padded for S/PDIF playback. If neither of those          // is present, we assume it is PCM audio.          // AC3 is always wrapped in iec61937 (ffmpeg "spdif"), while DTS          // may be just padded.          AVInputFormat *iformat2;          iformat2 = m_dllAvFormat.av_find_input_format("spdif");          if (iformat2 && iformat2->read_probe(&pd) > AVPROBE_SCORE_MAX / 4)          {            iformat = iformat2;          }          else          {            // not spdif or no spdif demuxer, try dts            iformat2 = m_dllAvFormat.av_find_input_format("dts");            if (iformat2 && iformat2->read_probe(&pd) > AVPROBE_SCORE_MAX / 4)            {              iformat = iformat2;            }            else if (trySPDIFonly)            {              // not dts either, return false in case we were explicitely              // requested to only check for S/PDIF padded compressed audio              CLog::Log(LOGDEBUG, "%s - not spdif or dts file, fallbacking", __FUNCTION__);              return false;            }          }        }      }      if(!iformat)      {        std::string content = m_pInput->GetContent();        /* check if we can get a hint from content */        if( content.compare("audio/aacp") == 0 )          iformat = m_dllAvFormat.av_find_input_format("aac");        else if( content.compare("audio/aac") == 0 )          iformat = m_dllAvFormat.av_find_input_format("aac");        else if( content.compare("video/flv") == 0 )          iformat = m_dllAvFormat.av_find_input_format("flv");        else if( content.compare("video/x-flv") == 0 )          iformat = m_dllAvFormat.av_find_input_format("flv");      }      if (!iformat)      {        CLog::Log(LOGERROR, "%s - error probing input format, %s", __FUNCTION__, CURL::GetRedacted(strFile).c_str());        return false;      }      else      {        if (iformat->name)          CLog::Log(LOGDEBUG, "%s - probing detected format [%s]", __FUNCTION__, iformat->name);        else          CLog::Log(LOGDEBUG, "%s - probing detected unnamed format", __FUNCTION__);      }    }    m_pFormatContext->pb = m_ioContext;    if (m_dllAvFormat.avformat_open_input(&m_pFormatContext, strFile.c_str(), iformat, NULL) < 0)    {      CLog::Log(LOGERROR, "%s - Error, could not open file %s", __FUNCTION__, CURL::GetRedacted(strFile).c_str());      Dispose();      return false;    }  }  // Avoid detecting framerate if advancedsettings.xml says so  if (g_advancedSettings.m_videoFpsDetect == 0)       m_pFormatContext->fps_probe_size = 0;    // analyse very short to speed up mjpeg playback start  if (iformat && (strcmp(iformat->name, "mjpeg") == 0) && m_ioContext->seekable == 0)    m_pFormatContext->max_analyze_duration = 500000;  // we need to know if this is matroska or avi later  m_bMatroska = strncmp(m_pFormatContext->iformat->name, "matroska", 8) == 0;// for "matroska.webm"  m_bAVI = strcmp(m_pFormatContext->iformat->name, "avi") == 0;  if (streaminfo)  {    /* too speed up dvd switches, only analyse very short */    if(m_pInput->IsStreamType(DVDSTREAM_TYPE_DVD))      m_pFormatContext->max_analyze_duration = 500000;    CLog::Log(LOGDEBUG, "%s - avformat_find_stream_info starting", __FUNCTION__);    int iErr = m_dllAvFormat.avformat_find_stream_info(m_pFormatContext, NULL);    if (iErr < 0)    {      CLog::Log(LOGWARNING,"could not find codec parameters for %s", CURL::GetRedacted(strFile).c_str());      if (m_pInput->IsStreamType(DVDSTREAM_TYPE_DVD)      ||  m_pInput->IsStreamType(DVDSTREAM_TYPE_BLURAY)      || (m_pFormatContext->nb_streams == 1 && m_pFormatContext->streams[0]->codec->codec_id == AV_CODEC_ID_AC3))      {        // special case, our codecs can still handle it.      }      else      {        Dispose();        return false;      }    }    CLog::Log(LOGDEBUG, "%s - av_find_stream_info finished", __FUNCTION__);  }  // reset any timeout  m_timeout.SetInfinite();  // if format can be nonblocking, let's use that  m_pFormatContext->flags |= AVFMT_FLAG_NONBLOCK;  // print some extra information  m_dllAvFormat.av_dump_format(m_pFormatContext, 0, strFile.c_str(), 0);  UpdateCurrentPTS();  CreateStreams();  return true;}

Dispose()

//關閉void CDVDDemuxFFmpeg::Dispose(){  m_pkt.result = -1;  m_dllAvCodec.av_free_packet(&m_pkt.pkt);  if (m_pFormatContext)  {    if (m_ioContext && m_pFormatContext->pb && m_pFormatContext->pb != m_ioContext)    {      CLog::Log(LOGWARNING, "CDVDDemuxFFmpeg::Dispose - demuxer changed our byte context behind our back, possible memleak");      m_ioContext = m_pFormatContext->pb;    }    m_dllAvFormat.avformat_close_input(&m_pFormatContext);  }  if(m_ioContext)  {    m_dllAvUtil.av_free(m_ioContext->buffer);    m_dllAvUtil.av_free(m_ioContext);  }  m_ioContext = NULL;  m_pFormatContext = NULL;  m_speed = DVD_PLAYSPEED_NORMAL;  DisposeStreams();  m_pInput = NULL;  m_dllAvFormat.Unload();  m_dllAvCodec.Unload();  m_dllAvUtil.Unload();}

Reset()

//複位void CDVDDemuxFFmpeg::Reset(){  CDVDInputStream* pInputStream = m_pInput;  Dispose();  Open(pInputStream);}

Flush()

void CDVDDemuxFFmpeg::Flush(){  // naughty usage of an internal ffmpeg function  if (m_pFormatContext)    m_dllAvFormat.av_read_frame_flush(m_pFormatContext);  m_iCurrentPts = DVD_NOPTS_VALUE;  m_pkt.result = -1;  m_dllAvCodec.av_free_packet(&m_pkt.pkt);}