XBMC源代码简析 5：视频播放器（dvdplayer）-解复用器（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

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

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

XBMC解复用器部分文件目录如下图所示：

在这里我们看一下解复用器中的FFMPEG解复用器。对应DVDDemuxFFmpeg.h和DVDDemuxFFmpeg.cpp

之前的分析类文章在解复用器这方面已经做过详细的分析了。在此就不多叙述了，代码很清晰。重点的地方已经标上了注释。

DVDDemuxFFmpeg.h源代码如下所示：

/** 雷霄骅* leixiaohua1020@126.com* 中国传媒大学/数字电视技术**/
#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解复用
class CDVDDemuxFFmpeg : public CDVDDemux
{
public:CDVDDemuxFFmpeg();virtual ~CDVDDemuxFFmpeg();//打开一个流bool Open(CDVDInputStream* pInput);void Dispose();//关闭void Reset();//复位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;//各种封装的DllDllAvFormat m_dllAvFormat;DllAvCodec  m_dllAvCodec;DllAvUtil   m_dllAvUtil;double   m_iCurrentPts; // used for stream length estimationbool     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 playerstruct{AVPacket pkt;       // packet ffmpeg returnedint      result;    // result from av_read_packet}m_pkt;
};

该类中以下几个函数包含了解复用器的几个功能。

bool Open(CDVDInputStream* pInput);//打开
void Dispose();//关闭
void Reset();//复位
void Flush();

我们查看一下这几个函数的源代码。

Open()

//打开一个流
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;}//注册解复用器// register codecsm_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 demuxerm_pFormatContext  = m_dllAvFormat.avformat_alloc_context();m_pFormatContext->interrupt_callback = int_cb;// try to abort after 30 secondsm_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 usedCURL url = m_pInput->GetURL();CStdString protocol = url.GetProtocol();AVDictionary *options = GetFFMpegOptionsFromURL(url);int result=-1;if (protocol.Equals("mms")){// try mmsh, then mmsturl.SetProtocol("mmsh");url.SetProtocolOptions("");//真正地打开result = m_dllAvFormat.avformat_open_input(&m_pFormatContext, url.Get().c_str(), iformat, &options);if (result < 0){url.SetProtocol("mmst");strFile = url.Get();} }//真正地打开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 openbool 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 datapd.buf = probe_buffer;pd.filename = strFile.c_str();// read data using avformat's bufferspd.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 againm_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 dtsiformat2 = 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 audioCLog::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);elseCLog::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 soif (g_advancedSettings.m_videoFpsDetect == 0) m_pFormatContext->fps_probe_size = 0;// analyse very short to speed up mjpeg playback startif (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 laterm_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 timeoutm_timeout.SetInfinite();// if format can be nonblocking, let's use thatm_pFormatContext->flags |= AVFMT_FLAG_NONBLOCK;// print some extra informationm_dllAvFormat.av_dump_format(m_pFormatContext, 0, strFile.c_str(), 0);UpdateCurrentPTS();CreateStreams();return true;
}

Dispose()

//关闭
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()

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

Flush()

void CDVDDemuxFFmpeg::Flush()
{// naughty usage of an internal ffmpeg functionif (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);
}

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