XBMC分析系列文章：
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 * [email protected] * 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：
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 * [email protected] * 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();
}