DirectShow播放视频流程

DirectShow框架简介

DirectShow框架是多媒体播放框架上一个非常经典的框架，现在已经十多年了，在Windows平台上依然无法替代，非常值得去学习研究。个人觉得从设计模式的角度上看，directshow框架的灵活性、复用性、可维护性、可拓展性这些方面做得非常不错，也是它经久不衰历久弥新的一个原因，现在的很多第三方的decoder和filter都基于directshow框架开发，可以很灵活的移植到directshow视频框架中，例如视骏开发的HEVC/H.265解码器，都可以直接挂载在directshow框架中进行视频解码。

---

图形化理解DirectShow

推荐一款工具GraphStudio,了解DirectShow框架必备工具，软件截图如下：

我们点击Graph可以插入我们在电脑系统中注册的Filter Render，默认情况下，我们将播放的视频加到GraphStudio中，会自动生成directshow的整个播放流程,然后就可以播放视频了。一般的播放效果流程如下：

GraphStudio会自动采用系统默认的一套Filter和Render,如果安装了K-Lite Codec Pack，就可以修改系统默认的这一套，如下图:

我们想测试我们自己的Filter和Render，都可以自定义插入，下面就以DirectShow中植入视骏的HEVC解码器为例子，了解DirecShow的整个播放流程，如下图所示：

DirectShow播放HEVC视频

可以参考雷老师关于DirectShow的介绍，
地址：http://blog.csdn.net/leixiaohua1020/article/details/42372419
播放的流程如下：

整个播放我们可以抽象出三个步骤：

Created with Raphaël 2.1.0 注册Filter和Render 链接Filter和Render 执行播放RenderFile

• 注册：播放HEVC视频需要的Strongene Mpeg-4 Demultiplexor,Lentoid HEVC Decoder,Video Renderer
• 链接：相当于上面GraphStudio图中的链接箭头
• 播放：将视频导入播放链路中，开始播放

注册Filter和Render

解码器属性

首先获取到这些Filter的Object name、CLSID、Filename和FilePath

如果已经将filter注册进Windows的系统中,就只需要用到Object Name,为了避免重新注册导致冲突；

//Name:File Source (Async.) {E436EBB5-524F-11CE-9F53-0020AF0BA770}
/**
Windows自带File Source (Async.)，dll路径：C:\Windows\SysWOW64\quartz.dll
CLSID  = 
*/

//MP4 Splitter {61F47056-E400-43D3-AF1E-AB7DFFD4C4AD} Name: Strongene Mpeg-4 Demultiplexor
static const GUID CLSID_MP4Splitter = {0x61f47056,0xe400,0x43d3,{0xaf,0x1e,0xab,0x7d,0xff,0xd4,0xc4,0xad}};

//h265-HEVC Decoder {658C5E1C-58E1-43CA-9D10-13735D465576} Name:Lentoid HEVC Decoder
static const GUID CLSID_HEVCDecoder = {0x658C5E1C,0x58E1,0x43CA,{0x9D,0x10,0x13,0x73,0x5D,0x46,0x55,0x76}};

//Name:Video Mixing Renderer {B87BEB7B-8D29-423F-AE4D-6582C10175AC}
/**
Windows自带VideoRenderer，dll路径：C:\Windows\SysWOW64\quartz.dll
*/

---

声明DirectShow播放需要的类和变量

IGraphBuilder * mGraph;//创建一个Filter Graph Manager组件
IMediaControl * mMediaControl;//提供控制过滤器图表中多媒体数据流的方法，包括运行、暂停和停止
IMediaEventEx * mEvent;//继承自IMediaEvent接口，处理过滤器图表的事件
IBasicVideo *   mBasicVideo;//用于设置视频特性，如视频显示的目的区域和源区域
IBasicAudio *   mBasicAudio;//用于控制音频流的音量和平衡
IVideoWindow  * mVideoWindow;//定义一个视频窗口的控制对象
IMediaSeeking * mSeeking;//提供搜索数据流位置和设置播放速率的方法

IBaseFilter *m_pSourceFilter = NULL;    
IBaseFilter *m_pSplitter = NULL;
IBaseFilter *m_pSplitter = NULL; 
IBaseFilter *m_pVideoHEVCDecoder = NULL;
IBaseFilter *m_pVideoRender = NULL; 

DWORD mObjectTableEntry = 0;

---

注册Filter：

• 加载解码器并获取DllGetClassObject指针,loadFilter()

bool loadFilter(LPCSTR chAx)
{
    //加载Filter所在的dll文件
    m_hInst = ::LoadLibrary(chAx);
    if (NULL == m_hInst)
    {
        return false;
    } 

    //获取DllGetClassObject函数指针
    m_pDllGetClassObject = ( DLL_GET_CLASS_OBJECT )::GetProcAddress(m_hInst, "DllGetClassObject");
    if (NULL == m_pDllGetClassObject)
    {
        return false;
    }
    return true;
}

---

• 动态创建解码器对象,createFilter()

bool createFilter(GUID clId, IBaseFilter** pBaseFilter)
{
    if (NULL == m_pDllGetClassObject)
    {
        return false;
    }

    //获取类工厂接口
    IClassFactory *p_IClassFactory = NULL;
    if (FAILED( m_pDllGetClassObject(clId, IID_IClassFactory, (void **)&p_IClassFactory) ))
    {
        return false;
    }

    //创建与类厂相关联的COM对象（Filter），并获取其IBaseFilter接口
    p_IClassFactory->CreateInstance(NULL, IID_IBaseFilter, (void **)pBaseFilter);
    p_IClassFactory->Release();
    p_IClassFactory = NULL;

    if ((NULL == pBaseFilter) || (NULL == *pBaseFilter))
    {
        return false;
    }
    return true;    
}

---

• 申明一个方法函数InitRegister()，

bool InitRegister()
{
    mGraph=NULL;
    mMediaControl=NULL;
    mEvent=NULL;
    mBasicVideo=NULL;
    mBasicAudio=NULL;
    mVideoWindow=NULL;
    mSeeking=NULL;

    if(!mGraph)
    {
        //建立 filter graph manager
        HRESULT hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER,IID_IGraphBuilder, (void **)&mGraph);
        if(mGraph != NULL)
        {
            LPCSTR  splitterDll, HEVCDecoderDll;
            LPCWSTR splitterName, HEVCDecoderName;
            GUID    splitterGuid, HEVCDecoderGuid;

            //Source Filter
            hr = CoCreateInstance(CLSID_AsyncReader, NULL, CLSCTX_INPROC,IID_IBaseFilter, (void **)&m_pSourceFilter);
            if(hr == S_OK)
            {
                mGraph->AddFilter(m_pSourceFilter, L"File Source Filter");
            }
            else
            {
                cout << "load source filter failed" << endl;
                return false;
            }

            //Splitter 
            splitterDll = ".\\Codec\\mp4demux.dll";
            splitterName = L"Strongene Mpeg-4 Demultiplexor";
            splitterGuid = CLSID_SMp4Demultiplexor;

            //HEVCDecoder
            HEVCDecoderDll = ".\\Codec\\hevcdecfltr.dll";
            HEVCDecoderName = L"Lentoid HEVC Decoder";
            HEVCDecoderGuid = CLSID_HEVCDecoder;

             //Splitter
            if (loadFilter(splitterDll))
            {
                if (createFilter(splitterGuid, &m_pSplitter))
                {
                    mGraph->AddFilter(m_pSplitter, splitterName);
                }
                else
                {
                    cout << "add spliter failed" << endl;
                    return false;
                }
            }
            else
            {
                cout << "load splitter faild" << endl;
                return false;
            }

            //HEVC Decoder
            if (loadFilter(HEVCDecoderDll))
            {
                if (createFilter(HEVCDecoderGuid, &m_pVideoHEVCDecoder))
                {
                    mGraph->AddFilter(m_pVideoHEVCDecoder, HEVCDecoderName);
                }
                else
                {
                    cout << "add decoder failed" << endl
                    return false;
                }
            }
            else
            {
                cout << "load decoder failed!" << endl;
                return false;
            }

            //Video Renderer
            hr = CoCreateInstance(CLSID_VideoMixingRenderer9, NULL, CLSCTX_INPROC, 
                IID_IBaseFilter, (void **)&m_pVideoRender);
            if(hr == S_OK)
            {
                mGraph->AddFilter(m_pVideoRender, L"Video Mixing Renderer 9");
            }
            else
            {
                cout << "load video renderer failed" << endl;
                return false;
            }
        }
    }
}

链接Filter和Renderer

• 查找空闲的filter的接口

HRESULT GetUnconnectedPin( IBaseFilter *pFilter, PIN_DIRECTION PinDir, IPin **ppPin, int iNum )
{
    *ppPin = NULL;
    IEnumPins* pEnum = NULL;
    IPin* pPin = NULL;
    int nIndex = 0;

    HRESULT hr = pFilter->EnumPins(&pEnum);
    if (FAILED(hr))
    {
        return hr;
    }

    while(pEnum->Next(1, &pPin, NULL) == S_OK)
    {
        PIN_DIRECTION ThisPinDir;
        pPin->QueryDirection(&ThisPinDir);
        if (ThisPinDir == PinDir)  //如果out/in类型符合
        {
            nIndex ++;
            IPin *pTmp = NULL;
            hr = pPin->ConnectedTo(&pTmp);  //如果已经被连接
            if (SUCCEEDED(hr))  
            {
                pTmp->Release();
            }
            else  
            {
                if(nIndex == iNum)  //若端口号与传入端口号同
                {
                    pEnum->Release();
                    *ppPin = pPin;
                    pPin->Release();
                    return S_OK;
                }
            }
        }
        pPin->Release();
    }
    pEnum->Release();
    cout << "GetUnconnectedPin ----> Next is null" << endl;
    return false;
}

• 查找空闲的splitter的空闲指针接口

HRESULT GetUnconnectedMajortypePin( IBaseFilter *pFilter, PIN_DIRECTION PinDir, IPin **ppPin, GUID myMajortype)
{
    *ppPin = NULL;
    IEnumPins* pEnum = NULL;
    IPin* pPin = NULL;
    int nIndex = 0;
    IEnumMediaTypes *pType;  
    AM_MEDIA_TYPE  *pMType;  

    HRESULT hr = pFilter->EnumPins(&pEnum);
    if (FAILED(hr))
    {
        return hr;
    }

    while(pEnum->Next(1, &pPin, NULL) == S_OK)
    {
        PIN_DIRECTION ThisPinDir;
        pPin->QueryDirection(&ThisPinDir);
        if (ThisPinDir == PinDir)  //如果out/in类型符合
        {
            nIndex ++;
            IPin *pTmp = NULL;
            hr = pPin->ConnectedTo(&pTmp);
            if (SUCCEEDED(hr))    //如果已经被连接
            {
                pTmp->Release();
            }
            else  
            {
                pPin->EnumMediaTypes(&pType);
                pType->Next(1, &pMType, 0);
                if(myMajortype == pMType->majortype)  //类型匹配
                {
                    pEnum->Release();
                    pType->Release();
                    *ppPin = pPin;
                    pPin->Release();
                    return S_OK;
                }

                pType->Release();
            }
        }
        pPin->Release();
    }
    pEnum->Release();
    cout << "GetUnconnectedMajortypePin failed" << endl;
    return false;
}

• DirectShow提供自动搜寻Filter，我们只需要将他们链接起来

bool LinkFilter()
{
    //定义pin对象
    IPin *ppinOut = NULL;
    IPin *ppinIn = NULL;
    IPin* Pin;
    //sourceOut -> Splitter
    if(m_pSourceFilter != NULL && m_pSplitter != NULL)
    {
        hr = GetUnconnectedPin(m_pSourceFilter, PINDIR_OUTPUT, &Pin, 1); //查找Filter空闲的pin
        if (SUCCEEDED(hr))
        {
            ppinOut = Pin;          
        }
        hr = GetUnconnectedPin(m_pSplitter, PINDIR_INPUT, &Pin, 1);
        if (SUCCEEDED(hr))
        {
            ppinIn = Pin;           
        }
        if (FAILED(mGraph->Connect(ppinOut, ppinIn)))
        {
            cout << "link source filter and spliter failed!" <return false;
        }
    }

    //Spliter -> hevcdecoder//解码HEVC
    if (m_pSplitter != NULL && m_pVideoHEVCDecoder != NULL)
    {
        hr = GetUnconnectedMajortypePin(m_pSplitter, PINDIR_OUTPUT, &Pin, MEDIATYPE_Video);//查找splitter空闲的video outpin
        if (SUCCEEDED(hr))
        {
            ppinOut = Pin;
        }
        hr = GetUnconnectedPin(m_pVideoHEVCDecoder, PINDIR_INPUT, &Pin, 1);
        if (SUCCEEDED(hr))
        {
            ppinIn = Pin;
        }
        if (FAILED(mGraph->Connect(ppinOut, ppinIn)))
        {
            return false;
            cout << "link splitter and decoder failed!" << endl;
        }
    }
    //hevcdecoder -> videorender
    if (m_pVideoDecoder != NULL && m_pVideoRender != NULL)
    {
        hr = GetUnconnectedPin(m_pVideoHEVCDecoder, PINDIR_OUTPUT, &Pin, 1); //查找Filter空闲的pin
        if (SUCCEEDED(hr))
        {
            ppinOut = Pin;
        }
        hr = GetUnconnectedPin(m_pVideoRender, PINDIR_INPUT, &Pin, 1);
        if (SUCCEEDED(hr))
        {
            ppinIn = Pin;
        }
        if (FAILED(mGraph->Connect(ppinOut, ppinIn)))
        {
            return false;
            cout<<"link decoder and video renderer failed!"<return true;
}                       

播放HEVC视频

bool RenderFile(const *char MediaUri)
{
    if (mGraph)
    {
        HRESULT hr;
        WCHAR    szFilePath[MAX_PATH];
        //该函数映射一个字符串到一个宽字符的字符串
        MultiByteToWideChar(CP_ACP, 0, MediaUri, -1, szFilePath, MAX_PATH);

        //source filter与视频文件关联
        IFileSourceFilter* pFSFilter = NULL; 

        //pFSFilter仅需要局部变量，用完释放
        m_pSourceFilter->QueryInterface(&pFSFilter);
        pFSFilter->Load(szFilePath, NULL);   //FilePath;
        pFSFilter->Release();
        pFSFilter = NULL;
        if(!LinkFilter())
        {
            cout << "link filter failed" << endl;
        }
    }
    else
    {
        cout << "render file failded" << endl;
        return false;
    }
}