创建一个directshow应用程序一

创建dshow应用程序一般有三个步骤：

1.创建一个Filter Graph Manager组件。

IGraphBuilder * pGraph = NULL;

HRESULT　hr = CoCreateInstance(CLSID_FilterGraph, NULL,

CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void**)&pGraph);,

2.根据实际的应用，创建一个filter链,比如播放一个本地文件，最简单快速的代码如下：

hr = pGraph->RenderFile(L"path", NULL);

3.调用Filter Graph Manager上的各个接口进行控制，并且完成Filter Graph Manager与应用程序的交互，比如调用IMediaControl接口方法控制Filter Graph的状态转换。

IMediaControl *pControl = NULL;

hr = pGraph->QueryInterface(IID_IMediaControl, (void**)pControl);

hr = pControl->Run();

通用的Filter Graph构建技术：

1.加入一个指定CLSID的Filter

给定了一个Filter的CLSID，就可以调用CoCreateInstance来创建它。并使用IFilterGraph::AddFilter接口将其加入到Filter Graph中。

代码如下：

HRESULT AddFilterByCLSID(    IGraphBuilder *pGraph,  // Pointer to the Filter Graph Manager.    const GUID& clsid,      // CLSID of the filter to create.    LPCWSTR wszName,        // A name for the filter.    IBaseFilter **ppF)      // Receives a pointer to the filter.{    if (!pGraph || ! ppF) return E_POINTER;    *ppF = 0;    IBaseFilter *pF = 0;    HRESULT hr = CoCreateInstance(clsid, 0, CLSCTX_INPROC_SERVER,        IID_IBaseFilter, reinterpret_cast<void**>(&pF));    if (SUCCEEDED(hr))    {        hr = pGraph->AddFilter(pF, wszName);        if (SUCCEEDED(hr))            *ppF = pF;        else            pF->Release();    }    return hr;}

要在Filter Graph中加入一个AVI Mux Filter

IBaseFilter *pMux;

hr = AddFilterByCLSID(pGraph, CLSID_AviDest, L"AVI Mux", &pMux);

if(SUCCEEDED(hr))

{

/*...*/

pMux->Release();

}

2.得到Filter上的未连接的Pin

当在程序中连接filter的时候，首先要取得filter上未连接的Pin或者输出Pin。方法是，枚举Filter上的所有的Pin，调用IPin::QueryDirection查询Pin的方向。然后调用IPin::ConnectedTo查看Pin的连接状态。

HRESULT GetUnconnectedPin(    IBaseFilter *pFilter,   // Pointer to the filter.    PIN_DIRECTION PinDir,   // Direction of the pin to find.    IPin **ppPin)           // Receives a pointer to the pin.{    *ppPin = 0;    IEnumPins *pEnum = 0;    IPin *pPin = 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)        {            IPin *pTmp = 0;            hr = pPin->ConnectedTo(&pTmp);            if (SUCCEEDED(hr))  // Already connected, not the pin we want.            {                pTmp->Release();            }            else  // Unconnected, this is the pin we want.            {                pEnum->Release();                *ppPin = pPin;                return S_OK;            }        }        pPin->Release();    }    pEnum->Release();    // Did not find a matching pin.    return E_FAIL;}

比如现在要得到一个未连接的输出Pin

IPin *pOut = NULL;

HRESULT hr = GetUnConnectedPin(pFilter, PINDIR_OUTPUT, &pOut);

if(SUCCEEDED(hr))

{

/*...*/

pOut->Release();

}

3.连接两个Filter

Filter Graph中连接两个Filter的函数有IFilterGraph::ConnectDirect和IFilterGraph::Connect

HRESULT ConnectFilters(    IGraphBuilder *pGraph, // Filter Graph Manager.    IPin *pOut,            // Output pin on the upstream filter.    IBaseFilter *pDest)    // Downstream filter.{    if ((pGraph == NULL) || (pOut == NULL) || (pDest == NULL))    {        return E_POINTER;    }#ifdef debug        PIN_DIRECTION PinDir;        pOut->QueryDirection(&PinDir);        _ASSERTE(PinDir == PINDIR_OUTPUT);#endif    // Find an input pin on the downstream filter.    IPin *pIn = 0;    HRESULT hr = GetUnconnectedPin(pDest, PINDIR_INPUT, &pIn);    if (FAILED(hr))    {        return hr;    }    // Try to connect them.    hr = pGraph->Connect(pOut, pIn);    pIn->Release();    return hr;}

不同参数的ConnectFilters 的函数重载形式:

HRESULT ConnectFilters(    IGraphBuilder *pGraph,     IBaseFilter *pSrc,     IBaseFilter *pDest){    if ((pGraph == NULL) || (pSrc == NULL) || (pDest == NULL))    {        return E_POINTER;    }    // Find an output pin on the first filter.    IPin *pOut = 0;    HRESULT hr = GetUnconnectedPin(pSrc, PINDIR_OUTPUT, &pOut);    if (FAILED(hr))     {        return hr;    }    hr = ConnectFilters(pGraph, pOut, pDest);    pOut->Release();    return hr;}

例如现在要加入一个AVI Mux Filter 和 一个File Writer Filter，然后将他们相连起来。代码如下：
IBaseFilter *pMux, *pWrite;

hr = AddFilterByCLSID(pGraph, CLSID_AviDest, L"AVI Mux", &pMux);

if(SUCCEEDED(hr))

{

hr = AddFilterByCLSID(pGraph, CLSID_FileWriter, L"File Writer", &pWrite);

if(SUCCEEDED(hr))

{

hr = ConnectFilters(pGraph, pMux, pWrite);

pWrite->Release();

}

pMux->Release();

}

4.查找Filter和Pin上的接口

我们需要枚举Graph中的所有的Filter，或者枚举Filter上所有的Pin，一个一个的找接口。

//查找Filter上实现的某个接口

HRESULT FindFilterInterface(    IGraphBuilder *pGraph, // Pointer to the Filter Graph Manager.    REFGUID iid,           // IID of the interface to retrieve.    void **ppUnk)          // Receives the interface pointer.{    if (!pGraph || !ppUnk) return E_POINTER;    HRESULT hr = E_FAIL;    IEnumFilters *pEnum = NULL;    IBaseFilter *pF = NULL;    if (FAILED(pGraph->EnumFilters(&pEnum)))    {        return E_FAIL;    }    // Query every filter for the interface.    while (S_OK == pEnum->Next(1, &pF, 0))    {        hr = pF->QueryInterface(iid, ppUnk);        pF->Release();        if (SUCCEEDED(hr))        {            break;        }    }    pEnum->Release();    return hr;}

//查找给定filter的Pin上实现的某个接口

HRESULT FindPinInterface(    IBaseFilter *pFilter,  // Pointer to the filter to search.    REFGUID iid,           // IID of the interface.    void **ppUnk)          // Receives the interface pointer.{    if (!pFilter || !ppUnk) return E_POINTER;    HRESULT hr = E_FAIL;    IEnumPins *pEnum = 0;    if (FAILED(pFilter->EnumPins(&pEnum)))    {        return E_FAIL;    }    // Query every pin for the interface.    IPin *pPin = 0;    while (S_OK == pEnum->Next(1, &pPin, 0))    {        hr = pPin->QueryInterface(iid, ppUnk);        pPin->Release();        if (SUCCEEDED(hr))        {            break;        }    }    pEnum->Release();    return hr;}

//综合了FindFilterInterface和FindPinInterfae两个函数的综合功能

HRESULT FindInterfaceAnywhere(    IGraphBuilder *pGraph,     REFGUID iid,     void **ppUnk){    if (!pGraph || !ppUnk) return E_POINTER;    HRESULT hr = E_FAIL;    IEnumFilters *pEnum = 0;    if (FAILED(pGraph->EnumFilters(&pEnum)))    {        return E_FAIL;    }    // Loop through every filter in the graph.    IBaseFilter *pF = 0;    while (S_OK == pEnum->Next(1, &pF, 0))    {        hr = pF->QueryInterface(iid, ppUnk);        if (FAILED(hr))        {            // The filter does not expose the interface, but maybe            // one of its pins does.            hr = FindPinInterface(pF, iid, ppUnk);        }        pF->Release();        if (SUCCEEDED(hr))        {            break;        }    }    pEnum->Release();    return hr;}

比如现在通过IGraphBuilder::RenderFile函数，构建了一条内含DV格式数据的AVI文件的回放链路。我们想要得到其中DV视频解码Filter上的IIPDVDec接口，以设置DV解码输出的图像大小为原始图像的四分之一，代码如下：
hr = pGraph->RenderFile(L"C:\\example.avi", 0);

if(SUCCEEDED(hr))

{

IIPDVDec* pDvDec;

hr = FindFilterInterface(pGraph, IID_IIPDVDec, (void**)&pDvDec);

if(SUCCEEDED(hr))

{

........

}

}

5.遍历Filter链路

给定一个Filter链路上的某个Filter，我们可以向上或者向下得到所有的其他的Filter。

HRESULT GetNextFilter(    IBaseFilter *pFilter, // Pointer to the starting filter    PIN_DIRECTION Dir,    // Direction to search (upstream or downstream)    IBaseFilter **ppNext) // Receives a pointer to the next filter.{    if (!pFilter || !ppNext) return E_POINTER;    IEnumPins *pEnum = 0;    IPin *pPin = 0;    HRESULT hr = pFilter->EnumPins(&pEnum);    if (FAILED(hr)) return hr;    while (S_OK == pEnum->Next(1, &pPin, 0))    {        // See if this pin matches the specified direction.        PIN_DIRECTION ThisPinDir;        hr = pPin->QueryDirection(&ThisPinDir);        if (FAILED(hr))        {            // Something strange happened.            hr = E_UNEXPECTED;            pPin->Release();            break;        }        if (ThisPinDir == Dir)        {            // Check if the pin is connected to another pin.            IPin *pPinNext = 0;            hr = pPin->ConnectedTo(&pPinNext);            if (SUCCEEDED(hr))            {                // Get the filter that owns that pin.                PIN_INFO PinInfo;                hr = pPinNext->QueryPinInfo(&PinInfo);                pPinNext->Release();                pPin->Release();                pEnum->Release();                if (FAILED(hr) || (PinInfo.pFilter == NULL))                {                    // Something strange happened.                    return E_UNEXPECTED;                }                // This is the filter we're looking for.                *ppNext = PinInfo.pFilter; // Client must release.                return S_OK;            }        }        pPin->Release();    }    pEnum->Release();    // Did not find a matching filter.    return E_FAIL;}