1) 视频捕捉Graph的构建
这里要重点了解捕捉Graph图和一般回放Graph图的定义。
一个能够捕捉音频或者视频的graph图都称之为捕捉graph图。捕捉graph图比一般的文件回放graph图要复杂许多，Directshow提供了一个Capture Graph Builder COM组件使得捕捉graph图的生成更加简单。Capture Graph Builder提供了一个ICaptureGraphBuilder2接口，这个接口提供了一些方法用来构建和控制捕捉graph图。首先创建一个Capture Graph Builder对象和一个graph manger对象（图对象的管理器)，然后用filter graph manager 作参数，调用ICaptureGraphBuilder2::SetFiltergraph来初始化Capture Graph Builder。看下面的代码吧：
HRESULT InitCaptureGraphBuilder(IGraphBuilder **ppGraph, //Receives the pointer
ICaptureGraphBuilder2 **ppBuilder) //Receives the pointer
{
if(!ppGraph || !ppBuilder)
{
return E_POINTER;
}
IGraphBuilder *pGraph = NULL;
ICaptureGraphBuilder2 *pBuild = NULL;
//Create the Capture Graph Builder
HRESULT hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL,
CLSCTX_INPROC_SERVER, IID_ICaptureGraphBuilder2,
(void**)&pBuild );
if(SECCEEDED(hr))
{
//Create the Filter Graph Manager
hr = CoCreateInstance(CLSID_FilterGraph, 0, CLSCTX_INPROC_SERVER,
IID_IGraphBuilder, (void**)&pGraph);
if(SECCEEDED(hr))
{
//Initialize the Capture Graph Builder
pBuild->SetFiltergraph(pGraph);
//Return both interface pointers to the caller
*ppBuild = pBuild;
*ppGraph = pGraph; //The caller must release both interface
return S_OK;
}
else
{
pBuild->Release();
}
}
return hr; //Failed
}
原文：http://blog.csdn.net/createdsign/article/details/18729395