Directshow 捕捉视频入门篇

一、关于视频捕捉(About Video Capture in Dshow)

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
}

未完，待续。。。。。哈哈，如有问题可以联系我：QQ:1906733710，我是从事电子签到软件、电子白板、互动投影软件、查询软件开发的，现在要开发视频录制的功能，在对Directshow 研究的过程当中。希望一起研究提高。有需要软件的也可以联系我。