DShow中实现抓图的几种方法.doc

文档介绍：,我们可以直接调用其接口(interface)ISampleGrabber。该接口可以获取经过该Filter的单独的MediaSamples。详情请参见DXSDK。,然后实现其虚函数,详情请参见SDK中的示例程序(DXSDKROOT\Samples\C++\DirectShow\Editing\GrabBitmaps)。,操作和效率都不乐观。所以我采用下面的方法:该方法传递的是时间,不是在播放的时候动态加入Filter然后截图,而是另外打开源文件进行操作。A)。申明以下接口:A)。申明以下接口:#001IGraphBuilder *pGraph =NULL;//forgraphbuilder#002IMediaControl *pControl =NULL;//mediacontrol#003IMediaSeeking *pSeeking =NULL;//mediaseeking#004IMediaEventEx *pEvent =NULL;//mediaenvent#005IBaseFilter *pNullFilter =NULL;//forholdingtheSamplegrabberFilterB)。初始化接口:#001JIF(CoCreateInstance(CLSID_FilterGraph,NULL,CLSCTX_INPROC,#002 IID_IGraphBuilder,(void**)&pGraph));#003#004JIF(CoCreateInstance(CLSID_NullRenderer,NULL,CLSCTX_INPROC,#005 IID_IBaseFilter,(void**)&pNullFilter));#006JIF(pGraph->QueryInterface(IID_IMediaControl,(void **)&pControl));#007JIF(pGraph->QueryInterface(IID_IMediaSeeking,(void **)&pSeeking));#008JIF(pGraph->QueryInterface(IID_IMediaEvent,(void **)&pEvent));C)。创建SampleGrabber#001//CreatetheSampleGrabber.#002IBaseFilter*pGrabberF=NULL;#003JIF(CoCreateInstance(CLSID_SampleGrabber,NULL,CLSCTX_INPROC_SERVER,#004 IID_IBaseFilter,(void**)&pGrabberF));#005#006JIF(pGraph->AddFilter(pGrabberF,L"SampleGrabber"));#007JIF(pGraph->AddFilter(pNullFilter,L"NullRenderFilter"));#008#009ISampleGrabber*pGrabber;#010JIF(pGrabberF->QueryInterface(IID_ISampleGrabber,(void**)&pGrabber));设置SampleGrabber的媒体格式:调用SetMediaType,该函数接受一个AM_MEDIA_TYPE的结构,主要是设置该结构中的majortype,和subtype域。D)。添加SourceFilter:#001IBaseFilter*pSrc;#002JIF(pGraph->AddSourceFilter(T2W(m_szFile),L"Source",&pSrc));E)。连接Grabber和NullRender两个Filter:#001IPin*pOutPin;#002hr=GetPin(pGrabberF,PINDIR_OUTPUT,&pOutPin);#003#004IPin*pInPin;#005hr=GetPin(pNullFilter,PINDIR_INPUT,&pInPin);#006#007pGraph->Connect(pOutPin,pInPin);F)。取得当前所连接媒体的类型#001AM_MEDIA_TYPEmt;#002hr=pGrabber->GetConnectedMediaType(&mt);#003//heformatblock.