GrabBitmaps抓图过程

看了DXSDK\Samples\C++\DirectShow\Editing\GrabBitmaps\的运行过程
把程序的枝叶去掉，看看程序主要是如何一下运行顺序,这样有利于明白其中的运行顺序，也好与看过它的朋友有个交流，其中的注释可能用得不对或不恰当，请指教或留言


声明对象:   
    CComPtr< ISampleGrabber > pGrabber;
    CComPtr< IBaseFilter >    pSource;
    CComPtr< IGraphBuilder >  pGraph;
    CComPtr< IVideoWindow >   pVideoWindow;
创建对象：   
pGrabber.CoCreateInstance( CLSID_SampleGrabber );
CComQIPtr< IBaseFilter, &IID_IBaseFilter > pGrabberBase( pGrabber );
pSource.CoCreateInstance( CLSID_AsyncReader );
pGraph.CoCreateInstance( CLSID_FilterGraph );
加入过滤器：
    hr = pGraph->AddFilter( pSource, L"Source" );
    hr = pGraph->AddFilter( pGrabberBase, L"Grabber" );
加载数据源：
CComQIPtr< IFileSourceFilter, &IID_IFileSourceFilter > pLoad( pSource );
hr = pLoad->Load( T2W( szFile ), NULL );
设置媒体类型：
  CMediaType GrabType;
    GrabType.SetType( &MEDIATYPE_Video );
    GrabType.SetSubtype( &MEDIASUBTYPE_RGB24 );
    hr = pGrabber->SetMediaType( &GrabType );

得到输出输入Pin
    CComPtr< IPin > pSourcePin;
    CComPtr< IPin > pGrabPin;
    pSourcePin = GetOutPin( pSource, 0 );
    pGrabPin   = GetInPin( pGrabberBase, 0 );
连结输出输入Pin:
    hr = pGraph->Connect( pSourcePin, pGrabPin );

CSampleGrabberCB CB;

得到源音频的长宽
  AM_MEDIA_TYPE mt;
    hr = pGrabber->GetConnectedMediaType( &mt );
    VIDEOINFOHEADER * vih = (VIDEOINFOHEADER*) mt.pbFormat;
    CB.Width  = vih->bmiHeader.biWidth;
    CB.Height = vih->bmiHeader.biHeight;
    FreeMediaType( mt );
   
得到输出Pin,以video renderer之用   
    CComPtr pGrabOutPin = GetOutPin( pGrabberBase, 0 );
    hr = pGraph->Render( pGrabOutPin );
   
抓取设置 
hr = pGrabber->SetBufferSamples( FALSE );
hr = pGrabber->SetOneShot( TRUE );
hr = pGrabber->SetCallback( &CB, 1 );

CComQIPtr< IMediaSeeking, &IID_IMediaSeeking > pSeeking( pGraph );

关于窗口:
CComQIPtr< IVideoWindow, &IID_IVideoWindow > pWindow = pGraph;
if (pWindow)
{
    hr = pWindow->put_AutoShow(OAFALSE);
}
输出图片:
for( int i = 0 ; i < NUM_FRAMES_TO_GRAB ; i++ )
{
    REFERENCE_TIME Start = i * UNITS;
    输出位置
    hr = pSeeking->SetPositions( &Start, AM_SEEKING_AbsolutePositioning,
                                 NULL, AM_SEEKING_NoPositioning );
    CComQIPtr< IMediaControl, &IID_IMediaControl > pControl( pGraph );
    运行
    hr = pControl->Run( );
    消息处理
    CComQIPtr< IMediaEvent, &IID_IMediaEvent > pEvent( pGraph );
    long EvCode = 0;
    hr = pEvent->WaitForCompletion( INFINITE, &EvCode );
}