提取DirectShow中视频采集的数据

DirectShow中,数据流(Data Flow)都是依次流过各个Filter的.它对数据的管理也有自己的方法,而且并没有向用户提供一个统一的接口,供用户操作数据流.这里以提取视频采集在的每帧为位图数据为例,说说如何在Directshow中提取数据.这里我们用到了DirectShow提供给我们的接口ISampleGrabber,并定义了一个供它回调的CSampleGrabberCB对象(继承ISampleGrabberCB接口).我们知道,DirectShow中的数据存储是通过Sample完成的,所以提取数据也需要通过SampleGrabber.步骤如下:1.建立CSampleGrabberCB对象. class CSampleGrabberCB : public ISampleGrabberCB
{ STDMETHODIMP BufferCB( double dblSampleTime, BYTE * pBuffer, long lBufferSize ) { //Callback method that receives a pointer to the sample buffer. } STDMETHODIMP SampleCB( double SampleTime, IMediaSample * pSample )
{
//Callback method that receives a pointer to the media sample.
} }2.定义ISampleGrabber接口并初始化 CComPtr< ISampleGrabber > m_pGrabber; HRESULT hr; hr = m_pGrabber.CoCreateInstance( CLSID_SampleGrabber ); if(FAILED(hr)) //error action;3.定义Grabber Filter,设置它的媒体类型,并将它加入Graph中 CComQIPtr< IBaseFilter, &IID_IBaseFilter > pGrabBase( m_pGrabber ); CMediaType VideoType;
VideoType.SetType(&MEDIATYPE_Video);
VideoType.SetSubtype(&MEDIASUBTYPE_RGB24);
hr = m_pGrabber->SetMediaType(&VideoType); hr = pGraph->AddFilter(pGrabBase,L"Grabber");4.设置回调(CallBack),使Grabber能够通过BufferCB自动完成采集数据. // don't buffer the samples as they pass through
//
hr = m_pGrabber->SetBufferSamples( FALSE ); // only grab one at a time, stop stream after
// grabbing one sample
//
hr = m_pGrabber->SetOneShot( FALSE ); // set the callback, so we can grab the one sample
//
hr = m_pGrabber->SetCallback( &mCB, 1 ); //mCB为CSampleGrabber对象这样,在DirectShow数据流动过程中,mCB.bufferCB会自动执行,提取Graph中的数据.