dshow,Sample Grabber 從攝像頭采集

char* CCameraDS::QueryFrame()
{
	long evCode, size = 0;
	


#if CALLBACKMODE
	static double lastSampleTime=0;
	if( lastSampleTime == cbInfo.dblSampleTime)
		return NULL;
	if(cbInfo.lBufferSize == 0)
		return NULL;
	if ( m_nBufferSize != cbInfo.lBufferSize)
	{
		if (m_pFrame)
		{
			free(m_pFrame);
		}
		m_nBufferSize = cbInfo.lBufferSize;
		m_pFrame = (char*)malloc(m_nBufferSize);//cvCreateImage(cvSize(m_nWidth, m_nHeight), IPL_DEPTH_8U, 3);
	}
	lastSampleTime = cbInfo.dblSampleTime;
	m_pFrame2 = (char*)cbInfo.pBuffer;
#else
	m_pMediaControl->Run();
	m_pMediaEvent->WaitForCompletion(INFINITE, &evCode);
	m_pSampleGrabber->GetCurrentBuffer(&size, NULL);
	if(size == 0)
		return NULL;
	//if the buffer size changed
	if (size != m_nBufferSize)
	{
		if (m_pFrame)
		{
			free(m_pFrame);
		}
		if (m_pFrame2)
		{
			free(m_pFrame2);
		}
		m_nBufferSize = size;
		m_pFrame = (char*)malloc(m_nWidth*m_nHeight*3);//cvCreateImage(cvSize(m_nWidth, m_nHeight), IPL_DEPTH_8U, 3);
		m_pFrame2 = (char*)malloc(m_nWidth*m_nHeight*3);
	}
	
	m_pSampleGrabber->GetCurrentBuffer(&m_nBufferSize, (long*)m_pFrame2);
	//cvFlip(m_pFrame);
#endif
	for(int i=0;i<m_nHeight;i++)
		memcpy(m_pFrame+m_nWidth*3*i,m_pFrame2+m_nWidth*3*(m_nHeight-1-i),m_nWidth*3);

	return m_pFrame;
}

1．緩沖區模式

 

#if !CALLBACKMODE
m_pSampleGrabber->SetBufferSamples(TRUE);
m_pSampleGrabber->SetOneShot(TRUE);
#endif

只能設置SetOneShot為TRUE， 因為使用SetPositions 函數始終返回 E_NOTIMPL：Method is not supported.如果為false,

WaitForCompletion(INFINITE, &evCode)函數會一直等待下去。

2.回調模式

回調模式每采到一直就會進入回調函數，可以在回調函數里面處理采到的數據。

#if CALLBACKMODE
m_pSampleGrabber->SetBufferSamples(FALSE);
m_pSampleGrabber->SetOneShot(FALSE);
// Set the callback, so we can grab the one sample
//
CB.Width = m_nWidth;
CB.Height = m_nHeight;
hr = m_pSampleGrabber->SetCallback( &CB, 1 );
m_pMediaControl->Run();
#endif

只用Run()一次即可。如果SetOneShot(TRUE)的話，也可以每請求一幀Run()一次，然后WaitForCompletion，再從回調函數的buffer中取出數據，這種其實和緩沖區模式一樣，只不過緩沖區變成了在回調函數中。

如果攝像頭采集幀率為30，SetOneShot(FALSE)回調模式，就一秒進去回調函數30次。而OneShot模式會取到重復的幀。