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From: minhdanh on 27 Jun 2008 10:30
I am using on the CameraCaptureSample to capture a video. Although the sample on its own works well, I want to improved it to grab the raw camera data and work on it. I have successfully written and added my null transform filter (CTransInPlaceFilter) to the graph by using the following code:

.....
// prepare the preview graph
hr = m_pCaptureGraphBuilder->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video, m_pVideoCaptureFilter, NULL, NULL);

//find the default renderer
hr = pFilterGraph->FindFilterByName(L"Video Renderer", &pVidRenderer);

//get input pin of the default renderer
IPin* ipin = GetPin(pVidRenderer, PINDIR_INPUT);

//find out who the renderer is connected to and disconnect from them
IPin* opin;
hr = ipin->ConnectedTo(&opin);
hr = ipin->Disconnect(); //disconnect default renderer output pin
hr = opin->Disconnect(); //disconnect video source output pin

//create our null transform filter
hr = pNullTransform.CoCreateInstance(CLSID_NullNull);
hr = pFilterGraph->AddFilter(pNullTransform, L"NullNull");

//find the input pin of the null transform filter and connect it to the output of the video source
IPin* nullRendIn = GetPin(pNullTransform, PINDIR_INPUT);
hr = pFilterGraph->Connect(opin, nullRendIn);

//connect the output of the null transform filter to the default renderer
IPin* nullRendOut = GetPin(pNullTransform, PINDIR_OUTPUT);
hr = pFilterGraph->Connect(nullRendOut, ipin);

//media control object
hr = pFilterGraph->QueryInterface(IID_IMediaControl, (void **)&pMediaControl);

//run the graph
hr = pMediaControl->Run();
.........

After this I can see that my null transform filter can receive the media sample in its function HRESULT Transform(IMediaSample *pSample) and I can successfully convert the buffer into the a bitmap file. This means, the null transform filter is working well.

However, with the presence of the null transform filter in the graph, I can no longer capture video into ASF file by using the sample code. I initialize the WM9 encoder as followed (copied from the sample code):

// Create the video encoder
CHK( pVideoEncoder.CoCreateInstance( CLSID_DMOWrapperFilter ));
CHK( pVideoEncoder.QueryInterface( &pWrapperFilter ));

// Load the WMV9 DMO
CHK( pWrapperFilter->Init( CLSID_CWMV9EncMediaObject, DMOCATEGORY_VIDEO_ENCODER ));

// Everything succeeded, let's add the encoder to the graph
CHK( pFilterGraph->AddFilter( pVideoEncoder, L"WMV9 DMO Encoder" ));

// file to save video to
CHK( m_pCaptureGraphBuilder->SetOutputFileName(&MEDIASUBTYPE_Asf, L\\test.asf, &pASFMultiplexer, &pFileSinkFilter ));

// Connect the video capture filter, the encoder and the multiplexer together
CHK( m_pCaptureGraphBuilder->RenderStream(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video, m_pVideoCaptureFilter, pVideoEncoder, pASFMultiplexer));

This code is put just before pMediaControl->Run() and there is no error.

To start capturing:

LONGLONG dwStart = 0, dwEnd = 0;
WORD wStartCookie = 1, wEndCookie = 2;
CaptureGraphBuilder->ControlStream( &PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video, NULL, &dwStart, &dwEnd, wStartCookie, wEndCookie );

To stop capturing:

dwStart = 0;
CHK( pFilterGraph->QueryInterface( &pMediaSeeking ));
CHK( pMediaSeeking->GetCurrentPosition( &dwEnd ));
CHK( m_pCaptureGraphBuilder->ControlStream( &PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video, NULL, &dwStart, &dwEnd, wStartCookie, wEndCookie ));
There are no errors, all HRESULTs return S_OK, but the video file is not created! If, however, I removed my custom filter from the graph then the video is captured properly.

Any ideas what the problem is? Thanks a lot!

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