I have been trying to use SampleGrabber to grab a frame from a webcam and save it as a bitmap but haven't had any luck. I used the Directshow video capture example on MSDN using ICaptureGraphBuilder2 along with the Sample grabber example as well.
I intended my filter graph to look like the following:
Webcam (source) -> Sample Grabber -> Null Renderer
Since I'm not interested in seeing a preview, I decided that a null renderer would be good enough for me.
The plan was to find my webcam by searching for a specific VID and PID (webcamCapture::findWebCam()), create my samplegrabber, create the null renderer and then connect them all together using pGraphBuilder->RenderStream(). Since I would need only one frame, I used the OneShot method and then used GetCurrentBuffer to retrieve the frame.
The problem occurs at this line:
pEvent->WaitForCompletion(2000, &evCode);
The HRESULT code returned was E_ABORT. Setting the timeout to INFINITE caused the program to freeze up possibly meaning that the filter never stops. The HRESULT from pControl->Run() was S_FALSE, meaning that the not all of the filters are running. I am not sure why that is happening and I have a feeling that something went wrong when building these filters.
Below is a dump of my source. I have created a class to handle the webcam capture. In use, basically two things get called:
webcamCapture::buildFilterGraph()
webcamCapture::runFilter()
runFilter would run the filter and save the frame as a bitmap file. I'm new to directshow and I'm pretty sure I'm missing something simple. Any insight would greatly appreciated!
Source
HRESULT webcamCapture::buildFilterGraph(void){
HRESULT hr;
if (FAILED(hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED))) {
return hr;
}
createCOMInstances();
// Use findWebCam() to find the webcam and add it to our capture graph
hr = findWebCam();
if(FAILED(hr)){
return hr;
}
// Add the sample grabber to the graph
hr = pGraph->AddFilter(pGrabberF, L"Sample Grabber");
if(FAILED(hr)){
return hr;
}
hr = pGrabberF->QueryInterface(IID_PPV_ARGS(&pGrabber));
if(FAILED(hr)){
return hr;
}
// Set media type for the sample grabber (24-bit RGB Uncompressed video)
ZeroMemory(&mt, sizeof(mt));
mt.majortype = MEDIATYPE_Video;
mt.subtype = MEDIASUBTYPE_RGB24;
hr = pGrabber->SetMediaType(&mt);
if(FAILED(hr)){
return hr;
}
hr = pGraph->AddFilter(pNullF, L"Null Filter");
if(FAILED(hr)){
return hr;
}
// Connect source (pCapF), sample grabber (pGrabberF) and null renderer (pNullF)
pGraphBuilder->RenderStream(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video, pCapF,pGrabberF, pNullF);
hr = pGrabber->SetOneShot(TRUE);
hr = pGrabber->SetBufferSamples(TRUE);
return S_OK;
}
HRESULT webcamCapture::runFilter(){
HRESULT hr;
FILTER_STATE filterState;
pBuffer = NULL;
hr = pControl->Run();
if(FAILED(hr)){
goto done;
}
pControl->GetState(1000, (OAFilterState*)&filterState);
long evCode;
hr = pEvent->WaitForCompletion(2000, &evCode);
if(FAILED(hr)){
goto done;
}
long cbBuffer;
hr = pGrabber->GetCurrentBuffer(&cbBuffer, NULL);
if(FAILED(hr)){
goto done;
}
pBuffer = (BYTE*)CoTaskMemAlloc(cbBuffer);
if(!pBuffer){
hr = E_OUTOFMEMORY;
goto done;
}
hr = pGrabber->GetCurrentBuffer(&cbBuffer, (long*)pBuffer);
if(FAILED(hr)){
goto done;
}
hr = pGrabber->GetConnectedMediaType(&mt);
if(FAILED(hr)){
goto done;
}
if((mt.formattype == FORMAT_VideoInfo) && (mt.cbFormat >= sizeof(VIDEOINFOHEADER)) && (mt.pbFormat != NULL)){
VIDEOINFOHEADER *pVih = (VIDEOINFOHEADER*)mt.pbFormat;
writeBitmap(L"test_image.bmp", &pVih->bmiHeader, mt.cbFormat - SIZE_PREHEADER, pBuffer, cbBuffer);
}
//FreeMediaType(mt);
done:
CoTaskMemFree(pBuffer);
pNullF->Release();
pNullF = NULL;
pCapF->Release();
pCapF = NULL;
pGrabber->Release();
pGrabber = NULL;
pGrabberF->Release();
pGrabberF = NULL;
pControl->Release();
pControl = NULL;
pEvent->Release();
pEvent = NULL;
pGraph->Release();
pGraph = NULL;
CoUninitialize();
return hr;
}
HRESULT webcamCapture::createCOMInstances(void){
HRESULT hr;
// Instructions to create a Capture Graph using CaptureGraphBuilder2 can be found at https://msdn.microsoft.com/en-us/library/windows/desktop/dd373396(v=vs.85).aspx
// Create Capture Graph Builder
hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pGraphBuilder));
if(FAILED(hr)){
return hr;
}
// Create Graph Manager
hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pGraph));
if(FAILED(hr)){
return hr;
}
// Initialize Capture Graph Builder by referencing pGraph (Graph Manager)
hr = pGraphBuilder->SetFiltergraph(pGraph);
if(FAILED(hr)){
pGraphBuilder->Release();
return hr;
}
// Set pointer to Media Control Interface
hr = pGraph->QueryInterface(IID_PPV_ARGS(&pControl));
if(FAILED(hr)){
return hr;
}
// Set pointer to Media Event Interface
hr = pGraph->QueryInterface(IID_PPV_ARGS(&pEvent));
if(FAILED(hr)){
return hr;
}
// Create Sample Grabber
// NOTE: ISampleGrabber is depreciated and may not be supported in later versions of Windows!
hr = CoCreateInstance(CLSID_SampleGrabber, NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pGrabberF));
if(FAILED(hr)){
return hr;
}
// Create the null renderer filter. We don't be previewing the camera feed so we can just drop the frames when we've converted them to bitmaps
hr = CoCreateInstance(CLSID_NullRenderer, NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pNullF));
if(FAILED(hr)){
return hr;
}
TRACE(_T("Interface Creation Successful\n"));
return S_OK;
}
// Function to find the MS HD3000 webcam (VID=0x045E PID=0x0779)
// For more info on finding devices for Video/Audio capture, see https://msdn.microsoft.com/en-us/library/windows/desktop/dd377566(v=vs.85).aspx
HRESULT webcamCapture::findWebCam(void){
HRESULT hr;
ICreateDevEnum *pDevEnum;
IEnumMoniker *pEnum;
IMoniker *pMoniker;
BOOL isDeviceFound = FALSE;
WORD wNumCameras = 0;
hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&pDevEnum));
if(FAILED(hr)){
return hr;
}
hr = pDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory, &pEnum, 0);
if(hr == S_FALSE){
return VFW_E_NOT_FOUND;
}
pDevEnum->Release();
// Go through each device moniker and read their Device Path properties. This is how we will find our webcam of interest
while(pEnum->Next(1, &pMoniker, NULL) == S_OK){
IPropertyBag *pPropBag;
VARIANT var;
hr = pMoniker->BindToStorage(0, 0, IID_PPV_ARGS(&pPropBag));
if(FAILED(hr)){
pMoniker->Release();
continue;
}
VariantInit(&var);
hr = pPropBag->Read(L"DevicePath", &var, 0);
if(SUCCEEDED(hr)){
// String search variables
CString csVidToCompare = _T("");
CString csPidToCompare = _T("");
WORD wVidSearchIndex = 0;
WORD wPidSearchIndex = 0;
CString csDevPath = var.bstrVal;
csDevPath.MakeLower();
wVidSearchIndex = csDevPath.Find(_T("vid_"), 0);
wPidSearchIndex = csDevPath.Find(_T("pid_"), 0);
csVidToCompare = csDevPath.Mid(wVidSearchIndex + 4, 4);
csPidToCompare = csDevPath.Mid(wPidSearchIndex + 4, 4);
// If MS Device is found
if(!csVidToCompare.Compare(_T("045e"))){
// If the 3000HD camera is found
if((!csPidToCompare.Compare(_T("0779"))) && (wNumCameras == 0)){
wNumCameras++;
hr = pMoniker->BindToObject(0, 0, IID_IBaseFilter, (void**)&pCapF);
if(FAILED(hr)){
return hr;
}
isDeviceFound = TRUE;
// Add the webcam to the filter graph
hr = pGraph->AddFilter(pCapF, L"Capture Filter");
if(FAILED(hr)){
TRACE(_T("Failed to add webcam to filter graph\n"));
return hr;
}
TRACE(_T("Webcam found and added to filter!\n"));
}
else if((!csPidToCompare.Compare(_T("0779"))) && (wNumCameras > 0)){
TRACE(_T("More than one HD3000 camera found!\n"));
continue;
}
else{
TRACE(_T("MS Device found, but not the camera\n"));
continue;
}
}
}
pPropBag->Release();
pMoniker->Release();
}
if(isDeviceFound == FALSE){
TRACE(_T("Webcam was not found\n"));
pEnum->Release();
return E_FAIL;
}
pEnum->Release();
return S_OK;
}
