Media Foundation - How to select input from crossbar? - c++

Question

Good Evening
I'm trying to put together a little video capture DLL using Media Foundation which is largely adapted from the SimpleCapture and CaptureEngine SDK samples. The whole thing works great when I the capture source is my inbuilt webcam.
The problem is when I try using an external USB frame grabber with multiple inputs (s-video, composite & stereo audio) there is no preview stream. I have got a function that uses the DShow interface which seems to successfully change the selected input on the cross bar (verified by looking at the options in AMCAP after running function) However I have not been able to get the device to preview at all.
Is there a Media Foundation way of selecting inputs from the crossbar? Or if not, can you suggest what may be wrong with the crossbar input selection code below:
HRESULT CaptureManager::doSelectInputUsingCrossbar(std::wstring deviceName, long input)
{
IGraphBuilder *pGraph = NULL;
ICaptureGraphBuilder2 *pBuilder = NULL;
IBaseFilter* pSrc = NULL;
ICreateDevEnum *pDevEnum = NULL;
IEnumMoniker *pClassEnum = NULL;
IMoniker *pMoniker = NULL;
bool bCameraFound = false;
IPropertyBag *pPropBag = NULL;
bool crossbarSet = false;
HRESULT hr = S_OK;
if (!(input == PhysConn_Video_Composite || input == PhysConn_Video_SVideo))
{
return S_FALSE;
}
// Create the Filter Graph Manager.
hr = CoCreateInstance(CLSID_FilterGraph, NULL,
CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void **)&pGraph);
if (SUCCEEDED(hr))
{
// Create the Capture Graph Builder.
hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL,
CLSCTX_INPROC_SERVER, IID_ICaptureGraphBuilder2,
(void **)&pBuilder);
if (SUCCEEDED(hr))
{
pBuilder->SetFiltergraph(pGraph);
}
else return hr;
}
else return hr;
//////////////////////////
// chooses the default camera filter
hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC,
IID_ICreateDevEnum, (void **)&pDevEnum);
if (FAILED(hr))
{
return E_FAIL;
}
// Create an enumerator for video capture devices.
if (FAILED(pDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory, &pClassEnum, 0)))
{
return E_FAIL;
}
if (pClassEnum == NULL)
{
CheckHR(hr, "Class enumerator is null - no input devices detected?");
pDevEnum->Release();
return E_FAIL;
}
while (!bCameraFound && (pClassEnum->Next(1, &pMoniker, NULL) == S_OK))
{
HRESULT hr = pMoniker->BindToStorage(0, 0, IID_IPropertyBag, (void**)(&pPropBag));
if (FAILED(hr))
{
pMoniker->Release();
continue; // Skip this one, maybe the next one will work.
}
// Find the description or friendly name.
VARIANT varName;
VariantInit(&varName);
hr = pPropBag->Read(L"Description", &varName, 0);
if (FAILED(hr))
{
hr = pPropBag->Read(L"FriendlyName", &varName, 0);
}
if (SUCCEEDED(hr))
{
if (0 == wcscmp(varName.bstrVal, deviceName.c_str()))
{
pMoniker->BindToObject(0, 0, IID_IBaseFilter, (void**)&pSrc);
bCameraFound = true;
break;
}//if
VariantClear(&varName);
}
pPropBag->Release();
pMoniker->Release();
}//while
pClassEnum->Release();
pDevEnum->Release();
if (!bCameraFound)//else
{
CheckHR(hr, "Error: Get device Moniker, No device found");
goto done;
}
hr = pGraph->AddFilter(pSrc, L"video capture adapter");
if (FAILED(hr))
{
CheckHR(hr, "Can't add capture device to graph");
goto done;
}
///////////////
IAMCrossbar *pxBar = NULL;
hr = pBuilder->FindInterface(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Interleaved, pSrc, IID_IAMCrossbar, (void **)&pxBar);
if (FAILED(hr))
{
hr = pBuilder->FindInterface(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video, pSrc, IID_IAMCrossbar, (void **)&pxBar);
if (FAILED(hr))
{
CheckHR(hr, "Failed to get crossbar filter");
goto done;
}
}//if
else
{
CheckHR(hr, "Failed to get crossbar (capture)");
goto done;
}
LONG lInpin, lOutpin;
hr = pxBar->get_PinCounts(&lOutpin, &lInpin);
BOOL IPin = TRUE; LONG pIndex = 0, pRIndex = 0, pType = 0;
while (pIndex < lInpin)
{
hr = pxBar->get_CrossbarPinInfo(IPin, pIndex, &pRIndex, &pType);
if (pType == input)
{
break;
}
pIndex++;
}
BOOL OPin = FALSE; LONG pOIndex = 0, pORIndex = 0, pOType = 0;
while (pOIndex < lOutpin)
{
hr = pxBar->get_CrossbarPinInfo(OPin, pOIndex, &pORIndex, &pOType);
if (pOType == PhysConn_Video_VideoDecoder)
{
break;
}
pIndex++;
}
hr = pxBar->Route(pOIndex, pIndex);
done:
SafeRelease(&pPropBag);
SafeRelease(&pMoniker);
SafeRelease(&pxBar);
SafeRelease(&pGraph);
SafeRelease(&pBuilder);
SafeRelease(&pSrc);
return hr;
}

Answer 1

USB frame grabber is not supported by Microsoft Media Foundation. Microsoft Media Foundation has supporting of live sources via USB Video Class devices driver. The modern web cameras support such driver, but USB frame grabber does not.
USB frame grabber support of DirectShow filters which based on PUSH model processing pipeline - sources send media samples into the media graph, while Microsoft Media Foundation uses PULL model processing pipeline - sinks send request for the new media samples and sources "listen" for such request.
With best.