1. Building DirectShow Application
Header file: dshow.h
Library files: strmiids.lib, quartz.lib
2. Calling the CoInitialize function, which initializes the COM library.
IGraphBuilder *pGraph; //filter graph manager interface. used to construct the filter graph
CoInitialize(NULL);
3. Then call the CoCreateInstance function to create the filter graph manager:
// create the filter graph – the object that contains all the filters ad interconnection info
HRESULT hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void **)&pGraph);
4. Create a tool to assist in the creation and connection of capture filters
ICaptureGraphBuilder2* pBuild = 0;
hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL, CLSCTX_INPROC_SERVER, IID_ICaptureGraphBuilder2,
(void **)&pBuild);
5. Connect the graph structure to the builder tool
hr = pBuild->SetFiltergraph(pGraph);
6. Find capture device and add it to filter graph
- Create the System Device Enumerator
CComPtr<ICreateDevEnum> pSysDevEnum;
CComPtr<IEnumMoniker> pEnumCat = NULL;
hr = pSysDevEnum.CoCreateInstance(CLSID_SystemDeviceEnum);
- Obtain a class enumerator for the video input device category
hr = pSysDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory, &pEnumCat, 0);
- Enumerate the monikers
CComPtr<IMoniker> pMoniker;
ULONG cFetched;
while(pEnumcat->Next(1, &pMoniker, &cFetched) == S_OK)
{
CComPtr<IPropertyBag> pProp;
pMoniker->BindToStorage(0, 0, IID_IPropertyBag, (void **) &pProp);
VARIANT varName;
VariantInit(&varName);
// get the friendly name.
hr = pProp->Read(L”FriendlyName”, &varName, 0);
if (SUCCEEDED(hr) && (wcscmp(CapName, varName.bstrVal) == 0))
{
- If the friendly name matched, make a capture filter from the device
hr = pMoniker->BindToObject(0,0,IID_IBaseFilter,(void **)&pCapture);
- add the vide device to graph
pGraph->AddFilter(pCapture,varName.bstrVal);
VariantClear(&varName);
break;
}
VariantClear(&varName);
pMoniker = NULL; // Release for the next loop.
}
7. Set video sub type
hr = SetUncompressedRGBVideoSubType(MEDIASUBTYPE_RGB24);
8. Create a sample grabber if need to capture the frame from the video
9. Set video decoder
10. Set resolution
11. if not render, add a NULL filter
12. Render stream
hr = pBuild->RenderStream(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video, pCapture, pF, NULL);
13. Use the filter graph manager interface pointer pGraph to query for other two interfaces that are needed
IMediaControl* pControl; //use to handle media straming in the filter graph
pGraph->QueryInterface(IID_IMediaControl, (void **)&pControl);
IMediaEvent* pEvent; // use to handle filter graph events
pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);
14. Control the media streaming in the filter graph
pControl->Run();
15. Handle filter graph events
pEvent->WaitForCompletion(INFINITE, &evCode);
In real application, you should avoid setting the wait interval to INFINIT, as this can block indefinitely. Also, you might want to respond to other filter graph events.
18. Clean up by release all the interface pointers nd the COM libray.
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