Sample code to control USB webcam and adjust its settings

Question

It took me many days to find enough examples that would allow me to do what's described in the subject and I thought it might be useful for others.  I got the code to select and turn on a camera here and spent a lot of time figuring out how to:

• set the resolution and color mode with IAMStreamControl
• control the camera (focus and exposure) with IAMCameraControl
• adjust its settings (brightness, saturation, etc) IAMVideoProcAmp

Please note:  I am not a programmer by trade and some of this code is ugly.  Especially the part where I selected the resolution and color mode by trial error (the start of a logical enumerate and selection is there, but I didn't finish it).  But it should be enough to get people started.  Feel free to point out flaws and suggest improvements.  If someone has better example code to submit or link to, by all means, post it.  I just could not find many useful examples, and I am normally quite good at searching the internet.

#include <stdio.h>
#include <streams.h>
#include <dshow.h>

int
main()
{
 // for playing
 IGraphBuilder *pGraphBuilder;
 ICaptureGraphBuilder2 *pCaptureGraphBuilder2;
 IMediaControl *pMediaControl;
 IBaseFilter *pDeviceFilter = NULL;

 // to select a video input device
 ICreateDevEnum *pCreateDevEnum = NULL;
 IEnumMoniker *pEnumMoniker = NULL;
 IMoniker *pMoniker = NULL;
 ULONG nFetched = 0;

 // initialize COM
 CoInitialize(NULL);

 //
 // selecting a device
 //

 // Create CreateDevEnum to list device
 CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER, 
   IID_ICreateDevEnum, (PVOID *)&pCreateDevEnum);
    
 // Create EnumMoniker to list VideoInputDevice 
 pCreateDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory,
   &pEnumMoniker, 0);
 if (pEnumMoniker == NULL) {
   // this will be shown if there is no capture device
   printf("no device\n");
   return 0;
 }

 // reset EnumMoniker
 pEnumMoniker->Reset();

 // get each Moniker
 while (pEnumMoniker->Next(1, &pMoniker, &nFetched) == S_OK) {
   IPropertyBag *pPropertyBag;
   TCHAR devname[256];

   // bind to IPropertyBag
   pMoniker->BindToStorage(0, 0, IID_IPropertyBag,
     (void **)&pPropertyBag);

   VARIANT var;

   // get FriendlyName
   var.vt = VT_BSTR;
   pPropertyBag->Read(L"FriendlyName", &var, 0);
   WideCharToMultiByte(CP_ACP, 0,
     var.bstrVal, -1, devname, sizeof(devname), 0, 0);
   VariantClear(&var);

   printf("%s\r\n", devname);
   printf("  select this device ? [y] or [n]\r\n");
   int ch = getchar();

   // you can start playing by 'y' + return key
   // if you press the other key, it will not be played.
   if (ch == 'y') {
     // Bind Monkier to Filter
     pMoniker->BindToObject(0, 0, IID_IBaseFilter,
         (void**)&pDeviceFilter );
   }

   // release
   pMoniker->Release();
   pPropertyBag->Release();

   if (pDeviceFilter != NULL) {
     // go out of loop if getchar() returns 'y'
     break;
   }
 }

 if (pDeviceFilter != NULL) {
   //
   // PLAY
   //

   // create FilterGraph
   CoCreateInstance(CLSID_FilterGraph,
     NULL,
     CLSCTX_INPROC,
     IID_IGraphBuilder,
     (LPVOID *)&pGraphBuilder);

   // create CaptureGraphBuilder2
   CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL, CLSCTX_INPROC, 
     IID_ICaptureGraphBuilder2, 
     (LPVOID *)&pCaptureGraphBuilder2);

   //============================================================
   //===========  MY CODE  ======================================
   //=============================================================
	HRESULT hr = CoInitialize(0);
	IAMStreamConfig *pConfig = NULL;
	hr = pCaptureGraphBuilder2->FindInterface(&PIN_CATEGORY_CAPTURE, 0, pDeviceFilter, IID_IAMStreamConfig, (void**)&pConfig);

	int iCount = 0, iSize = 0;
	hr = pConfig->GetNumberOfCapabilities(&iCount, &iSize);

	// Check the size to make sure we pass in the correct structure.
	if (iSize == sizeof(VIDEO_STREAM_CONFIG_CAPS))
	{
		// Use the video capabilities structure.

		for (int iFormat = 0; iFormat < iCount; iFormat++)
		{
			VIDEO_STREAM_CONFIG_CAPS scc;
			AM_MEDIA_TYPE *pmtConfig;
			hr = pConfig->GetStreamCaps(iFormat, &pmtConfig, (BYTE*)&scc);
			if (SUCCEEDED(hr))
			{
				/* Examine the format, and possibly use it. */
				if ((pmtConfig->majortype == MEDIATYPE_Video) &&
					(pmtConfig->subtype == MEDIASUBTYPE_RGB24) &&
					(pmtConfig->formattype == FORMAT_VideoInfo) &&
					(pmtConfig->cbFormat >= sizeof (VIDEOINFOHEADER)) &&
					(pmtConfig->pbFormat != NULL))
				{
					VIDEOINFOHEADER *pVih = (VIDEOINFOHEADER*)pmtConfig->pbFormat;
					// pVih contains the detailed format information.
					LONG lWidth = pVih->bmiHeader.biWidth;
					LONG lHeight = pVih->bmiHeader.biHeight;
				}
				if (iFormat == 26) { //2 = '1280x720YUV' YUV, 22 = '1280x800YUV', 26 = '1280x720RGB'
					hr = pConfig->SetFormat(pmtConfig);
				}
				// Delete the media type when you are done.
				DeleteMediaType(pmtConfig);
			}
		}
	}


	// Query the capture filter for the IAMCameraControl interface.
	IAMCameraControl *pCameraControl = 0;
	hr = pDeviceFilter->QueryInterface(IID_IAMCameraControl, (void**)&pCameraControl);
	if (FAILED(hr))
	{
		// The device does not support IAMCameraControl
	}
	else
	{
		long Min, Max, Step, Default, Flags, Val;
		
		// Get the range and default values 
		hr = pCameraControl->GetRange(CameraControl_Exposure, &Min, &Max, &Step, &Default, &Flags);
		hr = pCameraControl->GetRange(CameraControl_Focus, &Min, &Max, &Step, &Default, &Flags);
		if (SUCCEEDED(hr))
		{
			hr = pCameraControl->Set(CameraControl_Exposure, -11, CameraControl_Flags_Manual ); // Min = -11, Max = 1, Step = 1
			hr = pCameraControl->Set(CameraControl_Focus, 12, CameraControl_Flags_Manual );
		}
	}


	// Query the capture filter for the IAMVideoProcAmp interface.
	IAMVideoProcAmp *pProcAmp = 0;
	hr = pDeviceFilter->QueryInterface(IID_IAMVideoProcAmp, (void**)&pProcAmp);
	if (FAILED(hr))
	{
		// The device does not support IAMVideoProcAmp
	}
	else
	{
		long Min, Max, Step, Default, Flags, Val;
		
		// Get the range and default values 
		hr = pProcAmp->GetRange(VideoProcAmp_Brightness, &Min, &Max, &Step, &Default, &Flags);
		hr = pProcAmp->GetRange(VideoProcAmp_BacklightCompensation, &Min, &Max, &Step, &Default, &Flags);
		hr = pProcAmp->GetRange(VideoProcAmp_Contrast, &Min, &Max, &Step, &Default, &Flags);
		hr = pProcAmp->GetRange(VideoProcAmp_Saturation, &Min, &Max, &Step, &Default, &Flags);
		hr = pProcAmp->GetRange(VideoProcAmp_Sharpness, &Min, &Max, &Step, &Default, &Flags);
		hr = pProcAmp->GetRange(VideoProcAmp_WhiteBalance, &Min, &Max, &Step, &Default, &Flags);
		if (SUCCEEDED(hr))
		{
			hr = pProcAmp->Set(VideoProcAmp_Brightness, 142, VideoProcAmp_Flags_Manual);
			hr = pProcAmp->Set(VideoProcAmp_BacklightCompensation, 0, VideoProcAmp_Flags_Manual);
			hr = pProcAmp->Set(VideoProcAmp_Contrast, 4, VideoProcAmp_Flags_Manual);
			hr = pProcAmp->Set(VideoProcAmp_Saturation, 100, VideoProcAmp_Flags_Manual);
			hr = pProcAmp->Set(VideoProcAmp_Sharpness, 0, VideoProcAmp_Flags_Manual);
			hr = pProcAmp->Set(VideoProcAmp_WhiteBalance, 2800, VideoProcAmp_Flags_Manual);
		}
	}


   //============================================================
   //=========== END MY CODE  ======================================
   //=============================================================

   // set FilterGraph
   pCaptureGraphBuilder2->SetFiltergraph(pGraphBuilder);

   // get MediaControl interface
   pGraphBuilder->QueryInterface(IID_IMediaControl,
     (LPVOID *)&pMediaControl);

   // add device filter to FilterGraph
   pGraphBuilder->AddFilter(pDeviceFilter, L"Device Filter");

   // create Graph
   pCaptureGraphBuilder2->RenderStream(&PIN_CATEGORY_CAPTURE,
     NULL, pDeviceFilter, NULL, NULL);
   
   // start playing
   pMediaControl->Run();




   // to block execution
   // without this messagebox, the graph will be stopped immediately
   MessageBox(NULL,
     "Block Execution",
     "Block",
     MB_OK);

   // release
   pMediaControl->Release();
   pCaptureGraphBuilder2->Release();
   pGraphBuilder->Release();
 }

 // release
 pEnumMoniker->Release();
 pCreateDevEnum->Release();

 // finalize COM
 CoUninitialize();

 return 0;
}

Answer 1

Kevin,

Look in some of the OLD DirectX SDK's for a program called "AMCAP". (December 2002, Summer 2004, etc.)

It is a good starting point for learning how to setup DirectShow Graphs then make calls that allow you to adjust video configuration data etc.

Billnew

---

DirectShow Filter Graph Spy: http://alax.info/blog/777 Extremely helpful for finding deep details for DirectShow Graphs.

Answer 2

Bill,

That's actually where I started (it's actually included in the current Windows 7 SDK), but there was just so much code and so many different files that I wasn't able to get much out of it.  Maybe those with stronger programming experience wouldn't have as much trouble, but I have seen others complain about not being able to understand the DirectShow samples very well.

But I agree, people should definitely look at those examples.  They demonstrate a lot of functionality and are presumably much more well-programmed.  I think this example might be useful as a starting point for those that feel lost in the provided examples in the SDK.