multiple web cams in AMCap

I built the AMCap sample under direct show in SDK. It is able to handle 2 or more web cam, how do I modify the program for me to use them simultaneously… like press one button that says ‘start capture’ and make sure that all the cameras start capturing and one button that says ‘stop capture’ to stop all the came开发者_如何学Goras. i want the frames from different cameras to be save in different files. I am new to C++ and any kind of help is appreciated ! Thanks for your time!

Use GraphEdit tool. There you can build you own graph with all video input devices connected. Please see http://en.wikipedia.org/wiki/GraphEdit

If you're just starting out with DirectShow programming, this might be a bit of a hill climb, but I hope it's of some help, or points you in the right direction.

M$DN has a page describing how to select a capture device. It's a little thin on examples, so I've provided a simple implementation below.

The theory is that you need to enumerate all devices in the CLSID_VideoInputDeviceCategory, and attempt to create a render graph for each valid item in the category.

First I'll show you the code to iterate the names of the devices in the category. Below are 3 static functions you can use to iterate the devices in a category. Once you've added these functions to your project, you can list the devices in the Video Input Device category by calling the following function:

ListDevicesInCategory(CLSID_VideoInputDeviceCategory);

Okay, here are the three functions. ListDevicesInCategory() is where the work happens. It depends on other two functions, FindDeviceInCategory() and CountDevicesInCategory()

#define RFAIL(x) { HRESULT hr = x; if(FAILED(hr)) {return hr;} }


static HRESULT FindDeviceInCategory(IBaseFilter** pSrc, const IID& cls, wstring& wFilterName,int devNum)
{
    CComPtr<ICreateDevEnum> spDevEnum;
    CComPtr<IEnumMoniker>   spEnum;
    int                     i;

    RFAIL( spDevEnum.CoCreateInstance(CLSID_SystemDeviceEnum) );
    RFAIL( spDevEnum->CreateClassEnumerator(cls, &spEnum, 0) );

    if(spEnum == 0)
        return E_FAIL;

    for(i = 0; i >= 0; i++)
    {
        CComPtr<IMoniker> spiMoniker;

        if( spEnum->Next(1, &spiMoniker, 0) != S_OK )           
            return E_FAIL;          

        if( devNum == i)
        {
            CComVariant varName;
            CComPtr<IPropertyBag> spiPropBag;
            RFAIL(spiMoniker->BindToStorage(0, 0, IID_IPropertyBag,reinterpret_cast<void**>(&spiPropBag)));
            RFAIL(spiPropBag->Read(L"FriendlyName", &varName, 0));
            RFAIL(spiMoniker->BindToObject(0, 0, IID_IBaseFilter, reinterpret_cast<void**>(pSrc)));
            wFilterName = V_BSTR(&varName);

            varName.Clear();
            return S_OK;
        }
    }

    return E_FAIL;
}

static HRESULT CountDevicesInCategory( int *pCount, const IID& categoryClass )
{
    // pass in a category class like CLSID_VideoInputDeviceCategory, writes the count of the number of filters in that category 
    // available on the local machine
    HRESULT hr = S_OK;

    CComPtr<ICreateDevEnum> spIDevEnum;
    CComPtr<IEnumMoniker>   spIEnum;
    CComPtr<IMoniker>       spIMoniker;

    hr = CoCreateInstance(CLSID_SystemDeviceEnum, 0, CLSCTX_INPROC_SERVER, IID_ICreateDevEnum, reinterpret_cast<void**>(&spIDevEnum));
    if( ! SUCCEEDED(hr) || hr == S_FALSE )
    {
        *pCount = 0;
        return hr;
    }

    hr = spIDevEnum->CreateClassEnumerator( categoryClass, &spIEnum, 0 );
    if( ! SUCCEEDED(hr) || hr == S_FALSE )
    {
        *pCount = 0;
        return hr;
    }

    if( spIEnum )
    {
        while( spIEnum->Next(1, &spIMoniker, 0) == S_OK ) 
        { 
            (*pCount) ++; 
            spIMoniker.Detach();
        }       
    }

    return S_OK;
}

static HRESULT ListDevicesInCategory( const GUID & cls )
{
    CComPtr<IBaseFilter>    spSource;
    wstring *               psNextFilter        = NULL;
    int                     nDeviceNum          = 0;
    int                     nTotalNumDevices    = 0;
    HRESULT                 hr                  = S_OK;
    bool                    bComplete           = false;    
    DeviceNames             CaptureDeviceNames;


    if( FAILED(CountDevicesInCategory( &nTotalNumDevices, (IID)cls )) )
        bComplete = TRUE;

    if( nTotalNumDevices == 0 )
        bComplete = TRUE;


    while( ! bComplete )
    {   
        psNextFilter = new std::wstring;

        hr = FindDeviceInCategory( &spSource, (IID)cls, *psNextFilter, nDeviceNum++ );

        if( SUCCEEDED(hr) && spSource  )
        {
            if ( *psNextFilter )
            {
                wcout << *psNextFilter << endl;
                delete *psNextFilter;
                psNextFilter = NULL;
            }

            spSource.Release();
            spSource = NULL;
        }
        else
            bComplete = TRUE;
    }           

    return S_OK;
}   

Once you've identified an item in a category that you're interested in, you can add it to a graph with the IGraphBuilder::AddFilter call.

To add a filter to your graph, you'll first need to get an IBaseFilter* to that filter. I've got one more function for you to do this with.

Define an IBaseFilter smart pointer:

CComPtr<IBaseFilter> spSource;

Attach to the filter:

m_spSource.Attach(
                GetFilter(CLSID_VideoInputDeviceCategory, CComBSTR(L"Osprey-450e Video Device 1A"))
          );

Here's that last function - GetFilter:

static IBaseFilter * GetFilter( REFCLSID clsidDeviceClass, CComBSTR & sName )
{   
    HRESULT             hr;
    IBaseFilter *       pRetFilter      = NULL;
    ICreateDevEnum *    pSysDevEnum     = NULL;
    IEnumMoniker *      pEnum           = NULL;
    IMoniker *          pMoniker        = NULL;
    int                 nSameSrcCounter = 0;

    hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER, IID_ICreateDevEnum, (void**)&pSysDevEnum);

    if( pSysDevEnum )
        hr = pSysDevEnum->CreateClassEnumerator(clsidDeviceClass, &pEnum, 0);

    if (hr != S_OK) 
        return NULL;    

    USES_CONVERSION;


    while ( pEnum->Next(1, &pMoniker, NULL) == S_OK )
    {
        IPropertyBag *pPropBag = NULL;
        VARIANT var;
        VariantInit(&var);

        pMoniker->BindToStorage(0, 0, IID_IPropertyBag, (void **)&pPropBag);

        hr = pPropBag->Read(L"FriendlyName", &var, 0);
        if (SUCCEEDED(hr))
        {
            if(sName == OLE2T(var.bstrVal))
            {           
                hr = pMoniker->BindToObject(NULL, NULL, IID_IBaseFilter, (void**)&pRetFilter);
                if (FAILED(hr))                 
                    pRetFilter = NULL;                  

                VariantClear(&var); 
                pPropBag->Release();
                pMoniker->Release();
                break;
            }
        }

        VariantClear(&var); 
        pPropBag->Release();
        pMoniker->Release();
    }

    pSysDevEnum->Release();
    pEnum->Release();

    return pRetFilter;
}