求助，用directshow进行摄像头操作，提示连接到系统上的设备没有发挥作用

用directshow操作摄像头，当摄像头数量超过5个的时候提示连接到系统上的设备没有发挥作用，4个的时候都可以正常工作
代码是用的是directshow的samples改的
如下 int hr;            ISampleGrabber sampGrabber = null;
            IBaseFilter capFilter = null;
            IPin pCaptureOut = null;
            IPin pSampleIn = null;
            IPin pRenderIn = null;            // Get the graphbuilder object
            m_FilterGraph = new FilterGraph() as IFilterGraph2;            try
            {
#if DEBUG
                m_rot = new DsROTEntry(m_FilterGraph);
#endif
                // add the video input device
                hr = m_FilterGraph.AddSourceFilterForMoniker(dev.Mon, null, dev.Name, out capFilter);
                DsError.ThrowExceptionForHR(hr);                // Find the still pin
                m_pinStill = DsFindPin.ByCategory(capFilter, PinCategory.Still, 0);                // Didn't find one.  Is there a preview pin?
                if (m_pinStill == null)
                {
                    m_pinStill = DsFindPin.ByCategory(capFilter, PinCategory.Preview, 0);
                }                // Still haven't found one.  Need to put a splitter in so we have
                // one stream to capture the bitmap from, and one to display.  Ok, we
                // don't *have* to do it that way, but we are going to anyway.
                if (m_pinStill == null)
                {
                    IPin pRaw = null;
                    IPin pSmart = null;                    // There is no still pin
                    m_VidControl = null;                    // Add a splitter
                    IBaseFilter iSmartTee = (IBaseFilter)new SmartTee();                    try
                    {
                        hr = m_FilterGraph.AddFilter(iSmartTee, "SmartTee");
                        DsError.ThrowExceptionForHR(hr);                        // Find the find the capture pin from the video device and the
                        // input pin for the splitter, and connnect them
                        pRaw = DsFindPin.ByCategory(capFilter, PinCategory.Capture, 0);
                        pSmart = DsFindPin.ByDirection(iSmartTee, PinDirection.Input, 0);                        hr = m_FilterGraph.Connect(pRaw, pSmart);
                        DsError.ThrowExceptionForHR(hr);                        // Now set the capture and still pins (from the splitter)
                        m_pinStill = DsFindPin.ByName(iSmartTee, "Preview");
                        pCaptureOut = DsFindPin.ByName(iSmartTee, "Capture");                        // If any of the default config items are set, perform the config
                        // on the actual video device (rather than the splitter)
                        if (iHeight + iWidth + iBPP > 0)
                        {
                           // SetConfigParms(pRaw, iWidth, iHeight, iBPP);
                        }
                    }
                    finally
                    {
                        if (pRaw != null)
                        {
                            Marshal.ReleaseComObject(pRaw);
                        }
                        if (pRaw != pSmart)
                        {
                            Marshal.ReleaseComObject(pSmart);
                        }
                        if (pRaw != iSmartTee)
                        {
                            Marshal.ReleaseComObject(iSmartTee);
                        }
                    }
                }
                else
                {
                    // Get a control pointer (used in Click())
                    m_VidControl = capFilter as IAMVideoControl;                    pCaptureOut = DsFindPin.ByCategory(capFilter, PinCategory.Capture, 0);                    // If any of the default config items are set
                    if (iHeight + iWidth + iBPP > 0)
                    {
                        SetConfigParms(m_pinStill, iWidth, iHeight, iBPP);
                    }
                }                // Get the SampleGrabber interface
                sampGrabber = new SampleGrabber() as ISampleGrabber;                // Configure the sample grabber
                IBaseFilter baseGrabFlt = sampGrabber as IBaseFilter;
                ConfigureSampleGrabber(sampGrabber);
                pSampleIn = DsFindPin.ByDirection(baseGrabFlt, PinDirection.Input, 0);                // Get the default video renderer
                IBaseFilter pRenderer = new VideoRendererDefault() as IBaseFilter;
                hr = m_FilterGraph.AddFilter(pRenderer, "Renderer");
                DsError.ThrowExceptionForHR(hr);                pRenderIn = DsFindPin.ByDirection(pRenderer, PinDirection.Input, 0);                // Add the sample grabber to the graph
                hr = m_FilterGraph.AddFilter(baseGrabFlt, "Ds.NET Grabber");
                DsError.ThrowExceptionForHR(hr);                if (m_VidControl == null)
                {
                    // Connect the Still pin to the sample grabber
                    hr = m_FilterGraph.Connect(m_pinStill, pSampleIn);
                    DsError.ThrowExceptionForHR(hr);                    // Connect the capture pin to the renderer
                    hr = m_FilterGraph.Connect(pCaptureOut, pRenderIn);
                    DsError.ThrowExceptionForHR(hr);
                }
                else
                {
                    // Connect the capture pin to the renderer
                    hr = m_FilterGraph.Connect(pCaptureOut, pRenderIn);
                    DsError.ThrowExceptionForHR(hr);                    // Connect the Still pin to the sample grabber
                    hr = m_FilterGraph.Connect(m_pinStill, pSampleIn);
                    DsError.ThrowExceptionForHR(hr);
                }                // Learn the video properties
                SaveSizeInfo(sampGrabber);
                ConfigVideoWindow(hControl);                // Start the graph
                IMediaControl mediaCtrl = m_FilterGraph as IMediaControl;
                hr = mediaCtrl.Run();
                DsError.ThrowExceptionForHR(hr);
            }
hr = mediaCtrl.Run();当跑到这步的时候就报示连接到系统上的设备没有发挥作用