About DirctShowNet & C#

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C#

directshow

For days ,I tried to capture video streams by Web Camara with DirectShowLib.DLL and I gone through the samples to find the way .
At last I writed the codes like this:

DsDevice[] theDevices;
theDevices = DsDevice.GetDevicesOfCat(FilterCategory.VideoInputDevice );
this .Text =theDevices [0].Name .ToString ();
          
IFilterGraph2 theFilterGraph = new FilterGraph() as IFilterGraph2;
IMediaControl theMediaControl = null;
theMediaControl = theFilterGraph as IMediaControl;
            
IBaseFilter theCaptureFilter = null;
IBaseFilter theASFWriter = null;
ICaptureGraphBuilder2 theCAPBuilder = null;
            
            
IFileSinkFilter theSinkFilter = null;
SaveFileDialog theSaveDialog = new SaveFileDialog();
theSaveDialog.ShowDialog();
           
IConfigAsfWriter theConfig = (IConfigAsfWriter)theASFWriter;
Guid theGuid = typeof(IBaseFilter).GUID;
            
theCAPBuilder =(ICaptureGraphBuilder2 ) new CaptureGraphBuilder2();
//****************************************************
// Notice here: 
****************************************************
theConfig.ConfigureFilterUsingProfileGuid(theGuid);

theCAPBuilder.SetFiltergraph(theFilterGraph);
theFilterGraph.AddSourceFilterForMoniker(theDevices[0].Mon, 
                                         null, 
                                         theDevices[0].Name, 
                                         out theCaptureFilter);
theCAPBuilder.RenderStream(PinCategory.Capture, 
                           MediaType.Video, 
                           theCaptureFilter, 
                           null, 
                           theASFWriter);
theCAPBuilder.SetOutputFileName(MediaSubType.Asf,
                                theSaveDialog.FileName, 
                                out theASFWriter, 
                                out theSinkFilter);
            
theMediaControl.Run();
IVideoWindow theWindow = (IVideoWindow)theFilterGraph;
theWindow.put_Owner(this.Handle);
theWindow.put_WindowStyle(WindowStyle.Child | WindowStyle.ClipChildren);
theWindow.SetWindowPosition(0, 0, 
                            this.ClientSize.Width,  
                            this.ClientSize.Height);
theWindow.put_Visible(OABool.True);

OK,Now,run without the noticed line. I gave it a file name with the SaveFileDialog ,such as "j:\first.wmv",then,the form display,but,I can't see any thing except a black ground. Shuted it down ,I can't find the file - first.wmv

Obvious ,there is something wrong .Why,the sample goes well and my application is like this? Then ,I try to run it with the noticed line. It just throwed me a exception : should initialize the object with "new".

Oh,my God ,what is this?!

I have the IConfigAsfWriter like this:

IConfigAsfWriter theConfig = (IConfigAsfWriter)theASFWriter

,and ,I have the GUID Like this:

Guid theGuid = typeof(IBaseFilter).GUID

Why this exception ?

I tried other Configure ways in the list of IConfigAsfWriter ,but no help. Any one can show me the right way ? THANKS!!