Capture frames from ActiveX streaming media control

Hello

Not sure if this should be placed here. It may as well be in ATL or C# sections. I apologize if question is misplaced. Perhaps the problem i have is a bit specific but I'm sure the solution would be interesting for a lot of people.

Now to the point. I have an ActiveX control that plays streaming video. My goal is to get to every frame it plays and display them in external c# application over some windows control, a panel, for instance.

Here is the sample DirectShow transform filter:

STDMETHODIMP CTransform::Transform(BSTR bsResource, struct U_VideoFrame *pInFrame, struct U_VideoFrameData **pOutFrameData)
{
//Must allocate memory this way, the output size must be equal to input size
*pOutFrameData = (U_VideoFrameData*)CoTaskMemAlloc(sizeof(U_VideoFrameData));
(*pOutFrameData)->pFrame = (BYTE*)CoTaskMemAlloc(pInFrame->Frame.nLength);
(*pOutFrameData)->nLength = pInFrame->Frame.nLength;

//Now transform data contained in (*pOutFrameData)->pFrame;
//We simply copy data here
memcpy((*pOutFrameData)->pFrame, pInFrame->Frame.pFrame, pInFrame->Frame.nLength);

return S_OK;
}

My idea is that somewhere inside this method I should place a callback function that will call my managed code and pass pInFrame to it. How can I do it? Please help

P.S. I have read the great article http://stackoverflow.com/questions/2...dll-to-net-app. This is the most close solution to my problem. It works as described (of course). However, when I modify the code above to this:

typedef int (__stdcall * Callback)(const char* text);
static Callback Handler = 0;

extern "C" __declspec(dllexport)
void __stdcall SetCallback(Callback handler) {
Handler = handler;
}

extern "C" __declspec(dllexport)
void __stdcall TestCallback() {
int retval = Handler("hello world");
}


// CTransform

STDMETHODIMP CTransform::Transform(BSTR bsResource, struct U_VideoFrame *pInFrame, struct U_VideoFrameData **pOutFrameData)
{
//Must allocate memory this way, the output size must be equal to input size
*pOutFrameData = (U_VideoFrameData*)CoTaskMemAlloc(sizeof(U_VideoFrameData));
(*pOutFrameData)->pFrame = (BYTE*)CoTaskMemAlloc(pInFrame->Frame.nLength);
(*pOutFrameData)->nLength = pInFrame->Frame.nLength;

//Now transform data contained in (*pOutFrameData)->pFrame;
//We simply copy data here
memcpy((*pOutFrameData)->pFrame, pInFrame->Frame.pFrame, pInFrame->Frame.nLength);
if (Handler != 0)
int retval = Handler("Transform");
return S_OK;
}

then the event does not fire from Transform method.

I'm stuck. Any help will be greatly appreciated.