error loading MPG4DECD.dll

Question

Hi i am trying to load MPG4DECD.dll in my directshow project but app is crashing when i am adding the loaded filter in my graph. call stack shows that app is crashing in MPG4DECD.dll. Here is my code let me know what i am doing wrong here:

HRESULT CreateObjectFromPath(TCHAR* pPath, REFCLSID clsid, IUnknown** ppUnk)
{
    // load the target DLL directly
    HMODULE hLib = CoLoadLibrary(OLESTR("C:\\MPG4DECD.dll"), TRUE);
    if (!hLib)
    {
        return HRESULT_FROM_WIN32(GetLastError());
    }

	LPFNGETCLASSOBJECT pfnGetClassObject = NULL;
    // the entry point is an exported function
    pfnGetClassObject = (LPFNGETCLASSOBJECT)GetProcAddress(hLib, "DllGetClassObject");
    if (pfnGetClassObject == NULL)
    {
        return HRESULT_FROM_WIN32(GetLastError());
    }

    // create a class factory
    IUnknown* pUnk;
    HRESULT hr = pfnGetClassObject(clsid,  IID_IUnknown,  (void**)(IUnknown**)&pUnk);
    if (SUCCEEDED(hr))
    {
        IClassFactory* pCF = (IClassFactory*)pUnk;
        if (pCF == NULL)
        {
            hr = E_NOINTERFACE;
        }
        else
        {
            // ask the class factory to create the object
            hr = pCF->CreateInstance(NULL, IID_IUnknown, (void**)ppUnk);
        }
    }

	//CoFreeLibrary(hLib);
    return hr;
}

and in main mehtod 

IUnknown* pUnk;
	hr = CreateObjectFromPath(TEXT("c:\\MPG4C32.dll"), __uuidof(CLSID_CMpeg4DecMediaObject), &pUnk);
	if (SUCCEEDED(hr))
	{
		IBaseFilter* pFilter = (IBaseFilter*)pUnk; 
		g_pGB->AddFilter(pFilter, L"Private Filter");// this is the actual line of error
		g_pGB->RenderFile(wFileName, NULL);
	}

i am not using pPath so 

TEXT("c:\\MPG4C32.dll") 

will not make any diffrence

this code is based upon http://www.gdcl.co.uk/2011/June/UnregisteredFilters.htm

Regards

Answer 1

You should not be doing this, it's COM-incorrect:

IBaseFilter* pFilter = (IBaseFilter*)pUnk; //line giving access violation exception

To get one interface from another, you need to call IUnknown::QueryInterface. Or rather, since you don't seem to be a good old friend of COM, you can use CComQIPtr template to have it done for you.

CComQIPtr<IBaseFilter> pBaseFilter = pUnk;

It is COM basics, make sure to read some introductory information to learn these fundamentals.

---

http://alax.info/blog/tag/directshow

Answer 2

thanks alot will you please suggest some good introductory materiel for this

Answer 3

There are really good books published by MS Press, Inside COM, Inside ATL etc. I don't have a link handly but there should be no problem to google one.

---

http://alax.info/blog/tag/directshow

Answer 4

after doing this 
CComQIPtr<IBaseFilter> pBaseFilter = pUnk;
pBaseFilter is NULL does it mean that pUnk does not have the interface IBaseFilter if yes then how can i get filter from 
C:\\MPG4DECD.dll