I refered to the FFvfw
decoding engine of the ffdshow Package

I dont remember but you still got an older version of ffdshow installed right?
The recent ones are provided as just "ffdshow" packages (official name) but do come with an "internal" ffvfw engine included which will make ffdshow also able to "decode" FourCCs in "vfw" apps like Vdub or CCE or even the Avisource command of avisynth which uses vfw.
But there are still some Bugs related to the Filtersection in FFdshows vfw engine and that can be recognised as the filters wont work, just the stream is decoded by ffdshows vfw engine thats all - and Makeavis "avis" wont be decoded properly by the vfw decoding interface of ffdshow. But for that one I do point to an old ffvfw.dll outside of the system32 hierarchy.