dll ffmpeg with MinGW/msys

Hello,

I'm trying to compile ffmpeg as a DLL with MinGW/msys

From the ffmpeg-0.4.8 orignal i've done the following modifications:
1) In ffmpeg.c I've changed main() to ffmain()
2) I create a ffmpeg.h to export this dll
__declspec(dllexport) int GetDummyInt(void);
__declspec(dllexport) int amain(int argc, char **argv);

That's all.

the i compile the whole stuff.. using the command line
gcc -shared -Wl,--output-def,ffmpeg.def -o ffmpeg.dll -L./libavformat
-lavformat -L./libavcodec -lavcodec -lm

The result is a ffmeg.dll but it seems not to be a correct one !

I there any easier and better way to make a dll ?

Any ideas somewhere?
Thanks
Alain