This is an updated version of the vf_fade filter, which uses the current ffmpeg filter api.
To use, when building from source add the file to the libavfilters folder in ffmpeg, then:
Update libavfilters/Makefile with the following: OBJS-$(CONFIG_FADE_FILTER) += vf_fade.o
And finally update libavfilters/allfilters.c with the following: REGISTER_FILTER (FADE, fade, vf);
Afterwards you should be able to apply fades, such as the following: ffmpeg -i input.avi -vf "fade=in:0:30" output.avi