Looks like it was removed or renamed lately. Just removing the flag allowed me to compile correctly, though I didn't check what lavf was for.
same Problem here
Bump, I also encountered this.
Yup, apparently this flag was removed and apparently it never did anything in the first place! Removing it from the ebuild also worked for me... http://www.listware.net/201007/mplayer-ffmpeg-devel/102803-ffmpeg-devel-patch-12-remove-reference-to-the-unexisting-movie-filter-and-the-corresponding-useless-enable-avfilter-lav.html
change ebuild works too, but uncertain if it is wrong or not. --- ffmpeg-9999.ebuild.g2 2010-07-30 07:13:04.000000000 +0800 +++ ffmpeg-9999.ebuild 2010-07-30 07:08:50.000000000 +0800 @@ -184,8 +184,8 @@ --enable-gpl --enable-version3 --enable-postproc - --enable-avfilter - --enable-avfilter-lavf + --enable-filter=avfilter + --enable-filter=avfilter-lavf --disable-stripping ${myconf}"
fixed, thanks