'nother problem with linking as well.
for some reason, the configure script does not add links to needed libs from ffmpeg. I looked in configure.ac and it appears to just not be there.
so, when you load Gem in pd, you get lots of symbols undefined.
fix - link using these extra commands:
-lavformat -lavformat_pic -lavutil -lavutil_pic -lavcodec -lavcodec_pic -ldts
it should be in that order as well, otherwise you have this problem:
http://lists.zerezo.com/mplayer-dev-eng/msg00524.html
happy hacking -august.