Re: Install dependencies automatically from backports.
A good way to troubleshoot these problems (and an aide in writing
pinning files as well) is "apt-cache policy".
~$ apt-cache policy
500 http://www.debian-multimedia.org/ wheezy/main amd64 Packages
release v=None,o=Unofficial Multimedia Packages,a=testing,n=wheezy,l=Unofficial Multimedia Packages,c=main
In that, you can see the priority (500), and the various fields you can
pin based on.