policy mplayer mplayer:

ubuntu@ubuntu:~$ sudo apt-cache policy mplayer
mplayer:
  Installed: (none)
  Candidate: 2:1.0~rc4~try1.dsfg1-1ubuntu1+medibuntu1
  Version table:
     2:1.0~rc4~try1.dsfg1-1ubuntu1+medibuntu1 0
        500 http://packages.medibuntu.org/ maverick/non-free Packages
     2:1.0~rc3+svn20090426-1ubuntu16.1 0
        500 http://archive.ubuntu.com/ubuntu/ lucid-updates/multiverse Packages
     2:1.0~rc3+svn20090426-1ubuntu16 0
        500 http://archive.ubuntu.com/ubuntu/ lucid/multiverse Packages