benjaminang@benjaminang-feisty:~$ sudo aptitude install mplayer libxine-extracodecs
Reading package lists... Done
Building dependency tree     
Reading state information... Done
Reading extended state information     
Initializing package states... Done
Building tag database... Done     
No candidate version found for mplayer
No candidate version found for libxine-extracodecs
The following packages have been automatically kept back:
  linux-restricted-modules-common
The following packages have been kept back:
  app-install-data-commercial apport apport-gtk capplets-data
  gnome-control-center gnome-panel gnome-panel-data hwdb-client-common
  hwdb-client-gnome libgnome-window-settings1 libmetacity0
  libpanel-applet2-0 libslab0 libsmbclient metacity metacity-common python
  python-apport python-gdbm python-minimal python-problem-report python2.5
  python2.5-minimal rdesktop samba samba-common smbclient smbfs tzdata
  unattended-upgrades update-manager update-manager-core vim-common
  vim-tiny
0 packages upgraded, 0 newly installed, 0 to remove and 35 not upgraded.
Need to get 0B of archives. After unpacking 0B will be used.
Writing extended state information... Done

benjaminang@benjaminang-feisty:~$ sudo apt-get install mplayer
Password:
Reading package lists... Done
Building dependency tree     
Reading state information... Done
Package mplayer is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package mplayer has no installation candidate