xbmc@xbmc:~$ sudo apt-add-repository http://apt.tvheadend.org/stable
xbmc@xbmc:~$ sudo apt-get install tvheadend
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package tvheadend 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 'tvheadend' has no installation candidate
xbmc@xbmc:~$