Debian Multimedia vs dmo

Be careful:

• http://www.deb-multimedia.org [AKA "dmo",
  formerly debian-multimedia.org (CAUTION: as of June 2013, the old domain has expired and been taken over by some cybersquatters; thanks to the official Debian Project blog for news)]
  is not an official Debian repository —
  it's a private archive administered by a DD [Debian Developer] named Christian Marillat (with some assistance from another DD, Thibaut Varene):
  please read the explanation in the Debian Multimedia FAQ and a discussion between Christian Marillat & Stefano Zacchiroli (the DPL [Debian Project Leader] at that time) regarding the dmo domain name etc.;
• well, dmo contains some useful software which still hasn't made its way into Debian archives or simply can't be pushed there due to non-free licenses, software patents etc.;
  some packages duplicate the official Debian ones, but differ in some configurations etc.;
• installing multimedia software from dmo also pulls dmo versions of related libraries (e. g., libavcodec*);
  all installed packages which have corresponding dmo ones will get "upgraded" to dmo versions too (if you don't lock them explicitly);
  it can not only break some "unrelated" software functionality:
  if you decide to stop using dmo repository, you'll also need to restore the affected packages to Debian official versions manually
  due to version conflicts (e. g., to get a higher priority, dmo packages often use a greater "epoch" version number compared to packages in official Debian archives);
• the best way to use that resource is not to add it to the APT reposiories lists;
  instead of that, it's better to download & install individual packages from there;
  in many cases, dmo's binary DEB packages wouldn't install correctly on a clean Debian system, so you need to download the source packages, correct them (in most cases, all you need is just to correct / modify / clean the dependencies) and build the binary packages with an automated tool like pbuilder;
  after that, manually install the built packages:

  # dpkg -i somepackage.deb
  

  and attempt to resolve the dependencies:

  # apt-get -f install

• if you still want to use dmo as an APT repository, consider using mirrors to save some bandwidth for the main dmo website :)