On a Rasberry Pi 2, if you need packages which is not includes inside Raspbian repository, you can use debian repository (Wheezy for now).
Use these command lines to add Debian Wheezy repository
echo "deb http://ftp.debian.org/debian/ wheezy main" > backports.list echo "deb http://ftp.debian.org/debian/ wheezy-backports main" >> backports.list sudo mv backports.list /etc/apt/sources.list.d
When it’s done, try to make a sudo apt-get update. Usually, you can see that APT need to register the new repositories and request to add public keys.
First install a list of key server,
sudo apt-get install debian-keyring
Next register the keys provide by APT (replace the key 8B48AD6246925553 by yours),
gpg --recv-key 8B48AD6246925553 gpg -a --export 8B48AD6246925553 | sudo apt-key add -
and then update your packages list,
sudo apt-get update
Note: If you need a package in a specific repository used this kind of command
sudo apt-get install -t wheezy-backports gstreamer1.0*