I am trying to install gstreamer-sdk for ubuntu 12.04

When i run this command:
wget -q -O - http://www.freedesktop.org/software/gstreamer-sdk/sdk.gpg | sudo apt-key add -
to install gpg keys,it gives me an error after some time:
gpg: no valid OpenPGP data found

Don't know what is GPG keys,and how to resolve this issue.

I have checked the proxy settings and both $http_proxy and $https_proxy are correctly set.