I'm trying to install Ubuntu Restricted Extras via Software Manager and terminal but I'm failing. It started to download. I then went out for a while and on return I saw the download failed.

This is what I'm getting when trying to install:

"To install ubuntu restricted extras, these items must be removed:
Libav codec library
Libav utility library"

There's a continue anyway button. I click that, the download starts and stops right away giving me this error:

Please check your Internet connection:

Failed to fetch http://bd.archive.ubuntu.com/ubuntu/...0219-1_all.deb Size mismatch

What the heck? I am connected to the Internet and my browser and other apps (oDesk Team) are working nice.

What am I missing?