How Do I Install Application Plugins Offline In Ubuntu

When I try to play mp3 songs in Rythmbox it displays message, “Required plugin could not be found - python (v 2.7) requires to install plugins to play media files of the following type: MPEG-1 Layer 3 (mp3) decoder.”

I’ve downloaded gst-ffmpeg-0.10.2.tar and i don’t know how to install it. Help me install it in the easiest way please.