i'm new to ubuntu. before installing, i wanted to try it first. but, whenever i want to play media files using rhythmbox, it says "python (v2.7) requires to install plugins to play media files of the following type: MPEG-1 Layer 3 (MP3) decoder". i searched a bit on the net, and for that i'm required to install restricted-extras. but there's no option of "install" in Ubuntu software center. when i tried through terminal it said, "E: Unable to locate package ubuntu-restricted-extras". currently, i'm using ubuntu through bootable usb. so, is the restricted-extras package not available in demo version??? i need to install ubuntu to use them?
Ubuntu uses several repositories and even ppa to package programs.
As with an installation, all these packages are available when running a live CD/USB. The "problemes" you might have are that anything you install will be lost when you reboot and you might run out of space if you install a lot of packages or update.
To install restricted extras , see
There is even a link you simply click to install
If you are using regular, stock Ubuntu: Click here to install the ubuntu-restricted-extras package