If you installed K3b, you'd probably be getting a warning message, every time you start K3b. A message informing that no MP3 plug-in has been found, and that you won't be able to burn Audio CD's from an MP3 file.
To get rid of this message, and to install MP3 support, type in the following in terminal:
yum install k3b-extras-nonfree
Restart K3b and that message won't be displayed any more!
