k3b codecs for managing mp3 and other restricted formats come with a stand-alone package (called k3b-codecs). You have to install it manually, sicne it is not provided (nor installed) by OpenSuSE. You can also check this page
on the OpenSuSE Community site, to learn more about free and restricted formats. If you follow the links you can even install all the required stuff to manage restricted format in one-click. Feel free to ask for any problem.