Audio conversion mp3 to ogg

[eluser]Haskabab[/eluser]
Hey,

Since firefox 4 came out i've been experimenting with HTML5 and the <audio> element.

And it requires .ogg files, now if i want to create an application for let's say a music library etc.. I would want to let the users upload their mp3 and listen to it through the <audio> elemnt.

So i need to convert .mp3 files to .ogg

Does anyone know how to achieve this? Is there a library that can do this or a free webservice somewhere? I've searched for it for a while but couldn't find anything useful.

Thanks in advance,

Nick