Playing Music Cross browser - HTML5


I am experimenting with playingmusic on an HTML5 site… this doesn’t work on mobiles, what can I do to make this work cross platform with up to date code?

<audio controls preload="auto" autobuffer>
  <source src="track.mp3" />

Managed to get this working on android and iphone now.

However, firefox needs .OGG ?

I have tried to convert a 1mg .mp3 file, but any converter I use converts the file to a 15mb .OGG file.