The error is telling you that your Ubuntu OS doesn't have Apple Quicktime installed. AFAIK, Apple don't support Linux OS'. I'm not sure why Moodle is trying to embed MP3 audio as Quicktime.
Your best bet for media playback in Ubuntu is to use a Flash based player (make sure users have the "extras" package with all the non-free and open source apps installed: https://apps.ubuntu.com/cat/applications/ubuntu-restricted-extras/ )
See: http://docs.moodle.org/25/en/Multimedia_plugins_filter Moodle uses the FlowPlayer as its default media player: http://flowplayer.org/
Another solution is to embed the audio using the HTML5 audio tags: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/audio (See the section, "Audio element with source element").
I hope this helps!