One of the surprising omissions to K2 is the lack of the ability to add audio (mp3) files. Hacks to overcome this have been reported in community.getk2.org/forum/topics/found-a-way-to-add-mp3-files. As AllVideos supports playing mp3 files, it should not be that difficult to implement.
Simon, I would like to make a feature request for an Audio tab, next to the Video tab, that would allow the uploading of audio files, similar to the upload video tab. 

I had considered making a K2 plugin to add this functionality, which I think would be possible. However, I really think it should be part of core K2. For example, we create a lot of church websites. Audio sermons are standard fare now in church websites and many offer both video and audio of sermons. Of course, music websites also need the ability to play mp3s as well.

Simon, is it possible to get this request on the feature roadmap?

Hi Dan,

If you have the time and desire to make a plugin, that would be great.
It would be possible to do a plugin that does not over right core files, but work well, just like a plugin in the k2 item editor.
I would be able to feed this back to main K2 dev team to be considered for inclusion in a future release.

Simon
K2 Support