Mp3 Levels Possible or not?

Hi, ive been working with flash for a while and I have seen this at flash kit:

http://www.flashkit.com/soundfx/Ambience/

What I am refering to is the little flash movie next to the ‘add to myFK’ button. It has dynamic sound levels for each mp3, which I find quite impressive. I was wondering if anyone knows if this is pure code, a flash plug in or if its the result of some server side modification that enables them to do such processing, as I have been unable to find any ‘built in’ flash code or plugin to do exactly that.

Any help on how it was done?