which buffer to read while playing music at runtime

Hi,
I am implementing a android music player plugin for unity. With this plugin,I can search my device to see if there's any audio files and list it. I can play the musics I searched of course. What I want to ask is, where or which buffer should I read if I want to use the musics to do music visualizer?? While doing music visualizer I prebuild the music as a audio source so I know where to read, but with this plugin I totally have no idea. Might need some help here. Thanks for your help, anyway.