Audio Analysis?

Hello. I know you can use AudioSource.GetOutputData and AudioSource.GetSpectrumData to get info regarding the currently playing audio in a scene. Is there anyway to do this before the scene starts? Have a "analyzing" scene where the unity runs through the song (speed up, perhaps?), grabs the data needed and then, when the actual scene where that info is needed, the song is just playing and not being analyzed? Games that use audio to generate their levels (audiosurf, rhythm zone, etc.) use this technique(to increase performance I presume).

Also, Is there anyway to use an outside audio track as the material for an audio source? As in, letting the player use their own music? I know there is a file browser on the unity wiki, could that work?