2d/3d Audio visualization using FFT

Dear All,
What is the best way to:
[ul]
Capture the mixed audio played like in the SoundEffects example
Run an FFT on the data (possibly using fftw.org/)
Visualize the data either in 3d like so: youtube.com/watch?v=IRpm9Qcnp-k or like so:

998×497

Thanks,

This reminds me of another OSS project called projectM. There are two approaches that comes to mind immediately. Feed the FFT data to a custom geometry modeller. Or render a texture using the FFT data and let the shader samples the texture and uses the data there to affect the visualization of the audio.