Fixes for audio amplitude buffer

Hi James... this is the quick fix I needed to get meaningful waveforms from the clouds videos.

The original implementation accurately represents amplitude, but since the audio buffer was read as 32 bit floats instead of 16 bit shorts actually listening to the waveform just gave you noise. Note that this only handles 44100khz 16 bit PCM audio used in the Clouds doc… a more robust implementation would look at the audio metadata and handle different sound formats gracefully.