In this project, people in two separate rooms are videotaped. The two video feeds are fed through Processing, converted into silhouettes and superimposed over each other. Both rooms receive the same projection of the superimposed silhouettes. When silhouettes from the two rooms overlap, the overlapped area turns red and a midi note is sent to an external audio program (Reason, in this case).

The video feeds are initialized using a background subtraction technique, so only new objects in the space (ie: people) are fed back as silhouettes. The program sends midi notes using the RWMidi library. The program contains four different modes, some in which participants hear the same sounds, some in which they hear different sounds. All notes are currently in the C major scale. 

My version sounds like this (all sounds can be modulated in the sound program you choose):

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Processing Code