The original Piano Phase for two pianos was composed in 1967. Both pianists play the same repeating pattern but one of them gradually increases tempo so as to slowly move one-eighth note ahead or out of phase with the other. This process is repeated with three repeating patterns that get shorter in duration. The video portion of this piece was created by David Cossin in 2000 and utilizes a pre-recorded video of him playing the piece on MIDI percussion pads that then trigger piano samples of the notes of the piece. Against this pre-recorded video, projected on a screen in front of him, he then plays the moving part that gradually moves ahead, or out of phase with the recorded part. The audience can then see and hear the process unfolding.
— Steve Reich