Laser Data Communication : How it Works General Idea and Concept
All that is required is to establish a digital communication protocol based on pulsing the laser on and off with some means of encoding a '1' and a '0'. This method is used in fibre optic communication in telecoms and more recently in "fibre-broadband". The difference in your application is that the data is transmitted through the air.

Most music is stored and at least partially transmitted in digital form so there is little work to do to prepare it for transmission.