Writing interactive music is a complex operation because the player isn’t forced into hitting beats and bars. There has to be a system in place that makes sure that the music either cross fades in certain positions or the music has been written in such a way that means it can cross fade at any point. The music is able to adapt to the player movements by using two techniques. Horizontal re-sequencing is the method where pre composed segments of music can be re-shuffled according to the player’s position in the environment. Vertical re-orchestration is the technique of changing the mix of separate instruments in an on-going loop as the player moves round the game environment. Games such as Crysis, Far Cry, FarCry2 and Halo 2 use a combination of these techniques.