Their music for video games depends on play

If you happen to play the video game Resistance: Retribution after it's released next spring, you'll take on the role of a British soldier working to subvert an alien invasion in post-apocalyptic Europe. Schyman's soundtrack will accompany your virtual exploits, heightening your thrills and frustrations.

The game's creators want the 90-second piece he is creating now, "Luxembourg Suspense," to project despair as the hero is cornered by hordes of venomous creatures eager for their next meal. Which song will come next? That depends entirely on the player. If he fights, the game triggers a Schyman tune designed to crank up the adrenaline. A victory is rewarded by a triumphant score; death triggers a dirge.

In a few short years, as the visual effects and realism of video games have evolved, so too have their soundtracks -- from comical bleeps and annoying loops of ear candy to lush, epic soundtracks that instantly adapt to fit whatever a player decides to do. With an expected $50 billion in global sales this year, video games have turned into such a big business that established composers from film and television are signing on to create the sweeping scores and intricate sounds that help guide players through their missions.

Harry Gregson-Williams, who scored "Shrek," created the music for the action game Metal Gear Solid 4: Guns of the Patriots. Steve Jablonsky, the composer for "Transformers," wrote music for the Sims and Gears of War 2. Danny Elfman, whose theme music for the 1989 "Batman" movie won him a Grammy Award, scored the role-playing adventure game series Fable.

The gigs pay well: Composers can receive as much as $2,000 for each minute of music they write, with a typical game requiring 60 to 90 minutes of music. Including the allowance for hiring musicians, renting recording studios and post-production work, the music budgets for top-notch games can reach as high as half a million dollars.