Trailer music (a subset of production music) is the background music used for film previews, which is not always from the film's soundtrack. The purpose of this music is to complement, support and integrate the sales messaging of the mini-movie that is a film trailer. Because the score for a movie is usually composed after the film is finished (which is much after trailers are released), a trailer will incorporate music from other sources. Sometimes music from other successful films or hit songs is used as a subconscious tie-in method.
"Library" music, which is previously composed production music. Trailer music library companies typically do not offer their music to the public and develop and license music exclusively to the motion picture studios, although Immediate Music did release a commercial album called "Trailerhead,” Reeltime Music with a double CD called “Coming Soon” and Two Steps From Hell with three albums called "Invincible” (2010), "Archangel” (2011) and "SkyWorld" (2012). Brand X Music and Audiomachine have also released albums available to the public.