Trailer music
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 long 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. Trailer music is known for  its sound-design driven and hybrid orchestral style. Trailer music tracks can vary greatly in duration, depending on the theme and target of the album. Some albums contains only sound-effects instead of actual music. The music used in the trailer may be (or may have suggestive derivatives from):