Created as a way to neutralize the mechanical sounds of movie projectors, cinema soundtracks once accompanied silent films and almost always featured movie scores comprised of already recorded music played by pianists or guitarists (orchestras for larger box offices.)
Somewhere around 1925, Phonograph records replaced live musicians through Vitaphone soundsystems created by Western Electric and were mounted with the projector alongside the feature film. Though still using precomposed music, it wasn't until The Jazz Singer was released in October 6, 1927, that the first film embedded both dialogue and music into the film itself. The first complete original score composed for a film was by Max Steiner in 1933, for King Kong, followed by his scores for Gone with the Wind and Casablanca - weaving a lasting tradition of movie soundtracks that have become a fabric of filmmaking.
Though film encompasses every genre of music, there are just some compositions that hold that recognizable 'epic movie sound.'