I took a whole course on it in college (and you can even major in it in some music departments). Check out on amazon - there are lots of books like "Music in Film," "Hearing the Movies." Or, google various courses at colleges for a sample syllabus. Such as Music&Cinema at albright:
Required texts
Larry M. Timm. The Soul of Cinema: An Appreciation of Film Music. Englewood Cliffs, NJ: Prentice Hall, 2003.
Tony Thomas. Music for the Movies. 2nd Edition. Los Angeles: Silman-James Press, 1997.
Recommended readings:
Abel, Richard, and Altman, Rick, eds. The Sounds of Early Cinema. Bloomington: Indiana Univ. Press, 2001.
Altman, Rick, ed. Sound Theory Sound Practice. NY: Routledge, 1992.
Brown, Royal S. Overtones and Undertones : Reading Film Music. University of California Press, 1994
Eyman, Scott. The Speed of Sound: Hollywood and the Talkie Revolution, 1926-1930. NY: Simon & Schuster, 1997.
Gorbman, Claudia. Unheard melodies: Narrative film music. Indiana University Press, 1987.
Lack, Russell. Twenty-four Frames Under: A Buried History of Film Music. London: Quarter Books, 1997.
Marks, Martin M. Music and the silent film: Contexts and case studies, 1895-1924. Oxford, 1997.
Morgan, David. Knowing the Score: Film Composers Talk about the Art, Craft, Blood, Sweat, and Tears
Of Writing for Cinema. New York: Harper Collins, 2000.
Prendergast, Roy M. Film music: A neglected art. 2nd edition. W. W. Norton, 1992.
Weis, Elisabeth and John Belton, eds. Film sound: Theory and practice. Columbia Univ. Press, 1985.
