Interested in writing film music? Here's a link to a Vanity Fair article that claims that the majority of film composers, including "big-name" composers such as Hans Zimmer, farm out much of the composing to uncredited "ghost composers," most of whom are paid very poorly and gain no recognition for their work, even when their work leads to Oscar and Golden Globe awards for the big-name composers who take all the credit. Here's the link:
“The Minions Do the Actual Writing”: The Ugly Truth of How Movie Scores Are Made
John Williams is apparently a rare exception to this practice; he reputedly writes all his music himself.