[Nick Zwar]

The most “classically filmic” composer before actual film music was probably Richard Wagner. Hands down. Much of his output is basically “just” (and I put that in quotation marks) film music, except the film was performed on stage. There is really nothing that distinguishes Wagner’s music from film scores, because the entire concept is already there: leitmotifs functioning as character tags, orchestral textures engineered for maximum atmospheric impact, and harmonic pacing designed to manipulate narrative tension. In fact, if you dropped Wagner’s music into a Hollywood fantasy blockbuster, nobody would bat an eye. (Heck, EXCALIBUR just did it and nobody did bat an eye.)
Film music per se isn’t really different from any other form of music that was already there, it’s not as if film invented or required a “new type” of music, but certainly Hollywood talkies all of a sudden required an enormous amount of dramatic music, and/or music otherwise suitable to enhance and support drama, so a certain type of music and “bag of tricks” would be used often and in many compositions simply because there were so many movies… and then, like other forms of music, some film music compositions were inventive and cross-polinated classical compositions again and vice versa. It’s not as if film music is a singular “genre” of music, it’s basically just a venue for composers to work in.