Ask a rhetorical question . . . .

Personally, I’m thinking this is a no-brainer.  How is film music different from music written to accompany a ballet?

That has the look of a rhetorical question.  But . . . .

I’m writing a ballet.  The duration of the ballet, the component scenes, the sequence, every bar of the music — that is all under the complete control of one person, and that one person is the composer (in this case, myself).

Is there a film where this was ever the case?

Now, one may object that I am working under atypical conditions:  there is as yet no stage director, no choreographer, with whom I am working, and these are people who normally have some input in various details of the music to a ballet.

Two answers:

1]  When (as I hope, or we might say simply if) my piece reaches a point where a company will dance it, and the stage director or choreographer suggests cutting this, changing that, switching the order of these two numbers, taking this dance from Act IV and inserting it into Act II — I have the option of saying, No; this is the way I have written the ballet, and either you dance the piece the way I have written it, or you find some other ballet to do.

I ask again:  Where is the fellow who scored a film, who ever possessed a claim to that option?

2]  Even under more typical ballet-creation conditions, the composer has creative control over the final musical result, to a degree which is simply impossible in film.

You ask, How is film music different from music written to accompany a ballet?

Read Stravinsky’s biography where he is working on Agon.  Then read Hitchcock’s biography where he is working on Pyscho.  In the first case, Stravinsky is in the driver’s seat;  in the second, Hitchcock.

Only one of them was the composer involved in his respective project.