Your question is very interesting: it is, I think, an instance of a question that might generally be asked of any particular instance of any art: what is it that makes it the kind of work that it is? To fix ideas, consider the following question, which Stephen Dedalus, the protagonist of James Joyce's Portrait of the Artist as a Young Man , says that he's written down in a book at home: "If a man hacking in fury at a block of wood...make there an image of a cow, is that image a work of art? If not, why not?" Your question, like Stephen's, has to do with the difference between a genuine artwork and an otherwise identical grouping of sounds, not, however, produced in the context of a work of art. It therefore seems to me that brilliance alone is not enough for something to qualify as music; the birds outside my window sometimes produce a brilliant series of notes. But the sounds produced by the birds aren't music, even if they are musical, whereas the sounds heard on the soundtrack of ...

Treatments of music have long been a part of aesthetics: perhaps precisely because music is as abstract as it is--that is, it is not representational, or at least not obviously so--consideration of music raises questions about meaning, and human responses that are very different from those raised by representational arts such as painting or film. While there has been much written on the philosophy of music, I think that a very good place to start is with the work of the philosopher Peter Kivy, who has written on a wide range of topics in the aesthetics of music over the years.