Music is a much easier problem (tight structure, lots of existing data to quickly analyze), and the animation bit is already being pretty thoroughly explored by procedural generation in games. You'd still need a "director" to pick shots, but most of the other pieces are nearly in place. We have algorithms that can create new environments, and design and animate new characters.

But generating a coherent narrative, and good writing to "implement" that narrative. These are huge problems which - as far as I'm aware - would require major breakthroughs to achieve. Machine translation is still utter garbage, and that's fairly straightforward work. We're nowhere near an AI which actually understands language.