@bbalpert: Going off topic, but I feel that this is an interesting question: in the era of silent films, they would be projected with someone playing the piano in the room, often with music that accompanied specific scenes. Is this diegetic or non-diegetic? The music is coming from an obvious source, but it exists outside the film and therefore lacks an in-universe explanation. Or do we extend the world of the movie to include the real man on stage?
Non-diegetic. If you define diegetic as 'you can see where it's coming from' then you may as well say all sound is diegetic since you can see the loudspeakers.