Audio only Youtube player is against the Youtube terms of service. You have to display the video at a certain minimum size.
A friend of mine made something similar to this, but audio only, and - if I remember correctly - got a cease and desist. (Or, at least, he got some kind of "you're in breach of terms of service, cut it out" message, which freaked him out and prompted him to take the project offline).
They can mandate a minimum playback size, but do they mandate a minimum playback fps?
If you played the video back at a rate of 1/60fps (dropping all intermediate frames) would that satisfy their requirements and still save battery life or whatever for the people who would prefer not to see any video at all?
A friend of mine made something similar to this, but audio only, and - if I remember correctly - got a cease and desist. (Or, at least, he got some kind of "you're in breach of terms of service, cut it out" message, which freaked him out and prompted him to take the project offline).