Issue with YouTube - how do they determine they won't support your content?

I heard today on the news that YouTube were beginning to refuse some materials because of copyright problems. I didn't hear all of it just the tail-end of it when I put the radio on. So maybe there's something going on there or they are being over-zealous, as tends to happens with new rules and regulations at times. I have some video up there of me playing piano. The tunes I have chosen to play are quite old, so copyright is not an issue. I don't know if playing copyright songs on an instrument has the same problems as playing the actual recordings or not, and nobody else seems to know either.. But lots of musicians are playing quite up-to-date music. So maybe that's OK - Derek