The other replies are incorrect, the lower tier premium actually has no ads on most videos. When you subscribe, they explicitly let you know music videos will play ads, probably so this plan is not eating away profits of YouTube music.

Slightly unrelated but this is an awesome picture that I’d love to have a print of. Does anybody know the author or source?

Damn, may I ask how big your entire library is? At those sizes, you can store more music than I’ll ever need in a couple of gbs.