More details have leaked about Google's upcoming subscription service for YouTube, these in the form of screenshots posted by Android Police on Monday. The service, called YouTube Music Key, will give subscribers ad-free and offline playback of YouTube videos, as well as audio-only material. Per the screenshots, users will be able to play music on their mobile phones "with or without video, in the background, or with your screen off"—all things that the single-tasking YouTube apps could not previously do. Subscribers will also be able to play music via "YouTube Mix," a recently-added feature that works similarly to radio stations on other streaming services. A YouTube Music Key subscription provides access to a 20-million-song catalog, roughly the same size as that of Spotify and Rdio, as well as a collection of material the app refers to as "concerts, covers, and remixes."