"Album artwork, for the streaming age". This is how Spotify describes the Canvas option: the super short films that you occasionally see in the mobile Spotify app with a few larger artists. It is still a beta test, but the ability to add these 'looping visuals' has been made more widely available through a few weeks via Spotify for Artists.
If you want to be one of the first to use Canvas, you can sign up for a place on the waiting list via this link: https://canvas.spotify.com
[Update] The sign up link has since been removed by Spotify. It is not yet known when Spotify Canvas can be used by all artists.