I wonder if we should be concerned about videos that are on the page but not visible?  E.g., in a tabbed one-page webapp there might be a video in a hidden tab that is visible to the other person, that could be played but is not visible.

Arguably both decisions are fair (to play or not to play), and playing is simpler, so I suppose that's an okay default, but worth thinking about in the future.  Or maybe worth a comment.