YouTube is adding more features for Android Google Cardboard users. In a post today, Google announced what it calls VR videos, which from what we can tell are stereoscopic videos meant to be experienced through Google Cardboard, although it's possible to drag the point of view around on a flat screen. YouTube has supported 360-degree videos since March, and Google Cardboard supported playing them back as of May, but it wasn't pitching those specifically as "virtual reality."
There's a playlist of new VR videos on YouTube, including a Hunger Games trailer, and Google explains the basic idea in a short video here. Anyone with an Android phone and a Cardboard viewer should be able to get the update and start watching them in the headset. Users of the Jump camera rig setup can also produce their own VR videos.
Google is also picking some much lower-hanging fruit with this update. It's creating what it bills as a "virtual movie theater" for traditional flatscreen YouTube videos. Users can select an option to watch any video in Google Cardboard, then put it in a viewer and see it in what will appear as a very large screen in a dark room. It's essentially the same approach as tools like VR Cinema. Except that in this case, it'll (ideally) be much more painless to make the jump from watching video to watching it in VR.