You probably have come across vertical videos which showing two giant black bars on both sides which make many people dislike that kind of videos, yet only the hilarious ones still get popular and trending. Well, you won't have to feel awkward watching them videos any more, because YouTube has come up with the solutions.
Now on if someone uploads vertical or square videos it will automatically fill the screen of the watchers mobile devices, but you need to upload the video as it is. That means you can't burn anything on the side of those videos. If you do then the video watcher might not see in full screen.
This system still not good for desktop though. It will show you giant bars on both sides if you watch on desktop. But if you watch it on mobile device it will show full screen. You can take the video above as an example.