Better URL handling is a planned feature, but right now the web app only accepts YouTube urls with this format (example): https://www.youtube.com/watch?v=1v8mDF57WYs
This is also something that will be fixed in a future update.
Reload the page. In the future, there will be a way to "x" out of the video.
Not right now, but this will be an upcoming feature.
Also in the future ;)