They say that but I have never gotten it to actually find my chromecast. My goto for casting is now https://github.com/keredson/gnomecast which just works.
If you're using Linux it might be good to check if it's compiled in correctly. I use VLC with Chromecast on Android, it works well enough.
That's what I use to cast Youtube video.
CTRL+N -> Paste -> Enter
Good to go
VLC can stream Youtube videos??
Yup! Just "open network stream" (ctrl-n) and paste the URL in. It can even save or convert them.