I want to project, in real-time, both audio and video from the Ubuntu desktop directly to my Roku Ultra so that it then projects it onto the TV and soundsystem already configured. This is primarily audio/video playback from a web browser such as Chrome or Firefox, but not limited to that (but I would be ok with it being limited to the Chrome browser). How can I do this?
I do not want to buy Chromecast as the answers at How can I use Chromecast? talk about low level details such as iptables which seems rather difficult. Cost is not the issue; I would buy the Chromecast device in a heartbeat if it wasn't for the perceived difficulties of configuration with Ubuntu that seems would occur.
The other reason is that I already have a Roku Ultra hooked up and working with my TV and sound system and it will complicate things to add yet another HDMI input into the setup.
Reference unanswered Screencast to a TV through a Roku question. But that question was old and this applies to Ubuntu 17.04 64bit.
Reference minimum system requirements for Chromecast for Linux: https://support.google.com/chromecast/answer/3209990 (basically mileage may vary depending upon Linux installation).
