Download Mkchromcast for Ubuntu
There are multiple versions of Mkchromecast available for Ubuntu. The one you choose to use depends entirely on your set-up. In general, for most users, the catch-all installer linked below should work just fine.
Download Mkchromcast .deb file
You can also install this by using terminal:
sudo apt install mkchromecast
Install Mkchromecast through Ubuntu Software. This ensures all of the dependencies (and there are a few) are installed at the same time, including python-pychromecast, the core library that powers this app.
If you plan on also casting audio streams from desktop apps you will need to install pavucontrol.