Several options exist when it comes to casting media content from Linux to a Chromecast.

Casting the full desktop

You can use Google Chrome (audio is not supported).

Alternatively, you can use Firefox with fx_cast.

Casting a browser tab

Same as above, use Chrome.

Casting a file

Two options:

• Either VLC 3.0 (but it does not support subtitles yet)
• Or castnow

With VLC, open it and go to Preferences. Open the tab 'Video' and set Output to 'X11 video output (XCB)'. Then, try to find your Chromecast in the menu Video > Renderer > Scan. If unsuccessful, close it and run vlc from the command line:

 vlc --sout="#chromecast{ip=192.168.1.X}" myfile.mp4

Make sure you replace the IP with the one allocated to the Chromecast.

Another option is to use castnow:

npm install -g castnow
castnow --address '192.168.1.X' myfile.mp4 --subtitles mysubs.srt

Enjoy!