Chromecast Audio Stopped Working

Don't know why the audio on my Chromecast suddenly stopped working, but no resetting or restarting or replugging anything made any difference.  The volume wasn't set all the way down on the Chromecast, or the TV, or the app (which was YouTube, but I'm not sure that matters), and nothing was set to mute.

The thing that _did_ make a difference was changing a setting you can only get to via the Google Home app, so here are the details.

1. Open the "Google Home" app.
2. Select "devices" from the main menu.
3. Select "settings" from the popup menu for the "silent" Chromecast device.
4. Flip on the switch in the "Display" section labeled "Use 50Hz HDMI Mode"

I didn't bother to go find out why, but that got the sound working again.

BTW, the TV to which the Chromecast is connected is a little older but not so old that the default settings on Chromecast should prevent something as basic as _sound_!!!  Thanks a lot Google!!

Anyway, with all the useless forum post chatter out there suggesting "turning it off and on again", "The IT Crowd" style, I thought it might be useful to post an answer that actually did work.