At my school we do live video announcements (and occasional live events) to YouTube. We also have TVs in the hallways that display photos and announcement slides using Chromecasts that automatically display images from a Google Photos album.
So of course we want to tie these together and display live video on those TVs when we are broadcasting.
The best way I've come up with to accomplish this is to use AirParrot for screen mirroring to multiple receivers and Automator on a Mac, or perhaps AutoHotkey on a Windows machine, to automate it all. (edit: Unfortunately it seems that the new version of AirParrot doesn't have Automator/Applescript support, but it's something they are working on.)
First set up a computer to automatically launch the streaming URL (https://www.youtube.com/channel/[channelID]/live) at a certain time each day. There are instructions for Automator, but I'm sure it could be accomplished a number of other ways such as with a Windows scheduled task. Of course if you wanted to get fancy, you could use the YouTube Live API to launch the URL whenever the broadcast is live.
The next step is to have AirParrot send that YouTube broadcast to all of the Chromecasts. I haven't tried automating this part yet, but AirParrot supports Automator (on a Mac) and if you're on a Windows machine then AutoHotkey can click and type for you. I really like how AirParrot connects so smoothly and mirrors displays or programs to multiple receivers, including Chromecasts and Apple TVs.
As an aside note, through Humble Bundle you can pick up two copies of AirParrot 2 for about $1USD until the end of February 2017. This is about 95% off the regular price. While you're there check out some of the other bundles, they have great taste in games and such, and amazing deals. This is not a paid endorsement.
So I'm hoping that soon I'll have this all automated so that people can watch the live video announcements in the hallways as well as in the classrooms.