Quicktime could not find Apple TV, but Elmedia Player streams fine.

I have 2 main types of files (mp4 and mkv) that I stream on Apple TV via airplay. I use Elmedia Player to stream the mkv files from my iMac, and until recently, I used Quicktime to stream the mp4 files to my Apple TV. For some unknown reason, Quicktime has been unable to connect to my Apple TV. It gives me this message.

The Elmedia Player works fine. If I open the mp4 file with Elmedia Player, it will stream to Apple TV. How do I get Quicktime to stream mp4 files to my apple tv?