I can't play music from the Music app on my Mac to my AppleTV.

I bought a new AppleTV to replace an old one. The Music app on my Mac could play music from my local music library to the AppleTV. With the new AppleTV, the Music app recognizes the AppleTV, but sound won't play. Sometimes it will and sometimes it won't. Sometimes it will start playing and then quit, while the Music app thinks it is still playing (and I can switch back to the computer sound and it works). If I redirect the computer's sound from the menu bar, it works. Why won't the Music app work with the AppleTV?