When viewing some files with quicktime on my retina MacBook Pro (Sierra 10.12.6), I can view it on Apple TV and the sound works fine.
However some files produce the following behaviour:
- Select Apple TV / Airplay in Quicktime. Video appears on TV, but no sound (on TV or laptop).
- I click on the Sound Pref Pane and select Apple TV as the output. There is a slight pause, then the video switches back to the laptop, and the sound now comes out of the Apple TV
This is a similar problem to those reported here and here, but it's not exactly the same because the solutions suggested don't work for me, and this is consistently happening but only for a subset of my video files.
NB this exact same behaviour also happens when watching youtube videos in Safari.