chapter markers & AppleTV 4th gen

I recently purchased an AppleTV 4th generation. I have a library of m4a files that I
tagged with mp3tag. With previous AppleTV generation I was able to see the chapter markers,
but with the new device the chapter markers are gone. I did some research and others said I
need to specify a language for the chapters track. I have set the language tag to "eng", but it
did not fix the problem.

Any ideas?

Chapters are not supported by MP3tag.