MP4 Subtitles don't stream from Itunes to ATV 3

I have a handful of Japanese movies in MP4 format.
I used subler to add english SRT subtitles in passthru.

When I play the file in itunes I can turn the subtitles on and off, but when I use Airplay the subtitles disappear and the option to turn them on no longer works. I've googled to no avail.

Is there a way to hardcode them so they are always on or another way to get them to work on my apple tv?

Why are you using AirPlay? Add your movies to iTunes and stream them from your Mac (or PC) using Home Sharing.

https://support.apple.com/kb/ht4620