Airplay lock screen closed captions button

I have Airplay implemented in an app and the streams I'm airplaying have closed captions embedded in them. The captions show when airplaying and in the app normally so I know there aren't any issues there. During Airplay when the device is on the lock screen there's a closed captions button on the right side but it's always disabled. Has anyone been able to figure out how to add functionality for that button?


Under the MPRemoteCommandCenter the only relevant options seem to be "enableLanguageOptionCommand" and "disableLanguageOptionCommand" but neither of those seem to do anything.