You can cast subtitles with any on demand show which has subtitles available.
When your show starts, an S or Ⓢ symbol will appear alongside the video controls if subtitles are available for that show. Press the S button to switch the subtitles on and off. Your preference will be remembered for next time.
Subtitles are not currently available for any live shows but this is a feature we’re working on and they will be available soon.