Closed captions
From MythTV Official Wiki
Q: Is it possible to get closed captions to be functional with a pvr 500 using the ivtv module?
A: Not yet (13 Aug 2006) but support for VBI data is allegedly working for NTSC tuners in ivtv development drivers. So - eventually it'll be supported in released drivers (if an ivtv developer could throw some light on this it'd be helpful)