Letterbox bars (at the top and bottom) and side bars may be added to a show by the broadcaster, by the TiVo DVR, or by your TV. In some cases, it may be difficult to determine the source of the bars in order to determine how to eliminate them.
Set the TiVo DVR’s Letterbox Color to gray. From Settings & Messages > Settings > Video > Letterbox Color. Since most broadcasters add black bars, making the TiVo DVR bars gray will help you determine the source of the bars.
Make sure your TV Aspect Ratio is set correctly. From Settings & Messages > Settings > Video > TV Aspect Ratio.
Check your TV’s owner’s manual for information about how it may be adding letterbox or side bars to the picture.