webkitHasClosedCaptions and webkitClosedCaptionsVisible are on HTMLMediaElement, but should be on HTMLVideoElement. It doesn't make sense for an audio element to have captions, so this interface should be limited to video.
<rdar://problem/16193927>
These attributes have been on HTMLMediaElement since 2009, and are widely used on a number of large sites. I am not sure it is worth moving them to HTMLVideoElement.
FWIW, text tracks are on HTMLMediaElement.
Closing.