What kind of closed captioning is supported by standard definition NTSC video?
NTSC video supports CEA-608 closed captioning (sometimes referred to as line 21 captioning), with up to 4 channels of caption data (CC1-CC4), although typically only two are used at a time (CC1 & CC2, or CC1 & CC3). NTSC video can also have burned-in subtitles or open captions, but there is no way to turn those off once they’ve been burned into the video.
