How does closed captioning work?
Closed captioning is a digital signal included with the main TV
signal that a closed captioning decoder decodes, turning that into
letters and displaying it on your screen. Many TV's have closed
captioning decoders built in.
If you're ever watching TV and at the top you see some little
white lines, some short, some longer, that's actually the closed
captioning signal you're seeing on your screen. Most TV's don't
display it because of what they call, `overscan` but on some older
TV's when the TV ages, it'll become apparent.
If I remember correctly, closed captioning is included on line
18 of the video signal.
Closed captioning is a text version of a television show that can
be read on screen.