What are caption, closed caption, and open caption?
The caption in a book is the text under a picture, captions on a TV screen are text located somewhere on the picture. Closed captions are captions that are hidden in the video signal and are invisible without a special decoder. The place they are hidden is called Line 21 of the vertical blanking interval. Open caption are captions that have been decoded, in other words, it cannot be turned off.
