With a decoder, you can unscramble captions encoded to line 21 of the vertical blanking interval.
Open captions are a picture element.
They are captions that have been decoded already. They can t be switched on or off. We type the entire script into our captioning software, formatting as we go, along with any sound effects or music that the audience would need to know about. Then we go back through the program on a second pass to time each caption. Each caption is assigned a time to display and a time to erase, as well as a position on the screen.