Closed-captioning Captions transmitted in the form of a code. Nearly all North American TVs carry decoder chips as standard equipment now. Before built-in decoders were required by law, you needed an external decoder, which are still available in declining supply. Open-captioning Captions that are an indelible part of the picture and are always visible. Captions denote sound effects meaningful to the narrative or to understanding the program.
Captions move to indicate the position of the speaker.
Subtitles are a translation, ignore sound effects, and are always located in the same spot on-screen. Audio description Rendering visual details in a spoken narrative. In audio description, a special narrator succinctly describes action, settings, facial expressions, onscreen graphics, clothing, and other visual details. Narrators typically speak during pauses in dialogue or at other appropriate moments, but sometimes they narrate over dialogue, over music, and so on. The Common Issues homepage tells more.