closed captioning

"Closed" originally indicated that such captions were by default not visible until activated (opened) by the viewer turning them on, in contrast to "open captions" which are embedded in the video itself, visible to all.

closed captioning (uncountable)

1. The transcription, either verbatim or in edited form, of the dialogue and sometimes sound effects of a program, displayed onscreen and synchronized with the program, most frequently used by the deaf and language learners. Closed captions are encoded invisibly, and displayed by a decoder.
   • 2015 September 18, James O'Ehley, Erin Willard, The Take2 Guide to Lost: Mandatory television generated a sweeping dialogue … and here it is., Take2 Publishing, →ISBN:

     ... the closed captioning said, "There were no survivors of flight 815." [Note from Season 3: turns out it was "We're the survivors of flight 815."]

2. (formal) The analogue standard for this transcription, which analogue media like videotapes, laser discs, and cable television use, but also digital forms like satellite television and DVDs.^[1]

• close captioning