A: There are two types of closed captioning − live and prerecorded.
You see live realtime captions during sporting events and newscasts programs that are happening live. Live programming is captioned by specially trained realtime captioners who listen to a program as it is airing and write or respeak what they hear, often at speeds up to 250 words per minute. These words feed into customized software which transmits the captions to display them live on your television screen.
Prerecorded captions are created by highly trained captioners who listen to the program audio, transcribe words, sound effects, and music to give you a full sense of what is happening in the audio track of the program. Captions are timed to sync with the program audio and placed to match the speakers on the screen. The program is then watched all the way through to ensure accuracy in the timing, transcription, and overall readability.