Under normal conditions, the vertical blanking interval containing the captioning information is invisible to television viewers (this is why it's called closed-captioning). However, a person may activate the closed-captioning feature found on most modern television receivers, thereby causing the program's spoken-word dialogue to be displayed onscreen. Certain video presentations (now very rare) actually have the captions permanently burned into the video instead of encoded in the vertical blanking interval; this is known as open-captioning.

Since 1993, when the Television Decoder Circuitry Act became U.S. law, manufacturers of most television receivers sold in the U.S. have been required to include closed captioning. High-definition TV sets, receivers, and tuner cards are also covered, though the technical specifications are different.

Because closed-captions of live performances are done by live stenographers using court-reporting or stenomask equipment, they often include spelling errors or misquotes. The reasons for mistakes in other forms of captioning will differ, but can include low competence on the part of the captioner, changing the audio after the captioning is done, or technical failure.