Types of closed captioning and subtitling

There are two broad classes of captioning

The caption - in the form of an electrical signal - is buried on line 21 of the vertical blanking interval in the video signal. Government regulations have established the encoding method, available characters and caption layout (32 characters in four of 15 lines).

The viewer must have a decoder - now automatically built into all new televisions sets in the US - which interprets the information on line 21 and displays the caption on the viewer's screen.

Closed captioning is typically displayed as white block letters on a black background.

Subtitling

In subtitling no decoder is necessary, because the subtitle is permanently burned into the video. But rather than the rigid structure mandated for closed captioning, subtitling allows the captioner to use any font style, font colors, graphics, or background.

As a rule, though, subtitling uses proportionally spaced fonts displayed on a transparent background.

One variation on subtitling is used on DVDs. The viewer can choose from as many as 32 channels of subtitling. And, like closed captioning, the viewer can turn the captions off.

Types of Captioning

There are two broad classes of captioning