Teletext subtitling, also known as closed subtitling, involves adding a stream of character codes representing the subtitle characters into the broadcast video signal. Suitably equipped TV sets or receivers can be set to decode the data and display the subtitles on screen.
Historicaly this data is added into the VBI area of the video signal and this method is still used in analogue services. More recently the same data can be carried as a separate data stream in a DVB multiplex or as part of the VANC data in an HD digital video signal.
Teletext can be used to transmit data in addition to subtitles including information pages, clocks and private data. The individual characters that make up a Teletext subtitle are represented by single codes which are then transmitted to the receiving equipment. The Teletext receiver then looks up the codes in an on-board table and displays the required characters on screen. Teletext is not suitable for all languages and the character sets installed in the receivers can also be specific to a country or region.