Teletext

Teletext, or broadcast teletext, is a standard for displaying text and rudimentary graphics on suitably equipped television sets. Teletext sends data in the broadcast signal, hidden in the invisible vertical blanking interval (VBI) area at the top and bottom of the screen. The teletext decoder in the television buffers this information as a series of "pages", each given a number. The user can display chosen pages using their remote control. Teletext was uni-directional- the user could only receive, and not respond or send data of their own.

Teletext was created in the United Kingdom in the early 1970s by John Adams, Philips' lead designer for video display units to provide closed captioning to television shows for the hearing impaired. Public teletext information services were introduced by major broadcasters in the UK, starting with the BBC's Ceefax service in 1974. It offered a range of text-based information, typically including news, weather and TV schedules. Similar systems were subsequently introduced by other television broadcasters in the UK and mainland Europe in the following years.

Teletext inspired the later Videotex system that enabled bi-directional communication in a format later recognised as a prototype of the world wide web. Implementations included the French Minitel and Prestel, introduced by the UK's General Post Office. Prestel used Teletext's display standards but instead ran over bi-directional telephone lines using modems.

Teletext formed the basis for the World System Teletext standard (CCIR Teletext System B), an extended version of the original system. This standard saw widespread use across Europe starting in the 1980s, with almost all television sets including a decoder. Other standards were developed around the world, notably NABTS (CCIR Teletext System C) in the United States, Antiope (CCIR Teletext System A) in France and JTES (CCIR Teletext System D) in Japan, but these were never as popular as their European counterpart and most closed by the early 1990s.

Most European teletext services continued to exist in one form or another until well into the 2000s when the expansion of the Internet precipitated a closure of some of them. However, many European television stations continue to provide teletext services and even make teletext content available via web and dedicated apps.

The recent availability of digital television has led to more advanced systems being provided that perform the same task, such as MHEG-5 in the UK, and Multimedia Home Platform.

Teletext is a means of sending text and simple geometric shapes to a properly equipped television screen by use of one of the "vertical blanking interval" lines that together form the dark band dividing pictures horizontally on the television screen. Transmitting and displaying subtitles was relatively easy. It requires limited bandwidth; at a rate of perhaps a few words per second. However, it was found that by combining even a slow data rate with a suitable memory, whole pages of information could be sent and stored on the TV for later recall.

In the early 1970s, work was in progress in Britain to develop such a system. The goal was to provide UK rural homes with electronic hardware that could download pages of up-to-date news, reports, facts and figures targeting UK agriculture. The original idea was the brainchild of Philips (CAL) Laboratories in 1970.