videotext

Videotext is a term applied to a family of information services that embed textual and simple graphical data within a television broadcast signal. The earliest implementations emerged in the late 1960s and early 1970s, predominantly in Europe, and they used the spare time slots of analogue television broadcasting to transmit page-based information to compatible set‑top receivers. The most well‑known of these services is the British Teletext system introduced by the BBC in 1974, which became a model for similar services across continental Europe and in other countries, including the German Das Fernsehen, the French Teletext, and the Latvian Videotext. In North America, a analogous service called Information Cable Service (ICS) appeared in the United States during the 1980s.

The core technology relied on a form of line‑repeating modulation. Textual characters were encoded as 7‑bit ASCII or a proprietary character set and transmitted in a 40×25 or larger grid. The data stream was embedded in the line‑time allocation of the vertical blanking interval or in overscan areas, avoiding interference with the visible picture. A number of standard video lines were dedicated each frame to transmit the character bitmap and a page number, allowing the receiver to assemble a virtual page from successive frames. When not in use, the transmitter sent a blank line, which also served to displace the synchronization tone.

Because the signal was inaccessible to the consumer’s regular television, dedicated decoders or integrated receivers were needed. These decoded the character data, displayed it on a screen, and allowed user input for page navigation via a remote or on‑screen keys. The service was popular for news summaries, weather forecasts, sports scores, and commercial information. Its decline coincided with the transition to digital broadcasting, which offered higher‑capacity data streams and enabled more complex services such as set‑top box data and interactive television. Still, videotext was a pioneer in the field of broadcast‑based information delivery and influenced subsequent developments in on‑screen information, DVB‑T, and datacasting.