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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.
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 .
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.
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.
In 1971, CAL engineer John Adams created a design and proposal for UK broadcasters. His configuration contained all the fundamental elements of classic teletext including pages of 24 rows with 40 characters each, page selection, sub-pages of information and vertical blanking interval data transmission. A major objective for Adams during the concept development stage was to make teletext affordable to the home user. In reality, there was no scope to make an economic teletext system with 1971 technology. However, as the low cost was essential to the project's long-term success, this obstacle had to be overcome.
Meanwhile, the General Post Office (GPO), whose telecommunications division later became British Telecom, had been researching a similar concept since the late 1960s, known as Viewdata. Unlike Teledata, a one-way service carried in the existing TV signal, Viewdata was a two-way system using telephones. Since the Post Office owned the telephones, this was considered to be an excellent way to drive more customers to use the phones.
In 1972, the BBC demonstrated its system, now known as Ceefax ("seeing facts", the departmental stationery used the "Cx" logo), on various news shows. The Independent Television Authority (ITA) announced its own service in 1973, known as ORACLE (Optional Reception of Announcements by Coded Line Electronics). Not to be outdone, the GPO immediately announced a 1200/75 baud videotext service under the name Prestel (this system was based on teletext protocols, but telephone-based).
The TV-broadcast based systems were originally incompatible; Ceefax displayed pages of 24 lines with 32 characters each, while ORACLE offered pages of 22 lines with 40 characters each. In other ways the standards overlapped; for instance, both used 7-bit ASCII characters and other basic details. In 1974, all the services agreed on a standard for displaying the information. The display would be a simple grid of text, with some graphics characters for constructing simple graphics. The standard did not define the delivery system, so both Viewdata-like and Teledata-like services could at least share the TV-side hardware (which at that time was quite expensive).
Wireless World magazine ran a series of articles between November 1975 and June 1976 describing the design and construction of a teletext decoder using mainly TTL devices; however, development was limited until the first TV sets with built-in decoders started appearing in 1977.
The "Broadcast Teletext Specification" was published in September 1976 jointly by the IBA, the BBC and the British Radio Equipment Manufacturers' Association. The new standard also made the term "teletext" generic, describing any such system. The standard was internationalised as World System Teletext (WST) by ITU-R.
Other systems entered commercial service, like ORACLE (first broadcast on the ITV network in 1978) and Prestel (in 1979).
Teletext became popular in the United Kingdom when Ceefax, Oracle and the British government promoted teletext through a massive campaign in 1981.
By 1982, there were two million such sets, and by the mid-1980s they were available as an option for almost every European TV set, typically by means of a plug-in circuit board. It took another decade before the decoders became a standard feature on almost all sets with a screen size above 15 inches (Teletext is still usually only an option for smaller "portable" sets). From the mid-1980s, both Ceefax and ORACLE were broadcasting several hundred pages on every channel, slowly changing them throughout the day.
In 1986, WST was formalised as an international standard as CCIR Teletext System B. It was also adopted in many other European countries.
In France, where the SECAM standard is used in television broadcasting, a teletext system was developed in the late 1970s under the name Antiope. It had a higher data rate and was capable of dynamic page sizes, allowing more sophisticated graphics. It was phased out in favour of World System Teletext in 1991.
In North America, NABTS, the North American Broadcast Teletext Specification, was developed to encoding NAPLPS teletext pages, as well as other types of digital data. NABTS was the standard used for both CBS's ExtraVision and NBC's NBC Teletext services in the mid-1980s.
Japan developed its own JTES teletext system with support for Chinese, Katakana and Hiragana characters. Broadcasts started in 1983 by NHK.
In 1986, the four existing teletext systems were adopted into the international standard ITU-R 653 (now ITU-R BT.653) as CCIR Teletext System A (Antiope), B (World System Teletext), C (NABTS) and D (JTES).
In 2023, the Dutch public broadcasting organization NOS replaced the original underlying system for teletext that had been in use since the 1980s with a new system. The reason behind the replacement was that the original Cyclone system became harder to maintain over the years and the NOS even had to consult sometimes retired British teletext experts to deal with issues. For example, a recent issue was that a Windows update was incompatible with the old Cyclone system. Since NOS Teletekst is still popular in the Netherlands (with 3.5 million people using it weekly on televisions and 1 million people using it weekly as app on other devices), NOS decided to build a new modern underlying system to replace Cyclone. To make Teletekst look visually the same as on the old Cyclone system, the developers of the new system made use of reverse engineering.
| +Teletext systems used in various countries/geographical areas in 1998 !Country/geographical area !Teletext standard !Remarks | ||
| Australia | B | |
| Belgium | A, B | |
| Brazil | C (modified) | |
| Canada | C | |
| China | B | Extended character set with Chinese characters |
| Colombia | A | |
| Denmark | B | |
| Finland | B | |
| France | A | |
| Germany | B | |
| India | A | |
| Ireland | B | RTÉ Aertel launched in 1987 on RTE 1 and 2. Other services on launched later on TV3 and TG4 |
| Italy | B | |
| Japan | JTES | |
| Malaysia | B | |
| Netherlands | B | |
| New Zealand | B | |
| Norway | B | |
| Poland | B | Experimental |
| Singapore | B | |
| South Africa | B | Character set with variations to also accommodate Afrikaans |
| Spain | B | Character set with variations to accommodate Basque language, Catalan language and Galician |
| Sweden | B | |
| Turkey | B | Character set with variations to accommodate Turkish language |
| Ukraine | B | |
| United Kingdom | B | |
| United States | NABTS | |
| Yugoslavia | B | Extended character set |
As the web matured, many broadcasters ceased broadcast of Teletext — CNN in 2006 and the BBC in 2012. In the UK the decline of Teletext was hastened by the introduction of digital television, though an aspect of teletext continues in closed captioning. In other countries the system is still widely used on standard-definition DVB broadcasts.
A number of broadcast authorities have ceased the transmission of teletext services.
Subtitling still continues to use teletext in Australia, New Zealand, and Singapore with some providers switching to using image-based DVB subtitling for HD broadcasts. New Zealand solely uses DVB subtitling on terrestrial transmissions despite teletext still being used on internal SDI links.
Teletext is also used for carrying special packets interpreted by TVs and video recorders, containing information about subjects such as channels and programming.
Teletext allows up to eight 'magazines' to be broadcast, identified by the first digit of the three-digit page number (1–8). Within each magazine there may theoretically be up to 256 pages at a given time, numbered in hexadecimal and prefixed with the magazine number – for example, magazine 2 may contain pages numbered 200-2FF. In practice, however, non-decimal page numbers are rarely used as domestic teletext receivers will not have options to select hex values A-F, with such numbered pages only occasionally used for 'special' pages of interest to the broadcaster and not intended for public view.
The broadcaster constantly sends out pages in sequence in one of two modes: Serial mode broadcasts every page sequentially whilst parallel mode divides VBI lines amongst the magazines, enabling one page from each magazine to be broadcast simultaneously. There will typically be a delay of a few seconds from requesting the page and it being broadcast and displayed; the time is entirely dependent on the number of pages being broadcast in the magazine (parallel mode) or in total (serial mode) and the number of VBI lines allocated. In parallel mode, therefore, some magazines will load faster than others.
Teletext in the PAL B system can use the VBI lines 6–22 in first half image and 318–334 in the other to transmit 360 data bits including clock run-in and framing code during the active video period at a rate of using binary NRZ line coding.ETS 300 706, Enhanced Teletext specification (May 1997) The amplitude for a "0" is black level ±2% and a "1" is 66±6% of the difference between black and peak white level. The clock run in consist of of "10" and the framing code is "11100100". The two last bits of the clock-run in shall start within from the negative flank of the line synchronization pulse.
The rate is , i.e. the TV line frequency. Thus 625 × 25 × 444 = 6,937,500 Hz. Each bit will then be 144 ns long. The bandwidth amplitude is 50% at 3.5 MHz and 0% at 6 MHz. If the horizontal sync pulse during the vertical synchronization starts in the middle of the horizontal scan line. Then first interlace frame will be sent, otherwise, if vertical synchronization let the full video line complete the second interlace frame is sent.
Like EIA-608, bits are transmitted in the order of LSB to MSB with Parity bit coding of 7-bit character codes. However unlike EIA-608, the DVB version is transmitted the same way. For single bit error recovery during transmission, the packet address (page row and magazine numbers) and header bytes (page number, subtitle flag, etc.) use hamming code 8/4 with extended packets (header extensions) using hamming 24/18, which basically doubles the bits used.
The commonly used standard B uses a fixed PAL subtitling bandwidth of 8,600 (7,680 without page/packet header) bits/s per field for a maximum of 32 characters per line per caption (maximum three captions – lines 19 – 21) for a 25 frame broadcast. While the bandwidth is greater than EIA-608, so is the error rate with more bits encoded per field. Subtitling packets use a lot of non-boxed spacing to control the horizontal positioning of a caption and to pad out the fixed packet. The vertical caption position is determined by the packet address.
| + Teletext binary NRZ encodings |
| 97 |
| 32 |
| 40 |
| 31 |
| 5.734 |
| 32 |
| 100% cosine roll-off |
In the case of the Ceefax and ORACLE systems and their successors in the UK, the teletext signal is transmitted as part of the ordinary analog TV signal but concealed from view in the Vertical Blanking Interval (VBI) television lines which do not carry picture information. The teletext signal is digitally coded as 45-byte packets, so the resulting rate is 7,175 bits per second per line (41 7-bit 'bytes' per line, on each of 25 frames per second).
A teletext page comprises one or more frames, each containing a screen-full of text. The pages are sent out one after the other in a continual loop. When the user requests a particular page the decoder simply waits for it to be sent, and then captures it for display. In order to keep the delays reasonably short, services typically only transmit a few hundred frames in total. Even with this limited number, waits can be up to 30 seconds, although teletext broadcasters can control the speed and priority with which various pages are broadcast.
Modern television sets, however, usually have built-in memory, often for a few thousand different pages. This way, the teletext decoder captures every page sent out and stores it in memory, so when a page is requested by the user it can be loaded directly from memory instead of having to wait for the page to be transmitted. When the page is transmitted again, the decoder updates the page in memory.
The text can be displayed instead of the television image, or superimposed on it (a mode commonly called mix). Some pages, such as subtitles (closed captioning), are in-vision, meaning that text is displayed in a block on the screen covering part of the television image.
The original standard provides a monospaced 40×24 character grid. Characters are sent using a 7-bit codec, with an 8th bit employed for error detection.
The standard was improved in 1976 (World System Teletext Level 1) to allow for improved appearance and the ability to individually select the color of each character from a palette of eight. The proposed higher resolution Level 2 (1981) was not adopted in Britain (in-vision services from Ceefax & ORACLE did use it at various times, however, though even this was ceased by the BBC in 1996), although transmission rates were doubled from two to four lines a frame.
The most common implementation is Level 1.5, which supports languages other than English. Virtually any TV sold in Europe since the 1990s has support for this level. After 1994 some stations adopted Level 2.5 Teletext or Hi-Text, which allows for a larger color palette and higher resolution graphics.
The proposed higher content levels included geometrically specified graphics (Level 4), and higher-resolution photographic-type images (Level 5), to be conveyed using the same underlying mechanism at the transport layer. No TV sets currently implement the two most sophisticated levels.
Besides the hardware implementations, it is also possible to decode teletext using a PC and video capture or DVB board, as well as recover historical teletext from self-recorded VHS tapes.O'Malley, James (2016). The Teletext Salvagers: How VHS is bringing teletext back from the dead, PC Pro, March 4, 2016
The Acorn BBC Micro's default graphics mode (mode 7) was based on teletext display, and the computer could be used to create and serve teletext-style pages over a modem connection. With a suitable adapter, the computer could receive and display teletext pages, as well as Telesoftware over the BBC's Ceefax service, for a time. The Philips P2000 home computer's video logic was also based on a chip designed to provide teletext services on television sets.
Usually, the page initially contains a menu of options, from which the user chooses using the telephone keypad. When a choice has been made, the selected page is immediately broadcast for viewing. This is in contrast with usual teletext where the user has to wait for the selected page to be broadcast.
This technology enables teletext to be used for games, online chat, access to databases, etc. It overcomes the limitations on the number of available pages. On the other hand, only a limited number of users can be serviced at the same time, since one page number is allocated per user. Some channels solve this by taking into account where the user is calling from and by broadcasting different teletext pages in different geographical regions. In that way, two different users can be assigned the same page number at the same time as long as they do not receive the TV signals from the same source. Another drawback to the technology is the privacy concerns in that many users can see what a user is doing because the interactive pages are received by all viewers. Also, the user usually has to pay for the telephone call to the TV station.
In cooperation with Finnish state television Yle, the Museum of Teletext Art has been presenting and archiving international teletext art online, on air and in exhibitions since 2014.
A number of teletext services have been syndicated to web viewers, which mimic the look and feel of broadcast teletext. RSS feeds of news and information from the BBC are presented in Ceefax format in the web viewer.
In 2016, the Teefax teletext service was launched in the United Kingdom to coverage by the BBC, ITV and others. Using a Raspberry Pi computer card as a set-top box, it feeds its service to standard televisions. Teefax content is a mix of crowdsourcing, syndication and contributions from media professionals who contributed heavily to broadcast teletext services. Teefax is also syndicated to a web viewer.
Other countries use the same teletext streams as before on DVB transmissions, due to the DVB-TXT and DVB-VBI sub-standards. Those allow the emulation of analogue teletext on digital TV platforms, directly on the TV or set-top box, or by recreating analog output, reproducing the vertical blanking interval data in which teletext is carried.
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