Teletext (or "broadcast Teletext") is a television Commercially available since the late 1930s, the television set has become a common communications receiver in homes, businesses and institutions, particularly as a source of entertainment and news. Since the 1970s the availability of video cassettes, laserdiscs, DVDs and now Blu-ray discs, have resulted in the television set frequently being used information retrieval service developed in the United Kingdom The United Kingdom of Great Britain and Northern Ireland is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of Ireland, and many small islands. Northern Ireland is the only part of the UK with a land border, sharing it with in the early 1970s. It offers a range of text-based information, typically including national, international and sporting news, weather and TV schedules. Subtitle (or closed captioning Closed captioning is a term describing several systems developed to display text on a television or video screen to provide additional or interpretive information to viewers who wish to access it. Closed captions typically display a transcription of the audio portion of a program as it occurs , sometimes including non-speech elements) information is also transmitted in the teletext signal, typically on page 888[1] or 777.

Contents

History

Development

In c.1970 the BBC The British Broadcasting Corporation, usually referred to by its abbreviation "the BBC", is the world's largest broadcaster. In common with the public broadcasting organisations of many other European countries, it is funded yearly by a television licence fee. This is charged to all UK households owning a television capable of receiving had a brainstorming session in which it was decided to start researching ways to send closed captioning Closed captioning is a term describing several systems developed to display text on a television or video screen to provide additional or interpretive information to viewers who wish to access it. Closed captions typically display a transcription of the audio portion of a program as it occurs , sometimes including non-speech elements information to audience. As the Teledata research continued they became increasingly interested in using the same system for delivering any sort of information, not just closed captioning. Displaying subtitles requires limited bandwidth In computer networking and computer science, digital bandwidth, network bandwidth or just bandwidth is a measure of available or consumed data communication resources expressed in bit/s or multiples of it, at a rate of perhaps a few words per second. However, by combining even a slow data rate with a suitable memory, pages of information could be sent and stored in the TV for later recall.

Meanwhile the General Post Office The General Post Office was officially established in England in 1660 by Charles II and it eventually grew to combine the functions of both the state postal system and telecommunications carrier. Similar General Post Offices were established across the British Empire. In 1969 the GPO was abolished and the assets transferred to The Post Office, (whose telecommunications division later became British Telecom BT Group plc , is the privatised UK state telecommunications operator. It is the dominant fixed line telecommunications and broadband Internet provider in the United Kingdom. BT operates in more than 170 countries and over a third of its revenue now comes from its Global Services division) had been researching a similar concept since the late 1960s, known as Viewdata Viewdata is a Videotex implementation. It is a type of information retrieval service in which a subscriber can access a remote database via a common carrier channel, request data and receive requested data on a video display over a separate channel. The access, request and reception are usually via common carrier broadcast channels. This is in. Unlike Ceefax which was 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 their system, now known as Ceefax The system was announced in October 1972 and following test transmissions in 1973-1974 the Ceefax system went live on the 23 September 1974 with thirty pages of information. Developed by BBC engineers who were working on ways of providing televisual subtitles for the deaf, it was the first teletext system in the world. The then-BBC Director of ("see facts", the departmental stationery used the "Cx" logo), on various news shows. The Independent Television Authority (ITA) announced their 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 Prestel , the brand name for the UK Post Office's Viewdata technology, was an interactive videotex system developed during the late 1970s and commercially launched in 1979.

The systems were originally incompatible; Ceefax displayed 24 lines of 32 characters each, while ORACLE offered 22 lines of 40 characters each. In other ways the standards overlapped; for instance, both used 7-bit ASCII American Standard Code for Information Interchange , pronounced /ˈæski/ is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that work with text. Most modern character-encoding schemes—which support many more characters than did the characters and other basic details. In 1974 all the services agreed a standard for displaying the information. The display would be a simple 40 x 24 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 point in time was quite expensive).

Rollout

Following test transmissions in 1973–74, towards the end of 1974 the BBC news department put together an editorial team of nine, including and led by Editor Colin McIntyre, to develop a news and information service. Initially limited to 30 pages, the Ceefax service was later expanded to 100 pages and was launched formally in 1976. It was followed quickly by ORACLE and Prestel Prestel , the brand name for the UK Post Office's Viewdata technology, was an interactive videotex system developed during the late 1970s and commercially launched in 1979. Wireless World Wireless World was the pre-eminent British magazine for radio and electronics enthusiasts. It was one of the very few "informal" journals which were tolerated as a professional expense magazine ran a series of articles between November 1975 and June 1976 describing the design and construction of a Teletext decoder using mainly TTL Transistor–transistor logic is a class of digital circuits built from bipolar junction transistors (BJT) and resistors. It is called transistor–transistor logic because both the logic gating function (e.g., AND) and the amplifying function are performed by transistors (contrast this with RTL and DTL) devices, however development was limited until the first TV sets with built-in decoders started appearing in 1977.

By 1982 there were two million such sets, and by the mid-80s The 1980s or the Eighties, was the decade that ran from January 1, 1980 to December 31, 1989 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 over 15" (teletext is still usually only an option for smaller "portable" sets). From the mid-80s The 1980s or the Eighties, was the decade that ran from January 1, 1980 to December 31, 1989 both Ceefax and ORACLE were broadcasting several hundred pages on every channel, slowly changing them throughout the day.

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 revised in 1981 to become CEPT1, and again "World System B" (also known as WST, or World System Teletext).

North America

In the 1980s a similar system called Telidon was developed in Canada by the Department of Communications. It used a simple graphics language that would allow a more complex circuit in the TV to decode not only characters, but graphics as well. To do this, the graphic was encoded as a series of instructions (graphics primitives) like "polyline" which was represented as the characters PL followed by a string of digits for the X and Y values of the points on the line. This system was referred to as PDI (Picture Description Instructions). Later improved versions of Telidion were developed into NAPLPS.

Although there were numerous attempts to introduce NAPLPS services in North America, none of these were successful and eventually shut down. A number of special-purpose systems lived on for some time, similar to Prestel's lingering death, but the widespread rollout of internet access in the 1990s ended these efforts.

Technology

Teletext information is broadcast in the vertical blanking interval The vertical blanking interval , also known as the vertical interval or VBLANK, is the time difference between the last line of one frame or field of a raster display, and the beginning of the next. It is present in analog television, VGA, DVI and other signals. During the VBI the incoming data stream is not displayed on the screen. In cathode ray between image frames in a broadcast television signal. It is closely linked to the PAL PAL, short for Phase Alternating Line, is an analog television encoding system used in broadcast television systems in large parts of the world. Other common analogue television systems are SECAM and NTSC. This page primarily discusses the colour encoding system. See Broadcast television systems and analog television for additional discussion of broadcast system, and most PAL televisions include teletext decoders A decoder is a device which does the reverse of an encoder, undoing the encoding so that the original information can be retrieved. The same method used to encode is usually just reversed in order to decode. Other teletext systems have been developed to work with the SECAM SECAM, also written SÉCAM , is an analog color television system first used in France. A team led by Henri de France working at Compagnie Française de Télévision (later bought by Thomson) invented SECAM. It is, historically, the first European color television standard and NTSC NTSC is the analog television system that was used in most of the Americas, Japan, South Korea, Taiwan, Burma, and some Pacific island nations and territories (see map). NTSC is also the name of the U.S. standardization body that adopted the NTSC broadcast standard. The first black-and-white NTSC standard for broadcast was developed in 1941 and systems, but teletext failed to gain widespread acceptance in North America and other areas where NTSC is used. In contrast, teletext is nearly ubiquitous across Europe Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, and by the Caucasus Mountains to the southeast. Europe is washed upon to the north by the Arctic Ocean and as well as some other regions, with most major broadcasters providing a teletext service. Common teletext services include TV schedules, regularly updated current affairs and sport news, simple games (such as quizzes) and subtitling for deaf people or in different languages.

Teletext uses a numbered page metaphor to present its information, all of which is broadcast in sequence; when a viewer keys in a page number, the receiver waits until that information is broadcast again, typically within a few seconds, and retrieves it for display on-screen. More sophisticated systems use a buffer memory Random-access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order (i.e., at random). The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the to store some or all of the teletext pages, for instantaneous display.

Because of its presentation of user-requested graphic information, teletext can be seen as a predecessor of the World Wide Web The World Wide Web is a system of interlinked hypertext documents accessed via the Internet. With a Web browser, one can view Web pages that may contain text, images, videos, and other multimedia and navigate between them using hyperlinks. Using concepts from earlier hypertext systems, the World Wide Web was invented in 1989 by the English. Unlike the internet The Internet is a global system of interconnected computer networks that use the standardized Internet Protocol Suite . It is a network of networks that consists of millions of private and public, academic, business, and government networks of local to global scope that are linked by copper wires, fiber-optic cables, wireless connections, and, teletext is broadcast In computer networking, broadcasting refers to transmitting a packet that will be received by every device on the network. In practice, the scope of the broadcast is limited to a broadcast domain. Contrast unicasting and multicasting, so it does not slow down further as the number of users increase, although the greater number of pages, the longer one is likely to wait for each to be found in the cycle. For this reason, some pages (e.g. common index pages) are broadcast more than once in each cycle.

It has proved to be a reliable text news service during events such as the September 11, 2001 terrorist attacks The September 11 attacks were a series of coordinated suicide attacks by Al-Qaeda upon the United States on September 11, 2001. On that morning, 19 Al-Qaeda terrorists hijacked four commercial passenger jet airliners. The hijackers intentionally crashed two of the airliners into the Twin Towers of the World Trade Center in New York City, killing, during which the webpages of major news sites became inaccessible because of the high demand. Teletext is also used for carrying special packets interpreted by TVs and video recorders, containing information about channels, programming, etc. (see "Other Teletext-related services").

Although the term "teletext" tends to be used to refer to the PAL-based system, or variants, the recent availability of digital television Digital television is the sending and receiving of moving images and sound by discrete (digital) signals, in contrast to the analog signals used by analog TV has led to more advanced systems being provided that perform the same task, such as MHEG-5 MHEG-5, or ISO/IEC 13522-5, is part of a set of international standards relating to the presentation of multimedia information, standardised by the Multimedia and Hypermedia Experts Group . It is most commonly used as a language to describe interactive television services in the UK, and Multimedia Home Platform.

Data transmission

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 analogue TV signal but concealed from view in the Vertical Blanking Interval The vertical blanking interval , also known as the vertical interval or VBLANK, is the time difference between the last line of one frame or field of a raster display, and the beginning of the next. It is present in analog television, VGA, DVI and other signals. During the VBI the incoming data stream is not displayed on the screen. In cathode ray (VBI) television lines which do not carry picture information. The teletext signal is digitally coded as 45-byte packets, so resulting data rate is 7,175 bits per second In telecommunications and computing, bitrate is the number of bits that are conveyed or processed per unit of time per used lines (41 7-bit 'bytes' per line, on each of 25 frames per second).

A standard PAL signal contains 625 lines of video data per screen, broken into two "fields" containing half the lines of the whole image. Lines near the top of the screen are used to synchronize the display to the signal, and are not seen on-screen. CEPT1 hides the data in these lines, where they are not visible, using lines 6–22 on the first field and 318–335 on the second field. The system does not have to use all of these lines; a unique pattern of bits allows the decoder to identify which lines contain data. Some teletext services use a great number of lines, others, for reasons of bandwidth and technical issues, use fewer.

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 a 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 television checks if the page in memory is still up-to-date and updates it if necessary.

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 Closed captioning is a term describing several systems developed to display text on a television or video screen to provide additional or interpretive information to viewers who wish to access it. Closed captions typically display a transcription of the audio portion of a program as it occurs , sometimes including non-speech elements), 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. The standard was improved in 1976 to allow for improved appearance and the ability to individually select the color of each character from a palette of 8. 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 in 1981.

Decoders

The type of decoder circuitry is sometimes marked on televisions as CCT (Computer Controlled Teletext), or ECCT (Enhanced Computer Controlled Teletext).

Other systems

It has been suggested that this section be split into a new article. (Discuss)

A number of similar teletext services were developed in other countries, some of which attempted to address the limitations of the British-developed system, with its simple graphics and fixed page sizes.

France: Antiope

Main article: Antiope (teletext)

In France, where the SECAM SECAM, also written SÉCAM , is an analog color television system first used in France. A team led by Henri de France working at Compagnie Française de Télévision (later bought by Thomson) invented SECAM. It is, historically, the first European color television standard 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 standard teletext in 1991.

Canada:Telidon

Main article: Telidon

The CBC The Canadian Broadcasting Corporation , a Canadian crown corporation, is the country’s national public radio and television broadcaster. In French, it is called la Société Radio-Canada (Radio-Canada or SRC). The umbrella corporate brand is CBC/Radio-Canada ran a teletext service, IRIS, accessible only in Calgary Calgary is the largest city in the province of Alberta, Canada. Calgary CMA is the third most diverse in Canada in terms of visible minorities after Toronto and Vancouver when considering only CMAs with population greater than 200,000. It is located in the south of the province, in an area of foothills and high plains, approximately 80 km (50 mi), Toronto Toronto is the most populous city in Canada and the provincial capital of Ontario. It is located in Southern Ontario on the northwestern shore of Lake Ontario. With over 2.5 million residents, it is the fifth most populous municipality in North America. Toronto is at the heart of the Greater Toronto Area (GTA), and is part of a densely populated and Montreal. It ran from 1983 until about 1986, and used the Canadian-developed Telidon system, which was developed in 1980. Like Antiope, Telidon allowed significantly higher graphic resolution than standard teletext.

United States

A version of the European teletext standard designed to work with the NTSC NTSC is the analog television system that was used in most of the Americas, Japan, South Korea, Taiwan, Burma, and some Pacific island nations and territories (see map). NTSC is also the name of the U.S. standardization body that adopted the NTSC broadcast standard. The first black-and-white NTSC standard for broadcast was developed in 1941 and television standard used in North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and almost totally in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific Ocean; South America lies to the was first demonstrated in the USA in 1978 by American The United States of America is a federal constitutional republic comprising fifty states and a federal district. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D.C., the capital district, lie between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the television network CBS CBS Broadcasting Inc. is an American television network. The name is derived from the initials of the network's former name, Columbia Broadcasting System. The network is sometimes referred to as the Eye Network or more simply The Eye, in reference to the shape of the company's logo. It has also been called the Tiffany Network, which alludes to the, which decided to try both the British Ceefax The system was announced in October 1972 and following test transmissions in 1973-1974 the Ceefax system went live on the 23 September 1974 with thirty pages of information. Developed by BBC engineers who were working on ways of providing televisual subtitles for the deaf, it was the first teletext system in the world. The then-BBC Director of and French Antiope software for preliminary tryouts for a teletext service using station KMOX (now KMOV) in St. Louis, Missouri St. Louis is an independent city in the U.S. state of Missouri, located near the confluence of the Mississippi River and the Missouri River. St. Louis is at the center of the largest metropolitan area in Missouri. Sometimes written as Saint Louis, the city is named for King Louis IX of France. It is separate from St. Louis County, which borders as a testing ground. CBS decided on Antiope and mounted a large market trial in Los Angeles in partnership with NBC and PBS. Services premiered simultaneously on station KNXT (now KCBS-TV KCBS-TV is the flagship station of the CBS Television Network located in Los Angeles, California. KCBS-TV shares its offices and studio facilities with sister station KCAL-TV (channel 9) inside CBS Studio Center in the Studio City section of Los Angeles, and its transmitter is located atop Mount Wilson), KNBC and KCET (PBS) in Los Angeles Los Angeles is the largest city in the state of California and the second largest in the United States. Often abbreviated as L.A. and nicknamed The City of Angels, Los Angeles has an estimated population of 3.8 million and spans over 498.3 square miles (1,290.6 km2) in Southern California. Additionally, the Los Angeles metropolitan area is home to. All three services included an array of local news and information services. KCET's service also included service components for use in schools. Also in 1978, station KSL KSL-TV is an NBC affiliate in Salt Lake City, Utah that broadcasts locally in analog on VHF channel 5 and in digital on UHF channel 38. A large translator network extends coverage throughout the state and into portions of Arizona, Idaho, Nevada, and Wyoming. KSL-TV is owned by Bonneville International Corporation, which is in turn owned by The in Salt Lake City, Utah Salt Lake City is the capital and the most populous city of the U.S. state of Utah. The name of the city is often shortened to Salt Lake or SLC. Salt Lake City has a population of 181,698 as of July 1, 2008. The Salt Lake City metropolitan area spans Salt Lake, Summit and Tooele counties, and has a total estimated population of 1,115,692 as of, also premiered a teletext service using Ceefax.

Adoption in the United States was hampered due to a lack of a single teletext standard and consumer resistance to the high initial price of teletext decoders.

A significant reason for the demise of American teletext was when Zenith introduced built-in closed captioning Closed captioning is a term describing several systems developed to display text on a television or video screen to provide additional or interpretive information to viewers who wish to access it. Closed captions typically display a transcription of the audio portion of a program as it occurs , sometimes including non-speech elements decoders in TVs in the early '90s, as mandated by the FCC The Federal Communications Commission is an independent agency of the United States government, created, directed, and empowered by Congressional statute (see 47 U.S.C. § 151 and 47 U.S.C. § 154), and with the majority of its commissioners appointed by the current President. The FCC works towards six strategic goals in the areas of broadband,. It was not practical for Zenith to re-design their TV chassis models that previously had teletext decoder support to have both teletext and closed captioning support. So Zenith decided to drop the teletext features, therefore ending teletext service in the US in the early 1990s, considering Zenith was the only major manufacturer of teletext-equipped sets in America.

Nowadays, teletext or other similar technologies in the USA are practically non-existent, with the only technologies resembling such existing in the country being closed captioning Closed captioning is a term describing several systems developed to display text on a television or video screen to provide additional or interpretive information to viewers who wish to access it. Closed captions typically display a transcription of the audio portion of a program as it occurs , sometimes including non-speech elements, TV Guide On Screen, and Extended Data Services (XDS).

World System Teletext

Main article: World System Teletext

WST was also used for a short time in the USA, with services provided throughout the late 1970s and early 1980s by several regional American TV networks (such as the University of Wisconsin-Madison's Infotext service in the mid-1980s, which was carried on several TV stations across Wisconsin, and Agtext, provided by Kentucky Educational Television and carried on KET's stations, both services providing agriculturally oriented information) and major-market U.S. TV stations (such as Metrotext, which was formerly carried on station KTTV in Los Angeles, and KeyFax, formerly on WFLD in Chicago).

Zenith manufactured models of television sets in the USA in the 1980s, most notably their Digital System 3 line, that had built-in WST teletext decoders as a feature, much like most British/European TV sets. Teletext services in the USA like Electra could be received with one of these sets, but these were mostly more expensive higher-end sets offered by Zenith, possibly causing Electra (and American teletext in general) to never catch on with the public.

Australian company Dick Smith Electronics (DSE) also offered through their USA distributors a set-top WST teletext decoder kit. The kit used as its core the same teletext decoding module (manufactured by UK electronics company Mullard) installed in most British TV sets, with additional circuitry to adapt it for American NTSC video, and to utilize it in a separate set-top box.

The successor of WST in Europe and other countries is based on the Enhanced Teletext Specification from ETSI. ETSI EN300706 classifies Teletext in Level 1.5, Level 2.5 and Level 3.5. Level 1.5 covers all European languages plus Arabic and Hebrew. Level 2.5 provides display enhancements. Level 3.5 adds proportional fonts and high resolution graphics. Level 1.5 is the most popular Teletext standard in analogue and DVB transmissions in Europe. Sometimes it is called 'classical' Teletext. Level 3.5 was outperformed through the success of HTML and other modern standards.

Teletext differs in navigation methods provided by the broadcaster like FLOF (link information for a tree of pages) or TOP (Table of Pages).

NABTS

Main article: NABTS

Later, an official North American standard of teletext, called NABTS (North American Broadcast Teletext Specification) was developed in the early 1980s by Norpak, a Canadian company. NABTS provided improved graphic and text capability over WST, but was quite short-lived. This was mainly due to the expensive cost of NABTS decoders, costing in the thousands of dollars upon their release to the public. NABTS, however, was adopted for a short while by American TV networks NBC & CBS throughout the early-to-mid 80s, CBS using it for their short-lived ExtraVision teletext service, which premiered after the early Antiope & Ceefax trials by CBS & KNXT, and NBC, who had a NABTS-based service called NBC Teletext for a very short time in the mid-1980s. NBC discontinued their service in 1986 due to the cost of NABTS decoders not dropping to an affordable level for the consumer public.

The NABTS protocol received a revival of sorts in the late 90s, when it was used for the datacasting features of WebTV for Windows under Windows 98, and for Intel's now-defunct InterCast service (also for Windows as well), using a proper TV tuner card (such as the ATI All-In-Wonder or Hauppauge's Win-TV).

InterCast was a modern teletext-like system created by Intel in 1996, using a TV tuner card installed in a desktop PC running Windows with the InterCast Viewer software. The software would receive data representing HTML pages via the VBI (Vertical Blanking Interval) of a television channel's video, while displaying in a window in the InterCast software the TV channel itself. The HTML data received would then be displayed in another window in the Intercast software. It usually was extra supplemental information relevant to the TV program being viewed, such as extra clues for the viewer during a murder mystery show, or extra news headlines or extended weather forecasts during a newscast.

NBC, as well as The Weather Channel, CNN and M2 (now MTV2), utilized InterCast technology to complement their programming. InterCast, however, fell into disuse, and Intel discontinued support of InterCast a few years later.

Electra

Main article: Electra (teletext)

Perhaps the most prominent of American teletext providers was the Electra teletext service, which was broadcast starting in the early 1980s on the vertical blanking interval (VBI) of the American cable channel WTBS. Electra was owned and operated by Taft Broadcasting and Satellite Syndicated Systems (SSS). Electra ran up until 1993, when it was shut down due to Zenith, the prominent (and only) American TV manufacturer at the time offering teletext features in their sets decided to discontinue such features, as well as a lack of funding and lagging interest in teletext by the American consumer.

WaveTop

Main article: WaveTop

Another service in the USA similar in delivery and content to teletext was the WaveTop service, provided and operated by the Wavephore Corporation. It used the same types of InterCast-compatible TV tuner cards, and used an application that ran under Windows, like InterCast. In fact, WaveTop software was also bundled with TV tuner cards that had InterCast software bundled with them as well.

However, Wavetop was an independent service from InterCast, and wasn't a complementary service to a television program or channel like the latter. In fact, viewing television with a TV card was not possible while the WaveTop software was running, since the software utilized the TV tuner card as a full-time data receiver.

WaveTop provided content from several different providers in the form of HTML pages displayed in the WaveTop software, such as news articles from the New York Times, weather information provided by The Weather Channel, and sports from ESPN. It also delivered short video clips, usually commercials, that could be viewed in the software as well.

When it was in operation, WaveTop's data was delivered on the VBI of local public TV stations affiliated with the PBS network through their PBS National Datacast[2] division, that the TV card & WaveTop software tuned into to receive the service.

Guide+

Main article: Guide Plus

Yet another service in the U.S. that relied on data delivery via the VBI like teletext, was the Guide+ (Guide Plus, also referred to as GuidePlus+ as well) service provided and developed by Gemstar. There were several models of television sets made throughout the 90s by Thomson Consumer Electronics under the RCA and General Electric brands that had built-in Guide+ decoders. Guide+ was an on-screen interactive program guide that provided current TV schedule listings, as well as other information like news headlines. Some Guide+ equipped sets from RCA even had an IR-emitting sensor that could be plugged in to the back of the TV, to control a VCR to record programs which could be selected from the on-screen Guide+ listings. In some ways, this was very similar to the Video Programming by Teletext (VPT), Video Program System (VPS), and Programme Delivery Control (PDC) features of British/European teletext.

Guide+ was a free service, supported by advertisements displayed on-screen in the Guide+ menu and listing screens, not unlike banner ads displayed on web pages. Guide+ was delivered over the VBI of select local American TV stations.

Guide+ was discontinued by Gemstar in June 2004, and soon afterwards, Thomson dropped the Guide+ features from all RCA and GE television sets made afterward.

However, Guide+ in America has now been replaced by Gemstar with a similar service (delivered in the same fashion via VBI like Guide+), called TV Guide On Screen.[3] A small amount of televisions, DVD recorders, and digital video recorders are now being released with TV Guide On Screen capabilities. The Guide+ name & service is still used in Europe by Gemstar. (The same service is known in Japan as G-Guide).

Star Sight

Main article: Star Sight

Similar to Guide+ was Star Sight,[4] with its decoders built in to TVs manufactured by Zenith, Samsung, Sony, Toshiba, Magnavox, and others. This was an electronic program guide service similar to Guide+, but was a service that relied on monthly subscription fees paid by the user, not from revenue gathered from on-screen advertisements like Guide+. Star Sight discontinued operations on July 21, 2003, due to a lack of subscribers to the service. Star Sight's data was also delivered on the VBI of local PBS stations through the PBS National Datacast division, much like how WaveTop was delivered as mentioned previously in this article.

Later developments

While the basic teletext format has remained unchanged in more than 30 years, a number of improvements and additions have been made.

Video Program System

Main article: Video Program System

A closely related service is the Video Program System (VPS), introduced in Germany in 1985. Like teletext, this signal is also broadcast in the vertical blanking interval. It consists only of 32 bits of data, primarily the date and time for which the broadcast of the currently running TV programme was originally scheduled. Video recorders can use this information (instead of a simple timer) in order to automatically record a scheduled programme, even if the broadcast time changes after the user programmes the VCR. VPS also provides a PAUSE code; broadcasters can use it to mark interruptions and pause the recorders, however advertisement-financed broadcasters tend not to use it during their ad breaks. VPS (line 16) definition is now included in the PDC standard from ETSI.

Prestel

Main article: Prestel

Prestel was a British information-retrieval system based on Teletext protocols. However, it was essentially a different system, using a modem and the phone system to transmit and receive the data, comparable to systems such as France's Minitel. The modem was asymmetric, with data sent at 75-bit/s, and received 1200-bit/s. This two-way nature allowed pages to be served on request, in contrast to the TV-based systems' sequential rolling method. It also meant that a limited number of extra services were available such as booking event or train tickets and a limited amount of online banking.

Interactive teletext

Some TV channels offer a service called interactive teletext to remedy some of the shortcomings of standard teletext. To use interactive teletext, the user calls a special telephone number with a regular telephone. A computer then instructs the user to go to a certain teletext page which has been assigned to the customer for that session. Usually the page initially contains a menu with options and the user chooses among the options using the buttons on the telephone. When a choice has been made, the selected page is immediately broadcast and can be viewed by the user. This is in contrast with usual teletext where the customer has to wait for the selected page to be broadcast, because the pages are broadcast sequentially. This technology enables teletext to be used for games, chat, access to databases etc. It allows one to overcome the limitations on the number of available pages. On the other hand, only a limited number of users can use the service at the same time, since one page is allocated per user. Some channels solve this by taking into account where the user is geographically 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 don't 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. For these reasons, these services have largely been superseded by the World Wide Web.

Levels

These are taken from http://exampointers.com/teletext/teletext.phtml

Level Description
1 The initial specifications set out by the BBC, IBA, BREMA in September 1976.
2 Multi-language text, wider range of display attributes that may be non-spacing, wider range of colours and an extended mosaic pictorial set.
3 Dynamically Redefined Character Set (DRCS) allowing the display of non-Roman characters (e.g. Arabic and Chinese). Pictorial Graphic characters can also be defined.
4 Full geometric graphics. It needs computing power to generate the display from a sequence of drawing instructions. The colour palette has 250,000 shades.
5 Full-definition still pictures allows better quality than video cameras. Modulated onto a carrier. No noise added to the picture during transmission.

Level 2.5 teletext / Hi-Text

Comparison between Teletext Level 1.0 and Teletext Level 2.5.

A new graphic standard found its way to the European market around 2000: Level 2.5 or HiText. With Level 2.5 it is possible to set a background colour and have higher resolution text and images. However, very few television stations transmit their teletext in this new standard. One of the problems with Level 2.5 is that it often takes several transmission cycles before the higher resolution items show on the screen. In order to watch Level 2.5 teletext, a rather recent television set with a special decoder chip is required.

However, the system has not been widely implemented, with only a handful of European state broadcasters supporting it. Television stations which are known to transmit teletext in Level 2.5 include the Dutch public broadcaster NOS (background colour on all pages, and a test page with hi-res graphics) and the German ZDF and Bayerisches Fernsehen (completely backwards-compatible Level 2.5 teletext, with higher quality text and graphics on nearly all pages), as well as Arte and 3sat on some pages.

Digital teletext

NRK digital teletext

Digital television introduced "digital teletext" which, despite the previous teletext standard's digital nature, has entirely different standards, such as MHEG-5 and Multimedia Home Platform. However, standard teletext remains very popular. Some digital television platforms such as Sky Digital in the UK and Ireland incorporate separate teletext streams (used by the BBC from 1998 to 2004, and still used by Irish broadcaster RTÉ), which are provided to the television set in the normal analogue TV manner. Such emulation of analogue teletext on digital TV platforms may ensure its continued use for some time (particularly as there are no plans for an immediate transition to digital terrestrial transmission in some countries, such as Ireland). This emulation is only possible due to the DVB-TXT and DVB-VBI sub-standards of DVB, which allow a set-top box or integrated DVB TV to emulate the vertical blanking interval data in which teletext is carried.

Other Teletext-related services

Various other kinds of information are sent over the Teletext protocol. For instance, Programme Delivery Control signals—used by video recorders for starting/stopping recording at the correct time even during changes in programming—are sent as teletext packets. A similar, but different, standard Video Programming System is also used for this purpose.

Teletext pages may contain special packages allowing VCRs to interpret their contents. This is used in relation to the Video Programming by Teletext (also known as startext) system which allows users to program their videos for recording by simply selecting the program on a teletext page with a listing of programs.

Other standards define how special teletext packets may contain information about the name of the channel and the program currently being shown.

Cessation of service

A number of broadcast authorities have recently found fit to cease the transmission of teletext services, notably CNN International.[5] Most pages are still available, although they have not been updated since 31 October 2006.

The BBC has also announced that Ceefax is to be phased out in the run-up to the UK Digital Switchover in 2012. The full service is no longer carried on any digital services, although many channels on Sky still broadcast teletext subtitles and may still have a small number of active pages.[6] Teletext will end in each region after analogue broadcasts finish.

See also

References

  1. ^ Kawamoto, Kevin (2003). Digital Journalism: Emerging Media and the Changing Horizons of Journalism. Rowman & Littlefield. p. 32. ISBN 074252681X.
  2. ^ http://www.pbsnationaldatacast.com
  3. ^ http://www.gemstartvguide.com/whatwedo/tvgonscreen.asp
  4. ^ http://www.starsight.com
  5. ^ http://edition.cnn.com/cnntext/
  6. ^ http://teletext.mb21.co.uk/gallery/ceefax/end.shtml

External links

Look up teletext in Wiktionary, the free dictionary.
Broadcast video formats
Television
Analog
525 lines NTSC · NTSC-J · PAL-M
625 lines PAL · PAL-N/NC · PALplus · SECAM
Audio BTSC (MTS) · NICAM-728 · Zweiton (A2 / IGR) · EIAJ · SAP
Hidden signals Captioning · Teletext · CGMS-A · GCR · PDC · VBI · VEIL · VITC · WSS · XDS · EPG
Defunct systems Pre-1940 · Baird-Nipkow · 180 lines · 405 lines · 441 lines · 819 lines · MAC · MUSE
Digital
Interlaced SDTV (480i · 576i) · HDTV (1080i)
Progressive LDTV (240p · 288p · 1seg) · EDTV (480p · 576p) · HDTV (720p · 1080p)
MPEG-2 standards ATSC · DVB · ISDB · DMB-T/H
MPEG-4 AVC standards ATSC 2.0 (A/72) · DMB · DMB-T/H · DVB · SBTVD · 1seg
Audio AC-3 (5.1) · MPEG Multichannel · PCM · LPCM · AAC
Hidden signals Captioning · Teletext · CPCM · Broadcast flag · AFD · EPG
Digital cinema
Super Hi-Vision (2540p · 4320p) · DCI
Technical issues
14:9 compromise · Moving image formats · MPEG transport · Reverse Standards Conversion · Standards conversion · Video processing · Video on demand · HDTV blur

Categories: Teletext | BBC Research | Legacy systems

 

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