Teletext
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
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 VCR's 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 [4]. 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 [5]. Teletext will end in each region after analogue broadcasts finish.
[
See also
- List of teletext services
- Digital terrestrial television
- Digitiser
- Electronic program guide
- Multimedia Home Platform
- NAPLPS
- NABTS
- Programme Delivery Control
- Videotex
[
References
 |
This article does not cite any references or sources. (August 2006) Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. |
[
External links
- Broadcast Teletext Specification, September 1976 (HTML; graphics missing)
- Broadcast Teletext Specification, September 1976 (scanned copy of original document, MS-Word and Postscript files)
- History of Teletext
- History of Ceefax
- Teletext Then and Now
- Teletext Then and Now Gallery - pictures of teletext services in the UK, Ireland and around the world
- Timeline of Telecommunications, with some entries on teletext
- The page for the now-defunct Star Sight service
- A page on teletext in the USA
- Downloadable "Enhanced Teletext specification" (ETSI.org)
- Teletext Decoder Certification
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||
For more information review our copyright contact and privacy policy.