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Vertical
Blanking
Interval (VBI), Teletext & MINITEL
(Last updated in 2012)
To understand Teletext, it’s
helpful to understand television's Vertical Blanking Interval (VBI).
VBI - (Vertical
Blanking Interval) - The Vertical Blanking Interval (VBI), also
known as the vertical interval or VBLANK, is the time between the last
line of a frame, or field and the beginning of the next frame, or
field. It's present in analog television, VGA, and DVI
signals. During this very short time, the data transmitted is not
displayed on the screen (Wikipedia). Typically the VBI is expressed as the
number of horizontal lines scanned. The VBI signal however must be too
weak to adversely affect the electron beams carrying the main picture
signal. (Analog TV signals need to cause 0-beam intensity during the
VBI to ensure that the picture is not affected.) Fortunately it's
possible for circuitry in the TV to detect and interpret the weak VBI
signals.
The analog TV format for North and Central America, as
well as Japan, is set by the National Television Standards Committee
(NTSC.) They specified that 525 horizontal lines be scanned on
the TV picture (though only 486 are visible.) They also specified
that the 'frame refresh rate' be 60 Hz. For the VBI they
specified that 40 horizontal lines (which are part of the 525 just
mentioned,) be VBI lines.
The VBI can carry data such as closed
captioning or Teletext. (See
Teletext definition further below.) ATVEF standards allow the
VBI to be used for enhanced/interactive
TV content. However,
the limited bandwidth available in the VBI severely restricts the
amount of data that can be transmitted.
Work done to develop closed captioning was essential to
the discovery of how to use the VBI. The VBI was an unused portion of
the analog television signal for years. The VBI broadcasts closed
captioning and other data, including that which is HTML-based, to
television sets, set-top
boxes (connected to TVs,)
as well as computers with TV
tuner cards, DVR cards etc. Also
with the right hardware and software, including an appropriate video
capture card, you can send the VBI signal from your computer to your TV.
Originally, the VBI
was used for hardly anything, then in cooperation with ABC (the
network) the National Bureau of Standards funded early experiments to
send the time out over the television signal. Their experiments
failed to provide the desired results so ABC suggested text captions
instead. This, and other experiments throughout the 70's on programs
like the "Mod Squad", led to engineering partnerships with the Public
Broadcasting Service (PBS). With PBS, ABC developed early decoders (a
function of a set-top box or the like) to interpret the VBI signal and
display captioning on the screen. But, it wasn't until the public
television station WETA encoded and broadcasted data successfully on
line 21 of the VBI, that closed captioning became possible on a mass
scale.
After the government deregulated the VBI signal, two-way
enhanced platforms like Microsoft's WebTV for Windows, Intel's Intercast, Wink and
WorldGate were developed to provide graphical and informational
enhancements to their viewers. Europe's VBI Teletext can offer a great
many pages and is accessible using a remote control. Teletext and
Digital Teletext are the best Mailing List of the commercial use of the
VBI. Europe embraced VBI interactivity a lot more than America and
that's one reason the Internet initially didn't grow as fast in Western
Europe as in the States. Literally Teletext had already given many the
interactivity of the Internet, unlike in the States. In fact in France
alone, over 20 million users had access to over 25,000 online services
(early 2001 statistic.) In the UK, around 60% of televisions in
use, or being sold, have VBI viewing capacity (early 2001 statistic).
(That includes those that view the VBI through decoders connected to
TVs, and those that have TVs with the decoder built into it).
The limited amount of information that can be carried in
the VBI means that a page of standard teletext might take several
seconds to load. The low resolution of existing TVs means that
information displayed is often not readable when in small text sizes
(below about 14 point).
Digital Teletext
(Last updated in 2012)
(The pioneering
interactive TV service Teletext is being largely halted in 2009.
Teletext's owners Daily Mail & General Trust (DMGT), continue with
Teletext Holidays, which (at the time of this writing) has its own
Freeview channel, as well as related sites teletextholidays.co.uk,
thisistravel.co.uk & villarenters.co.uk.
Teletext is most popular in Europe and originated in
Great Britain. Teletext is information and data made available via the
unused VBI lines of the PAL & SECAM broadcasts. The display can
also be altered (made smaller) so that viewing of this information is
clearer. (Teletext is primarily used in Europe but teletext is
available in various parts of the States.) Teletext can be interactive
and was the most popular form of early interactive television. It's
been stated that every line of the television can carry Teletext
Teletext and Digital Teletext consists of information,
such as news and sports, viewed on a compatible television set, or via
a set-top box attached to a standard TV set. Its roots lie in the 70s,
when the BBC and Oracle started the first test services. A new and
improved version of Teletext was released in 1997. Some Teletext set-top
boxes/built-ins have the ability to cache multiple pages
of Teletext at a time for faster access times. (One such system is
known as FasText. Fastext is a shortcut key that allows quick,
one-button access to a particular page.) Microsoft incorporated
Teletext capacity into it's update of Windows 98, the "Windows
Millennium Edition".
As well as news and sports information, Teletext contains
financial information, such as the latest stock prices, also recipes,
entertainment listings, advertisements, movie schedules and reviews,
music and TV program reviews, additional information on various TV
programs, and more. Teletext also broadcasts subtitles (closed
captions) for various programs, and news bulletins that are overlaid on
top of the TV picture. The incorporation of Digital TVs by consumers
will not end Teletext use we're told but instead will enhance it. The MHEG-5 hypermedia standard has been picked as the
standard authoring language for Teletext services using the digital
terrestrial platform in the U.K. Also see MINITEL further below.
The teletext system
was initially devised in the early 1970's by engineers from the BBC and
the Independent Broadcasting Authority (IBA). The BBC version of
teletext was originally called "Teledata" but later it was changed to
"Ceefax". It was based on a Teletext page containing 24 rows of 32
characters per row while the IBA version, called ORACLE (Optional
Reception of Announcements by Coded Line Electronics,) allowed 22 rows
of 40 characters per row. The Teletext system became operational in
1976.
(Reference.)
Like Teletext, Viewdata (sometimes referred to as
Videotex) provided a public information system, but there are
significant differences between it and Teletext. This interactive
videotex system was developed in the late 1970s by the
telecommunications department of the Post Office. It became operational
in 1979. Later the name was changed to Prestel. (Reference.)
Antiope
Digital Teletext
Superteletext – A digital teletext browser core.
Teletext TVs - Televisions with the built-in ability to be teletext
compatible.
What
is MINITEL?
(Written in 2001)
MINITEL - A
largely French interactive television/telephone collection of networks
& service providers. MINITEL is a form of "Teletext". MINITEL
is composed of 25,000+ service providers. There are 20 million
plus French users, along with many, many thousands outside France. You
can book ferry rides, check tolls and road conditions, book ski
accommodations, check your bank accounts, pay holiday homes'
gas/electricity bills, book trains, tele-shopping with your credit card
and much, much more.
In the early 1980s, the French Government stated its
desire to start two experimental VIDEOTEX sites, one was in Paris, and the other
was in Ille et Villaine, situated in between Cotes du Nord, and
Mayenne. The idea was to use a low cost terminal in conjunction with a
computerized French Phone Directory. At the end of 1982, the Télétel
network had been introduced and there was a launch of the first service
to go live - the 11 or Onze.
In France you pay to look at these services by paying for
it on your phone bill.
Internet Appliance type devices are often used to access
the MINITEL system as well as Kiosks. Its existence is one reason
why Europeans were slower to jump on the Internet bandwagon than
Americans. Many Europeans already had Internet type capacities
that Americans only discovered with the Internet.
Minitel (France)
¤¤¤¤¤¤¤
What
is Internet Protocol over
the Vertical Blanking Interval?
IPVBI - (Internet
Protocol over the Vertical Blanking Interval) – The transmission of
data (including video & audio) over the VBI bands of
television. www.ietf.org
¤¤¤¤¤¤¤
What
is an Internet Appliance?
Internet
Appliance - (a.k.a. Information
Appliance, Intelligent Appliance, Net Appliance, Net Device)
–
These include intelligent kitchen appliances, intelligent
phones, portable
media devices, PDAs, home networked computers and
other devices connected to
the Internet so people can access and operate home equipment from a
distance. Teletext systems, (particularly MINITEL)
often
use Internet
Appliances.
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