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A set-top box (STB) or set-top unit (STU) is a device that connects to a
television and an external source of signal, turning the signal into content
which is then displayed on the television screen.
History
Before cable-ready TV sets, a set-top box known as a cable converter box was
used to receive analog cable TV channels and convert them to video that could be
seen on a regular TV. Nowadays, cable converter boxes are used to descramble
premium cable channels and to receive digital cable channels.
Many TV signal sources
The signal source might be an ethernet cable (see triple play), a satellite
dish, a coaxial cable (see cable television), a telephone line (including DSL
connections), Broadband over Power Line, or even an ordinary VHF or UHF antenna.
Content, in this context, could mean any or all of video, audio, Internet
webpages, interactive games, or other possibilities.
Ambiguities in the definition
With the advent of flat panel televisions set-top boxes are now deeper in
profile than the tops of most modern TV sets. Because of this set-top boxes are
often placed beneath televisions and the term set-top box has become something
of a misnomer.
A set-top box does not necessarily contain a tuner of its own. A box connected
to a television (or VCR) set's SCART connector is fed with the baseband
television signal from the set's tuner, and can ask the television to display
the returned processed signal instead.
The SCART feature is used for decoding Pay TV in Europe, and in the past was
used for decoding teletext, before decoders became built-in.
The outgoing signal can be of the same nature as the incoming signal, or RGB
component video, or even an "insert" over the original signal, thanks to the
"fast switching" feature of SCART. In case of Pay TV, this approach avoids the
need for a second remote control.
Digital television
Special digital set-top boxes are available for receiving digital television
broadcasts on TV sets that do not have a built in digital tuner. In the case of
direct broadcast satellite (mini-dish) systems such as SES Astra, Dish Network,
or DirecTV, the set-top box is an integrated receiver/decoder (or IRD).
In the United Kingdom, digital set-top boxes (often referred to as digiboxes,
after Sky Digital's trademark for their unit) are usually for digital
terrestrial television through services such as Freeview, a service operated by
the Freeview Consortium, or through digital satellite with BSkyB and also with
digital cable. They are used to access television as well as audio and
interactive services through the "Red Button" promoted by broadcasters such as
the BBC with BBCi or Sky with Sky Active.
In Australia set-top boxes are the principal means of receiving high-definition
television terrestrial broadcasts as comparably few television sets have
in-built HDTV tuners. The Foxtel set-top boxes (including the Foxtel iQ unit)
however are not HDTV-ready as of late 2007.
Globally, some boxes also have a built-in digital video recorder (or DVR) which
often utilises the electronic programme guide scheduling data and records
content to an internal hard drive.
IPTV
In IPTV networks, the set-top box is a small computer providing two-way
communications on an IP network, and decoding the video streaming media, using a
new technology called POE (Power over Ethernet), which eliminates the need for
any coaxial cabling. Using the new POE technology allows for instant updates to
boxes, making for a more manegable and reliable system.
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