- Set-top box
A set-top box (STB) or set-top unit (STU) is a device that connects to a
televisionand an external source of signal, turning the signal into contentwhich is then displayed on the television screen.
All-Channel Receiver Actof 1962 required US television receivers to be able to tune the entire VHFand UHFrange (which in North Americawas NTSC-Mchannels 2 through 83 on 54 to 890 MHz), a set-top box known as a UHF converter would be installed at the receiver to shift a portion of the UHF-TV spectrum onto low-VHF channels for viewing. As some 1960s-era twelve-channel TV sets remained in use for many years, and Canadaand Mexicowere slower than the US to require UHF tuners to be factory-installed in new TV's, a market for these converters continued to exist for much of the 1970s. Cable televisionrepresented a possible alternative to deployment of UHF converters as broadcasts could be frequency-shifted to VHF channels at the cable head-end instead of the final viewing location. Unfortunately, cable brought a new problem; most cable systems could not accommodate the full 54-890 MHz VHF/UHF frequency range and the twelve channels of VHF space were quickly exhausted on most systems. Adding any additional channels therefore needed to be done by inserting the extra signals into cable systems on non-standard frequencies, typically either below VHF channel 7(midband) or directly above VHF channel 13(superband).
These frequencies corresponded to non-television services (such as two-way radio) over-the-air and were therefore not on standard TV receivers. Before cable-ready TV sets became common in the late 1980s, a set-top box known as a
cable converter boxwas needed to receive the additional analog cable TV channels and convert them to frequencies that could be seen on a regular TV. These boxes often provided a wired or wireless remote control which could be used to shift one selected channel to a low-VHF frequency (most often channels 3 or 2) for viewing. Block conversion of the entire affected frequency band onto UHF, while less common, was used by some models to provide full VCRcompatibility and the ability to drive multiple TV sets, albeit with a somewhat non-standard channel numbering scheme.
Newer television receivers greatly reduced the need for external set-top boxes, although cable converter boxes continue to be used to descramble premium cable channels and to receive
digital cablechannels, along with using interactive services like video on demand, pay per view, and home shoppingthrough television. Satellite and microwave-based services also require specific external receiver hardware, so the use of set-top boxes of various formats never completely disappeared.
digitalset-top boxes are available for receiving digital televisionbroadcasts 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).
United Kingdom, digital set-top boxes (often referred to as " digiboxes", after Sky Digital's trademark for their unit) are usually for digital terrestrial televisionthrough services such as Freeview, a service operated by the Freeview Consortium, or through digital satellite with BSkyBand 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 BBCwith BBCior Sky with Sky Active. Current Freeview set-top boxes and digital televisions are not capable of decoding the protocol DVB-T2that terrestrial High-definitionwill use in 2009, so viewers will need to purchase an HD receiver when the time comes.
Australiaset-top boxes are the principal means of receiving digital terrestrial broadcasts as comparably few television sets have in-built digital tuners. The Foxtelset-top boxes (including the Foxtel iQunit) are also used to receive subscription television from Foxtel. For HDTVreceiving they are using Beyonwizmanufactured media centers which came to market at March 2007.
United States, deployment of a very basic coupon-eligible converter boxis supported through a $40 federal subsidy to encourage viewers of over-the-air television to adopt ATSCstandards ahead of the shutdown of full-power analog broadcasts planned for February 17, 2009. These boxes are not readily available in Canadaand Mexico, where broadcasters are not yet required to transition to digital television, although ATSC-capable tuners are appearing in some new TV's and television-related products such as computer video capturecards, satellite receivers and DVD recorders.
Globally, some boxes also have a built-in
digital video recorder(or DVR) which often utilises the electronic programme guidescheduling data and records content to an internal hard drive.
Many TV signal sources
The signal source might be an
ethernetcable , a satellite dish, a coaxial cable(see cable television), a telephoneline (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, Internetwebpages, interactivegames, or other possibilities.
IPTVnetworks, the set-top box is a small computer providing two-way communications on an IP network, and decoding the video streaming media. IP set-top boxes have a built in home networkinterface which can be Ethernetor one of the existing wire home networking technologies such as HomePNA.
In the US and France, IPTV is being used by telephone companies (often on
ADSLor optical fibrenetworks) as a means to compete with traditional local cable televisionmonopolies.
Most of the set top boxes in France are distributed by the Internet providers and allow the consumer to have access to IPTV, VoIP, Internet and media centre functionalities.
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
A set-top box does not necessarily contain a tuner of its own. A box connected to a television (or VCR) set's
SCARTconnector is fed with the basebandtelevision signal from the set's tuner, and can ask the television to display the returned processed signal instead.
This SCART feature had been used for connection to analogue decoding equipment by
Pay TVoperators in Europe, and in the past was used for connection to teletextequipment before the decoders became built-in. The outgoing signal could 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 analogue pay-TV, this approach avoided the need for a second
remote control. The use of digital televisionsignals in more modern pay-TV schemes requires that decoding take place before the digital-to-analogue conversion step, rendering the video outputs of an analogue SCART connector no longer suitable for interconnection to decryption hardware. Standards such as DVB's Common Interfaceand ATSC's CableCARDtherefore use a PCMCIA-like card inserted as part of the digital signal path as their alternative to a tuner-equipped set-top box.
The distinction between external tuner or demodulator boxes (traditionally considered to be "set-top boxes") and storage devices (such as VCR, DVD or disc-based PVR units) is also blurred by the increasing deployment of satellite and cable tuner boxes with
hard discs, network or USBinterfaces built-in.
computer terminal-like capabilities, such as the WebTVthin-client, also fall into a grey area.
As complexity of the set-top box increases, the software quality practices of the industry become obvious and many systems have bugs; [cite web|title=The Chimera of Software Quality|url=http://www.computer.org/portal/site/computer/menuitem.eb7d70008ce52e4b0ef1bd108bcd45f3/index.jsp?&pName=computer_level1&path=computer/homepage/Aug07&file=profession.xml&xsl=article.xsl&;jsessionid=HlLtV9yJh01bCLb3GTQCZJL2VxGNxZPZLvJWXJpJwsjg2711JmW9 080322 computer.org] this is a particularly troublesome issue with
digital televisionapparatus being rushed to market before the government-mandated shutdown of full-power analogue television broadcasts. See Comparison of CECB unitsfor details on individual units.
However, users of computer-based solutions such as
Linux MCEand MythTVhave a very flexible list of possible features ranging from basic DVR-like functionality to features such as DVD copying, home automation, and house-wide music/video file playing. They also can fix any software bugs just by joining the development team.
Connectivity: RS-232, USB, Bluetoothand Wi-Fi
Digital television adapter(DTA)
Integrated Services Digital Broadcasting
Cable Converter Box
Media extender, Digital media receiveror HDD media player
* The [http://www.telematicsfreedom.org/en/projects/freedom-box Freedom Box] , a STB with Free Software: [http://www.freedombox.tv www.freedombox.tv]
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