Before the mid-1950s all British television sets tuned only VHF Band I channels. Since all 5 Band I channels were occupied by BBC transmissions, ITV would have to use Band III. This meant all the TV sets in the country would require Band III converters which converted the Band III signal to a Band I signal. By 1955, when the first ITV stations started transmitting, virtually all new British Televisions had 13-channel tuners, quickly making Band III converters obsolete.
Before the All-Channel Receiver Act of 1962 required US television receivers to be able to tune the entire VHF and UHF range (which in North America was NTSC-M channels 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 Canada and Mexico were 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 television represented 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 box was 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 4) for viewing. Block conversion of the entire affected frequency band onto UHF, while less common, was used by some models to provide full VCR compatibility 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 cable channels, along with using interactive services like video on demand, pay per view, and home shopping through 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.
Professional set-top boxes are referred to as IRDs or integrated receiver/decoders in the professional broadcast audio/video industry. They are designed for more robust field handling and rack mounting environments, and are also technically superior, IRDs have the distinct feature of outputting uncompressed SDI signals, unlike consumer STBs which don’t mostly because of copyright reasons.
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, providers such as SES Astra, Dish Network, DirecTV, or Astro may use digital set-top boxes.
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, for example via British Sky Broadcasting or Freesat, 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 BBC Red Button or Sky Digital with Sky Active. Current Freeview set-top boxes and digital televisions are not capable of decoding the protocol DVB-T2 required for terrestrial High-definition in 2009, so viewers may need to purchase a new HD receiver.
In Australia, set-top boxes are the principal means of receiving digital terrestrial broadcasts, as comparably few television sets have in-built digital tuners. The Foxtel set-top boxes (including the Foxtel iQ unit) are also used to receive subscription television from Foxtel. For HDTV receiving, Foxtel is using Beyonwiz-manufactured media centers, which came to market in March 2007.
In the United States, deployment of a very basic coupon-eligible converter box had been supported through a $40 federal subsidy to encourage viewers of over-the-air television to adopt ATSC standards before the shutdown of full-power analog broadcasts. (This shutdown, originally planned for February 17, 2009, was re-scheduled for June 12, 2009, due to a concern that an insufficient number of affected viewers would be ready. The coupon programme ended in July 2009. Also, the transition of over-the-air channels from analog to digital should not be confused with similar digital conversions on cable networks.) These boxes were slow to be made available in Canada and Mexico, where broadcasters were not required to transition to digital television in 2009. While ATSC-capable tuners are beginning to appear in some new TVs and television-related products such as computer video capture cards, satellite receivers, and DVD recorders in these countries, many models do still require an external converter to receive DTV.
The signal source might be an ethernet cable, 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.
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. IP set-top boxes have a built in home network interface which can be Ethernet or one of the existing wire home networking technologies such as HomePNA or the ITU-T G.hn standard, which provides a way to create a high-speed (up to 1 Gigabit/s) Local area network using existing home wiring (power lines, phone lines, and coaxial cables).
In France, Internet providers distribute most of the set top boxes and allow the consumer to have access to IPTV, VoIP, Internet, and media center functionalities.
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, possibly helping the adoption of the term digibox.
In Europe, 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.
This SCART feature had been used for connection to analogue decoding equipment by pay TV operators in Europe, and in the past was used for connection to teletext equipment 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 television signals 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 Interface and ATSC's CableCARD therefore 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 USB interfaces built-in.
Set-top boxes were also made to enable closed captioning on older sets in North America, before this became a mandated inclusion in new TV sets. Some have also been produced to mute the audio (or replace it with noise) when profanity is detected in the captioning, where the offensive word is also blocked. Some also include a V-chip that allows only programmes of some television content ratings. A function that limits children's time watching TV or playing video games may also be built in, though some of these work on the mains electricity rather than the video signal.
As complexity of the set-top box increases, the software quality practices of the industry become obvious and many systems have bugs. However, users of software-based solutions such as Windows Vista's Media Center and MythTV have 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.