Digital television

Digital television (DTV) is the transmission of television signals, including the sound channel, using digital encoding, in contrast to the earlier television technology, analog television, in which the video and audio are carried by analog signals. It is an innovative advance that represents the first significant evolution in television technology since color television in the 1950s.[1] Digital TV transmits in a new image format called HDTV (high definition television), with greater resolution than analog TV, in a wide screen aspect ratio similar to recent movies in contrast to the narrower screen of analog TV. It makes more economical use of scarce radio spectrum space; it can transmit multiple channels, up to 7, in the same bandwidth occupied by a single channel of analog television,[2] and provides many new features that analog television cannot. A transition from analog to digital broadcasting began around 2006 in some countries, and many industrial countries have now completed the changeover, while other countries are in various stages of adaptation. Different digital television broadcasting standards have been adopted in different parts of the world; below are the more widely used standards:

  • Digital Video Broadcasting (DVB) uses coded orthogonal frequency-division multiplexing (OFDM) modulation and supports hierarchical transmission. This standard has been adopted in Europe, Singapore, Australia and New Zealand.
  • Advanced Television System Committee (ATSC) uses eight-level vestigial sideband (8VSB) for terrestrial broadcasting. This standard has been adopted by six countries: United States, Canada, Mexico, South Korea, Dominican Republic and Honduras.
  • Integrated Services Digital Broadcasting (ISDB) is a system designed to provide good reception to fixed receivers and also portable or mobile receivers. It utilizes OFDM and two-dimensional interleaving. It supports hierarchical transmission of up to three layers and uses MPEG-2 video and Advanced Audio Coding. This standard has been adopted in Japan and the Philippines. ISDB-T International is an adaptation of this standard using H.264/MPEG-4 AVC that been adopted in most of South America and is also being embraced by Portuguese-speaking African countries.
  • Digital Terrestrial Multimedia Broadcasting (DTMB) adopts time-domain synchronous (TDS) OFDM technology with a pseudo-random signal frame to serve as the guard interval (GI) of the OFDM block and the training symbol. The DTMB standard has been adopted in the People's Republic of China, including Hong Kong and Macau.[3]
  • Digital Multimedia Broadcasting (DMB) is a digital radio transmission technology developed in South Korea[4][5][6] as part of the national IT project for sending multimedia such as TV, radio and datacasting to mobile devices such as mobile phones, laptops and GPS navigation systems.

History

Digital TV's roots have been tied very closely to the availability of inexpensive, high performance computers. It wasn't until the 1990s that digital TV became a real possibility.[7]

In the mid-1980s, as Japanese consumer electronics firms forged ahead with the development of HDTV technology, and as the MUSE analog format was proposed by Japan's public broadcaster NHK as a worldwide standard, Japanese advancements were seen as pacesetters that threatened to eclipse U.S. electronics companies. Until June 1990, the Japanese MUSE standard—based on an analog system—was the front-runner among the more than 23 different technical concepts under consideration. Then, an American company, General Instrument, demonstrated the feasibility of a digital television signal. This breakthrough was of such significance that the FCC was persuaded to delay its decision on an ATV standard until a digitally based standard could be developed.

In March 1990, when it became clear that a digital standard was feasible, the FCC made a number of critical decisions. First, the Commission declared that the new ATV standard must be more than an enhanced analog signal, but be able to provide a genuine HDTV signal with at least twice the resolution of existing television images. Then, to ensure that viewers who did not wish to buy a new digital television set could continue to receive conventional television broadcasts, it dictated that the new ATV standard must be capable of being "simulcast" on different channels. The new ATV standard also allowed the new DTV signal to be based on entirely new design principles. Although incompatible with the existing NTSC standard, the new DTV standard would be able to incorporate many improvements.[7]

The final standard adopted by the FCC did not require a single standard for scanning formats, aspect ratios, or lines of resolution. This outcome resulted from a dispute between the consumer electronics industry (joined by some broadcasters) and the computer industry (joined by the film industry and some public interest groups) over which of the two scanning processes—interlaced or progressive—is superior. Interlaced scanning, which is used in televisions worldwide, scans even-numbered lines first, then odd-numbered ones. Progressive scanning, which is the format used in computers, scans lines in sequences, from top to bottom. The computer industry argued that progressive scanning is superior because it does not "flicker" in the manner of interlaced scanning. It also argued that progressive scanning enables easier connections with the Internet, and is more cheaply converted to interlaced formats than vice versa. The film industry also supported progressive scanning because it offers a more efficient means of converting filmed programming into digital formats. For their part, the consumer electronics industry and broadcasters argued that interlaced scanning was the only technology that could transmit the highest quality pictures then (and currently) feasible, i.e., 1,080 lines per picture and 1,920 pixels per line. Broadcasters also favored interlaced scanning because their vast archive of interlaced programming is not readily compatible with a progressive format.[7]

Inaugural launches

DirecTV in the U.S. launched the first commercial digital satellite platform in May 1994, using the Digital Satellite System (DSS) standard.[8][9] Digital cable broadcasts were tested and launched in the U.S. in 1996 by TCI and Time Warner.[10][11] The first digital terrestrial platform was launched in November 1998 as ONdigital in the United Kingdom, using the DVB-T standard.[12]

Technical information

Formats and bandwidth

Digital & Analog TV screen quality comparison-1
Comparison of image quality between ISDB-T (1080i broadcast, top) and NTSC (480i transmission, bottom)

Digital television supports many different picture formats defined by the broadcast television systems which are a combination of size and aspect ratio (width to height ratio).

With digital terrestrial television (DTT) broadcasting, the range of formats can be broadly divided into two categories: high definition television (HDTV) for the transmission of high-definition video and standard-definition television (SDTV). These terms by themselves are not very precise, and many subtle intermediate cases exist.

One of several different HDTV formats that can be transmitted over DTV is: 1280 × 720 pixels in progressive scan mode (abbreviated 720p) or 1920 × 1080 pixels in interlaced video mode (1080i). Each of these uses a 16:9 aspect ratio. HDTV cannot be transmitted over analog television channels because of channel capacity issues.

SDTV, by comparison, may use one of several different formats taking the form of various aspect ratios depending on the technology used in the country of broadcast. In terms of rectangular pixels, NTSC countries can deliver a 640 × 480 resolution in 4:3 and 854 × 480 in 16:9, while PAL can give 768 × 576 in 4:3 and 1024 × 576 in 16:9. However, broadcasters may choose to reduce these resolutions to reduce bit rate (e.g., many DVB-T channels in the United Kingdom use a horizontal resolution of 544 or 704 pixels per line).[13]

Each commercial broadcasting terrestrial television DTV channel in North America is permitted to be broadcast at a bit rate up to 19 megabits per second. However, the broadcaster does not need to use this entire bandwidth for just one broadcast channel. Instead the broadcast can use the channel to include PSIP and can also subdivide across several video subchannels (a.k.a. feeds) of varying quality and compression rates, including non-video datacasting services that allow one-way high-bit-rate streaming of data to computers like National Datacast.

A broadcaster may opt to use a standard-definition (SDTV) digital signal instead of an HDTV signal, because current convention allows the bandwidth of a DTV channel (or "multiplex") to be subdivided into multiple digital subchannels, (similar to what most FM radio stations offer with HD Radio), providing multiple feeds of entirely different television programming on the same channel. This ability to provide either a single HDTV feed or multiple lower-resolution feeds is often referred to as distributing one's "bit budget" or multicasting. This can sometimes be arranged automatically, using a statistical multiplexer (or "stat-mux"). With some implementations, image resolution may be less directly limited by bandwidth; for example in DVB-T, broadcasters can choose from several different modulation schemes, giving them the option to reduce the transmission bit rate and make reception easier for more distant or mobile viewers.

Receiving digital signal

There are several different ways to receive digital television. One of the oldest means of receiving DTV (and TV in general) is from terrestrial transmitters using an antenna (known as an aerial in some countries). This way is known as Digital terrestrial television (DTT). With DTT, viewers are limited to channels that have a terrestrial transmitter in range of their antenna.

Other ways have been devised to receive digital television. Among the most familiar to people are digital cable and digital satellite. In some countries where transmissions of TV signals are normally achieved by microwaves, digital MMDS is used. Other standards, such as Digital multimedia broadcasting (DMB) and DVB-H, have been devised to allow handheld devices such as mobile phones to receive TV signals. Another way is IPTV, that is receiving TV via Internet Protocol, relying on digital subscriber line (DSL) or optical cable line. Finally, an alternative way is to receive digital TV signals via the open Internet (Internet television), whether from a central streaming service or a P2P (peer-to-peer) system.

Some signals carry encryption and specify use conditions (such as "may not be recorded" or "may not be viewed on displays larger than 1 m in diagonal measure") backed up with the force of law under the World Intellectual Property Organization Copyright Treaty (WIPO Copyright Treaty) and national legislation implementing it, such as the U.S. Digital Millennium Copyright Act. Access to encrypted channels can be controlled by a removable smart card, for example via the Common Interface (DVB-CI) standard for Europe and via Point Of Deployment (POD) for IS or named differently CableCard.

Protection parameters for terrestrial DTV broadcasting

Digital television signals must not interfere with each other, and they must also coexist with analog television until it is phased out. The following table gives allowable signal-to-noise and signal-to-interference ratios for various interference scenarios. This table is a crucial regulatory tool for controlling the placement and power levels of stations. Digital TV is more tolerant of interference than analog TV, and this is the reason a smaller range of channels can carry an all-digital set of television stations.

System Parameters
(protection ratios)
Canada [13] USA [5] EBU [9, 12]
ITU-mode M3
Japan & Brazil [36, 37][14]
C/N for AWGN Channel +19.5 dB
(16.5 dB[15])
+15.19 dB +19.3 dB +19.2 dB
Co-Channel DTV into Analog TV +33.8 dB +34.44 dB +34 ~ 37 dB +38 dB
Co-Channel Analog TV into DTV +7.2 dB +1.81 dB +4 dB +4 dB
Co-Channel DTV into DTV +19.5 dB
(16.5 dB[15])
+15.27 dB +19 dB +19 dB
Lower Adjacent Channel DTV into Analog TV −16 dB −17.43 dB −5 ~ −11 dB[16] −6 dB
Upper Adjacent Channel DTV into Analog TV −12 dB −11.95 dB −1 ~ −10[16] −5 dB
Lower Adjacent Channel Analog TV into DTV −48 dB −47.33 dB −34 ~ −37 dB[16] −35 dB
Upper Adjacent Channel Analog TV into DTV −49 dB −48.71 dB −38 ~ −36 dB[16] −37 dB
Lower Adjacent Channel DTV into DTV −27 dB −28 dB −30 dB −28 dB
Upper Adjacent Channel DTV into DTV −27 dB −26 dB −30 dB −29 dB

Interaction

People can interact with a DTV system in various ways. One can, for example, browse the electronic program guide. Modern DTV systems sometimes use a return path providing feedback from the end user to the broadcaster. This is possible with a coaxial or fiber optic cable, a dialup modem, or Internet connection but is not possible with a standard antenna.

Some of these systems support video on demand using a communication channel localized to a neighborhood rather than a city (terrestrial) or an even larger area (satellite).

1-segment broadcasting

1seg (1-segment) is a special form of ISDB. Each channel is further divided into 13 segments. The 12 segments of them are allocated for HDTV and remaining segment, the 13th, is used for narrow-band receivers such as mobile television or cell phone.

Comparison of analog vs digital

DTV has several advantages over analog TV, the most significant being that digital channels take up less bandwidth, and the bandwidth needs are continuously variable, at a corresponding reduction in image quality depending on the level of compression as well as the resolution of the transmitted image. This means that digital broadcasters can provide more digital channels in the same space, provide high-definition television service, or provide other non-television services such as multimedia or interactivity. DTV also permits special services such as multiplexing (more than one program on the same channel), electronic program guides and additional languages (spoken or subtitled). The sale of non-television services may provide an additional revenue source.

Digital and analog signals react to interference differently. For example, common problems with analog television include ghosting of images, noise from weak signals, and many other potential problems which degrade the quality of the image and sound, although the program material may still be watchable. With digital television, the audio and video must be synchronized digitally, so reception of the digital signal must be very nearly complete; otherwise, neither audio nor video will be usable. Short of this complete failure, "blocky" video is seen when the digital signal experiences interference.

Analog TV began with monophonic sound, and later developed multichannel television sound with two independent audio signal channels. DTV allows up to 5 audio signal channels plus a sub-woofer bass channel, with broadcasts similar in quality to movie theaters and DVDs.[17]

Compression artifacts, picture quality monitoring, and allocated bandwidth

DTV images have some picture defects that are not present on analog television or motion picture cinema, because of present-day limitations of bit rate and compression algorithms such as MPEG-2. This defect is sometimes referred to as "mosquito noise".[18]

Because of the way the human visual system works, defects in an image that are localized to particular features of the image or that come and go are more perceptible than defects that are uniform and constant. However, the DTV system is designed to take advantage of other limitations of the human visual system to help mask these flaws, e.g. by allowing more compression artifacts during fast motion where the eye cannot track and resolve them as easily and, conversely, minimizing artifacts in still backgrounds that may be closely examined in a scene (since time allows).

Broadcast, cable, satellite, and Internet DTV operators control the picture quality of television signal encodes using sophisticated, neuroscience-based algorithms, such as the structural similarity (SSIM) video quality measurement tool, which was accorded each of its inventors a Primetime Emmy because of its global use. Another tool, called Visual Information Fidelity (VIF), is a top-performing algorithm at the core of the Netflix VMAF video quality monitoring system, which accounts for about 35% of all U.S. bandwidth consumption.

Effects of poor reception

Changes in signal reception from factors such as degrading antenna connections or changing weather conditions may gradually reduce the quality of analog TV. The nature of digital TV results in a perfectly decodable video initially, until the receiving equipment starts picking up interference that overpowers the desired signal or if the signal is too weak to decode. Some equipment will show a garbled picture with significant damage, while other devices may go directly from perfectly decodable video to no video at all or lock up. This phenomenon is known as the digital cliff effect.

Block error may occur when transmission is done with compressed images. A block error in a single frame often results in black boxes in several subsequent frames, making viewing difficult.

For remote locations, distant channels that, as analog signals, were previously usable in a snowy and degraded state may, as digital signals, be perfectly decodable or may become completely unavailable. The use of higher frequencies will add to these problems, especially in cases where a clear line-of-sight from the receiving antenna to the transmitter is not available.

Effect on old analog technology

Television sets with only analog tuners cannot decode digital transmissions. When analog broadcasting over the air ceases, users of sets with analog-only tuners may use other sources of programming (e.g. cable, recorded media) or may purchase set-top converter boxes to tune in the digital signals. In the United States, a government-sponsored coupon was available to offset the cost of an external converter box. Analog switch-off (of full-power stations) took place on December 11, 2006 in The Netherlands,[19] June 12, 2009 in the United States for full-power stations, and later for Class-A Stations on September 1, 2016,[20] July 24, 2011 in Japan,[21] August 31, 2011 in Canada,[22] February 13, 2012 in Arab states, May 1, 2012 in Germany, October 24, 2012 in the United Kingdom[23] and Ireland,[24] October 31, 2012 in selected Indian cities,[25] and December 10, 2013 in Australia.[26] Completion of analog switch-off is scheduled for December 31, 2017 in the whole of India,[25] December 2018 in Costa Rica and around 2020 for the Philippines.

Disappearance of TV-audio receivers

Prior to the conversion to digital TV, analog television broadcast audio for TV channels on a separate FM carrier signal from the video signal. This FM audio signal could be heard using standard radios equipped with the appropriate tuning circuits.

However, after the transition of many countries to digital TV, no portable radio manufacturer has yet developed an alternative method for portable radios to play just the audio signal of digital TV channels. (DTV radio is not the same thing.)

Environmental issues

The adoption of a broadcast standard incompatible with existing analog receivers has created the problem of large numbers of analog receivers being discarded during digital television transition. One superintendent of public works was quoted in 2009 saying; "some of the studies I’ve read in the trade magazines say up to a quarter of American households could be throwing a TV out in the next two years following the regulation change".[27] In 2009, an estimated 99 million analog TV receivers were sitting unused in homes in the US alone and, while some obsolete receivers are being retrofitted with converters, many more are simply dumped in landfills where they represent a source of toxic metals such as lead as well as lesser amounts of materials such as barium, cadmium and chromium.[28][29]

According to one campaign group, a CRT computer monitor or TV contains an average of 8 pounds (3.6 kg) of lead.[30] According to another source, the lead in glass of a CRT varies from 1.08 lb to 11.28 lb, depending on screen size and type, but the lead is in the form of "stable and immobile" lead oxide mixed into the glass.[31] It is claimed that the lead can have long-term negative effects on the environment if dumped as landfill.[32] However, the glass envelope can be recycled at suitably equipped facilities.[33] Other portions of the receiver may be subject to disposal as hazardous material.

Local restrictions on disposal of these materials vary widely; in some cases second-hand stores have refused to accept working color television receivers for resale due to the increasing costs of disposing of unsold TVs. Those thrift stores which are still accepting donated TVs have reported significant increases in good-condition working used television receivers abandoned by viewers who often expect them not to work after digital transition.[34]

In Michigan in 2009, one recycler estimated that as many as one household in four would dispose of or recycle a TV set in the following year.[35] The digital television transition, migration to high-definition television receivers and the replacement of CRTs with flatscreens are all factors in the increasing number of discarded analog CRT-based television receivers.

See also

Notes and references

  1. ^ Kruger, L. G. (2001). Digital Television: An Overview. Hauppauge, New York: Nova Publishers.
  2. ^ "HDTV Set Top Boxes and Digital TV Broadcast Information". Retrieved 28 June 2014. - dead link
  3. ^ Ong, C. Y., Song, J., Pan, C., & Li, Y.(2010, May). Technology and Standards of Digital Television Terrestrial Multimedia Broadcasting [Topics in Wireless Communications], Communications Magazine, IEEE , 48(5),119-127
  4. ^ "Korea's Terrestrial DMB: Germany to begin broadcast this May". ZDNet Korea. Retrieved 2010-06-17.
  5. ^ "picturephoning.com: DMB". Textually.org. Archived from the original on 2010-08-09. Retrieved 2010-06-17.
  6. ^ "South Korea : Social Media 답변 내용 : 악어새 - 리포트월드". Reportworld.co.kr. Archived from the original on 2009-08-17. Retrieved 2010-06-17.
  7. ^ a b c "The Origins and Future Prospects of Digital Television". Benton Foundation.
  8. ^ "History of U.S. Satellite Broadcasting Company, Inc. – FundingUniverse". www.fundinguniverse.com. Retrieved 9 August 2018.
  9. ^ "Business Insider: Digital satellite TV has Indy roots". Retrieved 9 August 2018.
  10. ^ "NextLevel signs cable deal - Dec. 17, 1997". money.cnn.com. Retrieved 9 August 2018.
  11. ^ "TCI faces big challenges - Aug. 15, 1996". money.cnn.com. Retrieved 9 August 2018.
  12. ^ "CANAL+ TECHNOLOGIES and the world's first digital terrestrial television service in the United Kingdom". Retrieved 9 August 2018.
  13. ^ Latest snapshots - Freeview/DTT bitrates (Mendip transmitter, UK)
  14. ^ ISDB-T (6 MHz, 64QAM, R=2/3), Analog TV (M/NTSC).
  15. ^ a b The Canadian parameter, C/(N+I) of noise plus co-channel DTV interface should be 16.5 dB.
  16. ^ a b c d Depending on analog TV systems used.
  17. ^ "Digital TV: A Cringley Crash Course — Digital Vs. Analog". Pbs.org. Retrieved 2014-01-13.
  18. ^ Le Dinh, Phuc-Tue; Patry, Jacques (February 24, 2006). "Video compression artifacts and MPEG noise reduction". Video Imaging DesignLine. Retrieved April 30, 2010.
  19. ^ "How Television went Digital in The Netherlands" (PDF). Open Society Foundations September 2011. Retrieved 2013-02-04.
  20. ^ "The Digital TV Transition: Will You Be Affected?". FCC. Retrieved 2009-11-02.
  21. ^ "New DTV Hard Date: July 24, 2011?". B&C. Retrieved 2009-11-02.
  22. ^ "DTV Post-Transition Allotment Plan" (PDF). Spectrum Management and Telecommunications. Retrieved 2009-11-02.
  23. ^ "End of analogue TV era as switchover completes in the UK" (PDF). Digital UK. Retrieved 2012-12-21.
  24. ^ "Analogue switch off has finally happened". SAORVIEW. Retrieved 2012-12-21.
  25. ^ a b "Find out when digital switch over is coming to you". Government of India Ministry of Information & Broadcasting. Retrieved 2012-12-21.
  26. ^ "Australia's ready for digital TV". Digital Ready AU. Retrieved 2013-12-25.
  27. ^ North Tonawanda: council discusses future TV disposal, Neale Gulley, Tonawanda News, January 27, 2009
  28. ^ Old Toxic TVs Cause Problems, USA TODAY, January 27, 2009
  29. ^ Unloading that old TV not quite so simple, Lee Bergquist, Milwaukee Journal-Sentinel, January 23, 2009
  30. ^ Campaigners highlight 'toxic TVs', Maggie Shiels, BBC News, 9 January 2009
  31. ^ "Lead in Cathode Ray Tubes (CRTs) Information Sheet**" (PDF). Electronic Industries Alliance. 2001-11-30. p. 1. Archived from the original (PDF) on 2011-05-20. Retrieved 2009-09-29.
  32. ^ Poon, C.S. (2008). "Management of CRT glass from discarded computer monitors and TV sets". Waste Management. 28 (9): 1499–1499. doi:10.1016/j.wasman.2008.06.001. PMID 18571917. Retrieved 2009-09-29. number of studies have demonstrated that the neck and funnel glasses of CRT are hazardous wastes, while the panel glass exhibits little toxicity.
  33. ^ What To Do With Your Old TV's, Mike Webster, WCSH-TV, January 28, 2009 - dead link
  34. ^ Many people throwing out perfectly good TVs over digital confusion, Daniel Vasquez, Sun-Sentinel, Florida, January 19, 2009
  35. ^ Trashing the tube: Digital conversion may spark glut of toxic waste, Jennifer Chambers, Detroit News, January 23, 2009

Further reading

External links

ATSC standards

Advanced Television Systems Committee (ATSC) standards are a set of standards for digital television transmission over terrestrial, cable, and satellite networks. It is largely a replacement for the analog NTSC standard, and like that standard, used mostly in the United States, Mexico and Canada. Other former users of NTSC, like Japan, have not used ATSC during their digital television transition because they adopted their own system called ISDB.

The ATSC standards were developed in the early 1990s by the Grand Alliance, a consortium of electronics and telecommunications companies that assembled to develop a specification for what is now known as HDTV. The standard is now administered by the Advanced Television Systems Committee. The standard includes a number of patented elements, and licensing is required for devices that use these parts of the standard. Key among these is the 8VSB modulation system used for over-the-air broadcasts.

ATSC includes two primary high definition video formats, 1080i and 720p. It also includes standard-definition formats, although initially only HDTV services were launched in the digital format. ATSC can carry multiple channels of information on a single stream, and it is common for there to be a single high-definition signal and several standard-definition signals carried on a single (former) NTSC channel allocation.

Canadian Broadcasting Corporation

The Canadian Broadcasting Corporation (French: Société Radio-Canada), branded as CBC/Radio-Canada, is a Canadian federal Crown corporation that serves as the national public broadcaster for both radio and television. The English- and French-language service units of the corporation are commonly known as CBC and Radio-Canada respectively, and both short-form names are also commonly used in the applicable language to refer to the corporation as a whole.

Although some local stations in Canada predate CBC's founding, CBC is the oldest existing broadcasting network in Canada, first established in its present form on November 2, 1936. Radio services include CBC Radio One, CBC Music, Ici Radio-Canada Première, Ici Musique and the international radio service Radio Canada International. Television operations include CBC Television, Ici Radio-Canada Télé, CBC News Network, Ici RDI, Ici Explora, Documentary Channel (part ownership), and Ici ARTV. The CBC operates services for the Canadian Arctic under the names CBC North and Radio-Canada Nord. The CBC also operates digital services including CBC.ca/Ici.Radio-Canada.ca, CBC Radio 3, CBC Music/ICI.mu and Ici.TOU.TV, and owns 20.2% of satellite radio broadcaster Sirius XM Canada, which carries several CBC-produced audio channels.

CBC/Radio-Canada offers programming in English, French and eight aboriginal languages on its domestic radio service, and in five languages on its web-based international radio service, Radio Canada International (RCI). However, budget cuts in the early 2010s have contributed to the corporation reducing its service via the airwaves, discontinuing RCI's shortwave broadcasts as well as terrestrial television broadcasts in all communities served by network-owned rebroadcast transmitters, including communities not subject to Canada's over-the-air digital television transition.

CBC's federal funding is supplemented by revenue from commercial advertising on its television broadcasts. The radio service employed commercials from its inception to 1974, but since its primary radio networks have been commercial-free. In 2013, CBC's secondary radio networks, CBC Music and Ici Musique, introduced limited advertising of up to four minutes an hour, but this was discontinued in 2016.

Create (TV network)

Create is an American digital broadcast television network. The network broadcasts how-to, DIY and other lifestyle-oriented instructional programming 24 hours a day.

Digital television in the United Kingdom

There are four major forms of digital television (DTV) broadcast in the United Kingdom: a direct-to-home satellite service from the Astra 28.2°E satellites provided by Sky UK, a cable television service provided by Virgin Media (known as Virgin TV); a free-to-air satellite service called Freesat; and a free-to-air digital terrestrial service called Freeview. In addition, an IPTV system known as BT Vision is provided by BT. Individual access methods vary throughout the country. 77% of the United Kingdom has access to HDTV via terrestrial digital television. Satellite is the only source of HDTV broadcast available for the remaining 23%.

Digital television transition

The digital television transition, also called the digital switchover, the analog switch-off (ASO), or the analog shutdown, is the process, mainly begun in 2006 (for terrestrial broadcasting), in which older analog television broadcasting technology is converted to and replaced by digital television. Conducted by individual nations on different schedules, this primarily involves the conversion of analog terrestrial television to digital terrestrial. However, it also involves analog cable conversion to digital cable or internet protocol television, as well as analog to digital satellite television. Terrestrial transition was begun by some countries around 2000. By contrast, satellite transition was well underway or completed in many counties by this time. It is an involved process because the existing analog television receivers owned by viewers cannot receive digital broadcasts; viewers must either purchase new digital TVs, or converter boxes which change the digital signal to an analog signal which can be viewed on the old TV.

In many countries, a simulcast service is operated where a broadcast is made available to viewers in both analog and digital at the same time. As digital becomes more popular, it is expected that the existing analog services will be removed. In most places this has already happened, where a broadcaster has offered incentives to viewers to encourage them to switch to digital. In other cases government policies have been introduced to encourage or force the switchover process, especially with regard to terrestrial broadcasts. Government intervention usually involves providing some funding for broadcasters and, in some cases, monetary relief to viewers, to enable a switchover to happen by a given deadline. Governments can also require all receiving equipment sold in a country to support the necessary digital reception 'tuner'.

The switchover process is being accomplished on different schedules in different countries; in some countries it is being implemented in stages as in Australia, Brazil, India, Mexico, and the United Kingdom, where each region has a separate date to switch off. In others, the whole country switches on one date, such as the Netherlands, which switched off its analog terrestrial services on 11 December 2006. On 3 August 2003, Berlin became the world's first city to switch off terrestrial analogue signals. Luxembourg was the first country to complete its terrestrial switchover, in September 2006.

Digital television transition in the United States

The digital transition in the United States was the switchover from analog to exclusively digital broadcasting of terrestial television television programming. According to David Rehr, then president and CEO of the National Association of Broadcasters, this transition represented "the most significant advancement of television technology since color TV was introduced." For full-power TV stations, the transition went into effect on June 12, 2009, with stations ending regular programming on their analog signals no later than 11:59 p.m. local time that day.Under the Digital Transition and Public Safety Act of 2005, full-power broadcasting of analog television in the United States was initially planned to have ceased after February 17, 2009. To help U.S. consumers through the conversion, the Act also established a federally sponsored DTV Converter Box Coupon Program.

The DTV Delay Act changed the mandatory analog cutoff date to June 12, although stations were permitted to cease analog transmissions before the new mandatory cutoff date. The legislation was enacted on February 4, 2009, and on February 11, 2009, President Barack Obama signed it into law. The purpose of the extension was to help the millions of households who had not been able to get their coupons for converters because demand for coupons exceeded the funding provided for in the initial bill, leaving millions on a waiting list to receive coupons. Funding for extra coupons was provided by the American Recovery and Reinvestment Act of 2009. By midnight on the original cut-off date of February 17, 2009, 641 stations representing 36 percent of U.S. full-power broadcasters were transmitting exclusively in digital.Analog broadcasting did not cease entirely following the June 12 deadline: under the provisions of the Short-term Analog Flash and Emergency Readiness Act, approximately 120 full-power stations briefly maintained analog "nightlight" service, ending no later than July 12. In a separate category, low power television stations were permitted to continue analog broadcasts for several more years.

On July 15, 2011, the FCC posted the required transition deadlines for low power television. Stations broadcasting on channels 52 to 69 were required to vacate those channels by December 31, 2011, and all analog television transmitters (primarily low-powered (LP), and Class-A low-powered (-CA) stations, and also broadcast translator (TX) repeaters in rural communities) were required to shut down by September 1, 2015. On April 24, 2015, it was announced that the conversion date for standard LPTVs and translators still broadcasting in analog had been suspended until further notice, due to economic problems that may arise from the then-upcoming spectrum auction; however, Class A low-powered stations were still required to convert by the original deadline date of September 1, 2015. After the auction's completion in 2017, the FCC announced on May 17 of that year that all analog low-power stations and transmitters must convert by July 13, 2021.

Digital terrestrial television

Digital terrestrial television (DTTV or DTT) is a technology for broadcast television in which land-based (terrestrial) television stations broadcast television content by radio waves to televisions in consumers' residences in a digital format. DTTV is a major technological advance over the previous analog television, and has largely replaced analog which had been in common use since the middle of the last century. Test broadcasts began in 1998 with the changeover to DTTV (aka Analog Switchoff (ASO) or Digital Switchover (DSO)) beginning in 2006 and is now complete in many countries. The advantages of digital terrestrial television are similar to those obtained by digitising platforms such as cable TV, satellite, and telecommunications: more efficient use of limited radio spectrum bandwidth, provision of more television channels than analog, better quality images, and potentially lower operating costs for broadcasters (after the initial upgrade costs).

Different countries have adopted different digital broadcasting standards; the major ones are:

ATSC DTV – Advanced Television Standards Committee (System A)

ATSC-M/H – Advanced Television Systems Committee Mobile & Handheld

ChinaDTV

DVB-H – Digital Video Broadcasting Handheld

DVB-T/DVB-T2 – Digital Video Broadcasting Terrestrial (System B)

ISDB-T – Integrated Services Digital Broadcasting Terrestrial (System C)

DMB-T/H

ISDB-TSB – Integrated Services Digital Broadcasting-Terrestrial Sound Broadcasting – (System F)

FLO – Forward Link Only (System M)

Digital terrestrial television in Canada

Digital terrestrial television in Canada (often shortened to DTT) is transmitted using the ATSC standard. Because Canada and the U.S. use the same standard and frequencies for channels, people near the Canada–United States border can watch digital television programming from television stations in either country where available. The ATSC standards are also used in Mexico, the Dominican Republic, Suriname and South Korea.

Jurisdiction over terrestrial broadcasting in Canada is primarily regulated by Innovation, Science and Economic Development Canada and the Canadian Radio-television and Telecommunications Commission (CRTC). Innovation, Science and Economic Development Canada has jurisdiction over the allotment of the terrestrial spectrum and the CRTC has jurisdiction over the allotment of broadcast licences.

The CRTC imposed in 28 mandatory markets a digital transition deadline for full power transmitters of August 31, 2011, with the exception of some CBC transmitters. Two weeks before the deadline, the CBC transmitters were given a temporary one-year extension to remain in analog. No digital transition deadline has been set for low-power analogue transmitters and analog transmitters outside the 28 mandatory markets.

In January 2007, Innovation, Science and Economic Development Canada stopped issuing licences within Canada for new television transmitters broadcasting in analogue.All remaining analog terrestrial television signals across Canada are scheduled to be shut down no later than 2022.

Digital terrestrial television in the United States

See digital television for more technical details, or DTV transition in the United States for specific information related to the analog-to-digital switchoverIn the United States, digital television broadcasts, or DTV, can be received via cable, via internet, via satellite, or via digital terrestrial television - much like analog television broadcasts have been. Full-power analog television broadcasts, however, were required by U.S. federal law to cease by June 12, 2009. Low-power, Class A, and TV Translator stations are not currently required to cease analog broadcasts. Also by law, digital broadcasts - when transmitted as OTA signals - must conform to ATSC standards.; it is unclear whether satellite operators are free to use their own proprietary standards; and many standards exist for Internet television (most are proprietary).

List of Canadian television stations

This page lists the table of every television station in Canada by call sign. For the list of television networks in Canada, see the List of Canadian television networks (table).

Under the current digital television transition, television stations in Mandatory Markets, in Canada are launching digital transmissions by August 31, 2011. On August 18, 2011, the CRTC issued a decision that allows CBC's mandatory market rebroadcasting transmitters in analog remain on-air until August 31, 2012. Where known, a digital channel assignment is noted below. Digital channels listed on a green background have already been launched, while those listed on a red background have not yet commenced operations. In some cases, the digital channels have been allocated but the stations have not applied to use them; as there is no requirement that Canadian stations begin digital broadcasts before the end-August 2011 analogue shutdown, it is currently unknown whether some broadcasters will ask to flash-cut on their existing frequencies or to continue on their assigned digital channel.

List of digital television deployments by country

This is a list of digital television deployments by country, which summarises the process and progress of transition from analogue to digital broadcasting.

The transition to digital television is a process that is happening at different paces around the world. Although digital satellite television is now commonplace, the switch to digital cable and terrestrial television has taken longer. See also Digital terrestrial television.

Not all countries are compatible within each standard DVB-T, ATSC (North America), DTMB (China), ISDB (of which there are two incompatible variations used in Japan and South America respectively). Countries that have adopted digital terrestrial recently may have a single MPEG4 based system for SD and HD, while countries with more established system may use MPEG2 for SD and MPEG4 for HD. There are also variations in middleware used. For example, Italy, Ireland and the UK are all DVB-T regions, but Ireland uses "MPEG4 + MHEG5 + DVB-T" for both SD and HD transmissions, while the UK uses "MPEG2 + MHEG5 + DVB-T" for SD and "MPEG4 + MHEG5 + DVB-T2" for HDTV, and Italy uses MHP rather than MHEG5 middleware. Since all MPEG4-capable receivers can decode the MPEG2 codec and all DVB-T2 tuners are capable of tuning DVB-T signals, UK HD set-top boxes are compatible with both the UK SD system and Irish SD/HD system, but Irish SD/HD tuners will only work with the SD system used in the UK. Digital cable broadcast tends to be DVB-C or very similar QAM in almost all countries. Broadband on cable is mostly DOCSIS which is DVB-C on the download path. This is important when buying a TV or set-box online rather than from a local retailer who would normally only stock the compatible system. Incompatible retail products are a severe problem in emerging retail digital markets where a neighbouring country has an older standard and dominates the retail trade, such as UK Freeview (rather than compatible "Freeview HD") products in Ireland.

Important DVB-T standards are UK D-book for UK Freeview and Nordig 2.2 for Scandinavia and Ireland. Ireland deviates from Nordig by using UK profile MHEG5 middleware rather than MHP.

Multiplex (television)

A multiplex or mux (called virtual sub-channel in the United States and Canada, and bouquet in France) is the popular term used for the grouping of program services that are sub-grouped as interleaved data packets for broadcast over a network or modulated multiplexed medium, which are split out at the receiving end. There are two different types of groupings, which are closely related but not identical.

In the United Kingdom, a terrestrial multiplex (usually abbreviated mux) has a fixed bandwidth of 8 MHz CODFM of interleaved H.222 packets containing a number of channels. In the United States, a similar arrangement using 6 MHz 8VSB is often described as a channel with virtual sub-channels.

Program and System Information Protocol

The Program and System Information Protocol (PSIP) is the MPEG (a video and audio industry group) and privately defined program-specific information originally defined by General Instrument for the DigiCipher 2 system and later extended for the ATSC digital television system for carrying metadata about each channel in the broadcast MPEG transport stream of a television station and for publishing information about television programs so that viewers can select what to watch by title and description.

Standard-definition television

Standard-definition television (SDTV or SD) is a television system which uses a resolution that is not considered to be either high or enhanced definition. The two common SDTV signal types are 576i, with 576 interlaced lines of resolution, derived from the European-developed PAL and SECAM systems; 480i based on the American NTSC system. SDTV and high-definition television (HDTV) are the two categories of display formats for digital television (DTV) transmissions.

In North America, digital SDTV is broadcast in the same 4:3 aspect ratio as NTSC signals, with widescreen content being center cut. However, in other parts of the world that used the PAL or SECAM color systems, standard-definition television is now usually shown with a 16:9 aspect ratio, with the transition occurring between the mid-1990s and mid-2000s depending on region. Older programs with a 4:3 aspect ratio are broadcast with a flag that switches the display to 4:3.Standards that support digital SDTV broadcast include DVB, ATSC, and ISDB. The last two were originally developed for HDTV, but are more often used for their ability to deliver multiple SD video and audio streams via multiplexing, than for using the entire bitstream for one HD channel.For SMPTE 259M-C compliance, a SDTV broadcast image is scaled to 720 pixels wide for every 480 NTSC (or 576 PAL) lines of the image with the amount of non-proportional line scaling dependent on either the display or pixel aspect ratio. The display ratio for broadcast widescreen is commonly 16:9, the display ratio for a traditional or letterboxed broadcast is 4:3.An SDTV image outside the constraints of the SMPTE standards requires no non-proportional scaling with 640 pixels for every line of the image. The display and pixel aspect ratio is generally not required with the line height defining the aspect. For widescreen 16:9, 360 lines define a widescreen image and for traditional 4:3, 480 lines define an image.

SDTV refresh rates can be 24, 25, 30, 50 or 60 frames per second with a possible rate multiplier of 1000/1001 for NTSC. 50 and 60 rates are generally frame doubled versions of 25 and 30 rates for jitter issues when using non-interlaced lines.

Digital SDTV in 4:3 aspect ratio has the same appearance as regular analog TV (NTSC, PAL, SECAM) without the ghosting, snowy images and white noise. However, if the reception has interference or is poor, where the error correction cannot compensate one will encounter various other artifacts such as image freezing, stuttering or dropouts from missing intra-frames or blockiness from missing macroblocks. The audio encoding is the last to suffer loss due to the lower bandwidth requirements.

Television in China

The television industry in China includes high-tech program production, transmission and coverage. China Central Television is China's largest and most powerful national television station. By the 1987, two-thirds of people in China had access to television, while today, over 3,000 channels are available in the country.

Chinese television drama has also proven to be a hot spot in today's popular culture (similar to K-dramas), with well received Chinese television dramas such as Princess Agents, Nirvana in Fire, The Journey of Flower, Eternal Love, The Princess Weiyoung, Just One Smile Is Very Alluring, The Legend of Mi Yue, Scarlet Heart, General and I and more garnering billions of views among China's most popular video websites, iQiyi, Youku, Tencent Video and Le Video. Some dramas have been so popular and widely acclaimed that they were remade into different languages, as well as spinning off with a sequel.

Chinese variety scene has also became widely successful with popular shows such as Happy Camp, Super Girl, Sing! China and more gaining worldwide recognition, garnering from millions to billions of viewership and winning numerous awards.

Television in France

Television in France was introduced in 1931, when the first experimental broadcasts began. Colour television was introduced in October 1967 on La Deuxième Chaîne.

Television in Hong Kong

Television in Hong Kong is primarily in Cantonese and English. It is delivered through analogue and digital terrestrial, cable, IPTV, and the Internet. Satellite TV is not common, although many housing estates have dishes and re-distribute a limited number of free channels through coaxial cables. The dominant broadcaster is TVB.

Television in Mexico

Television is a popular form of entertainment in Mexico, with mass entertainment playing an important role in creating a national, unified culture.

Video

Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media.Video was first developed for mechanical television systems, which were quickly replaced by cathode ray tube (CRT) systems which were later replaced by flat panel displays of several types.

Video systems vary in display resolution, aspect ratio, refresh rate, color capabilities and other qualities. Analog and digital variants exist and can be carried on a variety of media, including radio broadcast, magnetic tape, optical discs, computer files, and network streaming.

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.