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High-definition television

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High-definition television(HDTV) describes atelevisionor video system which provides a substantially higherimage resolutionthan the previous generation of technologies. The term has been used since at least 1933;[1]in more recent times, it refers to the generation followingstandard-definition television(SDTV). It is the standard video format used in most broadcasts:terrestrial broadcast television,cable television,satellite television.

Formats

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HDTV may be transmitted in various formats:

  • 720p(1280 × 720p): 921,600 pixels
  • 1080i(1920 × 1080i)interlacedscan: 1,036,800 pixels (≈1.04Mpx).
  • 1080p(1920 × 1080p) progressive scan: 2,073,600 pixels (≈2.07Mpx).
    • Some countries also use a non-standard CTA resolution, such as1440 × 1080i:777,600 pixels (≈0.78Mpx) per field or 1,555,200 pixels (≈1.56Mpx) per frame

When transmitted at two megapixels per frame, HDTV provides about five times as many pixels as SD (standard-definition television). The increased resolution provides for a clearer, more detailed picture. In addition, progressive scan and higher frame rates result in a picture with less flicker and better rendering of fast motion.[2]Modern HDTV began broadcasting in 1989 in Japan, under theMUSE/Hi-Vision analog system.[3]HDTV was widely adopted worldwide in the late 2000s.[4]

Standards

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Map ofdigital terrestrial television broadcasting standards by country

All modern high-definition broadcasts utilizedigital televisionstandards. The major digital television broadcast standards used for terrestrial, cable, satellite, and mobile devices are:

  • DVB,originating in Europe and also used in much of Asia, Africa, and Australia
  • ATSC,used in much of North America
  • DTMB,used in China and some neighboring countries
  • ISDB,used in two incompatible variations in Japan and South America
  • DMB,used by mobile devices in South Korea

These standards use a variety ofvideo codecs,some of which are also used forinternet video.

History

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Further information:Analog high-definition television system,history of television,andhigh-definition television transition

The termhigh definitiononce described a series of television systems first announced in 1933[1]and launched starting in August 1936;[5]however, these systems were only high definition when compared to earlier systems that were based on mechanical systems with as few as 30 lines of resolution. The ongoing competition between companies and nations to create true HDTV spanned the entire 20th century, as each new system became higher definition than the last. In the early 21st century, this race has continued with4K,5Kand8Ksystems.

The British high-definition TV service started trials in August 1936 and a regular service on 2 November 1936 using both the (mechanical) Baird 240 line sequential scan (later referred to asprogressive) and the (electronic) Marconi-EMI405 lineinterlaced systems. The Baird system was discontinued in February 1937.[6]In 1938 France followed with its own441-linesystem, variants of which were also used by a number of other countries. The USNTSC525-line system joined in 1941. In 1949 France introduced an even higher-resolution standard at819 lines,a system that would have been high definition even by modern standards, but was monochrome only and had technical limitations that prevented it from achieving the intended definition. All of these systems usedinterlacingand a 4:3aspect ratioexcept the 240-line system which was progressive (actually described at the time by the technically correct termsequential) and the 405-line system which started as 5:4 and later changed to 4:3. The 405-line system adopted the (at that time) revolutionary idea of interlaced scanning to overcome the flicker problem of the 240-line with its 25 Hz frame rate. The 240-line system could have doubled its frame rate but this would have meant that the transmitted signal would have doubled in bandwidth, an unacceptable option as the video baseband bandwidth was required to be not more than 3 MHz.

Color broadcasts started at similar line counts, first with the US NTSC color system in 1953, which was compatible with the earlier monochrome systems and therefore had the same 525 lines per frame. European standards did not follow until the 1960s, when thePALandSECAMcolor systems were added to the monochrome 625-line broadcasts.

TheNHK(Japan Broadcasting Corporation) began researching to "unlock the fundamental mechanism of video and sound interactions with the five human senses" in 1964, after the Tokyo Olympics. NHK set out to create an HDTV system that scored much higher in subjective tests than NTSC's previously dubbedHDTV.This new system, NHK Color, created in 1972, included 1125 lines, a 5:3 (1.67:1) aspect ratio and 60 Hz refresh rate. The Society of Motion Picture and Television Engineers (SMPTE), headed by Charles Ginsburg, became the testing and study authority for HDTV technology in the international theater. SMPTE would test HDTV systems from different companies from every conceivable perspective, but the problem of combining the different formats plagued the technology for many years.

There were four major HDTV systems tested by SMPTE in the late 1970s, and in 1979 an SMPTE study group releasedA Study of High Definition Television Systems:

  • EIA monochrome: 4:3 aspect ratio, 1023 lines, 60 Hz
  • NHK color: 5:3 aspect ratio, 1125 lines, 60 Hz
  • NHK monochrome: 4:3 aspect ratio, 2125 lines, 50 Hz
  • BBC colour: 8:3 aspect ratio, 1501 lines, 60 Hz[7]

Since the formal adoption ofDigital Video Broadcasting's (DVB) widescreen HDTV transmission modes in the mid to late 2000s; the 525-lineNTSC(andPAL-M) systems, as well as the European 625-linePALandSECAMsystems, have been regarded asstandard definitiontelevision systems.

Analog systems

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Main article:Analog high-definition television system

Early HDTV broadcasting usedanalogtechnology that was later converted todigital televisionwithvideo compression.

In 1949, France started its transmissions with an 819 lines system (with 737 active lines). The system was monochrome only and was used only on VHF for the first French TV channel. It was discontinued in 1983.

In 1958, theSoviet UniondevelopedТransformator(Russian:Трансформатор,meaningTransformer), the first high-resolution (definition) television system capable of producing an image composed of 1,125 lines of resolution aimed at providing teleconferencing for military command. It was a research project and the system was never deployed by either the military or consumer broadcasting.[8]

In 1986, theEuropean CommunityproposedHD-MAC,an analog HDTV system with 1,152 lines. A public demonstration took place for the1992 Summer Olympicsin Barcelona. However HD-MAC was scrapped in 1993 and the DVB project was formed, which would foresee development of a digital HDTV standard.[9]

Japan

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In 1979, the Japanese public broadcasterNHKfirst developed consumer high-definition television with a 5:3 display aspect ratio.[10]The system, known as Hi-Vision or MUSE after itsmultiple sub-Nyquist sampling encoding(MUSE) for encoding the signal, required about twice the bandwidth of the existing NTSC system but provided about four times the resolution (1035i/1125 lines). In 1981, the MUSE system was demonstrated for the first time in the United States, using the same 5:3 aspect ratio as the Japanese system.[11]Upon visiting a demonstration of MUSE in Washington, US PresidentRonald Reaganwas impressed and officially declared it "a matter of national interest" to introduce HDTV to the US.[12]NHK taped the1984 Summer Olympicswith a Hi-Vision camera, weighing 40 kg.[13]

Satellite test broadcasts started June 4, 1989, the first daily high-definition programs in the world,[14]with regular testing starting on November 25, 1991, or "Hi-Vision Day" – dated exactly to refer to its 1,125-lines resolution.[15]Regular broadcasting ofBS-9ch commenced on November 25, 1994, which featured commercial and NHK programming.

Several systems were proposed as the new standard for the US, including the Japanese MUSE system, but all were rejected by theFederal Communications Commission(FCC) because of their higher bandwidth requirements. At this time, the number of television channels was growing rapidly and bandwidth was already a problem. A new standard had to be more efficient, needing less bandwidth for HDTV than the existing NTSC.

Decrease of analog HD systems

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The limited standardization of analog HDTV in the 1990s did not lead to global HDTV adoption as technical and economic constraints at the time did not permit HDTV to use bandwidths greater than normal television. Early HDTV commercial experiments, such as NHK's MUSE, required over four times the bandwidth of a standard-definition broadcast. Despite efforts made to reduce analog HDTV to about twice the bandwidth of SDTV, these television formats were still distributable only by satellite. In Europe too, the HD-MAC standard was considered not technically viable.[16][17]

In addition, recording and reproducing an HDTV signal was a significant technical challenge in the early years of HDTV (Sony HDVS). Japan remained the only country with successfulpublic broadcastingof analog HDTV, with seven broadcasters sharing a single channel.[citation needed]

However, the Hi-Vision/MUSE system also faced commercial issues when it launched on November 25, 1991. Only 2,000 HDTV sets were sold by that day, rather than the enthusiastic 1.32 million estimation. Hi-Vision sets were very expensive, up to US$30,000 each, which contributed to its low consumer adaption.[18]A Hi-VisionVCRfromNECreleased at Christmas time retailed for US$115,000. In addition, the United States saw Hi-Vision/MUSE as an outdated system and had already made it clear that it would develop an all-digital system.[19]Experts thought the commercial Hi-Vision system in 1992 was already eclipsed by digital technology developed in the U.S. since 1990. This was an American victory against the Japanese in terms of technological dominance.[20]By mid-1993 prices of receivers were still as high as 1.5 millionyen(US$15,000).[21]

On February 23, 1994, a top broadcasting administrator in Japan admitted failure of its analog-based HDTV system, saying the U.S. digital format would be more likely a worldwide standard.[22]However this announcement drew angry protests from broadcasters and electronic companies who invested heavily into the analog system. As a result, he took back his statement the next day saying that the government will continue to promote Hi-Vision/MUSE.[23]That year NHK started development ofdigital televisionin an attempt to catch back up to America and Europe. This resulted in theISDBformat.[24]Japan started digital satellite and HDTV broadcasting in December 2000.[13]

Rise of digital compression

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High-definition digital television was not possible withuncompressed video,which requires abandwidthexceeding 1Gbit/sfor studio-quality HDdigital video.[25][26]Digital HDTV was made possible by the development ofdiscrete cosine transform(DCT)video compression.[27][25]DCT coding is alossyimage compression technique that was first proposed byNasir Ahmedin 1972,[28]and was later adapted into amotion-compensatedDCT algorithm forvideo coding standardssuch as theH.26xformats from 1988 onwards and theMPEGformats from 1993 onwards.[29][30]Motion-compensated DCT compression significantly reduces the amount of bandwidth required for a digital TV signal.[25][31]By 1991, it had achieveddata compression ratiosfrom 8:1 to 14:1 for near-studio-quality HDTV transmission, down to 70–140Mbit/s.[25]Between 1988 and 1991, DCT video compression was widely adopted as thevideo coding standardfor HDTV implementations, enabling the development of practical digital HDTV.[25][27][32]Dynamicrandom-access memory(DRAM) was also adopted asframebuffersemiconductor memory, with the DRAMsemiconductor industry's increased manufacturing and reducing prices important to the commercialization of HDTV.[32]

Since 1972,International Telecommunication Union's radio telecommunications sector (ITU-R) had been working on creating a global recommendation for Analog HDTV. These recommendations, however, did not fit in the broadcasting bands which could reach home users. The standardization ofMPEG-1in 1993 led to the acceptance of recommendationsITU-R BT.709.[33]In anticipation of these standards, the DVB organization was formed. It was alliance of broadcasters, consumer electronics manufacturers and regulatory bodies. The DVB develops and agrees upon specifications which are formally standardised byETSI.[34]

DVB created first the standard forDVB-Sdigital satellite TV,DVB-Cdigital cable TV andDVB-Tdigital terrestrial TV. These broadcasting systems can be used for both SDTV and HDTV. In the US theGrand Allianceproposed ATSC as the new standard for SDTV and HDTV. Both ATSC and DVB were based on theMPEG-2standard, although DVB systems may also be used to transmit video using the newer and more efficientH.264/MPEG-4 AVCcompression standards. Common for all DVB standards is the use of highly efficient modulation techniques for further reducing bandwidth, and foremost for reducing receiver-hardware and antenna requirements.[citation needed]

In 1983, the International Telecommunication Union's radio telecommunications sector (ITU-R) set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. One of the thornier issues concerned a suitable frame/field refresh rate, the world already having split into two camps, 25/50 Hz and 30/60 Hz, largely due to the differences inmainsfrequency. The IWP11/6 working party considered many views and throughout the 1980s served to encourage development in a number of video digital processing areas, not least conversion between the two main frame/field rates usingmotion vectors,which led to further developments in other areas. While a comprehensive HDTV standard was not in the end established, agreement on the aspect ratio was achieved.[citation needed]

Initially the existing 5:3 aspect ratio had been the main candidate but, due to the influence of widescreen cinema, the aspect ratio16:9(1.78) eventually emerged as being a reasonable compromise between 5:3 (1.67) and the common 1.85 widescreen cinema format. An aspect ratio of 16:9 was duly agreed upon at the first meeting of the IWP11/6 working party atthe BBC's Research and Developmentestablishment in Kingswood Warren. The resulting ITU-R Recommendation ITU-R BT.709-2 ( "Rec. 709") includes the 16:9 aspect ratio, a specifiedcolorimetry,and the scan modes1080i(1,080 actively interlaced lines of resolution) and1080p(1,080progressively scannedlines). The BritishFreeview HDtrials usedMBAFF,which contains both progressive and interlaced content in the same encoding.[citation needed]

It also includes the alternative 1440×1152HDMACscan format. (According to some reports, a mooted 750-line (720p) format (720 progressively scanned lines) was viewed by some at the ITU as an enhanced television format rather than a true HDTV format,[35]and so was not included, although 1920×1080i and 1280×720p systems for a range of frame and field rates were defined by several USSMPTEstandards.)[citation needed]

Inaugural HDTV broadcast in the United States

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HDTV technology was introduced in the United States in the early 1990s and made official in 1993 by theDigital HDTV Grand Alliance,a group of television, electronic equipment, communications companies consisting ofAT&T Bell Labs,General Instrument,Philips,Sarnoff,Thomson,Zenithand theMassachusetts Institute of Technology.Field testing of HDTV at 199 sites in the United States was completed August 14, 1994.[36]The first public HDTV broadcast in the United States occurred on July 23, 1996, when theRaleigh, North Carolinatelevision stationWRAL-HDbegan broadcasting from the existing tower ofWRAL-TVsoutheast of Raleigh, winning a race to be first with the HD Model Station inWashington, D.C.,which began broadcasting July 31, 1996 with the callsign WHD-TV, based out of the facilities ofNBCowned and operated stationWRC-TV.[37][38][39]The AmericanAdvanced Television Systems Committee(ATSC) HDTV system had its public launch on October 29, 1998, during the live coverage of astronautJohn Glenn's return mission to space on board theSpace ShuttleDiscovery.[40]The signal was transmitted coast-to-coast, and was seen by the public in science centers, and other public theaters specially equipped to receive and display the broadcast.[40][41]

European HDTV broadcasts

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Between 1988 and 1991, several European organizations were working ondiscrete cosine transform(DCT) based digitalvideo coding standardsfor both SDTV and HDTV. The EU 256 project by the CMTT and ETSI, along with research by Italian broadcasterRAI,developed a DCTvideo codecthat broadcast near-studio-quality HDTV transmission at about 70–140 Mbit/s.[25][42]The first HDTV transmissions in Europe, albeit not direct-to-home, began in 1990, when RAI broadcast the1990 FIFA World Cupusing several experimental HDTV technologies, including the digital DCT-based EU 256 codec,[25]the mixed analog-digitalHD-MACtechnology, and the analogMUSEtechnology. The matches were shown in 8 cinemas in Italy, where the tournament was played, and 2 in Spain. The connection with Spain was made via the Olympus satellite link fromRometoBarcelonaand then with afiber opticconnection from Barcelona toMadrid.[43][44]After some HDTV transmissions in Europe, the standard was abandoned in 1993, to be replaced by a digital format from DVB.[45]

The first regular broadcasts began on January 1, 2004, when the Belgian companyEuro1080launched the HD1 channel with the traditionalVienna New Year's Concert.Test transmissions had been active since the IBC exhibition in September 2003, but the New Year's Day broadcast marked the official launch of the HD1 channel, and the official start of direct-to-home HDTV in Europe.[46]

Euro1080, a division of the later defunct Belgian TV services company Alfacam, broadcast HDTV channels to break the pan-European stalemate of "no HD broadcasts mean no HD TVs bought means no HD broadcasts..." and kick-start HDTV interest in Europe.[47]The HD1 channel was initiallyfree-to-airand mainly comprised sporting, dramatic, musical and other cultural events broadcast with a multi-lingual soundtrack on a rolling schedule of four or five hours per day.[citation needed]

These first European HDTV broadcasts used the 1080i format with MPEG-2 compression on a DVB-S signal fromSES'sAstra 1Hsatellite. Euro1080 transmissions later changed to MPEG-4/AVC compression on a DVB-S2 signal in line with subsequent broadcast channels in Europe.[citation needed]

Despite delays in some countries,[48]the number of European HD channels and viewers has risen steadily since the first HDTV broadcasts, with SES's annualSatellite Monitormarket survey for 2010 reporting more than 200 commercial channels broadcasting in HD from Astra satellites, 185 million HD capable TVs sold in Europe (£60 million in 2010 alone), and 20 million households (27% of all European digital satellite TV homes) watching HD satellite broadcasts (16 million via Astra satellites).[49]

In December 2009, the United Kingdom became the first European country to deploy high-definition content using the newDVB-T2transmission standard, as specified in theDigital TV Group(DTG)D-book,on digital terrestrial television.[citation needed]

TheFreeview HDservice contains 13 HD channels (as of April 2016) and was rolled out region by region across the UK in accordance with thedigital switchoverprocess, finally being completed in October 2012. However, Freeview HD is not the first HDTV service over digital terrestrial television in Europe; Italy'sRAIstarted broadcasting in 1080i on April 24, 2008, using the DVB-T transmission standard.[citation needed]

In October 2008, France deployed five high definition channels using DVB-T transmission standard on digital terrestrial distribution.[citation needed]

Notation

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HDTV broadcast systems are identified with three major parameters:

  • Frame sizein pixels is defined asnumber of horizontal pixels × number of vertical pixels,for example1280 × 720or1920 × 1080.Often the number of horizontal pixels is implied from context and is omitted, as in the case of720pand1080p.
  • Scanning systemis identified with the letterpforprogressive scanningoriforinterlaced scanning.
  • Frame rateis identified as number of video frames per second. For interlaced systems, the number of frames per second should be specified, but it is not uncommon to see the field rate incorrectly used instead.

If all three parameters are used, they are specified in the following form:[frame size][scanning system][frame or field rate]or[frame size]/[frame or field rate][scanning system].[50]Often, frame size or frame rate can be dropped if its value is implied from context. In this case, the remaining numeric parameter is specified first, followed by the scanning system.[citation needed]

For example,1920×1080p25identifies progressive scanning format with 25 frames per second, each frame being 1,920pixelswide and 1,080 pixels high. The1080i25or1080i50notation identifies interlaced scanning format with 25 frames (50 fields) per second, each frame being 1,920 pixels wide and 1,080 pixels high. The1080i30or1080i60notation identifies interlaced scanning format with 30 frames (60 fields) per second, each frame being 1,920 pixels wide and 1,080 pixels high. The720p60notation identifies progressive scanning format with 60 frames per second, each frame being 720 pixels high; 1,280 pixels horizontally are implied.[citation needed]

Systems using 50 Hz support three scanning rates: 50i, 25p and 50p, while 60 Hz systems support a much wider set of frame rates: 59.94i, 60i, 23.976p, 24p, 29.97p, 30p, 59.94p and 60p. In the days of standard-definition television, the fractional rates were often rounded up to whole numbers, e.g. 23.976p was often called 24p, or 59.94i was often called 60i. Sixty Hertz high definition television supports both fractional and slightly different integer rates, therefore strict usage of notation is required to avoid ambiguity. Nevertheless, 29.97p/59.94i is almost universally called 60i, likewise 23.976p is called 24p.[citation needed]

For the commercial naming of a product, the frame rate is often dropped and is implied from context (e.g., a1080i television set). A frame rate can also be specified without a resolution. For example, 24p means 24 progressive scan frames per second, and 50i means 25 interlaced frames per second.[51]

There is no single standard for HDTV color support. Colors are typically broadcast using a (10-bits per channel)YUVcolor space but, depending on the underlying image generating technologies of the receiver, are then subsequently converted to aRGBcolor space using standardized algorithms. When transmitted directly through the Internet, the colors are typically pre-converted to 8-bit RGB channels for additional storage savings with the assumption that it will only be viewed only on a (sRGB) computer screen. As an added benefit to the original broadcasters, the losses of the pre-conversion essentially make these files unsuitable for professional TV re-broadcasting.[citation needed]

Most HDTV systems support resolutions and frame rates defined either in the ATSC table 3, or in EBU specification. The most common are noted below.[citation needed]

Display resolutions

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Video format supported [image resolution] Native resolution [inherent resolution] (W×H) Pixels Aspect ratio (W:H) Description
Actual Advertised (Megapixels) Image Pixel
720p
(HD ready)
1280×720 		1024 × 768
XGA 		786,432 0.8 4:3 (1.33:1) 1:1 (1.00:1) Typically a PC resolution (XGA); also a native resolution on many entry-level plasma displays with non-square pixels.
1280 × 720 921,600 0.9 16:9 (1.78:1) 1:1 Standard HDTV resolution and a typical PC resolution (WXGA), frequently used by high-endvideo projectors;also used for 750-line video, as defined in SMPTE 296M, ATSC A/53, ITU-R BT.1543.
1366 × 768
WXGA 		1,049,088 1.0 683:384
(approx. 16:9) 		1:1 A typical PC resolution (WXGA); also used by manyHD readyTV displays based onLCDtechnology.
1080p / 1080i
(Full HD)
1920×1080 		1920 × 1080 2,073,600 2.1 16:9 1:1 Standard HDTV resolution, used byfull HDandHD ready1080p TV displays such as high-end LCD, plasma andrear projectionTVs, and a typical PC resolution (lower thanWUXGA); also used for 1125-line video, as defined in SMPTE 274M, ATSC A/53, ITU-R BT.709
Video format supported Screen resolution (W×H) Pixels Aspect ratio (W:H) Description
Actual Advertised (Megapixels) Image Pixel
720p
(HD Ready)
1280×720 		1248 × 702
Clean Aperture 		876,096 0.9 16:9 1:1 Used for 750-line video with faster artifact/overscan compensation, as defined in SMPTE 296M.
1080i
(Full HD)
1920×1080 		1440 × 1080
HDCAM/HDV 		1,555,200 1.6 16:9 4:3 Used for anamorphic 1125-line video in the HDCAM and HDV formats introduced bySonyand defined (also as a luminance subsampling matrix) inSMPTE D11.
1080p
(Full HD)
1920×1080 		1888 × 1062
Clean aperture 		2,005,056 2.0 16:9 1:1 Used for 1124-line video with faster artifact/overscan compensation, as defined in SMPTE 274M.

At a minimum, HDTV has twice the linear resolution ofstandard-definition television(SDTV), thus showing greater detail than either analog television or regularDVD.The technical standards for broadcasting HDTV also handle the 16:9aspect ratioimages without usingletterboxingoranamorphicstretching, thus increasing the effective image resolution.

A very high-resolution source may require more bandwidth than available in order to be transmitted without loss of fidelity. Thelossy compressionthat is used in all digital HDTV storage and transmission systems will distort the received picture when compared to the uncompressed source.

Standard frame or field rates

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ATSC and DVB define the following frame rates for use with the various broadcast standards:[52][53]

  • 23.976 Hz (film-looking frame rate compatible withNTSCclock speed standards)
  • 24 Hz (international film and ATSC high-definition material)
  • 25 Hz (PAL film, DVB standard-definition and high-definition material)
  • 29.97 Hz (NTSC film and standard-definition material)
  • 30 Hz (NTSC film, ATSC high-definition material)
  • 50 Hz (DVB high-definition material)
  • 59.94 Hz (ATSC high-definition material)
  • 60 Hz (ATSC high-definition material)

The optimum format for a broadcast depends upon the type of videographic recording medium used and the image's characteristics. For best fidelity to the source, the transmitted field ratio, lines, and frame rate should match those of the source.

PAL, SECAM and NTSC frame rates technically apply only to analog standard-definition television, not to digital or high definition broadcasts. However, with the rollout of digital broadcasting, and later HDTV broadcasting, countries retained their heritage systems. HDTV in former PAL and SECAM countries operates at a frame rate of 25/50 Hz, while HDTV in former NTSC countries operates at 30/60 Hz.[54]

Types of media

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High-definition image sources includeterrestrial broadcast,direct broadcast satellite, digital cable,IPTV,Blu-rayvideo disc (BD), and internet downloads.

In the US, residents in the line of sight of television station broadcast antennas can receive free, over-the-air programming with a television set with anATSC tunervia aTV aerial.Laws prohibit homeowners' associations and city government from banning the installation of antennas.[citation needed]

Standard 35mmphotographic filmused for cinema projection has a much higherimage resolutionthan HDTV systems, and is exposed and projected at a rate of 24frames per second(frame/s). To be shown on standard television, in PAL-system countries, cinema film is scanned at the TV rate of 25 frame/s, causing a speedup of 4.1 percent, which is generally considered acceptable. In NTSC-system countries, the TV scan rate of 30 frame/s would cause a perceptible speedup if the same were attempted, and the necessary correction is performed by a technique called3:2 pulldown:Over each successive pair of film frames, one is held for three video fields (1/20 of a second) and the next is held for two video fields (1/30 of a second), giving a total time for the two frames of 1/12 of a second and thus achieving the correct average film frame rate.

Non-cinematic HDTV video recordings intended for broadcast are typically recorded either in 720p or 1080i format as determined by the broadcaster. 720p is commonly used for Internet distribution of high-definition video, because most computer monitors operate in progressive-scan mode. 720p also imposes less strenuous storage and decoding requirements compared to both 1080i and 1080p. 1080p/24, 1080i/30, 1080i/25, and 720p/30 is most often used on Blu-ray Disc.

Recording and compression

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Main article:High-definition pre-recorded media and compression

HDTV can be recorded toD-VHS(Digital-VHS or Data-VHS),W-VHS(analog only), to an HDTV-capabledigital video recorder(for exampleDirecTV's high-definition digital video recorder,Sky HD'sset-top box,Dish Network's VIP 622 or VIP 722 high-definition digital video recorder receivers (these set-top boxes allow for HD on the Primary TV and SD on the secondary TV (TV2) without a secondary box on TV2), orTiVo's Series 3 or HD recorders), or an HDTV-readyHTPC.Some cable boxes are capable of receiving or recording two or more broadcasts at a time in HDTV format, and HDTV programming, some included in the monthly cable service subscription price, some for an additional fee, can be played back with the cable company's on-demand feature.[citation needed]

The massive amount of data storage required to archive uncompressed streams meant that inexpensive uncompressed storage options were not available to the consumer. In 2008, the Hauppauge 1212 Personal Video Recorder was introduced. This device accepts HD content through component video inputs and stores the content in MPEG-2 format in a.ts file or in a Blu-ray-compatible format.m2tsfile on the hard drive or DVD burner of a computer connected to the PVR through a USB 2.0 interface. More recent systems are able to record a broadcast high definition program in its 'as broadcast' format or transcode to a format more compatible with Blu-ray.[citation needed]

Analog tape recorders with bandwidth capable of recording analog HD signals, such as W-VHS recorders, are no longer produced for the consumer market and are both expensive and scarce in the secondary market.[citation needed]

In the United States, as part of the FCC'splug and playagreement, cable companies are required to provide customers who rent HD set-top boxes with a set-top box with "functional"FireWire(IEEE 1394) on request. None of thedirect broadcast satelliteproviders have offered this feature on any of their supported boxes, but somecable TVcompanies have. As of July 2004,boxes are not included in the FCC mandate. This content is protected by encryption known as 5C.[55]This encryption can prevent duplication of content or simply limit the number of copies permitted, thus effectively denying most if not allfair useof the content.[citation needed]

See also

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References

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Further reading

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Wikimedia Commons has media related toHigh-definition television.

History

European adoption

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