High-definition television

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High-definition television (HDTV) means broadcast of television signals with a higher resolution than traditional formats (NTSC, SÉCAM, PAL) allow. Except for early analog formats in Europe and Japan, HDTV is broadcast digitally, and therefore its introduction sometimes coincides with the introduction of digital television (DTV).

Historically, the term high-definition television was also used to refer to television standards developed in the 1930s to replace the early experimental systems.

Contents

Notation

In the context of HDTV, the formats of the broadcasts are referred to using a notation describing:

For example, the format 720p60 is 1280 × 720 pixels, progressive encoding with 60 frames per second. The format 1080i50 is 1920 × 1080 pixels, interlaced encoding with 50 fields (25 frames) per second. Often the frame or field rate is left out. It can then usually be assumed to be either 50 or 60, except for 1080p which is only supported as either 1080p24, 1080p25 or 1080p30 by current technology.

A frame or field rate can also be specified without a resolution. For example 24p means 24 progressive frames per second and 50i means 25 interlaced frames per second.

Most HDTV systems supports some standard resolutions and frame or field rates. The most common are:

Standard resolutions

Image:Videores.png

Standard frame or field rates

  • 24p (photographic film)
  • 25p
  • 30p
  • 50p
  • 60p
  • 50i (PAL)
  • 60i (NTSC)

Comparison to SDTV

HDTV has at least twice the resolution of SDTV, thus allowing much more detail to be shown compared to analog television or regular DVDs. In addition, the technical standards for broadcasting HDTV are also able to handle 16:9 aspect ratio pictures without using letterboxing, thus further increasing the effective resolution for such content.

Close-up view

HDTV at four times the resolution of SDTV.

SDTV resolution.

Format considerations

The optimum format for a broadcast depends on the type of media used for the recording and the characteristics of the content. The field and frame rate should match the source, as should the resolution. On the other hand, a very high resolution may require more bandwidth than is available. The lossy compression that is used in all digital HDTV systems will then cause the picture to be distorted.

Photographic film destined for the theatre typically has a high resolution and is photographed at 24 frame/s. Depending on the available bandwidth and the amount of detail and movement in the picture, the optimum format is thus either 720p24 or 1080p24. Film may be converted to 25 or 50 frame/s by speeding it up by 4%, or to 60 frame/s through 3:2 pulldown. (See also: Telecine)

Older (pre-HDTV) recordings on video tape is often either in the form 480i60 or 576i50. These may be converted to a higher resolution format (720i), but removing the interlace to match the common 720p format may distort the picture or require filtering which actually reduces the resolution of video. (See also: Deinterlacing)

Noncinematic HDTV video recordings are typically recorded in 720p format which is adequate for that type of content.

To limit the complexity of the technology some broadcasters in the United States have standardised on a single format for all broadcasts. Fox, ABC, and ESPN (ABC and ESPN are both owned by Disney) currently broadcast 720p content. NBC and CBS currently broadcast 1080i content.

Technical details

MPEG-2 is most commonly used as the compression codec for digital HDTV broadcasts. Although MPEG-2 supports up to 4:2:2 YUV chroma subsampling and 10-bit quantization, HD broadcasts use 4:2:0 and 8-bit quantization to save bandwidth. Some broadcasters also plan to use MPEG-4.

HDTV is capable of "theater quality" audio because it uses the Dolby Digital (AC-3) format to support "5.1" surround sound.

The pixel aspect ratio of native HD signals is 1.0, or 1 pixel length x 1 pixel width. New HD formats such as HDV, a new HD compression found in low-end and prosumer cameras, use a aspect ratio of 1.33 to store data in a more mathmatically and algorithmically efficient compression.

For more technical details see the articles on ATSC, DVB, and ISDB, respectively.

Early Systems

SECAM 755i

When Europe resumed TV transmissions after WWII, i.e. in the late 1940s and early 1950s, different countries used different resolutions. England used 405 lines, most other countries 625 lines, but France decided in 1948 to go for 819 lines. The French TV system thus became the world's first HDTV system, and by today's standards, the French system could be called 755i (not all lines could be used for the actual image — some lines were lost during the vertical retrace). The French 819-line (or 755i) HDTV system was introduced in the 1950s. When, in the late 1960s, a second TV channel and color TV were introduced in Europe, England dropped its 405-line TV system and France dropped its 819-line system, making all European countries agree to use 625 lines (576i) for their TV transmissions.

The French "755i" 819-line HDTV system was used only in France and in Monaco, and in France only for the first French TV channel. It was discontinued in 1986. It was used only for black-and-white TV; color TV in 819-line SECAM never went beyond the experimental stage. It was transmitted only on VHF channels, and a French 819-line TV channel occupied 14 MHz of bandwidth.

MUSE

Main article: Multiple sub-nyquist sampling Encoding (MUSE)

Japan has the earliest working HDTV system still in use, with design efforts going back to 1979. Japan began broadcasting analog HDTV signals in the early 1990s using an interlaced resolution of 1035 lines (1035i). The Japanese MUSE system, developed by NHK Science and Technical Research Laboratories (STRL) in the 1980s, employed filtering tricks to reduce the original source signal to decrease bandwidth utilization.

MUSE in Operation

  • Typically three successive picture elements on a line were actually derived from three separate scans. Moving images were thus blurred in a manner similar to using 16mm movie film for HDTV projection.
  • Stationary images were transmitted at full resolution.
  • Whole camera pans would result in a loss of 50% of horizontal resolution.
  • Considering the technological limitations of the time, MUSE was a very cleverly designed analog system.
  • MUSE had a bit-reduced stereo audio transmission system that was notable in its design as it was not psychoacoustical like Musicam.

Though Japan has since switched to a digital HDTV system based on ISDB, the original MUSE based BS Satellite channel 9 (NHK BS Hi-vision) is still being broadcasted. It broadcasts the same programs as BS-digital channel 103, but will end sometime in 2007.

HD-MAC

Main article: HD-MAC

The European Commission established a European standard for uncompressed digital HDTV in a 1986 directive (MAC). However, it never became popular among broadcasters. It was required that all high-powered satellite broadcasters used MAC from that year. Owing to the advance of technology and the launch of middle powered satellites by SES Astra, broadcasters could avoid MAC, and lower transmission costs. HD-MAC (the high definition variant of MAC) was left for transcontinental satellite links, though.

Another reason for HD-MAC's failure was that it was not realistic to use 36 MHz for a high definition signal in terrestrial broadcasting (SDTV uses 6, 7 (VHF), or 8 MHz (UHF)). HD-MAC could only be used by cable and satellite providers, where there is a wider bandwidth available. Thus, analogue HDTV could not replace conventional SDTV (terrestrial) PAL/SECAM, making HD-MAC sets unattractive to potential consumers.

The HD-MAC standard was abandoned in 1993, and since then all EU and EBU efforts have focused on the DVB system (Digital Video Broadcasting), which allows both SDTV and HDTV.

See also: COUNCIL DIRECTIVE 92/38/EEC of 11 May 1992.

Contemporary systems

Australia

Australia started HD broadcasting in January 2001 but only in August 2003 was HD content mandated. Most cities in Australia that have a population of 40,000 or greater have at least one terrestrial DTV channel available (for example, Albany, Western Australia, has had DTV available for almost a year as of May, 2005). However, most Australian DTV broadcasters are still experimenting with HDTV transmission and DTV delivery.

Brazil

Brazilian universities, research and government institutions are discussing the best policies for a digital television system for use in Brazil.

A complete testbed is expected for 2006.

Canada

In Canada, on November 22 2003, CBC had their first broadcast in HD, in the form of the Heritage Classic outdoor NHL game between the Edmonton Oilers and the Montreal Canadiens. Bell ExpressVu, a Canadian satellite company, and Rogers Cable both provide somewhat more than 21 HDTV channels to their subscribers, typically for a non-trivial fee including TSN HD, SportsNet HD, Discovery HD (Canadian Edition), The Movie Network HD, and several U.S. stations plus some PBS feeds and a couple of pay-TV movie channels. CTV Toronto broadcast in HD along with its western counterpart, BC CTV. They were also the first to broadcast a terrestrial HD digital ATSC signal in Canada. Global joined the crowd in late 2004. Other networks are continuing to announce availability of HD signals. Citytv's CITY TV in Toronto was the first HDTV broadcaster in Canada, however very few shows are shown in HDTV beyond the well known ones such as CSI, ER, etc. as of early 2005. CBC officially launched HDTV programming on March 5 2005.

Europe

Main articles: High-definition television in Europe, Euro1080

Currently the pioneer in HDTV transmission in Europe is Euro1080, which started with its flagship channel (Euro1080 – HD1) back in 2004 and has since added HD2/HD5. HD1 is currently transmitted on Astra (German-speaking area), Hellas Sat 2 (rest of Europe, specially South and South-Eastern part) and Sirius satellites (Scandinavia).

With the announcement of Sky's first bouquet of HDTV channels for the UK/ROI; Premiere's bouquet of HDTV channels for the German-speaking population of Germany, Austria and Switzerland, and the French MPEG-4 pay per view terrestrial channels, HDTV seems to (slowly) take off in Europe. In the UK, Sky will launch high-definition TV in early 2006 with a large marketing budget. However, owing to Europe's late entry into the HDTV market, it has the advantage of being able to use more modern picture compression technology and so far all these major broadcasters have announced their intentions of eventually using H.264/MPEG-4 AVC in their programming. This will allow them to utilize broadcasting frequencies much more efficiently than in the United States since transmiting HDTV signals using using H.264 compression requires roughly half as much bandwidth as needed under the USA's ATSC system (ATSC had standardised utilising the less efficient MPEG-2 compression long before more modern codecs like H.264 became available). Most European favour using the 1080i format over 720p.

Although all of these channels are (and will remain) subscription-based, it is only a matter of time until European consumers have access to a wide offer of FTA HD channels (Prosieben HD and SAT1 HD being the pioneers).

Japan

Japan had pioneered HDTV for decades with an analog implementation. Their old system is not compatible with the new digital standards. Japan terrestrial broadcast of HD via ISDB-T started in December 2003. It is reported that two million HD receivers have been sold in Japan already.

Republic of Korea

After a long controversy between the government and broadcasters, ATSC was chosen over DVB-T. In 2005, digital services will be available in all the country.

It is required that at least 10 hours of HD content to be broadcast on a weekly basis during the first year of commercial digital service.

Mexico

A Mexican television company Televisa made experimental HDTV broadcasts in the early 1990s, in collaboration with Japan's NHK. Some events are now broadcast in high definition, but HDTV use is very limited.

During the first half of 2005, at least one cable provider in Mexico City (Cablevision) has begun to offer 5 HDTV channels to subscribers purchasing a digital video recorder (DVR).

Other television company TV Azteca has planned to broadcast the Mexican football tournament in HDTV. Also one retailer, Elektra started shipping televisions with HDTV receivers to support this broadcast.

XETV in Tijuana, Baja California across the border from San Diego, California is on the air in HDTV using 720p format. This affiliate of the American Fox TV Network is on UHF channel 23 broadcasting from Mt. San Antonio in Tijuana, Mexico with 403,000 watts, directed primarily northward at San Diego.

United States

Main article: High-definition television in the United States of America

In the United States, HDTV specifications are defined by the ATSC. An HDTV-compatible TV usually uses a 16:9 aspect ratio display with an integrated ATSC tuner. Lower resolution sources like regular DVDs may be upscaled to the native resolution of the TV.

Recording, compression, and prerecorded media

HDTV can be recorded to D-VHS (Data-VHS), W-VHS, to an HDTV-capable digital video recorder such as DirecTV's high-definition TiVo or Dish Network's DVR 921 or 942, or to a computer equipped with an HDTV capture card. In the U.S., the only current archival option is D-VHS. D-VHS digitally records a 28.2 Mbit stream onto a classic VHS tape, using a FireWire (IEEE 1394) digital transport to carry a compressed MPEG-2 Transport Stream from the tuning device to the recorder.

Unfortunately, the massive amount of data storage required to archive uncompressed streams make it unlikely that an uncompressed storage option will appear in the consumer market soon. Realtime MPEG-2 compression of an uncompressed digital HDTV signal is also prohibitively expensive for the consumer market at this time, but should become inexpensive within several years (although this is more relevant for consumer HD camcorders than recording HDTV). 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.

As part of the FCC's "plug and play" agreement cable companies are required to provide customers that rent HD set-top boxes with a set-top box with "functional" Firewire (IEEE 1394) upon request. None of the DBS providers have offered this feature on any of their supported boxes. As of July 2004 as they are not included in the FCC mandate. This content is protected by encryption known as 5C. This encryption can prevent someone from recording content at all or simply limit the number of copies.

Aside from scarce Japanese analog MUSE-encoded laser discs that are no longer produced, as of 2005 the only current available prerecorded HD media is D-Theater. Comprising less than 100 titles and utilizing a 28 Mbit/s MPEG2 stream at 720p or 1080i with either Dolby Digital 5.1 or DTS encoding, D-Theater is an encrypted D-VHS format and only D-Theater capable D-VHS players can play back these tapes. This format is superior to broadcast HDTV due to its higher bandwidth and, of course, the ability to do non-realtime optimization of the encoding which is not possible with broadcast HDTV. D-Theater is currently a small niche market even within the niche HDTV community and it appears as if the final D-Theater title was published in 2004.

Future media

HD programming may be recorded on optical disc using Blu-ray or on HD-DVD. Blu-ray technology is currently available only in Japan with a Japanese satellite/terrestrial tuner, but is expected to be released in other world markets in 2006. Blu-ray uses a blue-laser optical disc with an MPEG-2 or MPEG-4 codec.


The view - according to Microsoft

In an attempt to provide a bitrate-compatible high-definition format for high-definition video on standard DVD-ROMs, Microsoft introduced their Windows Media 9 Series codec with the ability to compress a high-definition bitstream into the same space as a conventional NTSC bitstream (approximately 5 to 9 megabits per second for 720p and higher). Microsoft is marketing its high-definition Windows Media 9 Series codec as WMV HD. It remains to be seen if the codec will be adopted for widespread use, if only as a Wi-Fi industry standard. As of November 2003, this format required a significant amount of processing power to encode and decode and the only commercially available movie that used the codec was the Terminator 2: Extreme Edition DVD (see 1). Since then, more titles have become available in this format, such as the acclaimed surf documentary Step Into Liquid. As of the start of 2005, Microsoft recomends a 3.0 GHz processor with 512 MB of RAM and a 128 MB video card for 1080p playback on Windows XP, though there are now commercially available DVD players, like the KiSS DP-600, that will play back WMV HD DVD ROMs in high definition on HDTV sets. The codec has been submitted to SMPTE and is in SMPTE's standardization process with an intent for it to become an official SMPTE standard known as VC-1 in the near future.

end of The view - according to Microsoft


What is happening in the broadcasting world

Other codecs are in contention such as AVC (MPEG-4 part 10, also known as H.264, approved by the ITU-T and MPEG standards bodies in early 2003) and the VP6 and now VP7 codecs from On2 Technologies.

H.264 as a standard has already been selected and adopted by the biggest broadcasters in the USA (DirecTV, DISH Network) and Europe (BSkyB, Premiere, Canal+, TPS, ...). H.264 was chosen for several reasons: First, the standard was validated as an open standard at least a year before VC-1 was seriously considered as a potential open standard, and then, there is a lot of uncertainty on the levies Microsoft may want impose once the algorithm is adopted. So far, only a handful of very minor broadcasters are seriously considering VC-1. It has been thought for a while that VC-1 was better adapted for the IPTV world than H.264, but press announcements have also already been made by some of the largest STB manufacturers like Amino, Pace, Kreatel demonstrating solutions based on H.264 standards.

The main areas of dominance of VC-1 seem currently to be in the Blu-Ray DVD (HD DVD have not yet announced support for VC-1) and, for obvious reason, the home PCs.

In fact, there is some concern in the community that Microsoft may have appropriated itself the H.264 standard, modified and improved upon it and are trying to resell the solution as VC-1, without providing dues to the MPEG-LA. However, this is currently a rumour and has not yet been challenged.

Example of broadcasters concerns.

end of What is happening in the broadcasting world


VP6 was reported by On2 to have been chosen by China for use in the Enhanced Versatile Disc (EVD) format initiative. This was reportedly as a result of China's desire to avoid royalties on WM9 or AVC. As an advantage, VP6 would not require royalties on recorded media (although royalties would be charged for player devices at a similar cost as for other codecs). As China starts to dominate manufacturing of TV and DVD units, the country's choice of standards becomes more important for everyone. A low cost for the codec itself is not a significant advantage over DVD, however, as the standalone hardware players will be incompatible with standard DVD-Video unless the manufacturer pays the royalties for the technologies necessary to make the player DVD-compatible. Very few titles were made available in any market for this format, although many would presumably be needed to drive purchase of incompatible players. It is unlikely any major U.S. studio will commit to movies in this format without some form of copy-protection, which is not yet specified. Soon after the announcement that VP6 would be used on EVD, negotiations between On2 and E-World (the consortium pushing EVD to become a standard) broke down. On2 filed multiple breach of contract claims for arbitration, but in March of 2005 the arbitrator ruled that E-World had not broken the contract and owed nothing to On2. It was unclear to On2 and the arbitrator whether the Chinese government ever approved the EVD proposal as a standard.

Recently, the DVD Forum and the Blu-ray group failed to agree on standards for high definition 12 cm discs. A format war is now very likely between the DVD Forum's HD-DVD (formerly "Advanced Optical Disc") standard and Sony's Blu-ray disc standard. To complicate things further, Sony also makes movies via its Columbia Pictures subsidiary. As a result, this will likely lead to certain films becoming available only on one format. Both sides of the HD disc camp are likely to leverage studio partners against each other through exclusive arrangements. A possible outcome of a messy format war could be the emergence of combo players, as the physical disc sizes are identical.

Although they disagree about physical format technology, both the HD-DVD and Blu-ray factions have selected the same three video codecs to be mandatory in their designs: specifically, MPEG-2 Part 2, VC-1, and H.264.

There are now some DVD players that will output enhanced or high-definition signals from standard-definition DVDs. These players, however, are not considered to be true HD-DVD players since they only include an integrated scaler to upconvert the standard-definition DVD video to high-definition video. This upconversion process generally can improve the perceived picture quality of standard-definition video.

Recently, Sony launched their first consumer HD camera called the HDR-FX1, which can record the 1080i60 format (the PAL version records 1080i50) on a Mini-DV tape using the HDV format. The camera uses the MPEG-2 codec to record the video and the audio and a 3-CCD system to accurately acquire color. Therefore, the HDR-FX1 closely matches a professional HD camera. JVC also released a consumer HD camera that records in 720p30 but uses a single CCD with only DV quality video. Apple's iMovie HD, Final Cut Express HD, and Final Cut Pro HD (with Lumiere HD installed) can edit MPEG-2 HD/HDV in a stable way. An Apple Macintosh computer is required to run this software. On the PC side, Adobe Premiere Pro 1.5 and Sony Vegas 6 can edit HD. The popular open source video editor Cinelerra also makes HDV editing possible and runs on a variety of different computer architectures.

Table of terrestrial HDTV transmission systems

Main characteristics of three DTTV systems
Systems ATSC DVB-T ISDB-T
Source coding
Video Main Profile syntax of ISO/IEC 13818-2 (MPEG-2 – Video)
Audio ATSC Standard A/52 (Dolby AC-3) ISO/IEC 13818-2 (MPEG-2 – Layer II Audio) and Dolby AC-3 ISO/IEC 13818-7 (MPEG-2 – AAC Audio)
Transmission system
Channel coding
Outer coding R-S (207, 187, t = 10) R-S (204, 188, t = 8)
Outer interleaver 52 R-S block 12 R-S block
Inner coding rate 2/3 trellis code PCC: rate 1/2, 2/3, 3/4, 5/6, 7/8; constraint length = 7, Polynomials (octal) = 171, 133
Inner interleaver 12 to 1 trellis code bit-wise, frequency bit-wise, frequency, selectable time
Data randomization 16-bit PRBS
Modulation 8-VSB and 16-VSB COFDM
QPSK, 16QAM and 64QAM
Hierarchical modulation: multi-resolution constellation (16QAM and 64QAM)
Guard interval: 1/32, 1/16, 1/8 & 1/4 of OFDM symbol
Two modes: 2k and 8k FFT 		BST-COFDM with 13 frequency segments
DQPSK, QPSK, 16QAM and 64QAM
Hierarchical modulation: choice of three different modulations on each segment
Guard interval: 1/32, 1/16, 1/8 & 1/4 of OFDM symbol
Three modes: 2k, 4k and 8k FFT

References

See also

External links

Wikiquote has a collection of quotations related to:
Look up HDTV on Wiktionary, the free dictionary.
Television resolution
LDTV 240i60, 288i50 (CIF)
SDTV 480i60 (NTSC), 480p30, 576i50 (PAL, SÉCAM), 576p25
EDTV 480p60, 576p50, 720i50, 720i60, 720p24, 720p25, 720p30
HDTV 720p50, 720p60, 1080p24, 1080p25, 1080p30, 1080i50, 1080i60
Progressive, Interlaced
Image:Videores.png
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