bharatkumar
Newbie
HDTV signals and colorimetry are defined by Rec. 709. MPEG-2 is most commonly used as the compression codec for digital HDTV broadcasts. Although MPEG-2 supports up to 4:2:2 YCbCr 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 H.264/MPEG-4 AVC, such as the BBC which is trialing such a system via satellite broadcast, which will save considerable bandwidth compared to MPEG-2 systems. Some German broadcasters already use H.264/MPEG-4 AVC together with DVB-S2 (Pro 7, Sat.1 and Premiere). Although MPEG-2 is more widely used at present, it seems likely that in the future all European HDTV may be H.264/MPEG-4 AVC, and Norway, which is currently in the progress of implementing digital television broadcasts, is using H.264/MPEG-4 AVC for present SD Digital as well as for future HDTV on terrestrial broadcasts. In parts of Sweden the standard is already in use for HDTV terrestrial broadcasting, reaching about 25-30% of the population. Brasil was the first country in the American continent to begin broadcasting H.264 AVC video and HE-AAC audio as the main program (or multi) compression and the same H.264 AVC in LDTV 240p using AAC-LC as audio for mobile DTV devices, not only mobile phones.
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 a "square" 1.0, in which each pixel's height equals its width. New HD compression and recording formats such as HDV use rectangular pixels to save bandwidth and to open HDTV acquisition for the consumer market. For more technical details see the articles on HDV, ATSC, DVB, and ISDB but the ISDB-Tb used primarily in Brasil uses HE-AAC that is more flexible than AC-3 and lower royalty fees.
Television studios as well as production and distribution facilities, use the HD-SDI SMPTE 292M interconnect standard (a nominally 1.485 Gbit/s, 75-ohm serial digital interface) to route uncompressed HDTV signals. The native bitrate of HDTV formats cannot be supported by 6-8 MHz standard-definition television channels for over-the-air broadcast and consumer distribution media, hence the widespread use of compression in consumer applications. SMPTE 292M interconnects are generally unavailable in consumer equipment, partially due to the expense involved in supporting this format, and partially because consumer electronics manufacturers are required (typically by licensing agreements) to provide encrypted digital outputs on consumer video equipment, for fear that this would aggravate the issue of video piracy.
Newer dual-link HD-SDI signals are needed for the latest 4:4:4 camera systems (Sony Cinealta F23 & Thomson Viper), where one link/coax cable contains the 4:2:2 YCbCr info and the other link/coax cable contains the additional 0:2:2 CbCr information.
Advantages of HDTV expressed in non-technical terms
High-definition television (HDTV) yields a better-quality image than standard television does, because it has a greater number of lines of resolution. The visual information is some 2-5 times sharper because the gaps between the scan lines are narrower or invisible to the naked eye.
The lower-case "i" appended to the numbers denotes interlaced; the lower-case "p" denotes progressive. The interlaced scanning method, the 1,080 lines of resolution are divided into two, the first 540 lines are painted on a frame, the second 540 lines are painted on a second frame, reducing the bandwidth. The progressive scanning method simultaneously displays all 1,080 lines of resolution at 60 frames per second, on a greater bandwidth. (See: An explanation of HDTV numbers and laymen's glossary)
Often, the broadcast HDTV video signal soundtrack is Dolby Digital 5.1 surround sound, enabling full, surround sound capabilities, while STBC television signals include either monophonic or stereophonic audio, or both. Stereophonic broadcasts can be encoded with Dolby Surround audio signal. Brasil opted to upgrade the ISDB-T Japanese standard to H.264/MPEG-4 AVC in the video compression and HE-AAC for audio compression because Dolby is not open and the royalty fees are more expensive than that of H.264 and renamed the upgraded standard to ISDB-Tb that now became the International ISDB-T standard.
Disadvantages of HDTV expressed in non-technical terms
In practice, the best possible HD quality is not usually achieved. The main problem is that many operators do not follow HDTV specifications fully. They may use slower bitrates or lower resolution to pack more channels within the limited bandwidth, reducing video quality.[14] The operators may use a format that is different from the original programming, introducing generation loss artifacts in the process of re-encoding.[15] Also, image quality may be lost if the television is not properly connected to the input device or not properly configured for the input's optimal performance, which may be difficult because of customer confusion regarding connections.
Appropriate cabling must be used. Either HDMI or component video cables must be used to support a high-definition signal. For instance, if composite or S-Video cables are used for connections from a cable box or satellite dish then only an SDTV quality picture will be seen. HDMI cables provide the best picture and sound but are also generally more expensive than component cables. Component video cables are RCA cables that are color coded for proper signal. They consist of three video cables (green, blue, and red), two audio cables (red and white), and they carry an analog signal. HDMI cables carry all the video and audio in one cable using a digital signal.
As high-definition video broadcasts are digital, the disadvantages of digital video broadcasting also apply. For example, digital video responds differently to analogue video when subject to interference. Unlike in analogue television broadcasting, in which interference causes only gradual image and sound degradation, interference in a digital television broadcast will freeze, skip, or display "garbage" information. This problem is particularly pronounced in the 8VSB modulation standard used for over-the-air transmission in the United States, which is highly sensitive to dynamic multipath interference that may be introduced by moving objects between the transmitting and receiving antennas. For instance, it is impossible to receive a 8VSB-modulated HDTV signal in a moving vehicle, and it may be difficult to maintain reception during high winds in locations where large trees are situated in the line between broadcasting antenna and receiver.
In order to view HDTV broadcasts, viewers may have to upgrade their TVs at some expense. Adding a new aspect ratio makes for consumer confusion if a display is capable of one or more ratios but must be switched to the correct one by the user. Traditional standard definition programs and feature films (mostly movies from before 1953) originally filmed in the standard 4:3 ratio, when displayed correctly on a HDTV monitor, will have empty display areas to the left and right of the image. Many consumers aren't satisfied with this unused display area and choose instead to distort their standard definition shows by stretching them horizontally to fill the screen, giving everything the appearance of being too wide or not tall enough. Alternatively, viewers may choose to zoom the image which removes content that was on the top and bottom of the original TV show.[16]
Broadcasters may demand, or cable-television operators may elect, to place HD signals in a premium band that requires higher cable fees. Some satellite companies may offer local HD channels as a service at additional cost (transmission comes from satellite). This leads some broadcasters to offer on-air broadcasts of local HD signals as a premium service to subscribers. Viewers may be denied some television channels that they expected, be allowed only access to the non-digital, and obviously sub-standard non-digital signal, or have to install an antenna to receive the digital broadcasts. Such issues entail economic and legal disputes more than technology.
Another disadvantage of HDTV compared to traditional television has been consumer confusion stemming from the different standards and resolutions, such as 1080i, 1080p, and 720p. Complicating the matter have been the changes in television connections from component video, to DVI, then to HDMI. Finally, the HD DVD vs. Blu-ray Disc high definition storage format war for a period of time created confusion for consumers. This particular format war was recently "settled" with Blu-ray emerging as the victorious standard.
Table of terrestrial HDTV transmission systems
Main characteristics of three HDTV 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) As defined in ETSI DVB TS 101 154 - as H.264 AVC and/or ISO/IEC 13818-2 (MPEG-2 – Layer II Audio) and/or 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 convolutional (I=12, M=17, J=1) 12 R-S block Inner coding rate 2/3 Trellis code Punctured convolution 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, selectable time Data randomization 16-bit PRBS Modulation 8VSB (Only used for over the air transmission)
16VSB (Designed for cable, but rejected by the cable industry, cable TV uses 64QAM or 256QAM modulation as a de facto standard) 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
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 a "square" 1.0, in which each pixel's height equals its width. New HD compression and recording formats such as HDV use rectangular pixels to save bandwidth and to open HDTV acquisition for the consumer market. For more technical details see the articles on HDV, ATSC, DVB, and ISDB but the ISDB-Tb used primarily in Brasil uses HE-AAC that is more flexible than AC-3 and lower royalty fees.
Television studios as well as production and distribution facilities, use the HD-SDI SMPTE 292M interconnect standard (a nominally 1.485 Gbit/s, 75-ohm serial digital interface) to route uncompressed HDTV signals. The native bitrate of HDTV formats cannot be supported by 6-8 MHz standard-definition television channels for over-the-air broadcast and consumer distribution media, hence the widespread use of compression in consumer applications. SMPTE 292M interconnects are generally unavailable in consumer equipment, partially due to the expense involved in supporting this format, and partially because consumer electronics manufacturers are required (typically by licensing agreements) to provide encrypted digital outputs on consumer video equipment, for fear that this would aggravate the issue of video piracy.
Newer dual-link HD-SDI signals are needed for the latest 4:4:4 camera systems (Sony Cinealta F23 & Thomson Viper), where one link/coax cable contains the 4:2:2 YCbCr info and the other link/coax cable contains the additional 0:2:2 CbCr information.
Advantages of HDTV expressed in non-technical terms
High-definition television (HDTV) yields a better-quality image than standard television does, because it has a greater number of lines of resolution. The visual information is some 2-5 times sharper because the gaps between the scan lines are narrower or invisible to the naked eye.
The lower-case "i" appended to the numbers denotes interlaced; the lower-case "p" denotes progressive. The interlaced scanning method, the 1,080 lines of resolution are divided into two, the first 540 lines are painted on a frame, the second 540 lines are painted on a second frame, reducing the bandwidth. The progressive scanning method simultaneously displays all 1,080 lines of resolution at 60 frames per second, on a greater bandwidth. (See: An explanation of HDTV numbers and laymen's glossary)
Often, the broadcast HDTV video signal soundtrack is Dolby Digital 5.1 surround sound, enabling full, surround sound capabilities, while STBC television signals include either monophonic or stereophonic audio, or both. Stereophonic broadcasts can be encoded with Dolby Surround audio signal. Brasil opted to upgrade the ISDB-T Japanese standard to H.264/MPEG-4 AVC in the video compression and HE-AAC for audio compression because Dolby is not open and the royalty fees are more expensive than that of H.264 and renamed the upgraded standard to ISDB-Tb that now became the International ISDB-T standard.
Disadvantages of HDTV expressed in non-technical terms
In practice, the best possible HD quality is not usually achieved. The main problem is that many operators do not follow HDTV specifications fully. They may use slower bitrates or lower resolution to pack more channels within the limited bandwidth, reducing video quality.[14] The operators may use a format that is different from the original programming, introducing generation loss artifacts in the process of re-encoding.[15] Also, image quality may be lost if the television is not properly connected to the input device or not properly configured for the input's optimal performance, which may be difficult because of customer confusion regarding connections.
Appropriate cabling must be used. Either HDMI or component video cables must be used to support a high-definition signal. For instance, if composite or S-Video cables are used for connections from a cable box or satellite dish then only an SDTV quality picture will be seen. HDMI cables provide the best picture and sound but are also generally more expensive than component cables. Component video cables are RCA cables that are color coded for proper signal. They consist of three video cables (green, blue, and red), two audio cables (red and white), and they carry an analog signal. HDMI cables carry all the video and audio in one cable using a digital signal.
As high-definition video broadcasts are digital, the disadvantages of digital video broadcasting also apply. For example, digital video responds differently to analogue video when subject to interference. Unlike in analogue television broadcasting, in which interference causes only gradual image and sound degradation, interference in a digital television broadcast will freeze, skip, or display "garbage" information. This problem is particularly pronounced in the 8VSB modulation standard used for over-the-air transmission in the United States, which is highly sensitive to dynamic multipath interference that may be introduced by moving objects between the transmitting and receiving antennas. For instance, it is impossible to receive a 8VSB-modulated HDTV signal in a moving vehicle, and it may be difficult to maintain reception during high winds in locations where large trees are situated in the line between broadcasting antenna and receiver.
In order to view HDTV broadcasts, viewers may have to upgrade their TVs at some expense. Adding a new aspect ratio makes for consumer confusion if a display is capable of one or more ratios but must be switched to the correct one by the user. Traditional standard definition programs and feature films (mostly movies from before 1953) originally filmed in the standard 4:3 ratio, when displayed correctly on a HDTV monitor, will have empty display areas to the left and right of the image. Many consumers aren't satisfied with this unused display area and choose instead to distort their standard definition shows by stretching them horizontally to fill the screen, giving everything the appearance of being too wide or not tall enough. Alternatively, viewers may choose to zoom the image which removes content that was on the top and bottom of the original TV show.[16]
Broadcasters may demand, or cable-television operators may elect, to place HD signals in a premium band that requires higher cable fees. Some satellite companies may offer local HD channels as a service at additional cost (transmission comes from satellite). This leads some broadcasters to offer on-air broadcasts of local HD signals as a premium service to subscribers. Viewers may be denied some television channels that they expected, be allowed only access to the non-digital, and obviously sub-standard non-digital signal, or have to install an antenna to receive the digital broadcasts. Such issues entail economic and legal disputes more than technology.
Another disadvantage of HDTV compared to traditional television has been consumer confusion stemming from the different standards and resolutions, such as 1080i, 1080p, and 720p. Complicating the matter have been the changes in television connections from component video, to DVI, then to HDMI. Finally, the HD DVD vs. Blu-ray Disc high definition storage format war for a period of time created confusion for consumers. This particular format war was recently "settled" with Blu-ray emerging as the victorious standard.
Table of terrestrial HDTV transmission systems
Main characteristics of three HDTV 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) As defined in ETSI DVB TS 101 154 - as H.264 AVC and/or ISO/IEC 13818-2 (MPEG-2 – Layer II Audio) and/or 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 convolutional (I=12, M=17, J=1) 12 R-S block Inner coding rate 2/3 Trellis code Punctured convolution 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, selectable time Data randomization 16-bit PRBS Modulation 8VSB (Only used for over the air transmission)
16VSB (Designed for cable, but rejected by the cable industry, cable TV uses 64QAM or 256QAM modulation as a de facto standard) 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