High Definition Television, or HDTV according to ABBREVIATIONFINDER.ORG, is one of the formats that, added to digital television (DTV), is characterized by broadcasting television signals in a digital quality superior to existing systems (PAL, NTSC and SECAM).
HDTV technical details
The HDTV screen uses a 16: 9 aspect ratio. The high resolution of the images (1920 pixels × 1080 lines or 1280 pixels × 720 lines) allows to show much more detail compared to analog or Standard Definition television (720 pixels x 576 lines according to the PAL standard).
The codec used for compression can be MPEG-2, H.264 or wmvhd (Windows Media Video High Definition), although MPEG-2 is currently falling out of date due to its low compression efficiency compared to other codecs. HDTV images are up to 5 times sharper than normal definition television, comparing PAL with higher HDTV resolution.
The 1920×1080 resolution is usually in interlaced mode, to reduce bandwidth demands. The lines are scanned alternately 60 times per second, similarly entangled at 60 Hz in NTSC. This format is called 1080i, or 1080i60.
In areas where the PAL standard at 50 Hz is traditionally used, 1080i50 is used.
Progressive tracking formats with a speed of 60 frames per second are also used. The 1280×720 format in practice is always progressive (refreshing the entire frame each time) and is thus called 720p. Several American television stations currently broadcast in 720p / 60.
Initial systems
MUSE
Japan had the first working HDTV system, its designs date back to 1979. Japan began broadcasting analog HDTV signals in the early 1990s, using a resolution of 1035 interlaced lines (1035i). The Japanese MUSE system, developed by NHK’s science and technical research laboratories in the 1980s, employing filtering systems to reduce the original source signal and thus decrease the necessary bandwidth. For example, three successive frame elements on a line were actually derived from three separate sweeps. A full camera panorama would lose 50% of the horizontal resolution. Since then, Japan has switched to an ISDB-based digital HDTV system.
HD-MAC
The European Commission established a European standard for uncompressed digital HDTV by directive in 1986 (MAC). However, it was never popular with broadcasting stations. It required all high-power satellite broadcasters to use MAC from that year on. Due to technological advancement and the launch of medium power satellites by SES SA, the stations could work without MAC to thus lower transmission costs. HD-MAC (the high definition variant of MAC) was left for intercontinental satellite links. Another cause of the failure of HD-MAC was that it was unrealistic to use 36 Mhz for a high definition signal in terrestrial broadcasts (SDTV uses 6, 7 (VHF) or 8 Mhz (UDF). HD-MAC could only be used by companies of cable and satellite, where there is a greater bandwidth available. Thus, the analog HDTV could not replace the traditional SDTV(terrestrial) PAL / SECAM, making the HD-MAC equipment unattractive to potential consumers. The Barcelona’92 OlympicsThey were recorded in this analog format (4: 3 format, with a definition of 1250 vertical lines). To store them, giant tape tapes the size of a suitcase each were used. Said tapes incorporated handles in their casing to make their transport and handling easier. The HD-MAC standard was abandoned in 1993, and since then all the efforts of the EU and EBU have focused on the DVB (Digital Video Broadcasting) system, which supports both SDTV and HDTV.
Recording
HDTV can be recorded on D-VHS (Data-VHS), W-VHS, or on a digital video recorder that supports HDTV such as the TiVo offered by DirecTV or the DVR 921 and DVR 942 offered by DISH Network. Currently, the only recording option in the United States is D-VHS. D-VHS records in digital form at a speed of 28.2 Mb on any VHS tape, requiring a FireWire (IEEE 1394) digital transport to couple the compressed MPEG-2 frame from the modulator device to the recorder.
Unfortunately, the enormous data storage capacity required to store uncompressed data makes it unlikely that an uncompressed storage option will appear on the market for years to come. MPEG-2 real – time compression of an uncompressed HDTV signal is also extremely expensive, making it prohibitive for the market, although its cost is predicted to drop in a few years (although this is actually more in the interest of consumers. HD video cameras than HDTV recorders). In addition, analog tape recorders with sufficient bandwidth for storing analog HD signals such as W-VHS recorders are now discontinued in the consumer market and are expensive and hard to come by in the aftermarket.
