HDTV
High-definition television (HDTV) is a digital television broadcasting system with greater resolution than traditional television systems (NTSC, SECAM, PAL). HDTV is digitally broadcast because digital television (DTV) requires less bandwidth if sufficient video compression is used.
Current HDTV broadcast standards include ATSC (US) and DVB (Europe, and most of the rest of the world). HDTV can also provide 5.1-channel surround sound audio using e.g. the Dolby Digital (AC-3) format. A HDTV compatible television set will not improve the quality of SDTV channels. To display a superior picture, high definition televisions require a High Definition (HD) signal. Typical sources of HD signals are as follows:
- Over the air with an antenna. Most cities in the US with major network affiliates broadcast over the air in HD. To receive this signal a HD tuner is required. Most newer high definition televisions have a HD tuner built in. For HDTV televisions without a built in HD tuner, a separate set-top HD tuner box can be rented from a cable or satellite company or purchased.
- Cable television companies often offer HDTV broadcasts as part of their digital broadcast service. This is usually done with a set-top box or CableCARD issued by the cable company. Alternatively one can usually get the network HDTV channels for free with basic cable by using a QAM tuner built into their HDTV or set-top box. Some cable carriers also offer HDTV on-demand playback of movies and commonly viewed shows.
- Satellite-based TV companies, such as DirecTV and Dish Network (both in North America), Sky Digital (in the UK and Ireland), Bell ExpressVu and Star Choice (both in Canada) and NTV Plus (in Russia), offer HDTV to customers as an upgrade. New satellite receiver boxes and a new satellite dish are often required to receive HD content.
- Video game systems, such as the Xbox, PlayStation 3, and Xbox 360, and digital set-top boxes that rely on an Internet connection, such as the Apple TV, can output a HD signal. The Xbox Live Marketplace, iTunes, and PlayStation Network services offer HD movies, TV shows, movie trailers, and clips for download, but at lower bitrates than Blu-ray.
- Most newer computer graphics cards have either HDMI or DVI interfaces, which can be used to output images or video to a HDTV.
- The optical disc standard Blu-ray Disc (25GB-50GB) can provide enough digital storage to store hours of HD video content.
Source: http://en.wikipedia.org/wiki/High-definition_television
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