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Standard-definition television (or SDTV) is a television system that has a resolution that meets standards but not considered either enhanced-definition television (EDTV) or high-definition television (HDTV). The term is usually used in reference to digital television, in particular when broadcasting at the same (or similar) resolution as analog systems. In the USA, SDTV refers to digital television broadcast in 4:3 aspect ratio, the same aspect ratio as NTSC signals.[1] When a television set is labeled "SDTV", this means that the set includes an ATSC tuner, but scans its picture in the same 480i pattern used in NTSC.[citation needed]

In the UK and most of Europe standard-definition television is mostly shown with a 16:9 aspect ratio as most people have a television with a 16:9 aspect ratio. Older programs with a 4:3 aspect ratio are shown in 4:3. The 16:9 aspect ratio is also known as 576i.

All content recorded for television broadcast in the UK and the Republic of Ireland have a 16:9 aspect ratio.

Standards that support digital SDTV broadcast include DVB, ATSC Standards and ISDB. The last two were originally developed for HDTV, but they have proved to be more often used for their ability to deliver multiple SD video and audio streams via multiplexing, than to use the entire bitstream for one HD channel.

In ATSC Standards, SDTV can be broadcast in 704 pixels × 480 lines with 16:9 aspect ratio (40:33 rectangular pixel), 704 pixels × 480 lines with 4:3 aspect ratio (10:11 rectangular pixel) or 640 pixels × 480 lines with 4:3 ratio. The refresh rate can be any of 24, 30 or 60 frames per second.

Digital SDTV in 4:3 aspect ratio has the same appearance as the regular analog TV (NTSC, PAL, SECAM) minus the ghosting, snowy images and white noise. However, if the reception is poor, one may encounter various other artifacts such as blockiness and stuttering.

When resolution is considered, both the resolution of the transmitted signal and the (native) display resolution of a TV set are taken into account. Digital NTSC, and PAL/SECAM-like signals (480i60 and 576i50 respectively), are transmitted at a horizontal resolution of 720 or 704 format.

Video Format (WxH) Name Pixel aspect ratio (W:H)
(Standard 4:3)
Pixel aspect ratio (W:H)
(Anamorphic 16:9)
Description
720×576 576i 16:15 64:45 Used on D1/DV PAL (ITU-R 601)
704×576 576p 12:11 16:11 Used on EDTV PAL
720×480 480i 8:9 32:27 Used on DV NTSC
720×486 480i 8:9 32:27 Used on D1 NTSC (ITU-R 601)
704×480 480p 10:11 40:33 Used on EDTV NTSC

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