Standard definition television
Standard-definition television or SDTV is one of the video formats used in digital television broadcasting.
SDTV can be broadcast in 704 pixels × 480 lines (16:9 and 4:3 aspect ratios) or 640 pixels × 480 lines (4:3 ratio). The refresh rate can be any of 24, 30 or 60 pictures per second.
SDTV in 4:3 aspect ratio has the same appearance as the regular analogue TV (NTSC, PAL, PAL2, SECAM) minus the ghosting, snowy images and static noises.
Both digital television standards (ATSC and DVB) are capable of transmitting SDTV. While both were originally developed for HDTV, they have proved to be more in demand for their ability to deliver multiple video and audio streams via multiplexing, than to use the entire bitstream for one channel.
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