Standard-definition television

[citation needed] Standards that support digital SDTV broadcast include DVB, ATSC, and ISDB.

[5] The last two were originally developed for HDTV, but are also used for their ability to deliver multiple SD video and audio streams via multiplexing.

In North America, digital SDTV is broadcast in the same 4:3 fullscreen aspect ratio as NTSC signals, with widescreen content often being center cut.

[5] In other parts of the world that used the PAL or SECAM color systems, digital standard-definition television is now usually shown with a 16:9 aspect ratio, with the transition occurring between the mid-1990s and late-2000s depending on the region.

For SMPTE 259M-C compliance, an SDTV broadcast image is scaled to 720 pixels wide for every 480 NTSC (or 576 PAL) lines of the image with the amount of non-proportional line scaling dependent on either the display or pixel aspect ratio.