All companies from digital industry have decided upon temporarily defaulting HD & ultra-HD streaming to SD content or offering only SD content, at bitrates no higher than 480p on cellular networks until 14th April.
In a nutshell, the difference between high definition and standard definition images is the number of pixels contained in the image on display. HD images have more pixels per square inch than standard definition videos.
It means that HD images can show much finer detail than SD images.
SD or “standard definition” is 640 pixels wide and 480 pixels tall in the U.S. (Slightly larger in Asia and Europe, where the format is different). HD or “high definition” is at least 1280 pixels wide, and in a wider format than SD.
Source : All India Radio