"i" is for "interlaced," where each frame is made up of two half-resolution "fields."
"p" is for "progressive," where each frame is made from one field rather than two interlaced ones.
Interlace - Wikipedia, the free encyclopedia Progressive scan - Wikipedia, the free encyclopedia
With camcorders, the "p" is often used misleadingly. Many consumer level camcorders that offer a so-called "progressive" mode are really giving you interlaced footage in a manner which can be converted to true progressive by using sophisticated editing software.
Andrew.
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