Video uses codecs which encode information in frames of various types; in particular, the I-frame is essentially a self-contained image, a bit like JPEG, and th

Video uses codecs which encode information in frames of various types; in particular, the I-frame is essentially a self-contained image, a bit like JPEG, and the P-frame only encodes the changes from the previous frame. The choice of when to have an I-frame or a P-frame is arbitrary, but the rendered video will look the same. However, too many I-frames can bloat the filesize, and too few can degrade the appearance significantly as errors add up. They act on a codec parameter related to the I-frame, to pick better rules for good compression without visible errors in the P-frame.