 So much so that very high-speed and theoretically lossless (in reality, there are rounding errors) conversion can be made from one format to the other, provided a couple of restrictions (color space and quantization matrix) are followed in the creation of the bitstream.The length between I-frames is known as the group of pictures (GOP) size.MPEG-1 most commonly uses a GOP size of 15-18. i.e.