Intra (I) frames, also known as reference or key frames, contain the necessary data to re-create a complete image. An I-frame stands by itself without requiring data from other frames in the Group of Pictures (GOP). Every GOP contains one I-frame, though it doesn t have to be the first frame of the Group. I-frames are the largest type of MPEG frame, but they re faster to decompress than other kinds of MPEG frames.