Group of pictures
In video coding, a group of pictures, or GOP structure, specifies the order in which intra- and inter-frames are arranged. The GOP is a collection of successive pictures within a coded video stream. Each coded video stream consists of successive GOPs, from which the visible frames are generated. Encountering a new GOP in a compressed video stream means that the decoder doesn't need any previous frames in order to decode the next ones, and allows fast seeking through the video. Description A GOP can contain the following picture types: I picture or I frame (intra coded picture, also called keyframe or i-frame) – a picture that is coded independently of all other pictures. Each GOP begins (in decoding order) with this type of picture. P picture or P frame (predictive coded picture) – contains motion-compensated difference information relative to previously decoded pictures. In older designs such as MPEG-1, H.262/MPEG-2 and H.263, each P picture can only reference one picture, and that picture must precede the P picture in display order as well as in decoding order and must be an I or P picture. These constraints do not apply in the newer standards H.264/MPEG-4 AVC and HEVC. B picture or