Group of pictures

In MPEG video encoding, a group of pictures, or GOP, specifies the order in which intra-frames and inter-frames are arranged.

The GOP is a group of successive pictures within a MPEG-coded film and/or video stream. Each MPEG-coded film and/or video stream consists of successive GOPs. From the MPEG pictures contained in it the visible frames are generated.

A GOP can contain the following picture types:

• I-picture and/or I-Frame (English intra coded picture) reference picture, corresponds to a fixed image and is independent of other picture types. Each GOP begins with this type of picture.
• P-picture and/or P-Frame (English predictive coded picture) contains difference information from the preceding i or P-Frame.
• B-picture and/or B-Frame (English bidirectionally predictive coded pictures) contains difference information from the preceding and/or following i or P-Frame.
• D-picture and/or D-Frame (English DC direct coded picture) serves the fast advance.

A GOP always begins with an I-Frame. Afterwards several P-Frames follow, in each case with some frames distance. In the remaining gaps are B-Frames. With the next I-Frame a new GOP begins.