In video coding, a group of pictures, or GOP structure, specifies the order in which intra- and inter-frames are arranged.
Each coded video stream consists of successive GOPs, from which the visible frames are generated.
In the newer designs found in H.264/MPEG-4 AVC and HEVC, encoders have much more flexibility about referencing structures.
This extra flexibility can improve compression efficiency, but it can cause propagation of errors if some data becomes lost or corrupted.
However, having more I frames substantially increases bit rate needed to code the video.
[7] Instead of the M parameter, the maximal count of B-frames between two consecutive anchor frames can be used; this is the approach used by ffmpeg.