Video Encoding GOP, M and N.

A GOP (Group of pictures) typically starts with an I-frame (Intra-coded frame) followed by P-frames (Predicted frames) and/or B-frames (Bi-directionally predicted frames). A common GOP structure might be "IBBPBBP..." or "IBBPBBPBBPBB..."

GOP M N.png

A sequence such as the above can be represented by two numbers: M and N. M represents the distance between two I or P frames, whereas N represents the distance between two I frames. The above GOP is described as M=3, N=12.
M: Represents the number of B-frames between two consecutive I-frames or P-frames.
N: Represents the distance between two consecutive I-frames, which is the GOP length.