The group of pictures layer is optional. It begins with a start code and a header

   The header carries

-time code information

-editing information

-optional user data

First encoded picture in a GOP is always an I picture

Typical length is 15 pictures with the following structure (in display order):

I B B P B B P B B P B B P B B

( See I Picture, P Picture, and B Picture)

This provides an I picture with sufficient frequency to allow a decoder to quickly begin correct decoding.  (See also I P B Picture Reordering.)

MPEG 2 Video Data Structures Topics:

- PIXEL

- BLOCK

- MACROBLOCK

- Field DCT Coding and Frame DCT Coding

- SLICE

- PICTURE

- GROUP of PICTURES (GOP)

- SEQUENCE

- PACKETIZED ELEMENTARY STREAM

Up to MPEG 2 Video Data Structures