User Guide

306 Appendix E, Digital Compression
Video Stream Data Hierarchy
Within the MPEG stream structure, there is a hierarchy of data structures:
Video Sequence Consists of a sequence header, one or more groups of pictures, and an end-
of-sequence code. The video sequence is another term for video stream.
Group of Pictures An optional syntax layer in the MPEG specification that divides series of
pictures along I-picture boundaries. It is defined to aid random access within a MPEG
stream. An I-picture always starts a GOP but there can be more than one I-picture in a GOP.
Picture The primary coding sequence of a video sequence. A picture consists of three
rectangular matrices representing luminance (Y) and two chrominance (CbCr) values. The Y
matrix has an even number of rows and columns. The Cb and Cr matrices are half the size
of the Y matrix in each direction (horizontal and vertical).
Note: MPEG terminology uses “picture” rather than “frame” because a picture can be one
or more fields (every frame consists of two fields).
Video Sequence
• • • • • •
Group of Pictures
Picture Block
Slice Macroblock
8
pixels
8
pixels