A.R.Drone Developer Guide - Abstract

7.2 The video stream
The embedded system uses a proprietary video stream format, based on a simplified version of
the H.263 UVLC (Universal Variable Length Code) format ( http://en.wikipedia.org/
wiki/H263). The images are encoded in the YCBCR color space format, 4:2:0 type (http:
//en.wikipedia.org/wiki/YCbCr), with 8 bits values. The proprietary format used by
the drone is described in 4.2.2, but here is firstly shown the way to produce it.
7.2.1 Image structure
An image is split in groups of blocks (GOB), which correspond to 16-lines-height parts of the
image, split as shown below :
GOB #0
GOB #1
GOB #2
GOB #3
GOB #4
GOB #5
GOB #6
GOB #7
Figure 7.2: Example image (source : http://en.wikipedia.org/wiki/YCbCr )
Each GOB is split in Macroblocks, which represents a 16x16 image.
MBlock #0 #1 #2 #3 #4 #5 #6 #7 #8 #9
Each macroblock contains informations of a 16x16 image, in Y CBCR format, type 4:2:0.
(see http://en.wikipedia.org/wiki/YCbCr,
http://en.wikipedia.org/wiki/Chroma_subsampling,
http://www.ripp-it.com/glossaire/mot-420-146-lettre-tous-Categorie-toutes.
html )
43