question about avi

Hi
I am working on a project with avi converting and I need to extract 
informations I need
from an avi file. Lately, I was informed that there is some data saved in 
user defined
data area. I am wondering if there is any place or chunk in avi files for 
this kind of self
defined data? I can't find any help from the web cuz the genreal avi file 
don't have this
kind of data. I would be greateful if you guys can help me out.
Sincerely,
Andy

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