You cannot play *.avi files with win32codecs. You definitely need one.

edit you /etc/apt/sources.list

deb http://ftp.tw.debian.org/debian-multimedia/ stable main


#apt-get update
#apt-get install win32codecs

you can use any mirror from debian-multimedia.org. I am using Taiwan mirror servers because it is quite fast, considering that i am in kota kinabalu.