Thanks for the answer =)
http://developer.android.com/google/play/expansion-files.html
“On most devices, Google Play downloads the expansion file(s) at the same time it
downloads the APK, so your application has everything it needs when the user opens it for the
first time. In some cases, however, your application must download the files from Google Play
when your application starts.”
What a pain…
I’ll try to see of I can easily use the .obb format, I’ll let you know 