Youtube - normal video signature vs VEVO signature

Youtube - normal video signature vs VEVO signature

I working on youtube downloader for google chrome . Download working fine
on normal YouTube videos, but not on VEVO videos.. the signature of normal
video is :
8FAC643C4F9DAA141655B9795E182FA546D3DF8D.5204E9A3F92192DC78171D723AFCB83277DFA44E
and VEVO is :
8A7EEAA2E4EB7DA2F7D48BD4A59C86AA22CF42910.EBA0192F5BAA03F0A60362C2CE9179B0D7BBC0A00AFE
but on firefox working downloaders is signature same as the normal video..
(size)
note: video url parsing from flashvars in normal video must change sign.
for download from: sig=(signature) to signature=(signature) on VEVO video
from s=(signature) to signature=(signature)
I do not know where the error may be.. Thanks for any help!