I find a similar post http://stackoverflow.com/questions/58510/using-net-how-can-you-find-the-mime-type-of-a-file-based-on-the-file-signature and it is the same result I want, I tried to use it but I received always application/octet-stream instead of video/x-flv or video/x-msvideo. I think I miss something, have you any suggest for me? Should I add some kind of information on my workspace?