If your IIS server throws a “404 not found” page every time you try to fetch a flash video file (flv or f4v), your server might be missing the MIME type declaration.
In the Internet Information Services Manager, right click the local computer server and select Properties, open MIME types, click New and enter the following for flv (technote):
Associated Extension box: .FLV MIME Type box: flv-application/octet-stream
and for f4v (technote):
Associated Extension box: .F4V MIME Type box: video/mp4
Digging around the internet, I’ve found people reporting these MIME types working too;
video/x-flv for .flv files, and
video/f4v for .f4v files.
Be advised that you may have to restart IIS for the changes to work.