Flash Video (with .FLV file extension) is the file format used to deliver video over the Internet using Adobe Flash Player (formerly known as Macromedia Flash Player). Notable users of the Flash Video format include YouTube, Google Video, Reuters.com and Yahoo! Video.
Signatures 58, 59 and 78 detect/prevent the downloading of .FLV video hosted by different streaming servers.
This SonicWALL signature identifies streaming MP4 video.