FLV files can be easily protected using htaccess.
Code:
RewriteCond %{HTTP_REFERER} !^$ [NC]
RewriteCond %{HTTP_REFERER} !^http://(.*@)?([a-z0-9-]+\.)?YOURDOMAIN\.com([0-9]+)?(/.*)?$ [NC]
RewriteRule .*\.(flv|css|asf|mpg|mpeg|wmv|avi|rm|gif|jpeg|jpg|zip|png|swf|mp4|m4v)$ - [NC,F,L]