Is there a way to detect if an uploaded file is of type .flv using PHP getimagesize ? I have looked but can not find any info. thanks in advance.
Why do you want to check a Flash video headers with getimagesize? This PHP Class seems to be doing what you want to: http://www.phpclasses.org/package/5899-PHP-Get-metadata-from-Flash-video-files.html
From the PHP manual it is apparent there is no direct support for flv formats using the getimagesize() function. As already mentioned there are classes and extensions which deal with these types of formats. I can also suggest looking at the mime type in the $_FILES array when uploading though, this may pose a security risk as the header can be easily manipulated client side.