When I look up the mime types of my .flv and f4v in php it states them as: application/octet-stream.
I always thought the mime types for these files were 'video/x-flv' and 'video/x-f4v'. Is this a new thing or are the files coming from a funky source or something?
I mention in this answer that both Winista and URLMon dont detect swf's or flv's properly. This is why the php component you're using cant fully identify the 'video/x-flv' and 'video/x-f4v' files.
Winista uses a magic file (that contains a list of MIME types and respective hex chars that indicate the starting bits of particular files).
I suggest you focus on why no-one else has been able to add flv detection to this magic file. The winista project to is a port from an old Java open source project.
The only other thought I have is trying ffmpeg, maybe it has the smarts to detect the exact MIME Type of these flv and f4v files.