OS X people may be interested in ffmpegX (shareware) which is a drag-n-drop app that sits on top of things like mencoder and can convert between several different video file formats. Of course VLC on OS X seems to be able to open FLV files fine, so that might be a possibility as well (system( "open -a /Applications/VLC.app $infile" );).

And I had to ++ the OP just for the choice of default URLs it pulls down. :)