Kaffiene error when playing certain flv videos

Hi all,

this error comes up on certain flv videoes that i download and try to watch with kaffiene or smplayer but will not play. in kaffiene, i get this message: Cannot find demux plugin for MRL. Anyone know what this means and how does one go about fixing it. This started happening after i upgraded from kde 4.7.4 to 4.8. am using 11.4