I'm not sure what exactly you are referring to. FLV videos support Sorenson Spark, Screen video, On2 VP6, Screen video 2, H.264 video codecs.

All FLV files I have tried were playing fine in SMPlayer. This includes the ones that show FLV1 as a video format (which use Sorenson Spark video codec) and are played with ffflv (FFMpeg Flash video) codec) and the one that show FLV4 as a video format (which use On2 VP6 video codec). But I use SMPlayer and Mplayer that comes with Ubuntu Linux, not a version for Windows.