To be able to work with FLV video you can install K Lite Codec Pack (full):
http://www.codecs.com/K_Lite_Codec_Pack_download.htmWhen installing be sure you check the points regarding FLV, FLV1 and VP6 (install FLV Splitter and set ffdshow to decode FLV1 and VP6 video). In other points about DivX, XviD, MP3 etc I recommend not to use ffdshow and use original codecs since ffdshow is not very stable.