.FLV files have different codecs (On2 vp6 video .FLV, H.263 video .FLV, Nelly Moser audio .FLV, MP3 audio .FLV and audio-only .FLV) so not every audio/video converter does the conversion job perfectly.

Anyway you should probably try freeware DVDFlick and MediaCoder first.

I also like Replay Converter and Cucusoft Ultimate Video Converter. They can convert to many formats. Of course they supports FLV to DVD-Video conversion. The programs are shareware so I strongly recommend to try their free demo versions before buying!