flash video conversion softwares are relatively rare in comparison to other video formats,but many people are demanding this type of video converters. flash/flv videos are usually contained in flv container and encoded in adobe flash format, and since it is not that easy to create directshow filters for flash videos, converters are rare. however i will mention some of these converters here:

this software can convert between almost any video formats. it is very easy to use for a novice user, but also offer detailed configuration options for a power user. and it certainly converts videos to flv/flash video formats