Last I checked something with their .flv support was bad. It might have been the splitter or something. With a lot of .flv's you couldn't seek to anywhere in the file.
Some encoders might not create the index properly, and some players might have tricks to seek (offline?) even without one.
To repair these files, see: http://muzso.hu/2008/12/18/fixing-flash-videos-flv-for-use-w...