Is there a way to have FlashVideo convert mp4 to flv?

Is there a way to have FlashVideo convert mp4 to flv?

I've tried various settings, also removing video/mp4 from Flash MIME Types, but without success.
The reason I ask is that I have problems with the Dash Player not playing mp4 video - only sound. Also I'd like consistency - all files uploaded should be converted to flv if not already flv...

Other file-types (like mpg) are converted just fine

Thanks
Roald