What i dont understand about the replay media catcher 4...

when streaming and converting to mpeg-4, the mpeg-4 files are much bigger than original stream-files i flv.

As i have problemems with media catcher 4 i installed again the media catcher 3, recored videos from a webiste and after that i converted it with replay converter 4. When i got the converted file that i also converted to mpeg-4 this file is smaller than the flv-file.

So why when converting with replay media catcher 4 the mpeg-4 files are lot of bigger than converting with replay converter in th same format.

what is the reason for that?