How much have you read about video compression? Remember that I can't teach such here, but in a nutshell or short paragraphs.
In short, video compression ratios depend not only on the settings but the content.
a few days ago i used Tmpgenc v2,5 to convert a 715 avi file to a 256 mpg
yesterday, using exactly the same procedure:
avi file #1 505M gave a 995M mpg
avi file #2 544M gave a 1G mpg
why such a HUGE difference in the resulting mpg file??
XP pro (sp2)
120G of HD