[MPlayer-users] smaller file size after mencoder recoding - why?

[Vladimir Mosgalin]

Hi everyone.

Can somebody explain why mencoder pass results in smaller files?
I take almost any avi (i've found this to work with any avi not coded
with mencoder), then run
mencoder file.avi -o file_.avi -ovc copy -oac copy -idx

file_.avi will be smaller then file.avi

i've tested this on some clips (20-50m size, mpeg4/divx), difference is
100-500k. I really don't understand this. Yes, mencoder repacks audio
and video without recoding, but how come that there were 500k of junk
inside properly-coded avi? Or wasn't it junk? Maybe mencoder throws out
something useful?

-- 

Vladimir