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

[Filip Kalinski]

On Fri, Jan 17, 2003 at 11:11:30AM -0500, D Richard Felker III wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> On Fri, Jan 17, 2003 at 02:43:07PM +0300, Vladimir Mosgalin wrote:
> > [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> > 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?
> 
> Try running it twice:
> 
> mencoder file.avi -o file_.avi -ovc copy -oac copy
> mencoder file_.avi -o file__.avi -ovc copy -oac copy
> 
> You should find file_.avi and file__.avi identical, so mencoder isn't
> losing frames or something. Most likely the program used to encode the
> original file.avi just sucked. I've been able to recover over 10 megs
> like this with mencoder on some broken files... :) It's especially
> nice when the file is just barely over 703M.
> 

Great hint! I have one file with 707M size (too large...), and after
re-encoding with -oac copy -ovc copy it has shrinked to 696M (great!).
Now I can fit it to CD without cutting :-)

-- 
Filip Kalinski <filon at pld.org.pl>