[MPlayer-users] Re: file size falls short of 700MB for multi pass

[Lubomir Blaha]

On Sun, Jun 22, 2003 at 07:22:28PM -0500, Jonathan Rogers wrote:
> >I used 3 pass encoding on a file, and specified the suggested bitrate for 
> >a 700MB cd given after the first pass.  However, the final filesize was 
> >only 580MB.
> >
> >what exactly does this mean?  that using more bits in this specific 
> >instance would not improve quality?
> 
> No, it almost certainly doesn't mean that more bits wouldn't improve 
> quality. Libavcodec's rate control is far from perfect. For most movies, 
> it gets pretty close, but on some, it uses way too few bits. So far, the 
> only way I've been able to fix it is to reencode, specifying a higher 
> bitrate.
It will not work :(
I had same problem and this strange behaviour can be suppressed with
vqmin=2 and vqmax=9 in -lavcopts.

Example:
1st pass (audio) done
2nd pass (1st video)
mencoder source -oac copy -ovc lavc -o /dev/null -lavcopts vcodec=mpeg4:vhq:vbitrate=1835:vqmin=2:vqmax=9:vpass=1
3rd pass (2nd video)
mencoder source -oac copy -ovc lavc -o dest.avi -lavcopts vcodec=mpeg4:vhq:vbitrate=1835:vqmin=2:vqmax=9:vpass=2

maybe in 3rd pass vqmin=2 and vqmax=9 is needless (values are taken from 2nd
pass text file), but I'm lazy edit whole line in shell history and this works
too :).

With this options, the encoded file's bitrate have exact desired value.

	Tritol


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