[MPlayer-users] Re: Low bitrate using 2-pass with libavcodec

[Rémi Guyomarch]

On Sun, Apr 21, 2002 at 12:21:31AM +0200, marcogi at libero.it wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Hallo,
> 
> I'm try to make some test encoding a dvd.
> I made first and second pass using:
> mencoder -dvd 1 -aid 131 -ovc frameno -lameopts q=4 -o frameno.avi
> mencoder -dvd 1 -oac copy -vop scale=512:256,crop=720:346:0:112 -ovc lavc
> -lavcopts vcodec=mpeg4:vbitrate=785:vhq:vme=5:vqmin=2 -pass 1 -o pass1.avi
> 
> Everything seems to work.
> But, when I try to do thirth pass mencoder drops video bitrate to about one
> half I set. The bitrate seems stable around 780 for the first frames; after
> about 300 frames bitrate drops quikly to 370. The obtained video quality
> is visibly lower then first pass one.

Don't use vhq on the first pass. The second pass will still be encoded
with a lower bitrate than the first, but the difference will be
minimal (less than 10%). Adjust the bitrate accordingly. For example,
on a 10 minutes sample I specified vbitrate=858 and got 797 on the
second pass. The ratio may depend on what you encode.

This is a bug in libavcodec and someone from ffmpeg said it will be
fixed (ie he is aware of the problem and he knows how to fix it).

-- 
Rémi