[MPlayer-users] variable bitrate, fixed quality

Nikolaus Rath Nikolaus at rath.org
Wed Jul 9 14:52:22 CEST 2003


First: Thank you for your excellent explanation. Now I understand
the whole thing much better. All the MPEG4 docs I've found so far
don't describe the rate control. Maybe you should include this posting
into the ffmpeg documentation.

D. Richard Felker, III <dalias at aerifal.cx> wrote:
>> According to an xvid page (http://roeder.goe.net/%7Ekoepi/xvid.shtml,
>> the "XViD Options Explained" PDF), the xvid codec supports such an
>> operation. The page says that I should set the "curve compression" to
>> 0 or 1 and the "payback delay" to 1. But these are the parameter
>> names in a different xvid gui, I can't find them in mencoder. So maybe
>> someone can tell me the equivalent mencoder options?
> The corresponding options for lavc are vqcomp, vqblur, vqsquish,
> vratetol, vrc_maxrate, vrc_minrate. However, the defaults are rather
> good.

Nevertheless, I would be happy if you could explain them too. :-)

> Increasing vqcomp (default is 0.5) to something near 1 will make
> quality more steady for the whole movie. Decreasing it will make
> bitrate more steady (close to constant bitrate).

I increased vqcomp up to 1. But the bitrate was still exactly as
specified. That is why I'm thinking that some of the other options
have wrong values (maybe mencoder sets them, so the defaults in ffmpeg
don't apply).


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