[MPlayer-users] variable bitrate, fixed quality

Nikolaus Rath Nikolaus at rath.org
Tue Jul 8 00:06:27 CEST 2003

D. Richard Felker, III <dalias at aerifal.cx> wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> On Mon, Jul 07, 2003 at 07:54:07PM +0200, Nikolaus Rath wrote:
>> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
>> Hans Meine <hans_meine at gmx.net> wrote:
>> > [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
>> > On Monday 07 July 2003 18:49, Nikolaus Rath wrote:
>> >> I want to encode a video with a completely variable bitrate but with a
>> >> fixed quality. I don't want to use a fixed quantizer too, because this
>> > 
>> > The bitrate is what you are looking for. Using 2-pass encoding will try to 
>> > achieve constant quality. If you don't want to constrain the quality, specify 
>> > an enormous bitrate (recall that bitrates above some value are not kbits 
>> > anymore, but bits, so add some more zeroes) and lavc will do as good as it 
>> > can.
>> This doesn't work. I tried it and lavc compressed nearly all frames
>> with a quantizer of 3, even if most of them would be perfect with 6. I
> They're NOT perfect with 6. Your eyes just can't tell the difference.
> Write a program that will determine when your eyes could tell the
> difference, and when they wouldn't, and then we'll incorporate it into
> lavc... :))

Do I understand correct: lavc cannot recognise if a frame looks better
or worse with a specific quantizer? But how does lavc decide which
quantizer to use in this case?

Maybe I described my problem the wrong way. I will retry:

I encoded a file with a fixed bitrate of 1500. Most of the video
looked good (I call these parts the "simple"), but some parts looked
bad (I call these "complex"). Now I increased the bitrate. The result
was good, but the video was much bigger than necessary because the
simple frames were encoded with a lower quantizer too. I'm searching
for a way to increase the bitrate just for the complex parts of the
video, where it is really necessary. 

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?


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