[MPlayer-users] variable bitrate, fixed quality

[Nikolaus Rath]

Hans Meine <hans_meine at gmx.net> wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Nikolaus Rath <Nikolaus at rath.org> writes:
>> >> 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
>> have the impression that lavc wants to reach the given bitrate at all
>> costs. If this isn't the case, I need an option to adjust the
>> quantizer selection (=the quality), because lavc uses to low
>> quantizers for simple frames.
> 
> Hmm, maybe you overestimate what a computer can theoretically do in
> this context. Since it has no intelligence (and that won't change in
> the next decades), it can not really know what you find "good quality"
> or "too low quantizer". All it can do is take the bitrate you give it,
> and try to distribute it between all frames.
> 
> If it takes too low quantizers, I'd try setting a lower bitrate?! If
> that increases the quantizers at the wrong places, there are the
> following possibilities:
> - the configurable limits for the quantizers are too narrow (fixable
>   by you)
> - mencoder does not vary the bitrate as much as it should (maybe
>   fixable by some pro(s) in months of work)

This seems to be reasonable solution. But what do you mean with a
"pro(s)"?

According to the xvid documentation, this codec already supports a
more varying bitrate. I just can't found the options in the mencoder
manpage (see my other mail).

   --Nikolaus