[Ffmpeg-devel] [PATCH] vbr audio encode

[Rich Felker]

On Sat, Aug 13, 2005 at 06:15:14PM +0200, Michael Niedermayer wrote:
> Hi
> 
> On Sat, Aug 13, 2005 at 12:40:13AM -0400, Justin Ruggles wrote:
> > Hello,
> > 
> > The patch for vbr audio is pretty much ready.  From what I can tell, the
> > only codecs that support vbr are all external to ffmpeg (vorbis, lame,
> > faac).  After this, I might revisit simplifying the work I was doing on
> > adding vbr to ffmpeg's ac3 encoder, but that's for another day.
> > 
> > I did implement both normalized & codec-specific quality scales.  The
> > normalized scale follows a similar pattern as video quality, using 0.01
> > to 255.  The options I chose were '-aq' for normalized, and '-aqc' for
> > codec-specific.
> > 
> > The guideline I've used is to scale the normalized value to codec value
> > by holding to 0.01->best, 255->worst, and 128->default.  This can result
> > in a non-linear scale, but keeps uniformity of intent across codecs when
> > using the normalized scale.  A linear scale actually works for lame, but
> > that won't always be the case.
> 
> a normalized scale if you want to add one should have the property that
> value X for one encoder gives approximately the same quality as value
> X for another encoder, that also contradicts a default == 128 rule
> 
> iam not sure though if this is worth the work, maybe we should just
> drop the normalized scale support idea ...

I agree, normalized is not very useful..
It's really almost impossible to compare quality levels between
codecs, at least without intensive double-blind testing.

Rich