# [vorbis] Re: Re: fitting lots of music into 10GB with Vorbis

John Edwards john.edwards33 at ntlworld.com
Sun Dec 29 09:00:58 PST 2002

```
I think you'll find that this comes pretty close:

float qc2approxBitrate(float qcValue) {
float approxBitrate;

if ( qcValue < 0){
approxBitrate = 64000. - 1000*((float)(((float)qcValue*-1./100.0)*19.));
}
else if ( qcValue < 410 ){
approxBitrate = 1000 * (float)(((float)qcValue/100.0)*16+64);
}
else if ( qcValue < 810 ){
approxBitrate = 1000 * (float)(((float)qcValue/100.0)*32);
}
else if ( qcValue < 910 ){
approxBitrate = 1000 *(float)((((float)qcValue/100.0)*32)+
((((float)qcValue/100)-8)*32));
}
else{
approxBitrate = 1000 * (float)((((float)qcValue/100.0)*32)+
((((float)qcValue/100)-8)*32)+((((float)qcValue/100)-9)*116));
}

return approxBitrate;
}

John
----- Original Message -----
From: "Daniel Schregenberger" <npfdd at gmx.net>
To: <vorbis at xiph.org>
Sent: Sunday, December 29, 2002 5:16 PM
Subject: Re: [vorbis] Re: Re: fitting lots of music into 10GB with Vorbis

<p>> James Chapman wrote:
>
> > > someone who actually knows the way the vorbis encoder calculates the
> > nominal
> > > bitrate would probably find the correct algebraic formula quicker than
i
> > > could.
> >
> > Obviously, being VBR, it's not possible to calculate the average
> > bitrate from the quality, the best you can do is give a rough estimate.
> > Going from q-1 to q10 the nominal bitrates would be
> > {48,64,80,96,112,128,160,192,224,256,320,500} for 44100 stereo.
>
> You may build 11 equations of the form
>
> a + quality * b = bitrate_for_that_quality
>
> and use some math program (matlab, maple, mathematica) or a calculator
(HP38,
> HP48, TI??, ...) to solve it (in this case to find a & b that fit best).
Or you
> do it by hand.
> For better results use equations of a higher order (eq. a + quality^2 * b
+
> quality * c = br)
>
> -- Daniel
>
> PS: You maybe have to shift the qualitys by 1, cause it might be better
without
> a -1
> --- >8 ----
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<p>--- >8 ----
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```