[FFmpeg-devel] [PATCH] AAC Encoder, Round 2

Kostya kostya.shishkov
Sun Aug 24 08:21:26 CEST 2008

On Sat, Aug 23, 2008 at 10:28:03PM +0200, Michael Niedermayer wrote:
> On Sat, Aug 23, 2008 at 06:31:30PM +0300, Kostya wrote:
> > I'm back (feeling even worse than before but nm).
> > 
> > Here is $subj is in a form of diff against FFmpeg SVN.
> now the psy model:
> [...]
> > +/**
> >   * Calculate Bark value for given line.
> >   */
> >  static inline float calc_bark(float f)
> >  {
> >      return 13.3f * atanf(0.00076f * f) + 3.5f * atanf((f / 7500.0f) * (f / 7500.0f));
> >  }
> why does vorbis_dec.c use a slightly different one?

I use generic formula available everywhere.
There's a comment in http://svn.xiph.org/trunk/vorbis/lib/scales.h:

/* The bark scale equations are approximations, since the original
   table was somewhat hand rolled.  The below are chosen to have the
   best possible fit to the rolled tables, thus their somewhat odd
   appearance (these are more accurate and over a longer range than
   the oft-quoted bark equations found in the texts I have).  The
   approximations are valid from 0 - 30kHz (nyquist) or so.

   all f in Hz, z in Bark */
> except that, i think the previous reviews have not been dealt with yet.
> That is the various suggestions for quality improvment should be tried
> what is better should be adopted
> Also everything that Gabriel Bouvign suggested should be tried.

Err, when I find a way to download them. $20 for three-page paper is a bit
high to me.
> I do not mind if we leave some of the harder things like viterbi based window
> decission to after svn ci, but the majority of the things suggested should
> be tried before the code is commited.

Comment on interface then or propose your own.
It will be needed to plug any psychoacoustic model.
Also it would allow to finish encoder faster and then concentrate on
> [...]
> -- 
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> Thouse who are best at talking, realize last or never when they are wrong.

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