[FFmpeg-devel] [RFC] Generic psychoacoustic model interface

Justin Ruggles justin.ruggles
Thu Aug 28 00:51:38 CEST 2008


Kostya wrote:
> Here's my first attempt to define codec-agnostic psy model.
> Here's an interface for it. I'm not sure about AC3, but
> it should be possible to use it with DCA, Vorbis,
> MPEG Audio Layers I-III and NBC, maybe WMA too.
> In case somebody codes an implementation, of course.
> Personally I plan to make my encoder use it backed with
> already implemented 3GPP model.

I'll comment on psychoacoustic models in AC3.  I forget the technical
term they use for it (hybrid backwards or something like that), but
basically AC3 encodes the difference between the results of the built-in
mandatory psychoacoustic model and an external model.  This the "delta
bit allocation" part of the encoding process.  The encoder would have to
determine if the added bits needed to encode the differences take up too
many bits that could be used instead for the coeff mantissas.

It could be put to other uses as well, such as window size decision or
selecting the best values for some of the the parameters in the built-in
psy model.


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