[FFmpeg-devel] Flac encoder and MPEG4 ALS
Sun Mar 30 15:55:49 CEST 2008
On Sun, Mar 30, 2008 at 09:44:51AM -0400, Justin Ruggles wrote:
> Kostya wrote:
> > I've looked at it once. Seems the most features are for floating-point
> > mode, baseline decoder should be comparatively easy. Especially if you
> > are the person who writes encoder to it ;)
> It has 2 entropy coders, plus another for floating-point. It has 2 ways
> of doing multi-channel. There are also several prediction methods. The
> spec does not specifically say what is "baseline" vs. extended, but it
> would be simple enough to break down the task.
IIRC, both entropy coders are VLC - classical Shannon-Fano scheme and
classical Golomb codes. Prediction is also standard LPC and RLS, the latter
is quite rare in codecs though (MLP, APE, TTA ?).
And yes, they overlooked the possibility to define baseline.
Also it leads me to the thought LPAC author just included an alternative
to each encoding step to (dis)satisfy all :-S
> > Too bad the spec costs money and available drafts allow you to write
> > some hybrid between LPAC and ALS. At least we have the reference
> > decoder and encoder sources.
> I have paid for the spec. If this becomes an SoC project, I will share
> it only with the student. I won't make it publicly available though.
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