Re: [codec] possible issues to track

Just to follow up.  i think that several of the bullets in the current
requirements draft reference specific techniques.  Though its not bad to
keep a list of potentially useful approaches somewhere, I don't think they
are actually requirements.  Time-stretching is perhaps one example, there
are several others.

Stephen Botzko

On Thu, Mar 25, 2010 at 3:54 PM, Benjamin M. Schwartz <
bmschwar@fas.harvard.edu> wrote:

> Michael Knappe wrote:
> > Ben, how would you approach channel counts larger than 2? Joint coding
> > between any two L-R pairs, with other channels (like the center channel)
> > left singular?
>
> I agree with Stephen Botzko that the mechanism should not be part of the
> requirements.  However, we will need to agree on an interface, i.e. the
> abstraction barriers.  I think:
>
> 1. The codec should provide an interface for coding a pair of closely
> coupled channels with the presumption that they represent something like a
> stereo pair.
>
> 2.  The format should provide an efficient way to pack multiple
> independent synchronized codec channels into a single stream.
>
> 3. The format should provide a way to specify N named output channels as
> linear combinations of the coded channels.
>
> Advantages:
>  - Stereo can be specially optimized.  There are mature techniques for
> efficient coding of stereo, and plenty of test samples.  CELT can already
> code joint stereo more efficiently than independent coding or a simple
> mid-side split.
>  - Surround sound can support all the various configurations (e.g. 5.1,
> Ambisonics, custom speaker sets) without any major work within the spec.
>  - The codec does not need to know anything about specific surround-sound
> configurations, saving development time and effort.
>
> Disadvantages:
>  - This approach cannot achieve maximally efficient coding of
> surround-sound, as can be achieved using techniques like those mentioned
> in [1] and [2].
>
> --Ben
> [1] http://people.xiph.org/~xiphmont/surround/demo.html<http://people.xiph.org/%7Exiphmont/surround/demo.html>
> [2] http://people.xiph.org/~xiphmont/surround/demo2.html<http://people.xiph.org/%7Exiphmont/surround/demo2.html>
>
>
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