Re: [codec] Multi-mode frame concatenation

Ralph Giles <giles@thaumas.net> Fri, 29 July 2011 17:53 UTC

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Date: Fri, 29 Jul 2011 10:53:02 -0700
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From: Ralph Giles <giles@thaumas.net>
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Subject: Re: [codec] Multi-mode frame concatenation
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On 29 July 2011 10:31, Benjamin M. Schwartz wrote:

> For some definitions of backwards compatibility, yes.  The draft's text
> indicates that this extensibility is deliberate.  I'm not sure where you
> get 14; I get (64-49)*4 = 60, at a minimum.

I was doing 63 - 48, or using the lower four bits of M when the upper two
bits are set, with b110000 taken for the maximum value of 48, which I
overcounted in the previous email. I now get 15 extension options.

Do you mean using lower values of M when the config field indicates
the frame has a longer duration?

> This is all extremely accurate.  I had originally intended (following the
> language in your diagram) for Compressed frame 1 to consist of N1-1 bytes,
> so that its entirety (including the TOC byte) had size N1.  However, I now
> see that your version is superior, as otherwise it would be impossible to
> represent the max-size frame (1275 bytes, or 1276 with the TOC byte).

Ok, good.

>> It's also possible to just discard the initial stereo flag and config
>> if the extra bandwidth is judged worth the complexity savings.
>
> This was my intent.  Without code, I think complexity is hard to judge, so
>  don't yet have a strong opinion.

The Opus framing tries hard to save bytes elsewhere, so it seems
reasonable to me. I look forward to your implementation experience. :)

Cheers,
 -r