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Re: [codec] Conformance with unusual sample rates

"Benjamin M. Schwartz" <bmschwar@fas.harvard.edu> Fri, 18 November 2011 15:56 UTC

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Date: Fri, 18 Nov 2011 10:56:20 -0500
From: "Benjamin M. Schwartz" <bmschwar@fas.harvard.edu>
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To: John Ridges <jridges@masque.com>
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Cc: codec@ietf.org
Subject: Re: [codec] Conformance with unusual sample rates
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On 11/18/2011 09:29 AM, John Ridges wrote:
> Is it possible to create a conforming (and
> thus unencumbered) Opus codec from the reference implementation that can
> use a sample rate of, say, 44100 Hz?

It depends what you mean.

One answer is "no".  Opus always operates at a fixed nominal samplerate of
48000 Hz.

Another answer is "yes", because you are of course always free to resample
your inputs before encoding, and to resample the outputs after decoding.
If you figure out a way to use less CPU by integrating your resampler into
the decoder then that's just a trivial implementation detail.

Another answer is "yes, in Opus-custom".  Opus-custom is a
non-interoperable Opus-derived codec development system, defined as part
of the Opus standard [1].  Opus-custom can be driven at different
samplerates, including 44100 Hz.

--Ben

P.S. I do agree that clarifying our text on this point might be helpful.

[1] http://tools.ietf.org/html/draft-ietf-codec-opus-10#section-6.2

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