Re: [codec] RTP Payload Format and File Storage Format for Opus Speech and Audio Codec - draft-spittka-payload-rtp-opus-00

"Benjamin M. Schwartz" <bmschwar@fas.harvard.edu> Tue, 05 July 2011 16:39 UTC

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Date: Tue, 05 Jul 2011 12:38:57 -0400
From: "Benjamin M. Schwartz" <bmschwar@fas.harvard.edu>
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Subject: Re: [codec] RTP Payload Format and File Storage Format for Opus Speech and Audio Codec - draft-spittka-payload-rtp-opus-00
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On 07/04/2011 08:06 PM, Julian Spittka wrote:
> Any feedback, questions, or comments are highly welcome.

Thank you for doing this work.  I think your proposed RTP and SDP formats
are very nice and a good step for us.

I have a few comments.

1.  I think the description of Opus should be removed.  There's no need to
duplicate the contents of the Opus RFC.

2.  I think the payload specification should make (almost) no mention of
Opus frames, modes, etc.  These aspects of Opus are entirely internal to
the payload, which is a "black box".  As far as the RTP specification is
concerned, Opus consists of (almost-)arbitrary-duration "packets" and
that's it.

3.  To avoid confusion, I think we should be very careful and clear about
the distinction between audio bandwidth and samplerate, as their
relationship in Opus is far from simple.

I have implemented these ideas, along with a few minor changes, as a patch
to the draft .xml, attached.  Please feel free to discard this patch; I
mean it only as a way to communicate my suggestions more clearly.

--Ben