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Re: [codec] Eric Rescorla's No Objection on draft-ietf-codec-ambisonics-07: (with COMMENT)

Jean-Marc Valin <jmvalin@jmvalin.ca> Mon, 13 August 2018 18:25 UTC

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To: Eric Rescorla <ekr@rtfm.com>, Jan Skoglund <jks@google.com>
Cc: Tim Terriberry <tterriberry@mozilla.com>, codec-chairs@ietf.org, draft-ietf-codec-ambisonics@ietf.org, codec@ietf.org, The IESG <iesg@ietf.org>
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From: Jean-Marc Valin <jmvalin@jmvalin.ca>
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Date: Mon, 13 Aug 2018 14:24:59 -0400
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Subject: Re: [codec] Eric Rescorla's No Objection on draft-ietf-codec-ambisonics-07: (with COMMENT)
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>     This is the reason the changes below to 7845 are necessary. I.e.,
>     not interpreting as channel mapping family 255, and instead “A
>     demuxer implementation encountering a 'channel mapping family'
>     value that it does not recognize SHOULD NOT attempt to decode the
>     packets“
> 
> Sorry, I'm not following. Is your point that previously it would have
> misdecoded it and now it will just refuse to play? That's a reasonable
> design choice, but it seems like it was always present in this design,
> so why does it need to change?

Basically, RFC 7845 didn't consider the possibility of new mappings
requiring some kind of transformation (in the case of family 3, a matrix
multiply) between the Opus streams and what the decoder needs to output.
Once you consider that, then it makes no sense to output the "raw"
decoded streams as if it were a family 255.

Cheers,

	Jean-Marc

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