[opus] [Patch] Non-diegetic support for channel mapping 254

[Drew Allen]

My apologies for the confusion, I think I have the mapping layout correct
in this patch.

Cheers!



On Tue, Apr 25, 2017 at 10:07 AM Jean-Marc Valin <jmvalin at jmvalin.ca> wrote:

> On 25/04/17 10:12 AM, Drew Allen wrote:
> > We assume that the input file is ordered first by ACN ambisonic channels
> > followed by a (possible) stereo track, and we want to swap the order for
> > the API in order to couple the stereo for coding.
>
> Well, if you look at section 5.1.1 of RFC7845:
>
>        The 'coupled stream
>        count' field indicates that the decoders for the first M Opus
>        streams are to be initialized for stereo (two-channel) output,
>        and the remaining (N - M) decoders are to be initialized for mono
>        (a single channel) only.
>
> In other words, it says that in the file itself (regardless of what you
> do in the API), you need to have the stereo channels first, followed by
> the mono channels. Where the channels go in the API itself is another
> question and you're free to put the non-diegetic stereo at the end for
> that.
>
> > The mapping code
> > appears to be working on files I've tested it on so far.
>
> Well, even if you get the mapping wrong, it's still going to work. It's
> just that your non-diegetic stream will be made from two mono streams
> and two of your directional channels will be coupled. That's one of the
> limitations of simple testing, since it's not going to catch these kinds
> of errors.
>
>         Jean-Marc
>
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