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Re: Audio-ISSUE-95 (ChannelLayouts): Channel Layouts are not sufficiently defined [Web Audio API]

From: Chris Rogers <crogers@google.com>
Date: Mon, 21 May 2012 13:10:10 -0700
Message-ID: <CA+EzO0=RL2whoDiJqpfzn+iBTSpb9Ze6csazMqvoHDUrNos-Ug@mail.gmail.com>
To: olivier Thereaux <olivier.thereaux@bbc.co.uk>
Cc: Audio Working Group <public-audio@w3.org>
On Mon, May 21, 2012 at 6:29 AM, olivier Thereaux <
olivier.thereaux@bbc.co.uk> wrote:

> On 18 May 2012, at 15:19, Audio Working Group Issue Tracker wrote:
> > Audio-ISSUE-95 (ChannelLayouts): Channel Layouts are not sufficiently
> defined [Web Audio API]
> >
> > http://www.w3.org/2011/audio/track/issues/95
> >
> > Raised by: Philip Jägenstedt
> > On product: Web Audio API
> >
> >
> https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#ChannelLayouts
> >
> > This section admits that "Other layouts can also be considered." It
> should be defined exactly which channel configurations must be supported.
> We discussed the question of channel handling in the recent past, as part
> of our handling of ISSUE-9
> http://www.w3.org/2011/audio/track/issues/9
> http://www.w3.org/2012/04/25-audio-minutes#item02
> http://lists.w3.org/Archives/Public/public-audio/2012AprJun/0077.html
> http://www.w3.org/2012/05/02-audio-minutes.html#item06
> My understanding of the consensus so far was that:
> * The API should support and (by default) match the channel configuration
> specified by the hardware

I've proposed a way to deal with multi-channel output for
AudioDestinationNode here:

> * The spec should not constrain the channel support to "typical"
> contemporary layouts

Yes, for example if it's an 8-channel system then we should just be able to
render 8-channels.

> I guess this leaves us with two questions:
> - Should we normatively specify the channel ordering/naming for typical
> layouts

I think we should, at least for the common cases of mono/stereo/5.1  These
are common enough that we should have straight-forward ways of dealing with
them.  For these the channel ordering should be defined (which it is right
now in the spec).

> - How can we ensure interoperability between implementation in their
> naming/ordering of channels in atypical layouts (say, a 100-speaker concert
> configuration)

My feeling is that for the non-simple layouts (mono/stereo/5.1) we should
just send out N-channels of output without interpretation.  The specific
application can matrix mix
the individual channels in a flexible way.

Another possibility is to do something like what Apple's CoreAudio has done
(in its CoreAudioTypes.h header file) and define a huge number of layouts
and specific channel names.  I don't believe we need to do this, and should
probably keep it simple.


> Olivier
Received on Monday, 21 May 2012 20:11:03 UTC

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