Re: channel layouts and up/down mixing

On Sat, Jan 12, 2013 at 11:35 AM, Chris Rogers <crogers@google.com> wrote:

> I'm not opposed to adding 7.1 into the currently defined layouts in the
> spec.  But obviously, given your example, I think it's best that we have a
> way to distinguish these types of cases where the number of channels is
> ambiguous.  If we had a .channelLayout attribute, this might be something
> as simple as defining constants for different speaker layouts, and also
> having a constant called something like DISCRETE_CHANNELS if it's just an
> 8-channel device with channels uninterpreted.


Given that both AAC and Vorbis define layouts for every number of channels
up to and including 8, it seems like a good idea for Web Audio to do so too.

Some operatings systems allow you to query the hardware setup so you can
> know the speaker config.  In this case, the AudioContext could have
> .channelLayout be set to that value.
>

Shouldn't the interpretation of channels be per-node?

Also, I think it would probably be best for the default to be that mixing
behavior does not vary based on OS configuration. (Imagine, for example, an
application where Web Audio is used to mix content that isn't actually
being played through the speakers of the host system.) Letting authors
detect and opt into using configuration-specific mixing behavior sounds
better to me.

I'm hoping to get multi-channel output working in WebKit soon, so we can
> get some real-world experience with how this all works in the real-world in
> the hands of both basic and advanced users.
>

Given this affects the observable behavior of the implementation you're
shipping, I hope we can come up with a thorough specification of all the
default mixing behaviors soon.

Thanks,
Rob
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