Re: channel layouts and up/down mixing

On Fri, Jan 11, 2013 at 3:06 PM, Robert O'Callahan <robert@ocallahan.org>wrote:

> 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?
>

Yes, that might be better.  We just have to be careful about the default
behavior.


>
> 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.
>

You might be right.


>
> 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.
>

I hope so too - we should be able to come up with something that seems
reasonable to both of us as a starting point.  I'm just anticipating that
we might discover some fine points once people have a chance to play with
something in real-world conditions.

Chris



>
> Thanks,
> Rob
> --
> Jesus called them together and said, “You know that the rulers of the
> Gentiles lord it over them, and their high officials exercise authority
> over them. Not so with you. Instead, whoever wants to become great among
> you must be your servant, and whoever wants to be first must be your
> slave — just as the Son of Man did not come to be served, but to serve,
> and to give his life as a ransom for many.” [Matthew 20:25-28]
>