Re: channel layouts and up/down mixing

On Mon, Jan 14, 2013 at 7:34 PM, Robert O'Callahan <robert@ocallahan.org>wrote:

> As far as the channel layout issue goes, Tim Terriberry advises me:
>
>> There are basically two commonly used channel orderings. The WAV
>> orderings (used by WAV files) and what I will call the Vorbis orderings
>> (which for 5 or more channels, follow the Dolby orderings used by, e.g.,
>> AC3 and AAC, and uses the obvious reductions of those to fewer channels).
>> The Web Audio spec appears to be using the WAV ordering for 5.1. I suggest
>> they also follow that ordering for 3 channels and for 5.0. For 6.1 and 7.1,
>> the WAV ordering actually depends on whether you call your channels "side
>> left" and "side right" or "back left" and "back right" (while, of course,
>> the actual standards call them "surround left" and "surround right", which
>> is neither of those things). We recently spent a few months going around
>> about what to do about this mess on flac-dev (because FLAC also uses the
>> WAV ordering). We finally reached a decision in this thread:
>> http://lists.xiph.org/pipermail/flac-dev/2013-January/003568.html. It
>> would be nice if they came to the same decision.
>>
>
What Tim says sounds reasonable.  I think we should be able to come up with
good channel orderings for the currently undefined ones he mentions.
 What's important, of course, is that we agree to the same ordering.
 Except for the very simple ones, the actual ordering can be somewhat
arbitrary.  Another thing to note is that the user agent may have to do
some amount of "channel swizzling" at the very final stage when talking to
the audio hardware to switch the Web Audio ordering of channels into the
actual physical ordering on that specific machine (which can vary depending
on configuration).

Chris



>
> Thanks,
> Rob
> --
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>