Re: channel layouts and up/down mixing

On 13-01-15 10:36 AM, Chris Rogers wrote:

> 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.

To be clear, what we settled on for FLAC is:

1 channel: mono.
2 channels: left, right.
3 channels: left, right, center.
4 channels: front left, front right, back left, back right.
5 channels: front left, front right, center,
            back/surround left, back/surround right.
6 channels: front left, front right, front center, LFE,
            back/surround left, back/surround right.
7 channels: front left, front right, front center,
            LFE, back center, side left, side right.
8 channels: front left, front right, front center, LFE,
            back left, back right, side left, side right.

This is based on identifying the standard Dolby surround speaker sets
for home theatre with the the channel designations and order in
http://msdn.microsoft.com/en-us/windows/hardware/gg463006.aspx

The 'back/surround' hedge is to clarify compatibility with media formats
and frameworks like Apple's CoreAudio which use the 'surround'
terminology. For 4, 5 and 6 channel speaker arrangements the distinction
between side, back, rear, and surround isn't meaningful.

As Tim says, there is confusion with 7 and 8 channel setups between
different standards as to whether 'surround' maps to 'side' or 'back',
and whether the rear centre channel in 6.1 is in line with the other two
surrounds or not. I think selecting 'side' and 'back' makes clear enough
how to map these channels to any physical speaker arrangement.

> 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).

Yes, of course.

 -r

Received on Tuesday, 15 January 2013 20:44:31 UTC