Subject: [clue] Fwd: [MMUSIC] Channel descriptions

From: Paul Kyzivat <[email-masked]>
Date: Mon, 06 Aug 2012 15:19:52 -0700

As described below, ISTM what is being described below could be similar 
to a clue audio capture. But the context in which this is being 
discussed is not clue.

I think we need to pay attention to whether this can lead to an 
independent definition of essentially the same thing.

	Thanks,
	Paul

-------- Original Message --------
Subject: 	Re: [MMUSIC] Channel descriptions
Date: 	Fri, 20 Jul 2012 08:44:05 -0600
From: 	Kevin Gross <[email-masked]>
To: 	Harald Alvestrand <[email-masked]>
CC: 	[email-masked]

I'm talking about a single audio signals. It a surround stream, a single
signal would be, for instance, the left front. Track is also a
reasonable description but people tend to associate that term with
recording and reproduction. The ability to label individual channels in
surround formats is important to distinguish the many formats and
conventions in use. See http://tech.ebu.ch/docs/r/r123.pdf.

In commercial applications, it is common, for efficiency, for multiple
loosely related channels to be carried in the same stream, e.g.
different background music source, paging signals for different zones.
Active audio crossover networks
(http://en.wikipedia.org/wiki/Audio_crossover#Active) are often used in
large sound reinforcement systems and different frequency components are
carried to the speakers as separate channels in the same stream.

In all cases it is important to correctly connect the channels to their
intended destinations. There are too many possibilities in most of these
use cases for the i= description to resolve the potential ambiguity.

Kevin Gross

On Fri, Jul 20, 2012 at 6:13 AM, Harald Alvestrand <[email-masked]
<mailto:[email-masked]>> wrote:

     Kevin,

     can you clarify what you mean by "channel" here?

     The term is used most often for components of a multisource audio
     signal, such as stereo, 5+1 or 22+2 - in most cases, those will be
     carried in a single SSRC, using an encoding that implicitly defines
     which channels go where.

     In WebRTC, we've converged on the word "track" for a single media
     flow such as one audio signal (mostly) carried in a single SSRC, and
     the word "stream" for multiple media flows (such as audio and video)
     that are related to each other in some fashion.

     If you have a definition you would like to use, please point to it -
     the discussion can get to be almighty confusing if we're not talking
     about the same thing!

     On 07/18/2012 01:57 AM, Kevin Gross wrote:
>     The i= attribute provides a means to describe a session. Sessions
>     often have multiple media streams or channels. Although RFC 3551
>     (page 8) suggests a convention for ordering of channels for
>     surround sound applications, other applications use multiple
>     channels in different ways. It would be useful if there were a
>     mechanism analogous to i= for describing individual channels in a
>     session. Does such a thing exist anywhere? I've searched the
>     archives here and didn't find anything.
>
>     Kevin Gross
>     +1-303-447-0517 <tel:%2B1-303-447-0517>
>     Media Network Consultant
>     AVA Networks - www.AVAnw.com <http://www.avanw.com/>, www.X192.org
>     <http://www.X192.org>
>
>
>
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