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Kevin Gross | 18 Jul 2012 01:57

Channel descriptions

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
Media Network Consultant
AVA Networks - www.AVAnw.com, www.X192.org 

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Charles Eckel (eckelcu | 18 Jul 2012 17:58
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Re: Channel descriptions

Hi Kevin,

Just to clarify my understanding of what you are asking, you can already have an i-line at the session level
and/or at the media level (i.e. per m-line). Are you looking for something that lets you differentiate
between multiple channels within a single m-line?

Cheers,
Charles  

> -----Original Message-----
> From: mmusic-bounces <at> ietf.org [mailto:mmusic-bounces <at> ietf.org] On
> Behalf Of Kevin Gross
> Sent: Tuesday, July 17, 2012 4:58 PM
> To: mmusic
> Subject: [MMUSIC] Channel descriptions
> 
> 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
> Media Network Consultant
> 
> AVA Networks - www.AVAnw.com <http://www.avanw.com/> ,
> www.X192.org
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Kevin Gross | 18 Jul 2012 19:35

Re: Channel descriptions

Yes. For a multichannel media specification such as:
m=audio 49152 RTP/AVP 96
i=Channels 1-8
a=rtpmap:96 L24/48000/8
a=sendonly
I get one description ("Channels 1-8") for all 8 channels in this stream. I'd like to also have the ability to supply a description per channel.

Kevin Gross
+1-303-447-0517
Media Network Consultant
AVA Networks - www.AVAnw.com, www.X192.org



On Wed, Jul 18, 2012 at 9:58 AM, Charles Eckel (eckelcu) <eckelcu <at> cisco.com> wrote:
Hi Kevin,

Just to clarify my understanding of what you are asking, you can already have an i-line at the session level and/or at the media level (i.e. per m-line). Are you looking for something that lets you differentiate between multiple channels within a single m-line?

Cheers,
Charles

> -----Original Message-----
> From: mmusic-bounces <at> ietf.org [mailto:mmusic-bounces <at> ietf.org] On
> Behalf Of Kevin Gross
> Sent: Tuesday, July 17, 2012 4:58 PM
> To: mmusic
> Subject: [MMUSIC] Channel descriptions
>
> 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
> Media Network Consultant
>
> AVA Networks - www.AVAnw.com <http://www.avanw.com/> ,
> www.X192.org


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Charles Eckel (eckelcu | 19 Jul 2012 00:03
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Re: Channel descriptions

It looks as if RFC 3190 defines some conventions for the channels for L24.
Otherwise, perhaps an extension to RFC 5576, assuming you are using different SSRCs for each channel.
In general, there are ongoing discussions ongoing in AVTCORE, RTCWEB, and CLUE regarding multiplexing
and some mechanism to describe the multiplexed streams will likely result.

Cheers,
Charles

> -----Original Message-----
> From: Kevin Gross [mailto:kevin.gross <at> avanw.com]
> Sent: Wednesday, July 18, 2012 10:35 AM
> To: Charles Eckel (eckelcu)
> Cc: mmusic
> Subject: Re: [MMUSIC] Channel descriptions
> 
> Yes. For a multichannel media specification such as:
> 
> 
> 	m=audio 49152 RTP/AVP 96
> 	i=Channels 1-8
> 	a=rtpmap:96 L24/48000/8
> 	a=sendonly
> 
> I get one description ("Channels 1-8") for all 8 channels in this stream. I'd
> like to also have the ability to supply a description per channel.
> 
> 
> Kevin Gross
> 
> +1-303-447-0517
> Media Network Consultant
> 
> AVA Networks - www.AVAnw.com <http://www.avanw.com/> ,
> www.X192.org
> 
> 
> 
> On Wed, Jul 18, 2012 at 9:58 AM, Charles Eckel (eckelcu)
> <eckelcu <at> cisco.com> wrote:
> 
> 
> 	Hi Kevin,
> 
> 	Just to clarify my understanding of what you are asking, you can
> already have an i-line at the session level and/or at the media level (i.e. per
> m-line). Are you looking for something that lets you differentiate between
> multiple channels within a single m-line?
> 
> 	Cheers,
> 	Charles
> 
> 
> 	> -----Original Message-----
> 	> From: mmusic-bounces <at> ietf.org [mailto:mmusic-
> bounces <at> ietf.org] On
> 	> Behalf Of Kevin Gross
> 	> Sent: Tuesday, July 17, 2012 4:58 PM
> 	> To: mmusic
> 	> Subject: [MMUSIC] Channel descriptions
> 	>
> 	> 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
> 
> 
>
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Harald Alvestrand | 20 Jul 2012 14:13
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Re: Channel descriptions

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
Media Network Consultant
AVA Networks - www.AVAnw.com, www.X192.org



_______________________________________________ mmusic mailing list mmusic <at> ietf.org https://www.ietf.org/mailman/listinfo/mmusic 


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Kevin Gross | 20 Jul 2012 16:44

Re: Channel descriptions

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 <harald <at> alvestrand.no> 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
Media Network Consultant
AVA Networks - www.AVAnw.com, www.X192.org



_______________________________________________ mmusic mailing list mmusic <at> ietf.org https://www.ietf.org/mailman/listinfo/mmusic



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