Re: [clue] a few issues on data model draft

["Roni Even" <[e-mail]>]

Andy,

The image attribute provides a better solution  to allow the consumer to ask
for a preferred image size which is not only the aspect ratio but the
resolution and pixel aspect ratio.  It can be specified per SSRC
http://tools.ietf.org/html/draft-lennox-mmusic-sdp-source-selection-03 

The consensus in RTCweb was to use this solution  based on
http://tools.ietf.org/html/draft-alvestrand-rtcweb-resolution-00 

 

Roni

 

From: Andy Pepperell [mailto:[e-mail]] 
Sent: 01 August, 2012 1:41 AM
To: Allyn Romanow (allyn)
Cc: Espen Berger (espeberg); Roni Even; CLUE
Subject: Re: [clue] a few issues on data model draft

 

>>>Currently it is not possible to tell whether a remote video source is
natively 4:3 or 16:9, for instance.
>>>If we have this, there might usefully be a "PREFERRED-ASPECT-RATIO" in
the consumer's stream selection message as part of the  (e.g. in
"<stream-description> / <encoding>").

>>Roni: RE: No need, first of all it does not work with switched capture
that may have different aspect ratios. Also this is available in the SDP as
well as a way for receiver to ask for specific ratio using the SDP image
attribute.

>AR - I'll let Andy respond to this

Many apologies for not doing so until now...

Roni, I think you're right in that at least the native aspect ratio as
potentially expressed in a provider's capture advertisement wouldn't work
for the switched capture case (or at least wouldn't work all the time - for
the endpoint case where the switched capture was a dynamic choice between
one of the "real" cameras' image then it would be possible (and
straightforward) to attach the same native aspect ratio to the switched
capture as was applicable to the non-switched captures). Even if it were
impossible to attach a "native aspect ratio" to the switched case, to my
mind this doesn't necessarily take away from the validity in this scenario
of the consumer supplying a "preferred aspect ratio" in its stream selection
message.

re: use of "imageattr" in the SDP, it's definitely pertinent here;
potentially this has some issues in relation to CLUE:

- it would have to be applied on a per m line basis (excluding payload type
differences) rather than per capture - within CLUE there would be a need (or
at least use) of the aspect ratio specification being more fine-grained and
separately specifiable per capture (this may depend in part on how we
eventually choose to manage main vs slides video in terms of RTP session
association though).

- by being in SDP, it's presumably the case that to correctly signal to the
consumer when, say, a 4:3 presentation source had been connected would
require an additional offer / answer cycle (and similarly if that source
were to be disconnected and a new 16:9 source attached) - this seems
slightly less lightweight than the equivalent operation would be if its
scope were restricted to just the CLUE provider capture advertisement. As a
side point, it also seems more heavyweight than SIP without the use of
imageattr too, where presumably the only impact of connecting such a
presentation source would be a BFCP exchange.

I'm happy to own up here to not having seen this attribute being present in
devices' SDP, so if any of the above are inaccurate due to my ignorance on
this, I apologise. It would certainly be interesting to get some sort of
picture of the adoption of "imageattr" within the vendor community - I don't
recall seeing this in use, but most of my exposure has been to systems not
necessarily running recent software versions. Obviously if the
already-defined "imageattr" does all we'd like within CLUE, then we should
use this already-defined scheme.

Regards,

Andy



On Sun, Jul 29, 2012 at 4:58 AM, Allyn Romanow (allyn) <[e-mail]>
wrote:

Hi Espen,

Thanks for your comments- 

Please see below-

Also inline in response to your inline J

 

From: Espen Berger (espeberg) 
Sent: Monday, July 23, 2012 8:27 AM
To: Allyn Romanow (allyn); Roni Even; 'CLUE'


Subject: RE: [clue] a few issues on data model draft

 

I have two questions to the data model draft. 

 

The first questions is related to naming differences between the CLUE
framework and the CLUE data model. Some examples of differences. the
framework uses Description and the data model uses capture-scene-text, the
framework uses capture and the data model uses capture-description . Isn't
it natural that both documents share the same vocabulary? 

 

AR - Christian also brought this up.   I believe that the documents will not
have the same vocabulary - but the concepts are the same.     The framework
was written first and it's goal is to describe things as clearly as possible
(we're not done with that.). The data model is more formal and the language
there is not casual. It was developed after the framework, so it sort of
distils the ideas in the framework.  

 

If there is a discrepancy of meaning, that is an issue and we should
definitely sort it out. But in terms of language, I think it's fine to
either leave it different or  change the framework at some point to be more
in keeping with the data model.. but I think it's a good idea to do that
later when the data model is about agreed upon.                 

 

I've put this on the list for discussion at the IETF meeting on Weds.


 

The second questions is related to the concept of doing a data model as the
basis for both advertisement and configuration messages. Playing around with
some XML examples messages it's not obvious that the two messages types
share a common data model. I do see similarities between the initial
advertisement, the current active configuration and the advantages of be
able to describe the state of a running CLUE system. Assume this will be
sorted out when we look at the details of how to do configuration in CLUE.  

 

AR - Okay, this is interesting. Guess I'll have to wait to see more
specifically what issues arise.

 

Additional comments inline. 

 

-Espen 

 

 

From:  <mailto:[e-mail]> [e-mail]
<mailto:[mailto:[e-mail]]> [mailto:[e-mail]] On
Behalf Of Allyn Romanow (allyn)


Sent: 18. juli 2012 23:00
To: Roni Even; 'CLUE'
Subject: Re: [clue] a few issues on data model draft

 

Hi Roni,

Sure, these are easy to add-

thanks

 

From: Roni Even  <mailto:[mailto:[e-mail]]>
[mailto:[e-mail]] 

Sent: Wednesday, July 18, 2012 2:56 PM
To: Allyn Romanow (allyn); 'CLUE'
Subject: RE: [clue] a few issues on data model draft

 

Hi,

Reviewed the draft, inline for your question (BTW: not all the new
attributes here are in BOLD for example captureID)

 

Other comments

 

1.       Need to add axis of capture to the media capture (now in the
framework)

2.       The capture scene text and language should be sets of (text,
language), I think is not the current structure

 

Thanks

Roni

 

From:  <mailto:[e-mail]> [e-mail]
<mailto:[mailto:[e-mail]]> [mailto:[e-mail]] On
Behalf Of Allyn Romanow (allyn)
Sent: 18 July, 2012 3:22 AM
To: CLUE ( <mailto:[e-mail]> [e-mail])
Subject: [clue] a few issues on data model draft

 

Folks,

There are several issues related to the data model that we'd like us to
consider. These are things that are not exactly the same as in the
framework, to a lesser or greater extent. They were brought up during the
data model presentation at the interim meeting. I wonder if we could work on
resolving them?

List based on draft-romanow-clue-data-model-01

1.  Any problem with using media-type for capture attribute as described in
the draft?

RE: OK


EBE> Supported, since its allow us to join the audio and video encodings
into a single list of encodings. 

2.  Any problem with using content-type for capture attribute as described
in the draft?

                RE: I did not see any difference from the framework in which
case I am OK.

               EBE> The framework use the 'content' name and the data model
the 'content-type' name. Why not use the same name?  

AR- as above

3.  DERIVED for capture attribute- Should we have a variable called
something like DERIVED, that takes various values, one of which is composed.
That would mean that if DERIVED is not =composed, that the capture is not
composed, and if it =composed then it is. I don't have another descriptor to
propose now, but there could be others either now or later.

Why this change from the framework? I think it is more general than composed
Boolean, yet semantically similar.

This does not prevent us from having qualifiers to describe composed, to
help  distinguish between different composed captures, as has  been
discussed. Also, it needs to be possible to have multiple values for
"DERIVED", that is the values should not be mutually exclusive.

                RE:  I am OK if this is for future extension but am not sure
about the structure  the high level derived which has Compose and future
something (not sure what). The composed has a value (true, false) and child
elements for extensions . Is this the proposed structure?

EBE> I like the idea of describing the origin of the capture with an
attribute that is more extensible than a Boolean. What about creating
enumerated values for the two origins we are currently discussing. We have
'composed' (composed=true) meaning that the media has been changed in some
way and original (composed=false). 

4.  Leave switched as a Boolean as in framework. The proposal in the draft
seems infeasible - we don't want CLUE  to have to include all the ways in
which products might want to implement switching. It would be better to make
this more general, but we have no suggestion for it at present- it does not
really match the meaning of a derived capture.

                RE: I think that if we have the extension for composed as I
outlined above we can have similar here.

5.  As part of the capture description, should we have a parameter
NATIVE-ASPECT-RATIO, which indicates the aspect ratio for the capture if
there is one, such as 4:3 for a video camera? The reason is that it can help
rendering.



Currently it is not possible to tell whether a remote video source is
natively 4:3 or 16:9, for instance. If we have this, there might usefully be
a "PREFERRED-ASPECT-RATIO" in the consumer's stream selection message as
part of the  (e.g. in "<stream-description> / <encoding>").

                RE: No need, first of all it does not work with switched
capture that may have different aspect ratios. Also this is available in the
SDP as well as a way for receiver to ask for specific ratio using the SDP
image attribute.

EBE> The image attribute (RFC6236) document talks about image resolution and
picture aspect ratio, and how they relates to codec specific parameters like
h264 max-fs and max-mbps.  An attribute can have a single value, a list of
values or a range. 

6.   Multiplex ID - Value sent by consumer in its stream selection message
with the encoding id and capture id. This is the mechanism by which the
consumer tells the provider which multiplex id to generate that stream with,
so that the consumer can demultiplex the stream correctly when receiving it.


This is the link between RTP and CLUE as discussed in
draft-lennox-clue-rtp-usage.

     Think should probably be re-named.

               RE: I do not see the need the mapping is to the capture ID
which is a numeric value. See
<http://tools.ietf.org/html/draft-even-clue-rtp-mapping-03>
http://tools.ietf.org/html/draft-even-clue-rtp-mapping-03 

           7.  AUDIO-RENDERING-ID -  If the notion of an audio rendering tag
is

     adopted, this would be needed. It is an ID provided by the consumer to
the

     provider. The provider uses the tag to associate an audio stream with a
video

    stream.

                RE; suggest to take this out at the moment until we agree if
needed and how to map.

EBE> I assume that matching RTCP SDES CNAME is still the preferred
mechanisms for syncing audio and video for lip-sync (as defined in RFC3550).
When we discussed audio tags last interim it as was presented as a tool for
improving directional audio. 

 

Clearly this doesn't cover all the data model issues, but it's a start.

 

Thanks,

Andy and Allyn

 

 


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