Subject: [MMUSIC] LS Regarding Indicating Image Size in Conversational Multimedia Sessions Esablished Using SIP/SDP

From: Gonzalo Camarillo <[email-masked]>
Date: Thu, 24 Apr 2008 13:47:28 +0300

Hi,

this liaison statement is addressed to the MMUSIC WG:

LS Regarding Indicating Image Size in Conversational Multimedia Sessions 
Esablished Using SIP/SDP

https://datatracker.ietf.org/documents/LIAISON/file541.doc

Cheers,

Gonzalo
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---

From: "Even, Roni" <[email-masked]>
Date: Thu, 24 Apr 2008 16:26:06 +0300

Hi,
I looked at the LS and would like to give the following feedback.

1. It is not clear if the request is from the video encoder to send any
resolution or from the sending terminal to scale the video picture.

2. Currently RFC4587 for H.261 and RFC4629 for H.263 enable the receiver
to ask for specific resolution. It also allows the receiver to ask for
different resolutions at different frame rates. This may be important on
limited BW connections since in some cases there may be a preference to
show low resolution at higher frame rate if motion is important. H.261
codec supports only fixed resolutions while H.263 may support custom
resolutions and RFC4629 defines them.

3. For H.264 requesting only the resolution may not be enough. H.264 has
also the sample aspect ratio value and if the receiver will not take it
into account the display image may have geometric distortion. For H.264
there is a work going on at the ITU on requesting a specific resolution
from the sender (if it supports it). This work will be approved next
week and we intend to add this also to H.264 payload specification.

4. Making a generic resolution parameter for indicating the screen size
may be interesting but I am not sure you can guarantee that every send
will be able to build the right image. An H.264 codec is not required to
have scaling capability and it is up to the receiver to scale to the
display. The work mentioned in point 3 will enable the sender to reply
with the scaling capabilities it has.

5. I think that the LS should also be sent to AVT.

Thanks
Roni Even 

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On
Behalf
> Of Gonzalo Camarillo
> Sent: Thursday, April 24, 2008 1:47 PM
> To: mmusic
> Cc: [email-masked]
> Subject: [MMUSIC] LS Regarding Indicating Image Size in Conversational
> Multimedia Sessions Esablished Using SIP/SDP
> 
> Hi,
>