Subject: [rtcweb] WG last call comments on use-case and requirement document, “multiple resolutions”

From: Stefan Håkansson LK <[email-masked]>
Date: Mon, 29 Apr 2013 16:05:46 +0200

This relates to the comments to the WG last call of the use-cases and 
requirements document [1].

There is a use-case (4.3.3) detailing the use of multiple resolutions of 
the data from one single source, with three options on how to meet that 
mentioned (scalable codec, simulcast and transcoding).

There has been a request ([2]) to clarify which method(s) that should be 
mandatory, but no conclusion yet.

To recap, the use case is about a multiparty video (and audio of course) 
communication session using a central node. At the screen of each 
endpoint/user, one video is displayed on a large surface, with other 
videos are shown as (live) thumbnails.

Which video to show at the large display surface is depending on speech 
activity; the video from the endpoint with currently talking user(s) is 
shown on the large surface - and this will usually change frequently 
during the session. This selection is handled by the central node which 
has access to all video and audio streams.

I think this is a quite common model, used by many services.
The current draft list three ways to support this use-case (use scalable 
video codecs, transcode in the central node, or use simulcast), but 
there are no requirements that back this up. We should pick at least one 
solution that must be supported, and then derive the corresponding 
requirements.

I am a proponent for simulcast as solution for this use-case.

Stefan

[1] http://www.ietf.org/mail-archive/web/rtcweb/current/msg06136.html

[2] http://www.ietf.org/mail-archive/web/rtcweb/current/msg06157.html