Re: [rtcweb] Resolution negotiation - mandatory / advisory resolutions

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

Hi Harald,
The reason for the language was that this is really what the receiver wished
to receive. The issue is that at least for H.264 there is no mandatory
requirement for the encoder to support all resolutions within the supported
level. The receiver must be able to crop and scale.
 
Roni Even

> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] On
> Behalf Of Harald Alvestrand
> Sent: Thursday, April 19, 2012 10:47 AM
> To: [e-mail]
> Subject: Re: [rtcweb] Resolution negotiation - mandatory / advisory
> resolutions
> 
> When discussing the issue of resolution negotiation locally, we found a
> quandary:
> 
> We have two different negotiation needs:
> - Maximum resolution that's possible to use in a given context
> - The preferred resolution for a given context
> 
> The current imageattr= spec (RFC 6236) doesn't specify clearly whether
> the result of the negotiation is to be considered mandatory or advisory
> (it uses the term "wishes" a lot), but the description reads most
> consistently if one assumes that it is a "MUST" type request.
> 
> One interpretation is that the highest functionality available in the
> spec is the "limit", while the highest q value is the "preference",
> thus:
> 
> recv [x=320,y=200,q=1.0] [x=200:1024,y=160:768,q=0.1]
> 
> would indicate that the receiver is capable of 200x160 to 1024x768, but
> wants 320x200.
> 
> This maps reasonably to the capabilities spec's talk about "mandatory"
> vs "optional" capabilities.
> 
> Does this interpretation make sense?
> 
>                        Harald
> 
> 
> On 04/12/2012 10:46 AM, Harald Alvestrand wrote:
> > Hello folks,
> >
> > after the IETF, I've attempted to gather together information about
> > resolution negotiation and what we might need to do there.
> >
> > I pulled together the paragraphs below - this may want to be
> > incorporated in an I-D on "SDP usage in RTCWEB", or it may want to go
> > somewhere else. Chairs' guidance is appreciated.
> >
> > At the moment, I have it in xml2rfc format, so it should be easy to
> do
> > cut-and-paste on it, but don't want to push it as a separate I-D
> > unless that's what the chairs desire.
> > Note - there are some QUERY sections in there - I'm unsure what those
> > should be resolved to.
> >
> > Comments?
> >
> >                          Harald
> >
> > 2.  Requirements
> >
> >    The relevant requirement for video resolution negotiation from the
> >    RTCWEB use cases document
> >    [I-D.ietf-rtcweb-use-cases-and-requirements] is:
> >
> >    o  F25 The browser SHOULD use encoding of streams suitable for the
> >       current rendering (e.g. video display size) and SHOULD change
> >       parameters if the rendering changes during the session.
> >
> >    The resulting need is:
> >
> >    o  To negotiate a maximum spatial resolution for all videos at
> call
> >       setup time
> >
> >    o  To negotiate a maximum temporal resolution ("frame rate")
> across
> >       all videos at call setup time
> >
> >    o  To indicate the desire of the recipient for a particular
> spatial
> >       or temporal resolution on a particular video source
> >
> >    o  To indicate the intent of the sender to send a video source in
> a
> >       particular spatial or temporal resolution
> >
> >    This document does not mention other requirements.
> 
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