Re: [rtcweb] Comments to use-cases/reqs document

Harald Alvestrand <harald@alvestrand.no> Tue, 12 July 2011 14:17 UTC

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Date: Tue, 12 Jul 2011 16:17:08 +0200
From: Harald Alvestrand <harald@alvestrand.no>
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Subject: Re: [rtcweb] Comments to use-cases/reqs document
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On 07/12/11 13:58, Stefan Håkansson LK wrote:
>>> All,
>>>
>>> some comments to
>>> <http://datatracker.ietf.org/doc/draft-ietf-rtcweb-use-cases-and-requirements/?include_text=1>
>>>
>>>
>>>
>>> 3. The "Video Size Change" use case derives F22; but that is already
>>> derived in "Simple Video Communication Service". I propose to remove
>>> the "Video Size Change" use case.
>> I disagree with this proposal.
>> While the "resizing" requirement is in "simple video communication
>> service" as
>> "The users can change the display sizes during the session", I believe
>> the basic use case does not derive the requirement that the change in
>> video size be communicated to the other party.
>>
>> I would propose the following changes:
>> - Reinstate the text below:
>>
>> 4.2.4.  Video Size Change
>>
>> 4.2.4.1.  Description
>>
>>     Alice and Bob are in a video call in their browsers and have
>>     negotiate a high resolution video.  Bob decides to change the size of
>>     the windows his browser is displaying video to a small size.
>>
>>     Bob's browser regenerates the video codec paramters with Alice's
>>     browser to change the resolution of the video Alice sends to match
>>     the smaller size.
> My preference is always to keep the number of use cases down.
We may have a difference of style here - I prefer to have explicit use 
cases that show only a single action or attribute that needs to be 
supported, which means that the number of use cases tends to be high.

I think this is especially important for the situation where a WG has to 
decide to drop an use case because no agreed-upon implementation can be 
found.
>   Could we not just add a sentence to the current "Simple Video Communication Service" use case so it reads something like "The users can change the sizes of the video displays during the session. Changes of the display size are communicated from the displaying browser to the one sending the stream so that the video codec parameters can be changed accordingly."
As per above - I would prefer the "Simple Video Communication Service" 
to be as simple as possible. Even resizing the window locally is more 
than "as simple as possible" - the Gtalk video client for my phone 
doesn't support that.
> But my preference is not strong - I'm happy to reinsert the use case if people think so.
>> 4.2.4.2.  Derived Requirements
>>
>>     F22 ( It SHOULD be possible to modify video codec parameters during a
>>     session.)
> F22 now reads "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"
>> - Change the text of F22 to be:
>>
>>    It SHOULD be possible for one party to request a change in video
>> codec parameters, such as size,
>>    during a session, and for the other party to react to this request.
> I think "party" is very vague. What does it mean - the browser, the user, the web app?
Since this is the IETF WG - the "party" is the browser, user and web app 
together; somehow the desire for a change has to be communicated across 
the network, and that's the requirement I think needs to be in the IETF 
requirements list.

The corresponding API requirement (which I'm not sure how to formulate - 
all this may go on in the browser and need no explicit API) needs to go 
into the W3C requirements list.