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Capabilities (Re: [Bug 25777] Capabilities seem under specified)

From: Harald Alvestrand <harald@alvestrand.no>
Date: Fri, 10 Oct 2014 15:00:02 +0200
Message-ID: <5437D852.8030904@alvestrand.no>
To: public-media-capture@w3.org
Putting discussion on the list rather than in the bug.....

On 10/09/2014 04:21 PM, bugzilla@jessica.w3.org wrote:
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=25777
>
> Jan-Ivar Bruaroey [:jib] <jib@mozilla.com> changed:
>
>             What    |Removed                     |Added
> ----------------------------------------------------------------------------
>                   CC|                            |jib@mozilla.com
>
> --- Comment #7 from Jan-Ivar Bruaroey [:jib] <jib@mozilla.com> ---
> While examples are nice, I would argue they're no replacement for
> specification.
>
> Are capabilities accurate?
>
> While it is possible to deduce from the applyConstraints algorithm [1] that
> capabilities are allowed to be a super-set of what the UA supports, I find no
> mention of this where Capabilities is defined [2].
>
> I've read the definition a couple of times, and even though it uses the word
> "subset" four times in one paragraph, it still seems to equate what the
> capabilities read with what "the UA supports", which doesn't allow for
> capabilities to be either-or (e.g. super framerate OR super resolution).
>
> I think it would help implementations if the spec stated that returned
> capabilities must a set or super-set of what the UA supports.

I think the definition is intended to say that it be a superset.
That's what the example was supposed to demonstrate: even though only 
two resolutions are supported, the values given are ranges.

>
> Are capabilities constant?
>
> I find conflicting text on this in the spec:
>
> "The UA may choose new settings for the Capabilities of the object at any time.
> When it does so it must attempt to satisfy the current Constraints, in the
> manner described in the algorithm above." [2]

I think "new settings for the Capabilities of the object" was meant to 
be parsed as

(new settings for) (the Capabilities of the object)

ie it is the settings that are new. The capabilities remain unchanged.
(and I think capitalizing Capabilities here is probably misleading).

>
> vs.
>
> "Source capabilities are effectively constant. Applications should be able to
> depend on a specific source having the same capabilities for any session." [3]
>
> [1]
> http://w3c.github.io/mediacapture-main/getusermedia.html#dfn-applyconstraints
> [2] http://w3c.github.io/mediacapture-main/getusermedia.html#capabilities
> [3] http://w3c.github.io/mediacapture-main/getusermedia.html#terminology
>
Received on Friday, 10 October 2014 13:00:35 UTC

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