W3C home > Mailing lists > Public > public-webrtc@w3.org > September 2015

Re: Resolution changes

From: Jan-Ivar Bruaroey <jib@mozilla.com>
Date: Mon, 14 Sep 2015 22:20:20 -0400
To: Harald Alvestrand <harald@alvestrand.no>, Martin Thomson <martin.thomson@gmail.com>, "public-webrtc@w3.org" <public-webrtc@w3.org>
Message-ID: <55F78064.1050802@mozilla.com>
On 9/14/15 9:17 PM, Harald Alvestrand wrote:
> On 09/14/2015 02:38 PM, Martin Thomson wrote:
>> What happens when MediaStreamTrack changes resolution to something
>> outside of the negotiated envelope of the session?  There is no
>> language in the spec.  Presumably if the resolution can be reduced,
>> reduce it.  Increasing resolution might be the only option we have in
>> the case that the session has a resolution floor.
> Section 5:
> Let's look at a slightly different situation starting from the same 
> point. In this case, instead of the first track attempting to apply a 
> conflicting constraint, the user physically locks the camera into a 
> mode where the fill light is on. At this point the source can no 
> longer satisfy the second track's mandatory constraint that the fill 
> light be off. The second track is transitioned into the muted state 
> and receives an|overconstrained| 
> <http://w3c.github.io/mediacapture-main/getusermedia.html#event-mediastreamtrack-overconstrained>event.
> More info in section 11.1.1.

Constraints are properties of the application, not the browser, and no 
constraints were violated here.

> > What happens when aspect ratio changes?  Letterbox & pillars?
> That's a better question. I remember discussing this subject in Boston, with one option being that one could have a constraint (or constraint-like setting) that chose one of the defined values for the object-fit CSS attribute: fill, contain, cover, none or scale-down.
> https://css-tricks.com/almanac/properties/o/object-fit/
> But nobody's suggested text in the intervening 2 years, so I guess it's not that important.
> (My suggestion would be to default to "contain", which causes letterbox and pillars.)

In browser-to-browser cases, this should not be an issue. In Firefox we 
already see this with replaceTrack: https://jsfiddle.net/oyabqd0j/ 
(shows changing dimensions, aspect and frame-rate without problems). No 
need for letterbox or pillars.

I'm no expert on SDP and "negotiated envelopes" but that sounds like 
edge-cases talking to legacy or special hardware, which may explain why 
no-one cares.

I think we should crop if this ever happens. FWIW, getUserMedia in 
Chrome crops. E.g. try 640x360 on OSX.

.: Jan-Ivar :.
Received on Tuesday, 15 September 2015 02:20:50 UTC

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