W3C home > Mailing lists > Public > public-media-capture@w3.org > February 2014

Re: About the Mandatory constraints

From: cowwoc <cowwoc@bbs.darktech.org>
Date: Wed, 05 Feb 2014 23:27:07 -0500
Message-ID: <52F30F1B.3000106@bbs.darktech.org>
To: public-media-capture@w3.org
Hi Stefan,

Correct me if I'm wrong, but doesn't the Capabilities API enable 
developers to query a camera's capabilities, before invoking 
getUserMedia(), all without triggering a prompt?

If so, why do we need mandatory/optional constraints at all? The 
developer can filter the reads of getCapabilities() and judge for 
themselves if their desired constraints are met or not. The constraints 
API is always going to be less expressive than a developer querying and 
filtering through the Capabilities themselves.

I am expecting something along these lines:

 1. var capabilities = Camera.getCapabilities();
 2. var preference = pickBest(capabilities); //application-specific
    definition of "best"
 3. If "preference" is undefined, the mandatory constraints were not
    met. Display a user-friendly error message and quit.
 4. Otherwise, invoke: getUserMedia(preference); //Provide a specific
    mode to open the camera in
 5. If the operation fails (the user disconnected the camera between
    steps 1 and 3) go back to step 1 and try again.


On 05/02/2014 1:34 PM, Stefan Håkansson LK wrote:
> There has been some discussion about mandatory constraints again lately
> in the context of constraints for the MediaStream Recorder.
> I think the use of constraints for the Recorder is something we have not
> really discussed yet, but I think (though I may be wrong) some mails
> tended to question the need for mandatory constraints also for gUM.
> Just to be clear: I think we have debated the mandatory constraints for
> gUM several times, and we always come back to the same conclusion:
> people want them. One use is when the app developer wants to avoid
> disturbing the user, or even indicate e.g. that video communication is
> possible, if the equipment does not fulfill the requirements the app
> developer has.
> Some people think it would be more natural to just get access to the
> camera (and in the process launch a prompt), then check what it can
> fulfill the needs, and if not tell the user that "sorry, your camera is
> not good enough". But those developers can skip using mandatory constraints.
> Let's not debate if we need mandatory constraints or not for gUM again.
> I think it would be much more fruitful if we could have the details in
> Constrainable reviewed for use with gUM and MediaStreamTracks. I would
> be really happy we could nail a design that fulfills the needs we have
> there.
> Stefan
Received on Thursday, 6 February 2014 04:27:37 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 16:26:24 UTC