Re: Fwd: draft proposal : active multiple devices for getUserMedia

On 2012-04-17 02:47, William Lin wrote:
>
> On Fri, Apr 13, 2012 at 9:47 PM, Harald Alvestrand <harald@alvestrand.no
> <mailto:harald@alvestrand.no>> wrote:
>
>     __
>     On 04/12/2012 04:53 AM, William Lin wrote:
>>     Hi,
>>
>>     in these days, Constraints and Capabilities API for getUserMedia
>>     were discussed while i found one scenario doesn't be covered:
>>     "users may want to initiate capture from multiple devices at one
>>     time in multiple media streams" (refer to
>>     http://www.w3.org/TR/capture-scenarios/#multiple-active-devices).
>>     is it possible adding the options to set the number of active
>>     devices? and the callback function needs to change:
>     Given that the normal case will be one device, what's the cost of
>     this relative to "just" calling getUserMedia multiple times?
>
>
> Seems it is one mean to  get 'all' devices. but suppose getUserMedia
> will be applied to 'monitor system', it is more sensible just calling
> one time.

I think we need to support this in some form. The home-security 
monitoring use case may not be the most common, but consider a mobile 
device with a front and a back camera, it's likely that people would 
like to toggle between the cameras. In that particular use case I see 
having one MediaStream with two video tracks as the most natural 
alternative.

>     And how do you see the user interaction dialog looking?
>
>
> in my opinion, it is depended on UA implementation: a list/checkgroup is
> ok (If native platform application can support user interaction in the
> multiple devices case, web runtime application will do).

If getUserMedia() is supposed to return several MediaStream objects then 
the UI will be responsible for grouping the different devices into 
MediaStreams which will add extra complexity to the UI. Therefore I'm 
more in favor of getUserMedia() providing one MediaStream object with 
several tracks (which we currently support). It would then be up to the 
application to create new MediaStream objects from the tracks of the 
LocalMediaStream if needed. This doesn't solve all of Williams problems, 
we still have the question about the app requesting, e.g., a certain 
number of video capture devices.

/Adam

Received on Tuesday, 17 April 2012 08:26:49 UTC