Re: CHANGE: Use a JS Object as an argument to getUserMedia

On Thu, Oct 6, 2011 at 21:55, Anant Narayanan <> wrote:

> Hi Tommy, Adam,
> On 10/5/2011 6:51 AM, Adam Bergkvist wrote:
>> I agree with Tommy. Right now, once you have a MediaStream you can start
>> using it. If getUserMedia returns a stream directly, it would have to be
>> empty (no tracks), and tracks would have to be added later. I think it
>> would simplify things (e.g. MediaStream playback and sending with
>> PeerConnection) if a MediaStream is immutable with regards to its track
>> list.
> I think it is unrealistic to assume that MediaStreams are immutable. Web
> developers are already very familiar with the concept that an XMLHttpRequest
> is a living object and that changes will happen to it continuously which
> they must monitor and respond to.
> A MediaStream is no different, and there are multiple circumstances under
> which a stream may change, some of which are:
> - Network disruption
> - Physical disconnection of webcam/microphone
> - Software mute at OS level of microphone
> Since the web application must be able to respond to any of these (and
> other) changes to the MediaStream, we will most likely standardize on
> several DOM events on the MediaStream object anyway. Taking it one step
> further and adding an event for track addition and removal feels very
> "webby" to me :)
> That being said, I'd like to hear about what you think the advantages of
> having an immutable track list are; and if you think user-agents are able to
> guarantee that?

I'm all for adding more events to PeerConnection, *MediaStream and
MediaStreamTrack*. Right now everything is solved by streaming black video
and/or silence when foobar happens.

>  On 2011-10-05 08:59, Tommy Widenflycht (ᛏᚮᛘᛘᚤ) wrote:
>>> Yeah, I understood that during the office hour call. Dunno, your
>>> suggestion seems less elegant and clear but that might just be because
>>> I am quite new to the JS world. Can you list some use cases where your
>>> suggestion will really make a difference?
> One of my primary goals is to make the getUserMedia API as close to other
> Web APIs as possible. In the simplest case of the web developer who wants
> both a video and audio stream, the call would look like:
> var stream = navigator.getUserMedia();
> stream.addEventListener("**readyState", streamIsReady);
> function streamIsReady() { ... // note that errors can be handled here too,
> if we choose to define readyState to be broad }
> In the current spec, this looks like:
> var stream = navigator.getUserMedia("audio,**video", streamIsReady,
> streamError);
> function streamIsReady() { ... }
> function streamError() { ... }
Sorry, but you are wrong about how the current spec looks like; getUserMedia
is a void function. The MediaStream object is delivered only to the
streamReady callback if the user granted access and the required hardware
was found. I like this way a lot.

> Two reasons why I prefer the former over the latter:
> - Events > Callbacks. Events propagate, can be chained (ala jQuery), and
> there can be multiple listeners for the same event which is useful in some
> cases. That is not true of explicit callbacks.
> - An event like "readyState" is broad enough (just like the event of the
> same name in XHR) to cover many cases, so in the typical case the developer
> has to attach only one event listener. Of course we can choose to add other
> events to provide even more flexibility, and the more sophisticated web-apps
> will have multiple event listeners (which is fine IMO).
> I feel that since developers will be attaching event listeners to a
> MediaStream anyway, asking them to do right after they get one from
> getUserMedia is not necessarily a bad thing. This is a paradigm we should
> try and encourage.
> I'm still open to arguments and can be convinced otherwise! But this makes
> it feel very close to some of the other async Web APIs out there and feels
> intuitive as a JS developer to me :)
> Thanks,
> -Anant

Tommy Widenflycht, Senior Software Engineer
Google Sweden AB, Kungsbron 2, SE-11122 Stockholm, Sweden
Org. nr. 556656-6880
And yes, I have to include the above in every outgoing email according to EU

Received on Friday, 7 October 2011 07:34:30 UTC