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Re: [Exposed] attribute on our APIs

From: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
Date: Tue, 19 May 2015 05:35:07 +0000
To: Mathieu Hofman <Mathieu.Hofman@citrix.com>, Harald Alvestrand <harald@alvestrand.no>, "public-media-capture@w3.org" <public-media-capture@w3.org>
CC: Iñaki Baz Castillo <ibc@aliax.net>, "annevk@annevk.nl" <annevk@annevk.nl>
Message-ID: <1447FA0C20ED5147A1AA0EF02890A64B1D219F38@ESESSMB209.ericsson.se>
On 19/05/15 01:03, Mathieu Hofman wrote:
> Anne and Stefan seem to have had an exchange about "Make MediaStream
> usable with postMessage" in October 2013. Did anything come out of
> that?

What basically happened as far as I remember was that Anne and I had 
some text that we (at least I) thought was OK. It was quite 

However (and remember we've been trying to get to last call for a long 
time :) ), in the interest of not delaying the LC I decided to stop 
pushing this feature as there was little interest from others at the 
time. This seems to have changed now.

It could be worth noting that we at the time had a brief discussion on 
whether the MediaStream(Track)'s should be transferred or structurally 
cloned, and ended up on cloning (just as you seem to have) since the 
MediaStream(Track) API is just a control surface that is pretty 
lightweight, the heavy media processing machinery executes in the 
platform and is not cloned itself.


> ________________________________________ From: Mathieu Hofman Sent:
> Monday, May 18, 2015 3:36 PM To: Harald Alvestrand;
> public-media-capture@w3.org Cc: Iñaki Baz Castillo Subject: RE:
> [Exposed] attribute on our APIs
> I'm not extremely familiar with how this would be specified, but here
> is what I think is needed: - Define in the Media Capture and Stream
> specification how MediaStream and MediaStreamTrack objects should
> implement HTML5 structured cloning
> (http://www.w3.org/TR/html5/infrastructure.html#structured-clone).
> Since these objects already support cloning, it might simply be a
> matter of mentioning that a structured clone is the result of
> implicitly calling the .clone() method? - Make sure that the
> MediaStream and MediaStreamTrack APIs are accessible from non-window
> contexts. - Have the ImageCapture APIs accessible from non-window
> Worker contexts as well.
> For the use case I mentioned previously, the work would be in both
> APIs.
> The structured cloning change would mean that a source can be
> accessed through track objects in different, potentially unrelated
> contexts. In particular, a page could obtain access to a media source
> and send its stream object to an iframe running in another domain.
> From a user perspective, I do not think this is a concern since the
> user already trusted the app to basically do anything it wants with
> the captured source. However, I have no idea what the implications
> are on browser implementations.
> This does however open the door to very interesting approaches, such
> as: - Media source processed by background worker (my previously
> described use case) - Media source acquired by installed browser
> app/extension then "transferred" to regular page for sharing/display.
> This could be an implementation path for some privileged "output"
> streams such as tab capture. - Media displayed/rendered in other
> windows of an app. E.g. allowing an app to pop out a video stream
> outside of its main UI. (Inaki's use case)
> I'd be happy to help writing a specific proposal, I'm just not sure
> how to do it right.
> Mathieu ________________________________________ From: Harald
> Alvestrand [harald@alvestrand.no] Sent: Saturday, May 16, 2015 1:16
> AM To: Mathieu Hofman; public-media-capture@w3.org Subject: Re:
> [Exposed] attribute on our APIs
> Den 15. mai 2015 22:50, skrev Mathieu Hofman:
>> Answering to myself here, I completely forgot about the
>> ImageCapture API. I think it would be useful for this API to be
>> available in a worker and be able to transfer a MediaStream(Track)
>> object to a worker through postMessage.
> Thanks for the input!
> Would you be willing and able to provide a proposal for exactly what
> we need to change in the spec in order for this to be possible?
> And - should this be done as part of the ImageCapture API work, or
> as part of the Media Capture and Streams specification?
>> Mathieu ________________________________________ From: Mathieu
>> Hofman Sent: Friday, May 15, 2015 1:41 PM To: Harald Alvestrand;
>> public-media-capture@w3.org Subject: RE: [Exposed] attribute on our
>> APIs
>> Sorry for missing this earlier.
>> One use case I could see is processing of the media video track in
>> a worker through a canvas element. Canvas can be manipulated in a
>> worker through the CanvasProxy object. However there is no way to
>> get the video content into the canvas from the worker, since the
>> only path right now is through attaching the media stream to a
>> video element and a canvas drawImage operation with the video
>> element as source. Because of this limitation it's probably fine to
>> mark the API as exposed on Window only, but I'd like us to explore
>> this use case and see if anything can be done to support it.
>> Mathieu ________________________________________ From: Harald
>> Alvestrand [harald@alvestrand.no] Sent: Tuesday, May 12, 2015 1:23
>> PM To: public-media-capture@w3.org Subject: Re: [Exposed] attribute
>> on our APIs
>> Den 04. mai 2015 19:20, skrev Harald Alvestrand:
>>> On 04/29/2015 05:17 PM, Harald Alvestrand wrote:
>>>> Den 22. april 2015 19:18, skrev Martin Thomson:
>>>>> On 22 April 2015 at 05:16, Harald Alvestrand
>>>>> <harald@alvestrand.no> wrote:
>>>>>> What considerations do people know of that dictate whether
>>>>>> or not we should expose APIs to workers or not?
>>>>> The primary consideration is whether we want to expose them
>>>>> to workers.
>>>>> Maybe you should ask if anyone plans to implement X in
>>>>> workers.
>>>> As amended by Martin:
>>>> Does anyone plan to implement any part of the Media Capture and
>>>> Streams API in workers?
>>> With all the responses I have seen so far:
>>> The conclusion is that nobody plans to implement any part of the
>>> Media Capture and Streams API in workers, and we'll mark all our
>>> APIs (where appropriate) with [Exposed=Window].
>>> I'll leave this open until Wednesday afternoon, and if the
>>> conclusion still stands, will take that as a consensus position
>>> and relay it to the editors for implementation.
>>> Harald
>> The conclusion has remained standing.

Received on Tuesday, 19 May 2015 05:35:37 UTC

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