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RE: Cloning and sharing of MediaStreamTracks - worth it?

From: Jim Barnett <Jim.Barnett@genesyslab.com>
Date: Fri, 10 May 2013 12:01:38 +0000
To: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
CC: Martin Thomson <martin.thomson@gmail.com>, "public-media-capture@w3.org" <public-media-capture@w3.org>, Harald Tveit Alvestrand <harald@alvestrand.no>, Robert O'Callahan <robert@ocallahan.org>
Message-ID: <57A15FAF9E58F841B2B1651FFE16D28103DF0D@GENSJZMBX02.msg.int.genesyslab.com>
  From pervious emails, I thought that you were saying that constraints/settings are always applied to the source _object_, i.e. that settings are implemented by changing the state of the underlying device.  Martin is saying that they are never applied to the source object (but instead realized in software in the Track.)  The difference is that in your model (as I understood it) a setting applied to one Track will affect the observed output of all other Tracks that share the same source.  In Martin's model, a setting applied to one Track will not affect the output of other Tracks.

And Harald's  model seems to be: maybe it does, maybe it doesn't, who knows? Life is short, it's up to the UA.  

I think we need to be clear on which of these models we are using, or the discussion will keep going in circles.  As an example, in Tuesday's call when the 'zoom' setting came up, it was clear that many people wanted it to apply to the camera's native zoom ability, and not to be some post-processing sleight of hand.  In Martin's model that would not be allowed.  If it is allowed, I think that  it would have to affect the output of all Tracks that share the source.  Which is it?

- Jim

-----Original Message-----
From: Stefan Håkansson LK [mailto:stefan.lk.hakansson@ericsson.com] 
Sent: Friday, May 10, 2013 2:17 AM
To: Jim Barnett
Cc: Martin Thomson; public-media-capture@w3.org; Harald Tveit Alvestrand; Robert O'Callahan
Subject: Re: Cloning and sharing of MediaStreamTracks - worth it?

On 5/10/13 12:09 AM, Jim Barnett wrote:
> Well, we'd better agree on this  soon or we'll be chasing our tails 
> forever.  People have radically different understandings of what a 
> Track actually does. I think that's one reason that the discussions of 
> cloning and constraints/settings never seems to progress.

Jim, I agree fully. But I don't think Martin and I really differ. I think we're both saying that

* enabled and the set of constraints are track properties
* mute and the media are source properties. The app can get info about the media currently generated by probing the state of the source serving the track: 

> -Jim
> *From:*Martin Thomson [mailto:martin.thomson@gmail.com]
> *Sent:* Thursday, May 09, 2013 4:09 PM
> *To:* Jim Barnett
> *Cc:* public-media-capture@w3.org; Harald Tveit Alvestrand; Stefan 
> Håkansson LK; Robert O'Callahan
> *Subject:* RE: Cloning and sharing of MediaStreamTracks - worth it?
> "Jim Barnett" <Jim.Barnett@genesyslab.com 
> <mailto:Jim.Barnett@genesyslab.com>> wrote:
>  >
>  > But see Stefan's email; _everything_ is a source attribute except 
> for 'enabled'.  I don't think that Track is doing much work.
> That isn't the model that I described. A large part of the state of 
> the source is actually transparent. The set of constraints, enabled, 
> and, consequently, the precise form of the track output are track properties.
> As far as I can tell, the only concrete properties the source has are
> invariant: mute, the media itself. The rest are derived from the set 
> of constraints provided by the enabled tracks that the source serves. 
> Those are the properties I'm interested in cloning.
Received on Friday, 10 May 2013 12:02:06 UTC

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