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RE: Early Holiday Present: Settings API version 6

From: Travis Leithead <travis.leithead@microsoft.com>
Date: Mon, 17 Dec 2012 19:36:20 +0000
To: Jim Barnett <Jim.Barnett@genesyslab.com>, Adam Bergkvist <adam.bergkvist@ericsson.com>
CC: "public-media-capture@w3.org" <public-media-capture@w3.org>
Message-ID: <9768D477C67135458BF978A45BCF9B3853AEDBFC@TK5EX14MBXW604.wingroup.windeploy.ntdev.microsoft.com>
I'll see if I can get this answered from the relevant experts in the media space at Microsoft...

> -----Original Message-----
> From: Jim Barnett [mailto:Jim.Barnett@genesyslab.com]
> Sent: Monday, December 17, 2012 11:34 AM
> To: Travis Leithead; Adam Bergkvist
> Cc: public-media-capture@w3.org
> Subject: RE: Early Holiday Present: Settings API version 6
> 
> Travis,
>   The sequence you describe below (with the muted/unmated events) makes
> sense.   My question is whether it is something that's _likely_ to happen,
> or something that the spec should require.  For example:
> 
> 1. Could there be a camera that could continue streaming while taking a
> photo?
> 2.  If there is such a camera, would we want to require that it stop
> streaming while taking a photo?
> 
> In other words, do we want to say that the UA _must_ raise muted/unmated
> events, or only that it is likely to do so given the way the camera will
> behave?
> 
> - Jim
> 
> -----Original Message-----
> From: Travis Leithead [mailto:travis.leithead@microsoft.com]
> Sent: Monday, December 17, 2012 1:08 PM
> To: Jim Barnett; Adam Bergkvist
> Cc: public-media-capture@w3.org
> Subject: RE: Early Holiday Present: Settings API version 6
> 
> > From: Jim Barnett [mailto:Jim.Barnett@genesyslab.com]
> >
> > That's a good question.  If taking a picture involves 'switching the
> > source into "high resolution photo mode"', what happens in other
> > streams that are using the same track?  Do they all suddenly go nuts?
> > This does seem like an operation that must take place on the
> > underlying device, so it can't be isolated to one copy of the Track.
> 
> Indeed. This is a source-modification action, so all tracks using this
> source will be affected. Think about this like how the mirror rotates on
> an SLR camera--for a brief moment your view must be interrupted in order
> for the picture to be taken. We can choose to make this as unobservable as
> possible, or to make it follow to rules that tracks/sources have
> established. If we assume the latter behavior, then I would expect the
> following for all tracks affected by the source transition for recording a
> snapshot:
> 1. The source temporarily stops -- "muted" events fire on respective
> tracks because the stream has stopped.
> 2. The source is reconfigured to match the photo settings (no events fire
> for this step) 3. The source records/encodes the photo (async -- the
> "photo" event can fire any time this step asynchronously completes) 4. The
> source is reconfigured back to the original stored settings (no events
> fire for this step) 5. The source resumes streaming -- "unmuted" events
> fire.
> 
> 
> Additional responses to Adam's mail below:
> 
> 
> > This problem will occur with any operation that changes the settings
> > of the underlying device.  I know we've discussed this, but I forget
> > what the resolution was.
> >
> > - Jim
> > P.S. The photo-taking functionality is being moved to the recording
> > spec, but the problem is the same.  It's just that now it's my problem
> > rather than yours....
> >
> >
> > From: Adam Bergkvist [mailto:adam.bergkvist@ericsson.com]
> >
> > On 2012-12-12 20:01, Travis Leithead wrote:
> > > http://dvcs.w3.org/hg/dap/raw-file/tip/media-stream-capture/proposal
> > > s/
> > > SettingsAPI_proposal_v6.html
> > >
> >
> > I think this look pretty good and I wouldn't object to putting it into
> > the spec.
> >
> > Here's some feedback (I haven't had time to read previous feedback so
> > I apologize if I've repeated something already noted.)
> >
> >  > Sources that must have an identifier are camera and microphone
> > sources; local file sources are not required to have an identifier.
> > Source identifiers let the application save, identify the availability
> > of, and directly request specific sources.
> >
> > In previous discussions we've talked about that applications shouldn't
> > be able to detect if a user has selected a file instead of a "real"
> > device. Can we maintain that feature with this proposal?
> 
> With source types you already can't know for sure what type the source is.
> When it's "readonly" that could mean a file or it could me a readonly
> camera. With unique source id's this anonymity is potentially broken as
> you note above. How would you propose addressing it? One idea is to give
> all sources an id, and just ensure that any sources that have id
> "readonly" get the same id no matter what their back-end [actual] source
> is. A similar approach could be used with "remote" source types.
> 
> On the other hand having these source ids be null offers the same level of
> anonymity but without any extra work on the user agent.
> 
> The other option seems to be to create random identifiers for each
> readonly/remote source type. That way they aren't distinguishable from
> actual devices (except that the _real_ devices export their ids from
> getSourceIds()).
> 
> I don't know how to satisfy Martin's suggestion of unique device ids
> without making real devices distinguishable from readonly/remote ones.
> 
> 
> >  > interface MediaStreamTrack : EventTarget {
> >               attribute DOMString           id;
> >
> > id should be readonly.
> 
> No problem--whatever's in the Media Capture and Stream spec trumps this.
> 
> 
> >  > Enumeration description
> > new	The track type is new and has not been initialized (connected to a
> > source of any kind). This state implies that the track's label will be
> > the empty string.
> >
> > s/label/sourceId/ ?
> 
> Actually, I intended to say "label". Is label being dropped? Is "kind"?
> But yes, "sourceId" would also be null in this state.
> 
> We do need to say what "label", "id", "enabled" are in the "new"
> readyState, and whether they change when a source is added/removed.
> 
> 
> >  > sourceId of type DOMString, readonly
> >      The application-unique identifier for this source. The same
> > identifier must be valid between sessions of this application, but
> > must also be different for other applications. Some sort of GUID is
> > recommended for the identifier.
> >
> > s/this source/the source that is providing this track with data/
> >
> > It also needs to have a value (null or ""?) when sourceType is "none".
> 
> Yes on both points (null rather than "" for consistency with everything
> else).
> 
> 
> 
> >  > interface VideoStreamTrack : MediaStreamTrack {
> >      static sequence<DOMString> getSourceIds ();
> >
> > I know we've talked about having this functionality on a global object
> > (e.g. navigator.userMedia-something). I'd like to see such a proposal.
> > It could also be the place where we attach a listener for new devices
> > (the probe example 7.8 feels a bit hackish).
> 
> If the group feels strongly that:
> navigator.getUserMediaVideoSourceIds() is better than
> VideoStreamTrack.getSourceIds() and
> navigator.getUserMediaAudioSrouceIds() is better than
> AudioStreamTrack.getSourceIds() then I'm OK with that. They seem about the
> same to me from a global object availability perspective.
> 
> Also if the use-case for discovering new devices merits it, then two(?)
> new APIs for requesting when new respective video/audio devices come on
> line can be easily added (would you want two more(?) APIs for
> unregistering too?).
> 
> 
> >  >  If the sourceType is "photo-camera", then this method temporarily
> > (asynchronously) switches the source into "high resolution photo mode"
> >
> > What should happen if another track is using this source for video
> > conferencing at the same time?
> >
> >
> >  > enum VideoFacingModeEnum {
> >      "notavailable",
> >
> > Could we use "not-available" instead? (for all occurrences)
> 
> No problem here.
> 
> 
> >  > interface MediaStreamTrackStateEvent : Event {
> >      readonly attribute DOMString[] states;
> >
> > Do we need to handle this in such a special way? Couldn't we use a
> > simple event and fire for every state change. That how it normally
> works.
> 
> Yes, we could do that, but the amount of work for this event would then
> increase linearly with each bit of state that is added. For readyState
> "none" to anything else, every state will change, and similarly for the
> "ended" transition. Since these transitions are guaranteed, and other
> transitions are most often application-initiated (by batches of constraint
> application), it seemed better to optimize on many states changing at once
> with minimum event noise. If you do want a minimalist approach then you
> must decide whether you want the notification to include the state that
> changed. If not, then a simple "statechanged" event would suffice (with no
> new Event object definition required). Otherwise, you'll still need the
> new event object just for "what-changed" state name, and if you want that,
> then you may as well allow the user agent to batch changes and support the
> event as defined in V6.
> 
> 
> >  > 7.2 Getting access to a specific video source (if available)
> > VideoStreamTrack.getSourceIds().forEach(...
> >
> > This example could be simplified a bit with indexOf() to see if the
> > old id exists.
> 
> Yeah, Martin suggested "some" (instead of "forEach") which simplifies this
> nicely.
> 
> 
Received on Monday, 17 December 2012 19:36:58 UTC

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