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Re: First draft of "MediaStream Capture Scenarios" now available

From: Harald Alvestrand <harald@alvestrand.no>
Date: Tue, 06 Dec 2011 22:50:02 +0100
Message-ID: <4EDE8E0A.2010603@alvestrand.no>
To: Travis Leithead <travis.leithead@microsoft.com>
CC: "public-media-capture@w3.org" <public-media-capture@w3.org>
On 12/06/2011 08:11 PM, Travis Leithead wrote:
> (-)public-device-api
>> -----Original Message-----
>> From: Harald Alvestrand [mailto:harald@alvestrand.no]
>> Sent: Monday, December 05, 2011 10:44 PM
>> On 12/06/2011 02:45 AM, Travis Leithead wrote:
>>> This draft is a combination of scenarios mingled with some commentary,
>> issues, and points of discussion.
>> Actually, I'm a bit disappointed with the scenarios part of this; there
>> are a lot of cases (rewind, take snapshot and so on) that I'd recognize
>> as scenarios / use cases, but they are not called out to a degree where
>> I can recognize them as specific scenarios; they are rather buried
>> within the commentary.
> Don't be too disappointed--it's a first draft :-)
I'm sure we'll have many more :-)
>> Would it be possible to pull out the specific scenarios that you would
>> like us to support, independent from the possible / current / proposed
>> implementation descriptions?
> Sure thing. I'll see about lifting them out into an independent top-level section
> (which I think would make them more clear). I can rename the current
> "scenarios" section as something else (possibly "Commentary")?
You can try with "Requirements and commentary" - once we have the 
scenarios, it's important to discuss exactly what kinds of functionality 
the scenarios imply.
>> Some detailed commentary:
>> - header: This should be listed as a WEBRTC/DAP task force item, not a
>> DAP item.
> I'm happy to change this, but don't know how. SOTD section is auto-generated
> from ReSpec. Any ReSpec experts out there that can provide pointers?
>> - intro: the use of the word "recording" should be avoided for the
>> WebRTC scenarios, since the whole subject of recording sessions is still
>> open in WEBRTC. "Capture" is the most common word, I think.
> OK
>> - 3.1 stream initialization: The result of initialization will have to
>> be available as a MediaStream. As long as the WebRTC API is totally
>> dependent on the MediaStream concept, this is not a question. If you
>> want to suggest other forms of the available capture, those may be
>> alternatives, or be something that can be converted into a MediaStream,
>> but current text is too weak on this point.
> I'm actually happy to hear that. Since the MediaStream interface wasn't
> included in the first draft of the getusermedia spec, it left me wondering
> if there was some other planned integration point. I'd prefer to build on the
> MediaStream interface.
>> - 3.2 reinitialization: We (WebRTC editors) have discussed moving the
>> "ended" event from the MediaStream to the MediaStreamTrack; it seems to
>> be easier to define it crisply there.
> That sounds like a good start. The subject of the MediaStreamTrack is
> actually where I believe some of the capture integration points should be
> made, but it will require some additional discreet factoring (i.e.,
> MediaStreamTrack ->  Audio/VideoTrack [3]).
we'll see about that. Last time I looked at that spec, it had arrays 
instead of track lists; we're worried that these are not exactly the 
tracks we're looking for.

Last I looked at that discussion, they were talking about adding a 
TextTrackList too; I think it makes sense for our purposes to model some 
common behaviours of tracks as a superclass.
>> - 3.6.3 It's unclear for me what you are pointing to when you refer to
>> the WebRTC "take a picture" scenario. I can't find it in our scenarios
>> document.
> I'll try to clear that up. I was drawing directly from the WebRTC spec,
> section 3.3 Examples (third example) [4].
Ah - we call those sections examples, not scenarios. That's what 
confused me.
>> - 3.10.1 In a streaming case, you may support rewind through recording
>> to a tail-drop buffer. So it's not impossible, just complex.
> I'll polish that up a bit. Thanks.
> [3] http://dev.w3.org/html5/spec/Overview.html#audiotracklist
> [4] http://dev.w3.org/2011/webrtc/editor/webrtc.html#examples
Received on Tuesday, 6 December 2011 21:50:33 UTC

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