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Re: A proposal for getUserMedia constraints based on the consensus reached in the DC interim

From: cowwoc <cowwoc@bbs.darktech.org>
Date: Mon, 09 Jun 2014 18:11:06 -0400
Message-ID: <539630FA.4080700@bbs.darktech.org>
To: Peter Thatcher <pthatcher@google.com>
CC: public-media-capture@w3.org
Fair enough. Thank you.

Gili

On 09/06/2014 5:34 PM, Peter Thatcher wrote:
> I also like the idea of changing the name of "advanced", but my 
> purpose here is to flesh out the consensus that was reached in DC, and 
> that was not part of the consensus, and I don't want to vary to much 
> from what we agreed on, lest we end up not agreeing on anything again.
>
>
> On Mon, Jun 9, 2014 at 2:32 PM, cowwoc <cowwoc@bbs.darktech.org 
> <mailto:cowwoc@bbs.darktech.org>> wrote:
>
>     I don't understand the meaning of:
>
>         “facingMode”: {"exact": “environment”},
>
>     In theory, this means I didn't read some documentation which
>     explains this. In practice, this means the convention is not
>     intuitive.
>
>     And I also suggest renaming "advanced" to something more
>     intuitive. The current name does not hint what the section
>     actually does.
>
>     Gili
>
>
>     On 09/06/2014 5:08 PM, Peter Thatcher wrote:
>
>         At the interim meeting in DC, we reached a consensus for a
>         form of getUserMedia constraints that has the following form:
>
>         var supports = DeviceManager.getSupportedConstraints("video");
>         if(!supports["aspectRatio"] || !supports["facingMode"]) {
>           // Treat like an error.
>         }
>         getUserMedia({“video”: {
>           “width”: {"min": 320, “ideal”: 1280, “max”: 1920},
>           “height”: {"min": 240, “ideal”: 720, “max”: 1080},
>           // Shorthand for ideal.
>           “framerate”: 30,
>           // "facingMode": "environment" would be optional.
>           “facingMode”: {"exact": “environment”},
>           "advanced": [...]
>         }}, ...);
>
>         And the following rules:
>
>         1.  "min", "max", and "exact" are required, except when in the
>         "advanced" list.
>         2.  "ideal" and a bare value or list of values are optional.
>         3.  The browser indicates what it supports via
>         DeviceManager.getSupportedConstraints, which the JS can use to
>         make sure the browser supports a certain constraint before
>         trying to use it.
>
>         Here is an example of "I want 720p, I can go up to 1080p, and
>         I can go down to VGA":
>
>         getUserMedia({“video”: {
>           “width”: {"min": 640, “ideal”: 1280, “max”: 1920},
>           “height”: {"min": 480, “ideal”: 720, “max”: 1080},
>         }}, ...);
>
>
>         Here is an example of "I want camera X, ideally with VGA":
>
>         var cameraSourceId = ...;
>         getUserMedia({“video”: {
>           "sourceId": {"exact": cameraSourceId},
>           "width": 640,
>           "height": 480
>         }}, ...);
>
>         Here is an example of "I want a front-facing camera and it
>         must be VGA":
>
>         var supports = DeviceManager.getSupportedConstraints("video");
>         if(supports["facingMode"]) {
>           getUserMedia({“video”: {
>             "facingMode": {"exact": "user"},
>             "width": {"exact": 640},
>             "height": {"exact": 480}
>           }}, ...);
>         }
>
>         Here is an advanced example of "I want 4k, then 1080, then
>         720p, and nothing else".
>
>         getUserMedia({“video”: {
>           "advanced": [
>             {"width": 4096, "height": 2160},
>             {"width": 1920, "height": 1080},
>             {"width": 1280, "height": 720}
>           ]
>         }}, ...);
>
>
>         I have looked through the existing WebIDL, and I believe this
>         is would be the best way to structure the new WebIDL.  Note
>         the assumption that there is a "DeviceManager" to be added
>         before this:
>
>         partial interface DeviceManager {
>           // Keys are constraint keys, and truthy values = supported and
>           // untruthy values = unsupported.
>           static Dictionary getSupportedConstraints(DOMString kind);
>         }
>
>         dictionary MediaTrackConstraints : MediaTrackConstraintSet {
>             sequence<MediaTrackConstraintSet> advanced;
>         };
>
>         dictionary MediaTrackConstraintSet {
>             ConstrainLong            width;
>             ConstrainLong            height;
>             ConstrainDouble          aspectRatio;
>             ConstrainDouble          frameRate;
>             ConstrainVideoFacingMode facingMode;
>             ConstrainDouble          volume;
>             ConstrainLong            sampleRate;
>             ConstrainLong            sampleSize;
>             boolean                  echoCancelation;
>             ConstrainDOMString       sourceId;
>         };
>
>         typedef (Long or ConstrainLongRange) ConstrainLong;
>         typedef (Double or ConstrainDoubleRange) ConstrainDouble;
>         typedef (DOMString or sequence<DOMString> or
>         ConstrainDOMStringParameters)
>           ConstrainDOMString;
>         typedef (VideoFacingModeEnum or sequence<VideoFacingModeEnum> or
>           ConstrainVideoFacingModeParameters) ConstrainVideoFacingMode;
>
>         dictionary ConstrainLongRange {
>             long max;
>             long min;
>             long exact;  // new
>             long ideal;  // new
>         }
>
>         dictionary ConstrainDoubleRange {
>             double min;
>             double max;
>             double exact;  // new
>             double ideal;  // new
>         };
>
>         // new
>         dictionary ConstrainDOMStringParameters {
>           (DOMString or sequence<DOMString>) exact;
>           (DOMString or sequence<DOMString>) ideal;
>         }
>
>         // new
>         dictionary ConstrainVideoFacingModeParameters {
>           (VideoFacingModeEnum or sequence<VideoFacingModeEnum>) exact;
>           (VideoFacingModeEnum or sequence<VideoFacingModeEnum>) ideal;
>         }
>
>         Note that it's possible, according to the type system, to have
>         "exact" and "ideal" in "advanced", which doesn't make sense
>         according to the algorithm.  But making that not possible
>         complicates the types a lot, which probably isn't worth it.
>          It would be much more simple to put a check in the runtime
>         rather than the type system to disallow that.
>
>
>         Now, two questions:
>
>         1.  Does everyone like these details?
>         2.  What are the next steps to add text and get in the spec?
>
>
>
>
Received on Monday, 9 June 2014 22:12:00 UTC

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