- From: Harald Alvestrand <harald@alvestrand.no>
- Date: Tue, 14 Aug 2012 22:56:19 +0200
- To: public-media-capture@w3.org
This seems like a good start on manipulating a camera, but I'm worried
about calling this a VideoStreamTrack.
I suspect there will be many VideoStreamTracks that do not originate in
cameras (of course my first favourite is the one that comes in through a
PeerConnection, but other examples are VideoStreamTracks that are fed
from a file or synthesized from a Canvas. We don't have those APIs yet,
but I'm pretty sure we will.
In the proposal from MS we're currently debating over in WEBRTC, the
concept of "decorating" a MediaStream occurs. I'm not sure how such
decorating really works (ie can you use both the original MediaStream
object and the "decorated" object after decorating it, or does the old
MediaStream object "disappear" somehow, and how do we carry this through
Webkit and friends?), but if that's a viable approach, I'd like to think
of a lot of the functionality Rich is proposing as a "camera decorator",
rather than a "video decorator".
Another aspect of the proposal is that it seems to add switching between
cameras - how does this interact with the permissions UI model, where
the user thinks he knows which camera(s) he gave a particular page the
right to access?
Note - the CLUE WG in the IETF (stuff for immersive telepresence) has
decided that they want to be able to represent a camera's position and
direction in detail in a room's coordinate system (X, Y, Z, horizontal
and vertical angle, horizontal and vertical field-of-view). We often
won't have that information, but if it is available, there should be a
single way to expose it.
On 08/14/2012 01:38 PM, Rich Tibbett wrote:
> Hi,
>
> During the last few months we've received a number of requests from
> developers to provide more granular control over camera streams
> provided via getUserMedia. Such requests have centered around
> providing auto-focus feature detection/setting/monitoring, zoom
> detection/setting/monitoring, enabling camera flash in a sensible way,
> and changing the rotation/orientation of a webcam stream. Because the
> current specification does not incorporate these features at present
> we did some brainstorming and came up with the following idea.
>
> Taking all of these use cases in to account, we would like to present
> the following proposal that allows a web application to:
>
> 1. Distinguish between audio and video media streams obtained via
> getUserMedia (by introducing VideoStreamTrack and AudioStreamTrack
> interfaces that inherit from the currently specified - generic -
> MediaStreamTrack interface).
>
> 2. Apply special behavior to VideoStreamTrack objects that allow a web
> developer to feature detect on the capabilities of a web camera, set
> their desired modes for a number of features related to a given Camera
> object, trigger certain features on-demand and listen for Camera
> feature start and end events where that makes sense.
>
> When we have the ability to distinguish video stream tracks from audio
> stream tracks (in point 1 above) it became clear that there were many
> other use cases that we could then naturally fit in to the same API
> architecture.
>
> The proposal herein therefore incorporates an initial set of controls
> for developers to tune certain web camera feature. We expect this will
> be of interest for a large number of other use cases, such as Camera
> capabilities detection and control in the form of a best-effort
> approach that is inclusive and 'webby' by design.
>
> Our primary concern at this time is to get a sense for whether there's
> agreement around supplying these options to developers or not and then
> to subsequently discuss whether the interface proposal provided is fit
> for purpose. If anyone else has alternative proposals then we'd be
> interested to discuss them further here of course.
>
>
> *** PROPOSAL START ***
>
> // +++ VIDEOSTREAMTRACK
>
> interface VideoStreamTrack {
>
> readonly attribute boolean locked; // true if object is not a
> // camera object or manipulation
> // is not otherwise supported
> // false if object can be
> // modified
>
> // CAMERA SELECTION
>
> readonly attribute boolean cameraChangeSupported; // true if camera
> // can be changed.
> // Otherwise, false.
>
> readonly attribute unsigned short numberOfCameras;
>
> readonly attribute unsigned short currentCamera;
>
> CameraInfo getCameraInfo(in unsigned short value);
>
> void setCamera(in unsigned short value);
>
> // AUTO-FOCUS
>
> readonly attribute boolean focusSupported; // true if camera focus
> // can be changed.
> // Otherwise, false.
>
> readonly attribute DOMString currentFocusMode;
>
> void setFocusMode(in DOMString value);
>
> // value argument above may be one of 'auto' (default),
> // 'continuous', 'edof' (Extended Depth of Field), 'fixed',
> // 'infinity' or 'macro' (close-up focus mode).
>
> void autoFocus(in optional Object xy);
> void cancelAutoFocus();
>
> // ZOOM
>
> readonly attribute boolean zoomSupported; // true if camera zoom can
> // be changed. Otherwise,
> // false.
>
> readonly attribute unsigned short currentZoom;
> readonly attribute unsigned short maxZoom;
>
> void startZoom(in unsigned short value);
> void stopZoom();
>
> // FLASH
>
> readonly attribute boolean flashSupported; // true if camera flash
> // mode can be changed.
> // Otherwise, false.
>
> readonly attribute DOMString currentFlashMode;
>
> void setFlashMode(in DOMString value);
>
> // value argument above may be one of 'auto' (default), 'off', 'on',
> // 'red-eye' or 'torch'.
>
> // ORIENTATION
>
> readonly attribute boolean orientationSupported; // true if camera
> // orientation be
> // changed.
> // Otherwise, false
>
> readonly attribute unsigned short currentDisplayOrientation;
> // 0<->360 degrees
>
> void setDisplayOrientation(in unsigned short degrees);
>
> // GENERAL FEATURES
>
> void takePicture();
>
> // takePicture first applies currentFocusMode and currentFlashMode
> // before taking a JPEG image snapshot from currentCamera and firing
> // a new 'picture' event, setting its data attribute as the value of
> // the JPEG image's ImageData.
>
> // VIEWING ANGLE
>
> readonly attribute float horizontalViewAngle;
> readonly attribute float verticalViewAngle;
>
> // EVENT LISTENERS
>
> attribute EventListener onfocusstart;
> attribute EventListener onfocusend;
>
> attribute EventListener onzoomstart;
> attribute EventListener onzoomend;
>
> attribute EventListener oncamerachange;
>
> attribute EventListener onpicture;
>
> }
>
> VideoStreamTrack implements MediaStreamTrack;
>
> VideoStreamTrack implements EventTarget;
>
> // VideoStreamTrack events: 'focusstart', 'focusend', 'zoomstart',
> // 'zoomend', 'camerachange' and 'picture'.
>
> ++ CAMERAINFO
>
> [NoInterfaceObject]
> interface CameraInfo {
>
> attribute unsigned short facing;
>
> // facing above will be either 'user' or 'environment'
>
> attribute unsigned short orientation;
>
> // orientation will be in the range 0 to 360 degrees
>
> }
>
> *** PROPOSAL END ***
>
>
> --
> Rich Tibbett (richt)
> CORE Platform Architect - Opera Software ASA
>
Received on Tuesday, 14 August 2012 20:56:49 UTC