Hi Media folks,
I already read through Media Capture and Streams API [1], but I'd like to
clarify myself about how to leverage the current getUserMedia() to retrieve
the video/audio tracks from the specific input like HDMI or AV for example,
which is needed in our coming TV product.
Could anyone please give us some directions about the following questions
when you're available? Thank you!
1. getUserMedia() will return a MediaStream based on the user's selection
on the pop-up prompt, but why the MediaStream can contain multiple
MediaStreamTracks where each of them could represent different media
sources [2]?
For example, when the user selects the "Webcam", it makes sense that
the returned MediaStream will contain one MediaStreamTrack for the
video stream and one MediaStreamTrack for the audio stream in terms of
a webcam, but how can it happen to contain either multiple videos or
multiple audios for one webcam? I mean why can getVideoTracks() or
getAudioTracks() returns an array?
2. It seems the pop-up prompt and the user's selection are always needed
to specify the media source. Can we directly specify it when calling
getUserMedia()? Say, the user only wants to retrieve the MediaStream
through the specific HDMI device.
3. Follow #2, the Constraints may help us do so but it is aimed to apply
the constraints (source settings) on the media source, instead of
selecting the media source. Does setting sourceId in the constrain
exactly work for this purpose [3][5]?
4. Follow #3, does the deviceId in MediaDeviceInfo [4] match the sourceId
at [5]? That would be helpful if we can set the deviceId in the
constraint to getUserMedia() as mentioned above.
5. It looks a bit weird to me that we can set constraints for calling
getUserMedia() and select the media source through the prompt at the
same time. What if the setting doesn't work for the media source the
user selects? Say, set the video width/height in the constraints but
the user chooses microphone by the prompt.
6. The getMediaDevices() can help us retrieve all the devices which are
currently available on the device [6]. One question here: does the menu
of the prompt rely on this function in practice?
7. Follow #6, how can the getMediaDevices() reflect some dynamic changes
whenever a device is hooked up or off at run-time? GamepadEvent [7]
might be a similar way to handle this, which is fired on the window,
but it means we have to add one event for each media source under the
window. Can we unify this kind of event under NavigatorUserMedia [6],
which can then be differentiated by the SourceTypeEnum [8]? IMO, I'd
suggest adding the following event handlers:
interface NavigatorUserMedia {
void getMediaDevices (MediaDeviceInfoCallback resultCallback);
attribute EventHandler onsourceconnected; // SourceEvent
attribute EventHandler onsourcedisconnected; // SourceEvent
};
interface SourceEvent : Event {
readonly attribute SourceTypeEnum type;
...
};
8. Can we extend the SourceTypeEnum [8] by adding "hdmi", "av" and so on?
Or the enum list has to be some formal spec defined at somewhere?
[1] http://dev.w3.org/2011/webrtc/editor/getusermedia.html
[2] http://dev.w3.org/2011/webrtc/editor/getusermedia.html#idl-def-MediaStream
[3]
http://dev.w3.org/2011/webrtc/editor/getusermedia.html#idl-def-MediaStreamConstraints
[4]
http://dev.w3.org/2011/webrtc/editor/getusermedia.html#idl-def-MediaDeviceInfo
[5]
http://dev.w3.org/2011/webrtc/editor/getusermedia.html#track-property-registrations
[6] http://dev.w3.org/2011/webrtc/editor/getusermedia.html#navigatorusermedia
[7]
https://dvcs.w3.org/hg/gamepad/raw-file/default/gamepad.html#gamepadevent-interface
[8]
http://dev.w3.org/2011/webrtc/editor/getusermedia.html#idl-def-SourceTypeEnum
Sorry for asking so many questions at one shot. I believe these are all
we have before moving forward. Looking forward to you experts' feedback. :)
Cheers,
Gene
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