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Re: CONCLUSION on "onaddstream" and beyond

From: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
Date: Thu, 1 Dec 2011 13:51:06 +0100
Message-ID: <4ED7783A.3090805@ericsson.com>
To: Adam Bergkvist <adam.bergkvist@ericsson.com>
CC: "public-webrtc@w3.org" <public-webrtc@w3.org>
On 11/30/2011 05:27 PM, Adam Bergkvist wrote:
> On 11/30/2011 10:51 AM, Stefan Håkansson LK wrote:
>> The conclusion of this discussion seems to be:
>>
>> 1. MediaStream objects should be created more or less immediately as
>> result of "getUserMedia" or "addStream" operations (in the later case a
>> MediaStream object on the remote side should be created as a result of
>> the signaling).
>>
>> 2. There is a need to, on a MediaStreamTrack level, notify the
>> application when live data is available (which can be a bit later than
>> the creation of the MediaStream object).
>>
>> The task is now on the Editors to change the drafts along these lines.
>
> A way of realizing the above is to expose the muted property on
> MediaStreamTrack. The concept of muting a track already exist in the
> spec in the PeerConnection-case where the A-side disables a track; it
> will then be muted (not disabled) on the B-side. It's however not
> possible to detect the muted state with the current spec. A muted track
> will produce blackness or silence when consumed.
>
> * getUserMedia
> When the NavigatorUserMediaSuccessCallback fires, information from the
> users' selections will be used to create the tracks in the resulting
> MediaStream's track list. No tracks are muted.
>
> * addstream
> When the addstream event listener fires, information from the signaling
> will be used to construct the track list. The tracks are all muted. Each
> tracks will be unmuted once data arrives on the underlying RTP stream.
> We can simply remove the readyState from MediaStream to avoid the
> problem with a LIVE stream that only has muted tracks and let the tracks
> deal with their own states.
IMO, the above gives the functionality we're after. Looks like a good 
start to me!

>
> The exposed MediaStreamTrack.muted property (along with its
> corresponding event listeners) can also be used to, e.g., show an image
> if the other side (of a PeerConnection) disables a track that is being
> transmitted to you. Another use case is to turn of image processing if
> an augmented reality case.
>
> * Changes to MediaStreamTrack/MediaStreamTrack interfaces
"MediaStream/MediaStreamTrack" I guess!
>
>    [Constructor (in MediaStreamTrackList trackList)]
>    interface MediaStream {
>        readonly attribute DOMString            label;
>        readonly attribute MediaStreamTrackList tracks;
>        MediaStreamRecorder record ();
> -    const unsigned short LIVE = 1;
> -    const unsigned short ENDED = 2;
> -    readonly attribute unsigned short       readyState;
> +    readonly attribute boolean 	     ended;
>                 attribute Function?            onended;
>    };
Should we align closer to the Media element by having separate 
attributes for audioTracks and videoTracks? This would make it simpler 
to detect if there is any audio/video ("ms.videoTracks.length").

>
>    interface MediaStreamTrack {
>        readonly attribute DOMString kind;
>        readonly attribute DOMString label;
>                 attribute boolean   enabled;
>
> +    readonly attribute boolean   muted;
> +
> +             attribute Function? onmute;
> +             attribute Function? onunmute;
> };
Should we separate AudioMediaStreamTrack and VideoMediaStreamTrack 
definitions as discussed in conjunction with DTMF?

And should we add

>
> * Examples
>
> navigator.webkitGetUserMedia({}, function (stream) {
>       selfView.src = webkitURL.createObjectURL(stream);
>
>       // all tracks are unmuted when the success callback is fired
>       for (var i = 0; i<  stream.tracks[i]; i++)
>           console.log(stream.tracks[i].muted); // "false"
> });
>
> // addstream event handler example 1.
> peerConn.onaddstream = function (evt) {
>       // all tracks are muted when the addstream event listener is fired
>       // (gets unmuted when data arrives)
>       for (var i = 0; i<  stream.tracks[i]; i++)
>           console.log(stream.tracks[i].muted); // "true"
>
>       // delay playback until all tracks have been unmuted (data has
>       // arrived on all tracks)
>       var tracks = evt.stream.tracks;
>       var numberOfMutedTracks = tracks.length;
>
>       for (var i = 0; i<  tracks.length; i++) {
>           tracks[i].onunmute = function (evt) {
>               evt.target.onunmute = null;
>               if (--numberOfMutedTracks == 0)
>                   selfView.src = webkitURL.createObjectURL(stream);
>           };
>       }
> };
>
> // addstream event handler example 2.
> peerConn.onaddstream = function (evt) {
>       // the MediaStreamTrack.muted property can also be used to display
>       // a pause screen in a video element if the sender has disabled the
>       // video track (appears as muted on your side)
>
>       // will show blackness until data arrives (muted tracks)..
>       remoteView.src = webkitURL.createObjectURL(evt.stream);
>       // ..showing pause screen in the meantime
>       showPauseScreen(remoteView);
>
>       var tracks = evt.stream.tracks;
>       var videoTrack;
>       for (var i = 0; i<  tracks.length; i++) {
>           if (tracks[i].type == "video") {
>               videoTrack = tracks[i];
>               break;
>           }
>       }
>
>       if (videoTrack) {
>           videoTrack.onmute = function () {
>               showPauseScreen(remoteView);
>           };
>
>           videoTrack.onunmute = function () {
>               showVideo(remoteView);
>           };
>       }
> };
>
> /Adam
Received on Thursday, 1 December 2011 12:51:43 UTC

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