Fixes flickering issue with simulcast.

config.js

     enableRecording: false,
     enableWelcomePage: false,
     enableSimulcast: false,
-    useNativeSimulcast: false,
     isBrand: false
 };

simulcast.js

     "use strict";
 
     // TODO(gp) split the Simulcast class in two classes : NativeSimulcast and ClassicSimulcast.
-    this.debugLvl = 1;
+
+    // Once we properly support native simulcast, enable it automatically in the
+    // supported browsers (Chrome).
+    this.useNativeSimulcast = false;
+
+    // TODO(gp) we need a logging framework for javascript à la log4j or the
+    // java logging framework that allows for selective log display
+    this.debugLvl = 0;
 }
 
 (function () {
      * @returns {*}
      */
     Simulcast.prototype.transformAnswer = function (desc) {
-        if (config.enableSimulcast && config.useNativeSimulcast) {
+        if (config.enableSimulcast && this.useNativeSimulcast) {
 
             var sb = desc.sdp.split('\r\n');
 
 
         if (config.enableSimulcast) {
 
-            if (config.useNativeSimulcast) {
+            if (this.useNativeSimulcast) {
                 sb = desc.sdp.split('\r\n');
 
                 this._explodeLocalSimulcastSources(sb);
      * @returns {*}
      */
     Simulcast.prototype.transformLocalDescription = function (desc) {
-        if (config.enableSimulcast && !config.useNativeSimulcast) {
+        if (config.enableSimulcast && !this.useNativeSimulcast) {
 
             var sb = desc.sdp.split('\r\n');
 
             this._cacheRemoteVideoSources(sb);
             this._removeSimulcastGroup(sb); // NOTE(gp) this needs to be called after updateRemoteMaps because we need the simulcast group in the _updateRemoteMaps() method.
 
-            if (config.useNativeSimulcast) {
+            if (this.useNativeSimulcast) {
                 // We don't need the goog conference flag if we're not doing
                 // native simulcast.
                 this._ensureGoogConference(sb);
             : stream;
     };
 
-    var stream;
+    var localStream, displayedLocalVideoStream;
 
     /**
      * GUM for simulcast.
         console.log('HQ constraints: ', constraints);
         console.log('LQ constraints: ', lqConstraints);
 
-        if (config.enableSimulcast && !config.useNativeSimulcast) {
+        if (config.enableSimulcast && !this.useNativeSimulcast) {
 
             // NOTE(gp) if we request the lq stream first webkitGetUserMedia
             // fails randomly. Tested with Chrome 37. As fippo suggested, the
 
             navigator.webkitGetUserMedia(constraints, function (hqStream) {
 
+                localStream = hqStream;
+
                 // reset local maps.
                 localMaps.msids = [];
                 localMaps.msid2ssrc = {};
 
                 navigator.webkitGetUserMedia(lqConstraints, function (lqStream) {
 
+                    displayedLocalVideoStream = lqStream;
+
                     // NOTE(gp) The specification says Array.forEach() will visit
                     // the array elements in numeric order, and that it doesn't
                     // visit elements that don't exist.
                     // add lq trackid to local map
                     localMaps.msids.splice(0, 0, lqStream.getVideoTracks()[0].id);
 
-                    hqStream.addTrack(lqStream.getVideoTracks()[0]);
-                    stream = hqStream;
-                    success(hqStream);
+                    localStream.addTrack(lqStream.getVideoTracks()[0]);
+                    success(localStream);
                 }, err);
             }, err);
         } else {
 
                 // add hq stream to local map
                 localMaps.msids.push(hqStream.getVideoTracks()[0].id);
-                stream = hqStream;
-                success(hqStream);
+                displayedLocalVideoStream = localStream = hqStream;
+                success(localStream);
             }, err);
         }
     };
                 trackid = tid;
                 return true;
             }
-        }) && stream.getVideoTracks().some(function(track) {
+        }) && localStream.getVideoTracks().some(function(track) {
             // Start/stop the track that corresponds to the track id
             if (track.id === trackid) {
                 track.enabled = enabled;
     };
 
     Simulcast.prototype.getLocalVideoStream = function() {
-        var track;
-
-        stream.getVideoTracks().some(function(t) {
-            if ((track = t).enabled) {
-                return true;
-            }
-        });
-
-        return new webkitMediaStream([track]);
+        return displayedLocalVideoStream;
     };
 
     $(document).bind('simulcastlayerschanged', function (event, endpointSimulcastLayers) {

videolayout.js

     var currentDominantSpeaker = null;
     var lastNCount = config.channelLastN;
     var lastNEndpointsCache = [];
-    var largeVideoNewSrc = '';
+    var largeVideoState = {
+        updateInProgress: false,
+        newSrc: ''
+    };
 
     my.changeLocalAudio = function(stream) {
         connection.jingle.localAudio = stream;
             localVideoSelector.addClass("flipVideoX");
         }
         // Attach WebRTC stream
-        RTC.attachMediaStream(localVideoSelector, stream);
+        var simulcast = new Simulcast();
+        var videoStream = simulcast.getLocalVideoStream();
+        RTC.attachMediaStream(localVideoSelector, videoStream);
 
         localVideoSrc = localVideo.src;
 
         console.log('hover in', newSrc);
 
         if ($('#largeVideo').attr('src') != newSrc) {
-            largeVideoNewSrc = newSrc;
-
-            var isVisible = $('#largeVideo').is(':visible');
 
-            // we need this here because after the fade the videoSrc may have
-            // changed.
-            var isDesktop = isVideoSrcDesktop(newSrc);
+            // Due to the simulcast the localVideoSrc may have changed when the
+            // fadeOut event triggers. In that case the getJidFromVideoSrc and
+            // isVideoSrcDesktop methods will not function correctly.
+            //
+            // Also, again due to the simulcast, the updateLargeVideo method can
+            // be called multiple times almost simultaneously. Therefore, we
+            // store the state here and update only once.
+
+            largeVideoState.newSrc = newSrc;
+            largeVideoState.isVisible = $('#largeVideo').is(':visible');
+            largeVideoState.isDesktop = isVideoSrcDesktop(newSrc);
+            largeVideoState.userJid = getJidFromVideoSrc(newSrc);
+
+            // Screen stream is already rotated
+            largeVideoState.flipX = (newSrc === localVideoSrc) && flipXLocalVideo;
+
+            var oldSrc = $('#largeVideo').attr('src');
+            largeVideoState.oldJid = getJidFromVideoSrc(oldSrc);
+
+            var fade = false;
+            if (largeVideoState.oldJid != largeVideoState.userJid) {
+                fade = true;
+                // we want the notification to trigger even if userJid is undefined,
+                // or null.
+                $(document).trigger("selectedendpointchanged", [largeVideoState.userJid]);
+            }
 
-            var userJid = getJidFromVideoSrc(newSrc);
-            // we want the notification to trigger even if userJid is undefined,
-            // or null.
-            $(document).trigger("selectedendpointchanged", [userJid]);
+            if (!largeVideoState.updateInProgress) {
+                largeVideoState.updateInProgress = true;
 
-            $('#largeVideo').fadeOut(300, function () {
-                var oldSrc = $(this).attr('src');
+                var doUpdate = function () {
 
-                $(this).attr('src', newSrc);
+                    $('#largeVideo').attr('src', largeVideoState.newSrc);
 
-                // Screen stream is already rotated
-                var flipX = (newSrc === localVideoSrc) && flipXLocalVideo;
+                    var videoTransform = document.getElementById('largeVideo')
+                        .style.webkitTransform;
 
-                var videoTransform = document.getElementById('largeVideo')
-                                        .style.webkitTransform;
+                    if (largeVideoState.flipX && videoTransform !== 'scaleX(-1)') {
+                        document.getElementById('largeVideo').style.webkitTransform
+                            = "scaleX(-1)";
+                    }
+                    else if (!largeVideoState.flipX && videoTransform === 'scaleX(-1)') {
+                        document.getElementById('largeVideo').style.webkitTransform
+                            = "none";
+                    }
 
-                if (flipX && videoTransform !== 'scaleX(-1)') {
-                    document.getElementById('largeVideo').style.webkitTransform
-                        = "scaleX(-1)";
-                }
-                else if (!flipX && videoTransform === 'scaleX(-1)') {
-                    document.getElementById('largeVideo').style.webkitTransform
-                        = "none";
-                }
+                    // Change the way we'll be measuring and positioning large video
+
+                    getVideoSize = largeVideoState.isDesktop
+                        ? getDesktopVideoSize
+                        : getCameraVideoSize;
+                    getVideoPosition = largeVideoState.isDesktop
+                        ? getDesktopVideoPosition
+                        : getCameraVideoPosition;
+
+                    if (largeVideoState.isVisible) {
+                        // Only if the large video is currently visible.
+                        // Disable previous dominant speaker video.
+                        if (largeVideoState.oldJid) {
+                            var oldResourceJid = Strophe.getResourceFromJid(largeVideoState.oldJid);
+                            VideoLayout.enableDominantSpeaker(oldResourceJid, false);
+                        }
 
-                // Change the way we'll be measuring and positioning large video
-
-                getVideoSize = isDesktop
-                                ? getDesktopVideoSize
-                                : getCameraVideoSize;
-                getVideoPosition = isDesktop
-                                    ? getDesktopVideoPosition
-                                    : getCameraVideoPosition;
-
-                if (isVisible) {
-                    // Only if the large video is currently visible.
-                    // Disable previous dominant speaker video.
-                    var oldJid = getJidFromVideoSrc(oldSrc);
-                    if (oldJid) {
-                        var oldResourceJid = Strophe.getResourceFromJid(oldJid);
-                        VideoLayout.enableDominantSpeaker(oldResourceJid, false);
-                    }
+                        // Enable new dominant speaker in the remote videos section.
+                        if (largeVideoState.userJid) {
+                            var resourceJid = Strophe.getResourceFromJid(largeVideoState.userJid);
+                            VideoLayout.enableDominantSpeaker(resourceJid, true);
+                        }
 
-                    // Enable new dominant speaker in the remote videos section.
-                    var userJid = getJidFromVideoSrc(newSrc);
-                    if (userJid)
-                    {
-                        var resourceJid = Strophe.getResourceFromJid(userJid);
-                        VideoLayout.enableDominantSpeaker(resourceJid, true);
+                        largeVideoState.updateInProgress = false;
+                        if (fade) {
+                            // using "this" should be ok because we're called
+                            // from within the fadeOut event.
+                            $(this).fadeIn(300);
+                        }
                     }
+                };
 
-                    $(this).fadeIn(300);
+                if (fade) {
+                    $('#largeVideo').fadeOut(300, doUpdate);
+                } else {
+                    doUpdate();
                 }
-            });
+            }
         }
     };
 
      * disabled
      */
     my.enableDominantSpeaker = function(resourceJid, isEnable) {
-        var displayName = resourceJid;
-        var nameSpan = $('#participant_' + resourceJid + '>span.displayname');
-        if (nameSpan.length > 0)
-            displayName = nameSpan.text();
-
-        console.log("UI enable dominant speaker",
-                    displayName,
-                    resourceJid,
-                    isEnable);
 
         var videoSpanId = null;
         var videoContainerId = null;
             videoContainerId = videoSpanId;
         }
 
+        var displayName = resourceJid;
+        var nameSpan = $('#' + videoContainerId + '>span.displayname');
+        if (nameSpan.length > 0)
+            displayName = nameSpan.text();
+
+        console.log("UI enable dominant speaker",
+            displayName,
+            resourceJid,
+            isEnable);
+
         videoSpan = document.getElementById(videoContainerId);
 
         if (!videoSpan) {
         }
     });
 
-    $(document).bind('simulcastlayerstarted simulcastlayerstopped', function(event) {
-        var localVideoSelector = $('#' + 'localVideo_' + connection.jingle.localVideo.id);
-        var simulcast = new Simulcast();
-        var stream = simulcast.getLocalVideoStream();
-
-        var updateLargeVideo = (connection.emuc.myroomjid
-            == getJidFromVideoSrc(largeVideoNewSrc));
-        var updateFocusedVideoSrc = (localVideoSrc == focusedVideoSrc);
-
-        // Attach WebRTC stream
-        RTC.attachMediaStream(localVideoSelector, stream);
-
-        localVideoSrc = $(localVideoSelector).attr('src');
-
-        if (updateLargeVideo) {
-            VideoLayout.updateLargeVideo(localVideoSrc);
-        }
-
-        if (updateFocusedVideoSrc) {
-            focusedVideoSrc = localVideoSrc;
-        }
-    });
-
     /**
      * On simulcast layers changed event.
      */
                 var selRemoteVideo = $(['#', 'remoteVideo_', session.sid, '_', msidParts[0]].join(''));
 
                 var updateLargeVideo = (ssrc2jid[videoSrcToSsrc[selRemoteVideo.attr('src')]]
-                    == ssrc2jid[videoSrcToSsrc[largeVideoNewSrc]]);
+                    == ssrc2jid[videoSrcToSsrc[largeVideoState.newSrc]]);
                 var updateFocusedVideoSrc = (selRemoteVideo.attr('src') == focusedVideoSrc);
 
                 var electedStreamUrl = webkitURL.createObjectURL(electedStream);