added config 'cameraIndex' to select the camera by index

src/input/camera_access.js

@@ -84,11 +84,19 @@ function normalizeConstraints(config, cb) {
 
     if ( typeof MediaStreamTrack !== 'undefined' && typeof MediaStreamTrack.getSources !== 'undefined') {
         MediaStreamTrack.getSources(function(sourceInfos) {
-            var videoSourceId;
+            var videoSourceId, facingDetected, videoIndex = 0;
             for (var i = 0; i < sourceInfos.length; ++i) {
                 var sourceInfo = sourceInfos[i];
-                if (sourceInfo.kind === "video" && sourceInfo.facing === videoConstraints.facing) {
+                if (sourceInfo.kind === "video" && !facingDetected) {
-                    videoSourceId = sourceInfo.id;
+                    if (sourceInfo.facing === videoConstraints.facing) {
+                        facingDetected = true;
+                    }
+                    
+                    if (!config.cameraIndex || config.cameraIndex <= videoIndex) {
+                        videoSourceId = sourceInfo.id;
+                    }
+                    
+                    videoIndex++;
                 }
             }
             constraints.video = {