use 'number' instead of 'exact' value only when share screen

Author: xiewenlong1202

src/sdk/base/mediastream-factory.js

@@ -202,10 +202,21 @@ export class MediaStreamFactory {
       if (constraints.video.resolution &&
           constraints.video.resolution.width &&
           constraints.video.resolution.height) {
-        mediaConstraints.video.width = 
-            constraints.video.resolution.width;
-        mediaConstraints.video.height = 
-            constraints.video.resolution.height;
+            if (constraints.video.source ===
+              MediaFormatModule.VideoSourceInfo.SCREENCAST) {
+              mediaConstraints.video.width =
+                constraints.video.resolution.width;
+              mediaConstraints.video.height =
+                constraints.video.resolution.height;
+            } else {
+              mediaConstraints.video.width = Object.create({});
+              mediaConstraints.video.width.exact =
+                  constraints.video.resolution.width;
+              mediaConstraints.video.height = Object.create({});
+              mediaConstraints.video.height.exact =
+                  constraints.video.resolution.height;
+
+            }
       }
       if (typeof constraints.video.deviceId === 'string') {
         mediaConstraints.video.deviceId = { exact: constraints.video.deviceId };