Update MainActivity.java

app/src/main/java/net/ossrs/yasea/demo/MainActivity.java

@@ -232,6 +232,15 @@ public class MainActivity extends AppCompatActivity implements RtmpHandler.RtmpL
         return super.onOptionsItemSelected(item);
     }
 
+    @Override
+    protected void onStart() {
+        super.onStart();
+        if(mPublisher.getCamera() == null){
+            //if the camera was busy and available again
+            mPublisher.startCamera();
+        }
+    }                           
+                          
     @Override
     protected void onResume() {
         super.onResume();