video: verify AVDevice type

This commit adds type verification when an AVCaptureDevice is added.
The notification that a new device got connected, is received for both
video and audio devices.

Change-Id: Id48fb4182589234df164ab6337fb5d4863987a15
Tuleap: #149

src/media/video/osxvideo/video_device_monitor_impl.mm

@@ -98,14 +98,16 @@ void VideoDeviceMonitorImpl::start()
                                     object:nil
                                     queue:[NSOperationQueue mainQueue]
                                     usingBlock:^(NSNotification *note) {
-                                      AVCaptureDevice* dev = (AVCaptureDevice*)note.object;
+                                        auto dev = (AVCaptureDevice*)note.object;
+                                        if([dev hasMediaType:AVMediaTypeVideo])
                                             monitor_->addDevice([[dev uniqueID] UTF8String]);
                                     }];
     id deviceWasDisconnectedObserver = [notificationCenter addObserverForName:AVCaptureDeviceWasDisconnectedNotification
                                         object:nil
                                         queue:[NSOperationQueue mainQueue]
                                         usingBlock:^(NSNotification *note) {
-                                          AVCaptureDevice* dev = (AVCaptureDevice*)note.object;
+                                            auto dev = (AVCaptureDevice*)note.object;
+                                            if([dev hasMediaType:AVMediaTypeVideo])
                                                 monitor_->removeDevice([[dev uniqueID] UTF8String]);
                                         }];
     observers = [[NSArray alloc] initWithObjects:deviceWasConnectedObserver, deviceWasDisconnectedObserver, nil];