Add AVMediaTypeMuxed capture devices to AVFoundation, just as QTKit does.

modules/videoio/src/cap_avfoundation_mac.mm

@@ -305,7 +305,8 @@ int CvCaptureCAM::startCaptureDevice(int cameraNum) {
     NSAutoreleasePool *localpool = [[NSAutoreleasePool alloc] init];
 
     // get capture device
-    NSArray *devices = [AVCaptureDevice devicesWithMediaType: AVMediaTypeVideo];
+    NSArray *devices = [[AVCaptureDevice devicesWithMediaType: AVMediaTypeVideo]
+            arrayByAddingObjectsFromArray:[AVCaptureDevice devicesWithMediaType:AVMediaTypeMuxed]];
 
     if ( devices.count == 0 ) {
         fprintf(stderr, "OpenCV: AVFoundation didn't find any attached Video Input Devices!\n");