Add video codec setting to AppRTCMobile on iOS.

webrtc/examples/objc/AppRTCMobile/mac/APPRTCViewController.m

 /*
  *  Copyright 2014 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 351 matching lines @@
 - (void)appRTCMainView:(APPRTCMainView*)mainView
         didEnterRoomId:(NSString*)roomId
               loopback:(BOOL)isLoopback {
 
   if ([roomId isEqualToString:@""]) {
     [self.mainView displayLogMessage:@"Missing room id"];
     return;
   }
 
   [_client disconnect];
-  ARDAppClient *client = [[ARDAppClient alloc] initWithDelegate:self];
+  ARDAppClient *client = [[ARDAppClient alloc] initWithDelegate:self
+                                               preferVideoCodec:@"H264"];
   [client connectToRoomWithId:roomId
                    isLoopback:isLoopback
                   isAudioOnly:NO
             shouldMakeAecDump:NO
         shouldUseLevelControl:NO];
   _client = client;
 }
 
 #pragma mark - Private
 
@@ skipping 15 matching lines @@
   [self.mainView.remoteVideoView renderFrame:nil];
   [self.mainView.localVideoView renderFrame:nil];
 }
 
 - (void)disconnect {
   [self resetUI];
   [_client disconnect];
 }
 
 @end