Use 15fps for iPhone 4S

webrtc/sdk/objc/Framework/Headers/WebRTC/UIDevice+RTCDevice.h

+/*
+ *  Copyright 2016 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.
+ */
+
+#import <UIKit/UIKit.h>
+
+typedef NS_ENUM(NSInteger, RTCDeviceType) {
+  RTCDeviceTypeUnknown,
+  RTCDeviceTypeIPhone1G,
+  RTCDeviceTypeIPhone3G,
+  RTCDeviceTypeIPhone3GS,
+  RTCDeviceTypeIPhone4,
+  RTCDeviceTypeIPhone4Verizon,
+  RTCDeviceTypeIPhone4S,
+  RTCDeviceTypeIPhone5GSM,
+  RTCDeviceTypeIPhone5GSM_CDMA,
+  RTCDeviceTypeIPhone5CGSM,
+  RTCDeviceTypeIPhone5CGSM_CDMA,
+  RTCDeviceTypeIPhone5SGSM,
+  RTCDeviceTypeIPhone5SGSM_CDMA,
+  RTCDeviceTypeIPhone6Plus,
+  RTCDeviceTypeIPhone6,
+  RTCDeviceTypeIPhone6S,
+  RTCDeviceTypeIPhone6SPlus,
+  RTCDeviceTypeIPodTouch1G,
+  RTCDeviceTypeIPodTouch2G,
+  RTCDeviceTypeIPodTouch3G,
+  RTCDeviceTypeIPodTouch4G,
+  RTCDeviceTypeIPodTouch5G,
+  RTCDeviceTypeIPad,
+  RTCDeviceTypeIPad2Wifi,
+  RTCDeviceTypeIPad2GSM,
+  RTCDeviceTypeIPad2CDMA,
+  RTCDeviceTypeIPad2Wifi2,
+  RTCDeviceTypeIPadMiniWifi,
+  RTCDeviceTypeIPadMiniGSM,
+  RTCDeviceTypeIPadMiniGSM_CDMA,
+  RTCDeviceTypeIPad3Wifi,
+  RTCDeviceTypeIPad3GSM_CDMA,
+  RTCDeviceTypeIPad3GSM,
+  RTCDeviceTypeIPad4Wifi,
+  RTCDeviceTypeIPad4GSM,
+  RTCDeviceTypeIPad4GSM_CDMA,
+  RTCDeviceTypeIPadAirWifi,
+  RTCDeviceTypeIPadAirCellular,
+  RTCDeviceTypeIPadMini2GWifi,
+  RTCDeviceTypeIPadMini2GCellular,
+  RTCDeviceTypeSimulatori386,
+  RTCDeviceTypeSimulatorx86_64,
+};
+
+@interface UIDevice (RTCDevice)
+
++ (RTCDeviceType)deviceType;
++ (NSString *)stringForDeviceType:(RTCDeviceType)deviceType;
+
+@end