Disable encoder scaling on iPhone4S.

webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm

 /*
  *  Copyright 2015 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 557 matching lines @@
   int64_t capture_time;
 };
 
 AVFoundationVideoCapturer::AVFoundationVideoCapturer()
     : _capturer(nil), _startThread(nullptr) {
   // Set our supported formats. This matches kDefaultPreset.
   std::vector<cricket::VideoFormat> supported_formats;
 #if TARGET_OS_IPHONE
   if ([UIDevice deviceType] == RTCDeviceTypeIPhone4S) {
     supported_formats.push_back(cricket::VideoFormat(kIPhone4SFormat));
+    set_enable_video_adapter(false);
   } else {
     supported_formats.push_back(cricket::VideoFormat(kDefaultFormat));
   }
 #else
   supported_formats.push_back(cricket::VideoFormat(kDefaultFormat));
 #endif
   SetSupportedFormats(supported_formats);
   _capturer =
       [[RTCAVFoundationVideoCapturerInternal alloc] initWithCapturer:this];
 }
@@ skipping 130 matching lines @@
   }
 
   OnFrame(cricket::WebRtcVideoFrame(buffer, webrtc::kVideoRotation_0,
                                     translated_camera_time_us, 0),
           captured_width, captured_height);
 
   CVBufferRelease(image_buffer);
 }
 
 }  // namespace webrtc