Add method on AVFoundation capturer to adapt output format.

webrtc/sdk/objc/Framework/Classes/RTCAVFoundationVideoSource.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 14 matching lines @@
   // the source, it should be ok to keep a raw pointer to the
   // capturer.
   _capturer = new webrtc::AVFoundationVideoCapturer();
   rtc::scoped_refptr<webrtc::VideoTrackSourceInterface> source =
       factory.nativeFactory->CreateVideoSource(
           _capturer, constraints.nativeConstraints.get());
 
   return [super initWithNativeVideoSource:source];
 }
 
+- (void)adaptOutputFormatToWidth:(int)width
+                          height:(int)height
+                             fps:(int)fps {
+  self.capturer->AdaptOutputFormat(width, height, fps);
+}
+
 - (BOOL)canUseBackCamera {
   return self.capturer->CanUseBackCamera();
 }
 
 - (BOOL)useBackCamera {
   return self.capturer->GetUseBackCamera();
 }
 
 - (void)setUseBackCamera:(BOOL)useBackCamera {
   self.capturer->SetUseBackCamera(useBackCamera);
 }
 
 - (AVCaptureSession *)captureSession {
   return self.capturer->GetCaptureSession();
 }
 
 - (webrtc::AVFoundationVideoCapturer *)capturer {
   return _capturer;
 }
 
 @end