ObjC: Fix quality scaling for injected encoders

webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm

 /*
  *  Copyright 2017 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 "WebRTC/RTCVideoCodecH264.h"
 
 #include <vector>
 
 #import "RTCVideoCodec+Private.h"
 #import "WebRTC/RTCVideoCodec.h"
 #import "WebRTC/RTCVideoFrame.h"
 #import "WebRTC/RTCVideoFrameBuffer.h"
 
 #include "webrtc/rtc_base/timeutils.h"
 #include "webrtc/sdk/objc/Framework/Classes/Video/objc_frame_buffer.h"
 #include "webrtc/sdk/objc/Framework/Classes/VideoToolbox/decoder.h"
 #include "webrtc/sdk/objc/Framework/Classes/VideoToolbox/encoder.h"
 #include "webrtc/system_wrappers/include/field_trial.h"
 
 const size_t kDefaultPayloadSize = 1440;
 
 const char kHighProfileExperiment[] = "WebRTC-H264HighProfile";
 
+// These thresholds deviate from the default h264 QP thresholds, as they have been found to work
+// better on devices that support VideoToolbox
+const int kLowH264QpThreshold = 28;
+const int kHighH264QpThreshold = 39;
+
 bool IsHighProfileEnabled() {
   return webrtc::field_trial::IsEnabled(kHighProfileExperiment);
 }
 
 // H264 specific settings.
 @implementation RTCCodecSpecificInfoH264
 
 @synthesize packetizationMode = _packetizationMode;
 
 - (webrtc::CodecSpecificInfo)nativeCodecSpecificInfo {
@@ skipping 124 matching lines @@
     nativeFrameTypes.push_back((webrtc::FrameType)rtcFrameType);
   }
 
   return _videoToolboxEncoder->Encode(videoFrame, &codecSpecificInfo, &nativeFrameTypes);
 }
 
 - (BOOL)setBitrate:(uint32_t)bitrateKbit framerate:(uint32_t)framerate {
   return _videoToolboxEncoder->SetRates(bitrateKbit, framerate) == WEBRTC_VIDEO_CODEC_OK;
 }
 
+- (RTCVideoEncoderQpThresholds *)scalingSettings {
+  return [[RTCVideoEncoderQpThresholds alloc] initWithThresholdsLow:kLowH264QpThreshold
+                                                               high:kHighH264QpThreshold];
+}
+
 @end
 
 // Decoder.
 @implementation RTCVideoDecoderH264 {
   webrtc::H264VideoToolboxDecoder *_videoToolboxDecoder;
   H264VideoToolboxDecodeCompleteCallback *_toolboxCallback;
 }
 
 - (instancetype)init {
   if (self = [super init]) {
@@ skipping 101 matching lines @@
 - (id<RTCVideoDecoder>)createDecoder:(RTCVideoCodecInfo *)info {
   return [[RTCVideoDecoderH264 alloc] init];
 }
 
 - (NSArray<RTCVideoCodecInfo *> *)supportedCodecs {
   NSString *codecName = [NSString stringWithUTF8String:cricket::kH264CodecName];
   return @[ [[RTCVideoCodecInfo alloc] initWithPayload:0 name:codecName parameters:@{}] ];
 }
 
 @end