ObjC: Fix quality scaling for injected encoders

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

Index: webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm
diff --git a/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm b/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm
index 7cd6a7f0d075deb3ad2c7567b0bffa1b8a2ef5a3..7b38ec047cec1dfd2f1ee3080e91b7982117f077 100644
--- a/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm
+++ b/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm
@@ -27,6 +27,11 @@ 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);
 }
@@ -171,6 +176,11 @@ class H264VideoToolboxDecodeCompleteCallback : public webrtc::DecodedImageCallba
   return _videoToolboxEncoder->SetRates(bitrateKbit, framerate) == WEBRTC_VIDEO_CODEC_OK;
 }
 
+- (RTCVideoEncoderQpThresholds *)scalingSettings {
+  return [[RTCVideoEncoderQpThresholds alloc] initWithThresholdsLow:kLowH264QpThreshold
+                                                               high:kHighH264QpThreshold];
+}
+
 @end
 
 // Decoder.