Field trial support to whenever possible turn off the AGC and HPF

webrtc/media/engine/webrtcvoiceengine.cc

 /*
  *  Copyright (c) 2004 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 318 matching lines @@
     const AudioOptions& options) {
   RTC_DCHECK(worker_thread_checker_.CalledOnValidThread());
   return new WebRtcVoiceMediaChannel(this, config, options, call);
 }
 
 bool WebRtcVoiceEngine::ApplyOptions(const AudioOptions& options_in) {
   RTC_DCHECK(worker_thread_checker_.CalledOnValidThread());
   LOG(LS_INFO) << "WebRtcVoiceEngine::ApplyOptions: " << options_in.ToString();
   AudioOptions options = options_in;  // The options are modified below.
 
+  // Set and adjust echo canceller options.
   // kEcConference is AEC with high suppression.
   webrtc::EcModes ec_mode = webrtc::kEcConference;
   if (options.aecm_generate_comfort_noise) {
     LOG(LS_VERBOSE) << "Comfort noise explicitly set to "
                     << *options.aecm_generate_comfort_noise
                     << " (default is false).";
   }
 
 #if defined(WEBRTC_IOS)
-  // On iOS, VPIO provides built-in EC, NS and AGC.
+  // On iOS, VPIO provides built-in EC.
   options.echo_cancellation = rtc::Optional<bool>(false);
-  options.auto_gain_control = rtc::Optional<bool>(false);
-  options.noise_suppression = rtc::Optional<bool>(false);
-  LOG(LS_INFO)
-      << "Always disable AEC, NS and AGC on iOS. Use built-in instead.";
+  options.extended_filter_aec = rtc::Optional<bool>(false);
+  LOG(LS_INFO) << "Always disable AEC on iOS. Use built-in instead.";
 #elif defined(ANDROID)
   ec_mode = webrtc::kEcAecm;
-#endif
-
-#if defined(WEBRTC_IOS) || defined(ANDROID)
-  options.typing_detection = rtc::Optional<bool>(false);
-  options.experimental_agc = rtc::Optional<bool>(false);
   options.extended_filter_aec = rtc::Optional<bool>(false);
-  options.experimental_ns = rtc::Optional<bool>(false);
 #endif
 
   // Delay Agnostic AEC automatically turns on EC if not set except on iOS
   // where the feature is not supported.
   bool use_delay_agnostic_aec = false;
 #if !defined(WEBRTC_IOS)
   if (options.delay_agnostic_aec) {
     use_delay_agnostic_aec = *options.delay_agnostic_aec;
     if (use_delay_agnostic_aec) {
       options.echo_cancellation = rtc::Optional<bool>(true);
       options.extended_filter_aec = rtc::Optional<bool>(true);
       ec_mode = webrtc::kEcConference;
     }
   }
 #endif
 
+// Set and adjust noise suppressor options.
+#if defined(WEBRTC_IOS)
+  // On iOS, VPIO provides built-in NS.
+  options.noise_suppression = rtc::Optional<bool>(false);
+  options.typing_detection = rtc::Optional<bool>(false);
+  options.experimental_ns = rtc::Optional<bool>(false);
+  LOG(LS_INFO) << "Always disable NS on iOS. Use built-in instead.";
+#elif defined(ANDROID)
+  options.typing_detection = rtc::Optional<bool>(false);
+  options.experimental_ns = rtc::Optional<bool>(false);
+#endif
+
+// Set and adjust gain control options.
+#if defined(WEBRTC_IOS)
+  // On iOS, VPIO provides built-in AGC.
+  options.auto_gain_control = rtc::Optional<bool>(false);
+  options.experimental_agc = rtc::Optional<bool>(false);
+  LOG(LS_INFO) << "Always disable AGC on iOS. Use built-in instead.";
+#elif defined(ANDROID)
+  options.experimental_agc = rtc::Optional<bool>(false);
+#endif
+
+#if defined(WEBRTC_IOS) || defined(WEBRTC_ANDROID)
+  // Turn off the gain control if specified by the field trial. The purpose of the field trial is to reduce the amount of resampling performed inside the audio processing module on mobile platforms by whenever possible turning off the fixed AGC mode and the high-pass filter. (https://bugs.chromium.org/p/webrtc/issues/detail?id=6181).
+  if (webrtc::field_trial::IsEnabled(
+          "WebRTC-Audio-MinimizeResamplingOnMobile")) {
+    options.auto_gain_control = rtc::Optional<bool>(false);
+    LOG(LS_INFO) << "Disable AGC according to field trial.";
+    if (!(options.noise_suppression.value_or(false) or
+          options.echo_cancellation.value_or(false))) {
+      // If possible, turn off the high-pass filter.
+      LOG(LS_INFO) << "Disable high-pass filter in response to field trial.";
+      options.highpass_filter = rtc::Optional<bool>(false);
+    }
+  }
+#endif
+
 #if (WEBRTC_INTELLIGIBILITY_ENHANCER == 0)
   // Hardcode the intelligibility enhancer to be off.
   options.intelligibility_enhancer = rtc::Optional<bool>(false);
 #endif
 
   if (options.echo_cancellation) {
     // Check if platform supports built-in EC. Currently only supported on
     // Android and in combination with Java based audio layer.
     // TODO(henrika): investigate possibility to support built-in EC also
     // in combination with Open SL ES audio.
@@ skipping 1938 matching lines @@
                       ssrc);
   if (it != unsignaled_recv_ssrcs_.end()) {
     unsignaled_recv_ssrcs_.erase(it);
     return true;
   }
   return false;
 }
 }  // namespace cricket
 
 #endif  // HAVE_WEBRTC_VOICE