Activating 48 kHz processing support in the audio processing module for ARM

On ARM devices, WebRTC always performs the audio processing at a maximum
of 32 kHz. The reason for this is that previously the 48 kHz splitting
filters used caused issues related to CPU-performance on ARM. This has
now been addressed and this CL activates 48 kHz processing at 32 kHz.

The CL also adds a kill-switch that can be used to turn off this support
for ARM devices, in case it would turn out to be an issue.

Bug: webrtc:6181
Change-Id: I3c31d6d1724a784e56391def673a3d7140ece457
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2404921
Commit-Queue: Olga Sharonova <olka@chromium.org>
Reviewed-by: Olga Sharonova <olka@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806193}

media/webrtc/webrtc_switches.cc

@@ -26,6 +26,12 @@ namespace features {
 const base::Feature kWebRtcEnableCaptureMultiChannelApm{
     "WebRtcEnableCaptureMultiChannelApm", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Kill-switch allowing deactivation of the support for 48 kHz internal
+// processing in the WebRTC audio processing module when running on an ARM
+// platform.
+const base::Feature kWebRtcAllow48kHzProcessingOnArm{
+    "WebRtcAllow48kHzProcessingOnArm", base::FEATURE_ENABLED_BY_DEFAULT};
+
 // Enables the WebRTC Agc2 digital adaptation with WebRTC Agc1 analog
 // adaptation. Feature for http://crbug.com/873650. Is sent to WebRTC.
 const base::Feature kWebRtcHybridAgc{"WebRtcHybridAgc",

media/webrtc/webrtc_switches.h

@@ -21,6 +21,9 @@ namespace features {
 COMPONENT_EXPORT(MEDIA_WEBRTC)
 extern const base::Feature kWebRtcEnableCaptureMultiChannelApm;
 
+COMPONENT_EXPORT(MEDIA_WEBRTC)
+extern const base::Feature kWebRtcAllow48kHzProcessingOnArm;
+
 COMPONENT_EXPORT(MEDIA_WEBRTC)
 extern const base::Feature kWebRtcHybridAgc;
 

third_party/blink/renderer/modules/mediastream/media_stream_audio_processor.cc

@@ -67,6 +67,11 @@ bool UseMultiChannelCaptureProcessing() {
       features::kWebRtcEnableCaptureMultiChannelApm);
 }
 
+bool Allow48kHzApmProcessing() {
+  return base::FeatureList::IsEnabled(
+      features::kWebRtcAllow48kHzProcessingOnArm);
+}
+
 constexpr int kAudioProcessingNumberOfChannels = 1;
 constexpr int kBuffersPerSecond = 100;  // 10 ms per buffer.
 
@@ -603,6 +608,12 @@ void MediaStreamAudioProcessor::InitializeAudioProcessingModule(
     blink::EnableTypingDetection(&apm_config, typing_detector_.get());
   }
 
+  // Ensure that 48 kHz APM processing is always active. This overrules the
+  // default setting in WebRTC of 32 kHz for ARM platforms.
+  if (Allow48kHzApmProcessing()) {
+    apm_config.pipeline.maximum_internal_processing_rate = 48000;
+  }
+
   apm_config.residual_echo_detector.enabled = false;
   audio_processing_->ApplyConfig(apm_config);
 }