Changed mixing to be done at the minimal possible frequency.

webrtc/modules/audio_mixer/audio_mixer_impl.cc

 /*
  *  Copyright (c) 2012 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 119 matching lines @@
 AudioMixerImpl::SourceStatusList::iterator FindSourceInList(
     AudioMixerImpl::Source const* audio_source,
     AudioMixerImpl::SourceStatusList* audio_source_list) {
   return std::find_if(
       audio_source_list->begin(), audio_source_list->end(),
       [audio_source](const std::unique_ptr<AudioMixerImpl::SourceStatus>& p) {
         return p->audio_source == audio_source;
       });
 }
 
+// Rounds the maximal audio source frequency up to an APM-native
+// frequency.
+int CalculateMixingFrequency(
+    const AudioMixerImpl::SourceStatusList& audio_source_list) {
+  if (audio_source_list.empty()) {
+    return AudioMixerImpl::kDefaultFrequency;
+  }
+  using NativeRate = AudioProcessing::NativeRate;
+  int maximal_frequency = 0;
+  for (const auto& source_status : audio_source_list) {
+    const int source_needed_frequency =
+        source_status->audio_source->PreferredSampleRate();
+    RTC_DCHECK_LE(NativeRate::kSampleRate8kHz, source_needed_frequency);
+    RTC_DCHECK_LE(source_needed_frequency, NativeRate::kSampleRate48kHz);
+    maximal_frequency = std::max(maximal_frequency, source_needed_frequency);
+  }
+
+  static constexpr NativeRate native_rates[] = {
+      NativeRate::kSampleRate8kHz, NativeRate::kSampleRate16kHz,
+      NativeRate::kSampleRate32kHz, NativeRate::kSampleRate48kHz};
+  const auto rounded_up_index = std::lower_bound(
+      std::begin(native_rates), std::end(native_rates), maximal_frequency);
+  RTC_DCHECK(rounded_up_index != std::end(native_rates));
+  return *rounded_up_index;
+}
+
 }  // namespace
 
 AudioMixerImpl::AudioMixerImpl(std::unique_ptr<AudioProcessing> limiter)
     : audio_source_list_(),
       use_limiter_(true),
       time_stamp_(0),
       limiter_(std::move(limiter)) {
   SetOutputFrequency(kDefaultFrequency);
 }
 
@@ skipping 29 matching lines @@
   }
 
   if (limiter->gain_control()->Enable(true) != limiter->kNoError) {
     return nullptr;
   }
 
   return rtc::scoped_refptr<AudioMixerImpl>(
       new rtc::RefCountedObject<AudioMixerImpl>(std::move(limiter)));
 }
 
-void AudioMixerImpl::Mix(int sample_rate,
-                         size_t number_of_channels,
+void AudioMixerImpl::Mix(size_t number_of_channels,
                          AudioFrame* audio_frame_for_mixing) {
   RTC_DCHECK(number_of_channels == 1 || number_of_channels == 2);
   RTC_DCHECK_RUNS_SERIALIZED(&race_checker_);
 
+  const int sample_rate = [&]() {
+    rtc::CritScope lock(&crit_);
+    return CalculateMixingFrequency(audio_source_list_);
+  }();
+
   if (OutputFrequency() != sample_rate) {
     SetOutputFrequency(sample_rate);
   }
 
   AudioFrameList mix_list;
   {
     rtc::CritScope lock(&crit_);
     mix_list = GetAudioFromSources();
 
     for (const auto& frame : mix_list) {
@@ skipping 140 matching lines @@
 
   const auto iter = FindSourceInList(audio_source, &audio_source_list_);
   if (iter != audio_source_list_.end()) {
     return (*iter)->is_mixed;
   }
 
   LOG(LS_ERROR) << "Audio source unknown";
   return false;
 }
 }  // namespace webrtc