A simple copy of the old mixer to a new directory. I also plan to run 'git cl format'. In another C…

webrtc/modules/audio_mixer/source/new_audio_conference_mixer_impl.cc

Index: webrtc/modules/audio_mixer/source/new_audio_conference_mixer_impl.cc
diff --git a/webrtc/modules/audio_mixer/source/new_audio_conference_mixer_impl.cc b/webrtc/modules/audio_mixer/source/new_audio_conference_mixer_impl.cc
new file mode 100644
index 0000000000000000000000000000000000000000..36d70b217133e9f77643eadb4c02516b1f9109ca
--- /dev/null
+++ b/webrtc/modules/audio_mixer/source/new_audio_conference_mixer_impl.cc
@@ -0,0 +1,898 @@
+/*
+ *  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.
+ */
+
+#include "webrtc/modules/audio_mixer/source/new_audio_conference_mixer_impl.h"
+
+#include <algorithm>
+
+#include "webrtc/modules/audio_conference_mixer/source/audio_frame_manipulator.h"
+#include "webrtc/modules/audio_mixer/include/audio_mixer_defines.h"
+#include "webrtc/modules/audio_processing/include/audio_processing.h"
+#include "webrtc/modules/utility/include/audio_frame_operations.h"
+#include "webrtc/system_wrappers/include/critical_section_wrapper.h"
+#include "webrtc/system_wrappers/include/trace.h"
+
+namespace webrtc {
+namespace {
+
+struct ParticipantFrameStruct {
+  ParticipantFrameStruct(MixerAudioSource* p, AudioFrame* a, bool m)
+      : participant(p), audioFrame(a), muted(m) {}
+  MixerAudioSource* participant;
+  AudioFrame* audioFrame;
+  bool muted;
+};
+
+typedef std::list<ParticipantFrameStruct*> ParticipantFrameStructList;
+
+// Mix |frame| into |mixed_frame|, with saturation protection and upmixing.
+// These effects are applied to |frame| itself prior to mixing. Assumes that
+// |mixed_frame| always has at least as many channels as |frame|. Supports
+// stereo at most.
+//
+// TODO(andrew): consider not modifying |frame| here.
+void MixFrames(AudioFrame* mixed_frame, AudioFrame* frame, bool use_limiter) {
+  assert(mixed_frame->num_channels_ >= frame->num_channels_);
+  if (use_limiter) {
+    // Divide by two to avoid saturation in the mixing.
+    // This is only meaningful if the limiter will be used.
+    *frame >>= 1;
+  }
+  if (mixed_frame->num_channels_ > frame->num_channels_) {
+    // We only support mono-to-stereo.
+    assert(mixed_frame->num_channels_ == 2 && frame->num_channels_ == 1);
+    AudioFrameOperations::MonoToStereo(frame);
+  }
+
+  *mixed_frame += *frame;
+}
+
+// Return the max number of channels from a |list| composed of AudioFrames.
+size_t MaxNumChannels(const AudioFrameList* list) {
+  size_t max_num_channels = 1;
+  for (AudioFrameList::const_iterator iter = list->begin(); iter != list->end();
+       ++iter) {
+    max_num_channels = std::max(max_num_channels, (*iter).frame->num_channels_);
+  }
+  return max_num_channels;
+}
+
+}  // namespace
+
+MixerAudioSource::MixerAudioSource() : _mixHistory(new NewMixHistory()) {}
+
+MixerAudioSource::~MixerAudioSource() {
+  delete _mixHistory;
+}
+
+bool MixerAudioSource::IsMixed() const {
+  return _mixHistory->IsMixed();
+}
+
+NewMixHistory::NewMixHistory() : _isMixed(0) {}
+
+NewMixHistory::~NewMixHistory() {}
+
+bool NewMixHistory::IsMixed() const {
+  return _isMixed;
+}
+
+bool NewMixHistory::WasMixed() const {
+  // Was mixed is the same as is mixed depending on perspective. This function
+  // is for the perspective of NewAudioConferenceMixerImpl.
+  return IsMixed();
+}
+
+int32_t NewMixHistory::SetIsMixed(const bool mixed) {
+  _isMixed = mixed;
+  return 0;
+}
+
+void NewMixHistory::ResetMixedStatus() {
+  _isMixed = false;
+}
+
+NewAudioConferenceMixer* NewAudioConferenceMixer::Create(int id) {
+  NewAudioConferenceMixerImpl* mixer = new NewAudioConferenceMixerImpl(id);
+  if (!mixer->Init()) {
+    delete mixer;
+    return NULL;
+  }
+  return mixer;
+}
+
+NewAudioConferenceMixerImpl::NewAudioConferenceMixerImpl(int id)
+    : _id(id),
+      _minimumMixingFreq(kLowestPossible),
+      _mixReceiver(NULL),
+      _outputFrequency(kDefaultFrequency),
+      _sampleSize(0),
+      _audioFramePool(NULL),
+      _participantList(),
+      _additionalParticipantList(),
+      _numMixedParticipants(0),
+      use_limiter_(true),
+      _timeStamp(0),
+      _timeScheduler(kProcessPeriodicityInMs),
+      _processCalls(0) {}
+
+bool NewAudioConferenceMixerImpl::Init() {
+  _crit.reset(CriticalSectionWrapper::CreateCriticalSection());
+  if (_crit.get() == NULL)
+    return false;
+
+  _cbCrit.reset(CriticalSectionWrapper::CreateCriticalSection());
+  if (_cbCrit.get() == NULL)
+    return false;
+
+  Config config;
+  config.Set<ExperimentalAgc>(new ExperimentalAgc(false));
+  _limiter.reset(AudioProcessing::Create(config));
+  if (!_limiter.get())
+    return false;
+
+  MemoryPool<AudioFrame>::CreateMemoryPool(_audioFramePool,
+                                           DEFAULT_AUDIO_FRAME_POOLSIZE);
+  if (_audioFramePool == NULL)
+    return false;
+
+  if (SetOutputFrequency(kDefaultFrequency) == -1)
+    return false;
+
+  if (_limiter->gain_control()->set_mode(GainControl::kFixedDigital) !=
+      _limiter->kNoError)
+    return false;
+
+  // We smoothly limit the mixed frame to -7 dbFS. -6 would correspond to the
+  // divide-by-2 but -7 is used instead to give a bit of headroom since the
+  // AGC is not a hard limiter.
+  if (_limiter->gain_control()->set_target_level_dbfs(7) != _limiter->kNoError)
+    return false;
+
+  if (_limiter->gain_control()->set_compression_gain_db(0) !=
+      _limiter->kNoError)
+    return false;
+
+  if (_limiter->gain_control()->enable_limiter(true) != _limiter->kNoError)
+    return false;
+
+  if (_limiter->gain_control()->Enable(true) != _limiter->kNoError)
+    return false;
+
+  return true;
+}
+
+NewAudioConferenceMixerImpl::~NewAudioConferenceMixerImpl() {
+  MemoryPool<AudioFrame>::DeleteMemoryPool(_audioFramePool);
+  assert(_audioFramePool == NULL);
+}
+
+// Process should be called every kProcessPeriodicityInMs ms
+int64_t NewAudioConferenceMixerImpl::TimeUntilNextProcess() {
+  int64_t timeUntilNextProcess = 0;
+  CriticalSectionScoped cs(_crit.get());
+  if (_timeScheduler.TimeToNextUpdate(timeUntilNextProcess) != 0) {
+    WEBRTC_TRACE(kTraceError, kTraceAudioMixerServer, _id,
+                 "failed in TimeToNextUpdate() call");
+    // Sanity check
+    assert(false);
+    return -1;
+  }
+  return timeUntilNextProcess;
+}
+
+void NewAudioConferenceMixerImpl::Process() {
+  size_t remainingParticipantsAllowedToMix = kMaximumAmountOfMixedParticipants;
+  {
+    CriticalSectionScoped cs(_crit.get());
+    assert(_processCalls == 0);
+    _processCalls++;
+
+    // Let the scheduler know that we are running one iteration.
+    _timeScheduler.UpdateScheduler();
+  }
+
+  AudioFrameList mixList;
+  AudioFrameList rampOutList;
+  AudioFrameList additionalFramesList;
+  std::map<int, MixerAudioSource*> mixedParticipantsMap;
+  {
+    CriticalSectionScoped cs(_cbCrit.get());
+
+    int32_t lowFreq = GetLowestMixingFrequency();
+    // SILK can run in 12 kHz and 24 kHz. These frequencies are not
+    // supported so use the closest higher frequency to not lose any
+    // information.
+    // TODO(henrike): this is probably more appropriate to do in
+    //                GetLowestMixingFrequency().
+    if (lowFreq == 12000) {
+      lowFreq = 16000;
+    } else if (lowFreq == 24000) {
+      lowFreq = 32000;
+    }
+    if (lowFreq <= 0) {
+      CriticalSectionScoped cs(_crit.get());
+      _processCalls--;
+      return;
+    } else {
+      switch (lowFreq) {
+        case 8000:
+          if (OutputFrequency() != kNbInHz) {
+            SetOutputFrequency(kNbInHz);
+          }
+          break;
+        case 16000:
+          if (OutputFrequency() != kWbInHz) {
+            SetOutputFrequency(kWbInHz);
+          }
+          break;
+        case 32000:
+          if (OutputFrequency() != kSwbInHz) {
+            SetOutputFrequency(kSwbInHz);
+          }
+          break;
+        case 48000:
+          if (OutputFrequency() != kFbInHz) {
+            SetOutputFrequency(kFbInHz);
+          }
+          break;
+        default:
+          assert(false);
+
+          CriticalSectionScoped cs(_crit.get());
+          _processCalls--;
+          return;
+      }
+    }
+
+    UpdateToMix(&mixList, &rampOutList, &mixedParticipantsMap,
+                &remainingParticipantsAllowedToMix);
+
+    GetAdditionalAudio(&additionalFramesList);
+    UpdateMixedStatus(mixedParticipantsMap);
+  }
+
+  // Get an AudioFrame for mixing from the memory pool.
+  AudioFrame* mixedAudio = NULL;
+  if (_audioFramePool->PopMemory(mixedAudio) == -1) {
+    WEBRTC_TRACE(kTraceMemory, kTraceAudioMixerServer, _id,
+                 "failed PopMemory() call");
+    assert(false);
+    return;
+  }
+
+  {
+    CriticalSectionScoped cs(_crit.get());
+
+    // TODO(henrike): it might be better to decide the number of channels
+    //                with an API instead of dynamically.
+
+    // Find the max channels over all mixing lists.
+    const size_t num_mixed_channels =
+        std::max(MaxNumChannels(&mixList),
+                 std::max(MaxNumChannels(&additionalFramesList),
+                          MaxNumChannels(&rampOutList)));
+
+    mixedAudio->UpdateFrame(-1, _timeStamp, NULL, 0, _outputFrequency,
+                            AudioFrame::kNormalSpeech, AudioFrame::kVadPassive,
+                            num_mixed_channels);
+
+    _timeStamp += static_cast<uint32_t>(_sampleSize);
+
+    // We only use the limiter if it supports the output sample rate and
+    // we're actually mixing multiple streams.
+    use_limiter_ = _numMixedParticipants > 1 &&
+                   _outputFrequency <= AudioProcessing::kMaxNativeSampleRateHz;
+
+    MixFromList(mixedAudio, mixList);
+    MixAnonomouslyFromList(mixedAudio, additionalFramesList);
+    MixAnonomouslyFromList(mixedAudio, rampOutList);
+
+    if (mixedAudio->samples_per_channel_ == 0) {
+      // Nothing was mixed, set the audio samples to silence.
+      mixedAudio->samples_per_channel_ = _sampleSize;
+      mixedAudio->Mute();
+    } else {
+      // Only call the limiter if we have something to mix.
+      LimitMixedAudio(mixedAudio);
+    }
+  }
+
+  {
+    CriticalSectionScoped cs(_cbCrit.get());
+    if (_mixReceiver != NULL) {
+      const AudioFrame** dummy = NULL;
+      _mixReceiver->NewMixedAudio(_id, *mixedAudio, dummy, 0);
+    }
+  }
+
+  // Reclaim all outstanding memory.
+  _audioFramePool->PushMemory(mixedAudio);
+  ClearAudioFrameList(&mixList);
+  ClearAudioFrameList(&rampOutList);
+  ClearAudioFrameList(&additionalFramesList);
+  {
+    CriticalSectionScoped cs(_crit.get());
+    _processCalls--;
+  }
+  return;
+}
+
+int32_t NewAudioConferenceMixerImpl::RegisterMixedStreamCallback(
+    OldAudioMixerOutputReceiver* mixReceiver) {
+  CriticalSectionScoped cs(_cbCrit.get());
+  if (_mixReceiver != NULL) {
+    return -1;
+  }
+  _mixReceiver = mixReceiver;
+  return 0;
+}
+
+int32_t NewAudioConferenceMixerImpl::UnRegisterMixedStreamCallback() {
+  CriticalSectionScoped cs(_cbCrit.get());
+  if (_mixReceiver == NULL) {
+    return -1;
+  }
+  _mixReceiver = NULL;
+  return 0;
+}
+
+int32_t NewAudioConferenceMixerImpl::SetOutputFrequency(
+    const Frequency& frequency) {
+  CriticalSectionScoped cs(_crit.get());
+
+  _outputFrequency = frequency;
+  _sampleSize =
+      static_cast<size_t>((_outputFrequency * kProcessPeriodicityInMs) / 1000);
+
+  return 0;
+}
+
+NewAudioConferenceMixer::Frequency
+NewAudioConferenceMixerImpl::OutputFrequency() const {
+  CriticalSectionScoped cs(_crit.get());
+  return _outputFrequency;
+}
+
+int32_t NewAudioConferenceMixerImpl::SetMixabilityStatus(
+    MixerAudioSource* participant,
+    bool mixable) {
+  if (!mixable) {
+    // Anonymous participants are in a separate list. Make sure that the
+    // participant is in the _participantList if it is being mixed.
+    SetAnonymousMixabilityStatus(participant, false);
+  }
+  size_t numMixedParticipants;
+  {
+    CriticalSectionScoped cs(_cbCrit.get());
+    const bool isMixed = IsParticipantInList(*participant, _participantList);
+    // API must be called with a new state.
+    if (!(mixable ^ isMixed)) {
+      WEBRTC_TRACE(kTraceWarning, kTraceAudioMixerServer, _id,
+                   "Mixable is aready %s", isMixed ? "ON" : "off");
+      return -1;
+    }
+    bool success = false;
+    if (mixable) {
+      success = AddParticipantToList(participant, &_participantList);
+    } else {
+      success = RemoveParticipantFromList(participant, &_participantList);
+    }
+    if (!success) {
+      WEBRTC_TRACE(kTraceError, kTraceAudioMixerServer, _id,
+                   "failed to %s participant", mixable ? "add" : "remove");
+      assert(false);
+      return -1;
+    }
+
+    size_t numMixedNonAnonymous = _participantList.size();
+    if (numMixedNonAnonymous > kMaximumAmountOfMixedParticipants) {
+      numMixedNonAnonymous = kMaximumAmountOfMixedParticipants;
+    }
+    numMixedParticipants =
+        numMixedNonAnonymous + _additionalParticipantList.size();
+  }
+  // A MixerAudioSource was added or removed. Make sure the scratch
+  // buffer is updated if necessary.
+  // Note: The scratch buffer may only be updated in Process().
+  CriticalSectionScoped cs(_crit.get());
+  _numMixedParticipants = numMixedParticipants;
+  return 0;
+}
+
+bool NewAudioConferenceMixerImpl::MixabilityStatus(
+    const MixerAudioSource& participant) const {
+  CriticalSectionScoped cs(_cbCrit.get());
+  return IsParticipantInList(participant, _participantList);
+}
+
+int32_t NewAudioConferenceMixerImpl::SetAnonymousMixabilityStatus(
+    MixerAudioSource* participant,
+    bool anonymous) {
+  CriticalSectionScoped cs(_cbCrit.get());
+  if (IsParticipantInList(*participant, _additionalParticipantList)) {
+    if (anonymous) {
+      return 0;
+    }
+    if (!RemoveParticipantFromList(participant, &_additionalParticipantList)) {
+      WEBRTC_TRACE(kTraceError, kTraceAudioMixerServer, _id,
+                   "unable to remove participant from anonymous list");
+      assert(false);
+      return -1;
+    }
+    return AddParticipantToList(participant, &_participantList) ? 0 : -1;
+  }
+  if (!anonymous) {
+    return 0;
+  }
+  const bool mixable =
+      RemoveParticipantFromList(participant, &_participantList);
+  if (!mixable) {
+    WEBRTC_TRACE(
+        kTraceWarning, kTraceAudioMixerServer, _id,
+        "participant must be registered before turning it into anonymous");
+    // Setting anonymous status is only possible if MixerAudioSource is
+    // already registered.
+    return -1;
+  }
+  return AddParticipantToList(participant, &_additionalParticipantList) ? 0
+                                                                        : -1;
+}
+
+bool NewAudioConferenceMixerImpl::AnonymousMixabilityStatus(
+    const MixerAudioSource& participant) const {
+  CriticalSectionScoped cs(_cbCrit.get());
+  return IsParticipantInList(participant, _additionalParticipantList);
+}
+
+int32_t NewAudioConferenceMixerImpl::SetMinimumMixingFrequency(Frequency freq) {
+  // Make sure that only allowed sampling frequencies are used. Use closest
+  // higher sampling frequency to avoid losing information.
+  if (static_cast<int>(freq) == 12000) {
+    freq = kWbInHz;
+  } else if (static_cast<int>(freq) == 24000) {
+    freq = kSwbInHz;
+  }
+
+  if ((freq == kNbInHz) || (freq == kWbInHz) || (freq == kSwbInHz) ||
+      (freq == kLowestPossible)) {
+    _minimumMixingFreq = freq;
+    return 0;
+  } else {
+    WEBRTC_TRACE(kTraceError, kTraceAudioMixerServer, _id,
+                 "SetMinimumMixingFrequency incorrect frequency: %i", freq);
+    assert(false);
+    return -1;
+  }
+}
+
+// Check all AudioFrames that are to be mixed. The highest sampling frequency
+// found is the lowest that can be used without losing information.
+int32_t NewAudioConferenceMixerImpl::GetLowestMixingFrequency() const {
+  const int participantListFrequency =
+      GetLowestMixingFrequencyFromList(_participantList);
+  const int anonymousListFrequency =
+      GetLowestMixingFrequencyFromList(_additionalParticipantList);
+  const int highestFreq = (participantListFrequency > anonymousListFrequency)
+                              ? participantListFrequency
+                              : anonymousListFrequency;
+  // Check if the user specified a lowest mixing frequency.
+  if (_minimumMixingFreq != kLowestPossible) {
+    if (_minimumMixingFreq > highestFreq) {
+      return _minimumMixingFreq;
+    }
+  }
+  return highestFreq;
+}
+
+int32_t NewAudioConferenceMixerImpl::GetLowestMixingFrequencyFromList(
+    const MixerAudioSourceList& mixList) const {
+  int32_t highestFreq = 8000;
+  for (MixerAudioSourceList::const_iterator iter = mixList.begin();
+       iter != mixList.end(); ++iter) {
+    const int32_t neededFrequency = (*iter)->NeededFrequency(_id);
+    if (neededFrequency > highestFreq) {
+      highestFreq = neededFrequency;
+    }
+  }
+  return highestFreq;
+}
+
+void NewAudioConferenceMixerImpl::UpdateToMix(
+    AudioFrameList* mixList,
+    AudioFrameList* rampOutList,
+    std::map<int, MixerAudioSource*>* mixParticipantList,
+    size_t* maxAudioFrameCounter) const {
+  WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
+               "UpdateToMix(mixList,rampOutList,mixParticipantList,%d)",
+               *maxAudioFrameCounter);
+  const size_t mixListStartSize = mixList->size();
+  AudioFrameList activeList;
+  // Struct needed by the passive lists to keep track of which AudioFrame
+  // belongs to which MixerAudioSource.
+  ParticipantFrameStructList passiveWasNotMixedList;
+  ParticipantFrameStructList passiveWasMixedList;
+  for (MixerAudioSourceList::const_iterator participant =
+           _participantList.begin();
+       participant != _participantList.end(); ++participant) {
+    // Stop keeping track of passive participants if there are already
+    // enough participants available (they wont be mixed anyway).
+    bool mustAddToPassiveList =
+        (*maxAudioFrameCounter >
+         (activeList.size() + passiveWasMixedList.size() +
+          passiveWasNotMixedList.size()));
+
+    bool wasMixed = false;
+    wasMixed = (*participant)->_mixHistory->WasMixed();
+    AudioFrame* audioFrame = NULL;
+    if (_audioFramePool->PopMemory(audioFrame) == -1) {
+      WEBRTC_TRACE(kTraceMemory, kTraceAudioMixerServer, _id,
+                   "failed PopMemory() call");
+      assert(false);
+      return;
+    }
+    audioFrame->sample_rate_hz_ = _outputFrequency;
+
+    auto ret = (*participant)->GetAudioFrameWithMuted(_id, audioFrame);
+    if (ret == MixerAudioSource::AudioFrameInfo::kError) {
+      WEBRTC_TRACE(kTraceWarning, kTraceAudioMixerServer, _id,
+                   "failed to GetAudioFrameWithMuted() from participant");
+      _audioFramePool->PushMemory(audioFrame);
+      continue;
+    }
+    const bool muted = (ret == MixerAudioSource::AudioFrameInfo::kMuted);
+    if (_participantList.size() != 1) {
+      // TODO(wu): Issue 3390, add support for multiple participants case.
+      audioFrame->ntp_time_ms_ = -1;
+    }
+
+    // TODO(henrike): this assert triggers in some test cases where SRTP is
+    // used which prevents NetEQ from making a VAD. Temporarily disable this
+    // assert until the problem is fixed on a higher level.
+    // assert(audioFrame->vad_activity_ != AudioFrame::kVadUnknown);
+    if (audioFrame->vad_activity_ == AudioFrame::kVadUnknown) {
+      WEBRTC_TRACE(kTraceWarning, kTraceAudioMixerServer, _id,
+                   "invalid VAD state from participant");
+    }
+
+    if (audioFrame->vad_activity_ == AudioFrame::kVadActive) {
+      if (!wasMixed && !muted) {
+        RampIn(*audioFrame);
+      }
+
+      if (activeList.size() >= *maxAudioFrameCounter) {
+        // There are already more active participants than should be
+        // mixed. Only keep the ones with the highest energy.
+        AudioFrameList::iterator replaceItem;
+        uint32_t lowestEnergy = muted ? 0 : CalculateEnergy(*audioFrame);
+
+        bool found_replace_item = false;
+        for (AudioFrameList::iterator iter = activeList.begin();
+             iter != activeList.end(); ++iter) {
+          const uint32_t energy = muted ? 0 : CalculateEnergy(*iter->frame);
+          if (energy < lowestEnergy) {
+            replaceItem = iter;
+            lowestEnergy = energy;
+            found_replace_item = true;
+          }
+        }
+        if (found_replace_item) {
+          RTC_DCHECK(!muted);  // Cannot replace with a muted frame.
+          FrameAndMuteInfo replaceFrame = *replaceItem;
+
+          bool replaceWasMixed = false;
+          std::map<int, MixerAudioSource*>::const_iterator it =
+              mixParticipantList->find(replaceFrame.frame->id_);
+
+          // When a frame is pushed to |activeList| it is also pushed
+          // to mixParticipantList with the frame's id. This means
+          // that the Find call above should never fail.
+          assert(it != mixParticipantList->end());
+          replaceWasMixed = it->second->_mixHistory->WasMixed();
+
+          mixParticipantList->erase(replaceFrame.frame->id_);
+          activeList.erase(replaceItem);
+
+          activeList.push_front(FrameAndMuteInfo(audioFrame, muted));
+          (*mixParticipantList)[audioFrame->id_] = *participant;
+          assert(mixParticipantList->size() <=
+                 kMaximumAmountOfMixedParticipants);
+
+          if (replaceWasMixed) {
+            if (!replaceFrame.muted) {
+              RampOut(*replaceFrame.frame);
+            }
+            rampOutList->push_back(replaceFrame);
+            assert(rampOutList->size() <= kMaximumAmountOfMixedParticipants);
+          } else {
+            _audioFramePool->PushMemory(replaceFrame.frame);
+          }
+        } else {
+          if (wasMixed) {
+            if (!muted) {
+              RampOut(*audioFrame);
+            }
+            rampOutList->push_back(FrameAndMuteInfo(audioFrame, muted));
+            assert(rampOutList->size() <= kMaximumAmountOfMixedParticipants);
+          } else {
+            _audioFramePool->PushMemory(audioFrame);
+          }
+        }
+      } else {
+        activeList.push_front(FrameAndMuteInfo(audioFrame, muted));
+        (*mixParticipantList)[audioFrame->id_] = *participant;
+        assert(mixParticipantList->size() <= kMaximumAmountOfMixedParticipants);
+      }
+    } else {
+      if (wasMixed) {
+        ParticipantFrameStruct* part_struct =
+            new ParticipantFrameStruct(*participant, audioFrame, muted);
+        passiveWasMixedList.push_back(part_struct);
+      } else if (mustAddToPassiveList) {
+        if (!muted) {
+          RampIn(*audioFrame);
+        }
+        ParticipantFrameStruct* part_struct =
+            new ParticipantFrameStruct(*participant, audioFrame, muted);
+        passiveWasNotMixedList.push_back(part_struct);
+      } else {
+        _audioFramePool->PushMemory(audioFrame);
+      }
+    }
+  }
+  assert(activeList.size() <= *maxAudioFrameCounter);
+  // At this point it is known which participants should be mixed. Transfer
+  // this information to this functions output parameters.
+  for (AudioFrameList::const_iterator iter = activeList.begin();
+       iter != activeList.end(); ++iter) {
+    mixList->push_back(*iter);
+  }
+  activeList.clear();
+  // Always mix a constant number of AudioFrames. If there aren't enough
+  // active participants mix passive ones. Starting with those that was mixed
+  // last iteration.
+  for (ParticipantFrameStructList::const_iterator iter =
+           passiveWasMixedList.begin();
+       iter != passiveWasMixedList.end(); ++iter) {
+    if (mixList->size() < *maxAudioFrameCounter + mixListStartSize) {
+      mixList->push_back(FrameAndMuteInfo((*iter)->audioFrame, (*iter)->muted));
+      (*mixParticipantList)[(*iter)->audioFrame->id_] = (*iter)->participant;
+      assert(mixParticipantList->size() <= kMaximumAmountOfMixedParticipants);
+    } else {
+      _audioFramePool->PushMemory((*iter)->audioFrame);
+    }
+    delete *iter;
+  }
+  // And finally the ones that have not been mixed for a while.
+  for (ParticipantFrameStructList::const_iterator iter =
+           passiveWasNotMixedList.begin();
+       iter != passiveWasNotMixedList.end(); ++iter) {
+    if (mixList->size() < *maxAudioFrameCounter + mixListStartSize) {
+      mixList->push_back(FrameAndMuteInfo((*iter)->audioFrame, (*iter)->muted));
+      (*mixParticipantList)[(*iter)->audioFrame->id_] = (*iter)->participant;
+      assert(mixParticipantList->size() <= kMaximumAmountOfMixedParticipants);
+    } else {
+      _audioFramePool->PushMemory((*iter)->audioFrame);
+    }
+    delete *iter;
+  }
+  assert(*maxAudioFrameCounter + mixListStartSize >= mixList->size());
+  *maxAudioFrameCounter += mixListStartSize - mixList->size();
+}
+
+void NewAudioConferenceMixerImpl::GetAdditionalAudio(
+    AudioFrameList* additionalFramesList) const {
+  WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
+               "GetAdditionalAudio(additionalFramesList)");
+  // The GetAudioFrameWithMuted() callback may result in the participant being
+  // removed from additionalParticipantList_. If that happens it will
+  // invalidate any iterators. Create a copy of the participants list such
+  // that the list of participants can be traversed safely.
+  MixerAudioSourceList additionalParticipantList;
+  additionalParticipantList.insert(additionalParticipantList.begin(),
+                                   _additionalParticipantList.begin(),
+                                   _additionalParticipantList.end());
+
+  for (MixerAudioSourceList::const_iterator participant =
+           additionalParticipantList.begin();
+       participant != additionalParticipantList.end(); ++participant) {
+    AudioFrame* audioFrame = NULL;
+    if (_audioFramePool->PopMemory(audioFrame) == -1) {
+      WEBRTC_TRACE(kTraceMemory, kTraceAudioMixerServer, _id,
+                   "failed PopMemory() call");
+      assert(false);
+      return;
+    }
+    audioFrame->sample_rate_hz_ = _outputFrequency;
+    auto ret = (*participant)->GetAudioFrameWithMuted(_id, audioFrame);
+    if (ret == MixerAudioSource::AudioFrameInfo::kError) {
+      WEBRTC_TRACE(kTraceWarning, kTraceAudioMixerServer, _id,
+                   "failed to GetAudioFrameWithMuted() from participant");
+      _audioFramePool->PushMemory(audioFrame);
+      continue;
+    }
+    if (audioFrame->samples_per_channel_ == 0) {
+      // Empty frame. Don't use it.
+      _audioFramePool->PushMemory(audioFrame);
+      continue;
+    }
+    additionalFramesList->push_back(FrameAndMuteInfo(
+        audioFrame, ret == MixerAudioSource::AudioFrameInfo::kMuted));
+  }
+}
+
+void NewAudioConferenceMixerImpl::UpdateMixedStatus(
+    const std::map<int, MixerAudioSource*>& mixedParticipantsMap) const {
+  WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
+               "UpdateMixedStatus(mixedParticipantsMap)");
+  assert(mixedParticipantsMap.size() <= kMaximumAmountOfMixedParticipants);
+
+  // Loop through all participants. If they are in the mix map they
+  // were mixed.
+  for (MixerAudioSourceList::const_iterator participant =
+           _participantList.begin();
+       participant != _participantList.end(); ++participant) {
+    bool isMixed = false;
+    for (std::map<int, MixerAudioSource*>::const_iterator it =
+             mixedParticipantsMap.begin();
+         it != mixedParticipantsMap.end(); ++it) {
+      if (it->second == *participant) {
+        isMixed = true;
+        break;
+      }
+    }
+    (*participant)->_mixHistory->SetIsMixed(isMixed);
+  }
+}
+
+void NewAudioConferenceMixerImpl::ClearAudioFrameList(
+    AudioFrameList* audioFrameList) const {
+  WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
+               "ClearAudioFrameList(audioFrameList)");
+  for (AudioFrameList::iterator iter = audioFrameList->begin();
+       iter != audioFrameList->end(); ++iter) {
+    _audioFramePool->PushMemory(iter->frame);
+  }
+  audioFrameList->clear();
+}
+
+bool NewAudioConferenceMixerImpl::IsParticipantInList(
+    const MixerAudioSource& participant,
+    const MixerAudioSourceList& participantList) const {
+  WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
+               "IsParticipantInList(participant,participantList)");
+  for (MixerAudioSourceList::const_iterator iter = participantList.begin();
+       iter != participantList.end(); ++iter) {
+    if (&participant == *iter) {
+      return true;
+    }
+  }
+  return false;
+}
+
+bool NewAudioConferenceMixerImpl::AddParticipantToList(
+    MixerAudioSource* participant,
+    MixerAudioSourceList* participantList) const {
+  WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
+               "AddParticipantToList(participant, participantList)");
+  participantList->push_back(participant);
+  // Make sure that the mixed status is correct for new MixerAudioSource.
+  participant->_mixHistory->ResetMixedStatus();
+  return true;
+}
+
+bool NewAudioConferenceMixerImpl::RemoveParticipantFromList(
+    MixerAudioSource* participant,
+    MixerAudioSourceList* participantList) const {
+  WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
+               "RemoveParticipantFromList(participant, participantList)");
+  for (MixerAudioSourceList::iterator iter = participantList->begin();
+       iter != participantList->end(); ++iter) {
+    if (*iter == participant) {
+      participantList->erase(iter);
+      // Participant is no longer mixed, reset to default.
+      participant->_mixHistory->ResetMixedStatus();
+      return true;
+    }
+  }
+  return false;
+}
+
+int32_t NewAudioConferenceMixerImpl::MixFromList(
+    AudioFrame* mixedAudio,
+    const AudioFrameList& audioFrameList) const {
+  WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
+               "MixFromList(mixedAudio, audioFrameList)");
+  if (audioFrameList.empty())
+    return 0;
+
+  uint32_t position = 0;
+
+  if (_numMixedParticipants == 1) {
+    mixedAudio->timestamp_ = audioFrameList.front().frame->timestamp_;
+    mixedAudio->elapsed_time_ms_ =
+        audioFrameList.front().frame->elapsed_time_ms_;
+  } else {
+    // TODO(wu): Issue 3390.
+    // Audio frame timestamp is only supported in one channel case.
+    mixedAudio->timestamp_ = 0;
+    mixedAudio->elapsed_time_ms_ = -1;
+  }
+
+  for (AudioFrameList::const_iterator iter = audioFrameList.begin();
+       iter != audioFrameList.end(); ++iter) {
+    if (position >= kMaximumAmountOfMixedParticipants) {
+      WEBRTC_TRACE(
+          kTraceMemory, kTraceAudioMixerServer, _id,
+          "Trying to mix more than max amount of mixed participants:%d!",
+          kMaximumAmountOfMixedParticipants);
+      // Assert and avoid crash
+      assert(false);
+      position = 0;
+    }
+    if (!iter->muted) {
+      MixFrames(mixedAudio, iter->frame, use_limiter_);
+    }
+
+    position++;
+  }
+
+  return 0;
+}
+
+// TODO(andrew): consolidate this function with MixFromList.
+int32_t NewAudioConferenceMixerImpl::MixAnonomouslyFromList(
+    AudioFrame* mixedAudio,
+    const AudioFrameList& audioFrameList) const {
+  WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
+               "MixAnonomouslyFromList(mixedAudio, audioFrameList)");
+
+  if (audioFrameList.empty())
+    return 0;
+
+  for (AudioFrameList::const_iterator iter = audioFrameList.begin();
+       iter != audioFrameList.end(); ++iter) {
+    if (!iter->muted) {
+      MixFrames(mixedAudio, iter->frame, use_limiter_);
+    }
+  }
+  return 0;
+}
+
+bool NewAudioConferenceMixerImpl::LimitMixedAudio(
+    AudioFrame* mixedAudio) const {
+  if (!use_limiter_) {
+    return true;
+  }
+
+  // Smoothly limit the mixed frame.
+  const int error = _limiter->ProcessStream(mixedAudio);
+
+  // And now we can safely restore the level. This procedure results in
+  // some loss of resolution, deemed acceptable.
+  //
+  // It's possible to apply the gain in the AGC (with a target level of 0 dbFS
+  // and compression gain of 6 dB). However, in the transition frame when this
+  // is enabled (moving from one to two participants) it has the potential to
+  // create discontinuities in the mixed frame.
+  //
+  // Instead we double the frame (with addition since left-shifting a
+  // negative value is undefined).
+  *mixedAudio += *mixedAudio;
+
+  if (error != _limiter->kNoError) {
+    WEBRTC_TRACE(kTraceError, kTraceAudioMixerServer, _id,
+                 "Error from AudioProcessing: %d", error);
+    assert(false);
+    return false;
+  }
+  return true;
+}
+}  // namespace webrtc