Stylizing AudioConferenceMixer.

webrtc/modules/audio_conference_mixer/source/audio_conference_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 52 matching lines @@
 }  // namespace
 
 MixerParticipant::MixerParticipant()
     : _mixHistory(new MixHistory()) {
 }
 
 MixerParticipant::~MixerParticipant() {
     delete _mixHistory;
 }
 
-int32_t MixerParticipant::IsMixed(bool& mixed) const {
-    return _mixHistory->IsMixed(mixed);
+bool MixerParticipant::IsMixed() const {
+    return _mixHistory->IsMixed();
 }
 
 MixHistory::MixHistory()
     : _isMixed(0) {
 }
 
 MixHistory::~MixHistory() {
 }
 
-int32_t MixHistory::IsMixed(bool& mixed) const {
-    mixed = _isMixed;
-    return 0;
+bool MixHistory::IsMixed() const {
+    return _isMixed;
 }
 
-int32_t MixHistory::WasMixed(bool& wasMixed) const {
+bool MixHistory::WasMixed() const {
     // Was mixed is the same as is mixed depending on perspective. This function
     // is for the perspective of AudioConferenceMixerImpl.
-    return IsMixed(wasMixed);
+    return IsMixed();
 }
 
 int32_t MixHistory::SetIsMixed(const bool mixed) {
     _isMixed = mixed;
     return 0;
 }
 
 void MixHistory::ResetMixedStatus() {
     _isMixed = false;
 }
@@ skipping 146 matching lines @@
             default:
                 assert(false);
 
                 CriticalSectionScoped cs(_crit.get());
                 _processCalls--;
                 return -1;
             }
         }
 
         UpdateToMix(&mixList, &rampOutList, &mixedParticipantsMap,
-                    remainingParticipantsAllowedToMix);
+                    &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");
@@ skipping 17 matching lines @@
                                 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 <= kAudioProcMaxNativeSampleRateHz;
 
-        MixFromList(*mixedAudio, &mixList);
-        MixAnonomouslyFromList(*mixedAudio, &additionalFramesList);
-        MixAnonomouslyFromList(*mixedAudio, &rampOutList);
+        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.
-            if(!LimitMixedAudio(*mixedAudio))
+            if(!LimitMixedAudio(mixedAudio))
                 retval = -1;
         }
     }
 
     {
         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 retval;
 }
 
 int32_t AudioConferenceMixerImpl::RegisterMixedStreamCallback(
-    AudioMixerOutputReceiver& mixReceiver) {
+    AudioMixerOutputReceiver* mixReceiver) {
     CriticalSectionScoped cs(_cbCrit.get());
     if(_mixReceiver != NULL) {
         return -1;
     }
-    _mixReceiver = &mixReceiver;
+    _mixReceiver = mixReceiver;
     return 0;
 }
 
 int32_t AudioConferenceMixerImpl::UnRegisterMixedStreamCallback() {
     CriticalSectionScoped cs(_cbCrit.get());
     if(_mixReceiver == NULL) {
         return -1;
     }
     _mixReceiver = NULL;
     return 0;
 }
 
 int32_t AudioConferenceMixerImpl::SetOutputFrequency(
-    const Frequency frequency) {
+    const Frequency& frequency) {
     CriticalSectionScoped cs(_crit.get());
 
     _outputFrequency = frequency;
     _sampleSize =
         static_cast<size_t>((_outputFrequency*kProcessPeriodicityInMs) / 1000);
 
     return 0;
 }
 
 AudioConferenceMixer::Frequency
 AudioConferenceMixerImpl::OutputFrequency() const {
     CriticalSectionScoped cs(_crit.get());
     return _outputFrequency;
 }
 
 int32_t AudioConferenceMixerImpl::SetMixabilityStatus(
-    MixerParticipant& participant,
-    bool mixable) {
+    MixerParticipant* 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);
+            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);
@@ skipping 16 matching lines @@
             numMixedNonAnonymous + _additionalParticipantList.size();
     }
     // A MixerParticipant 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;
 }
 
-int32_t AudioConferenceMixerImpl::MixabilityStatus(
-    MixerParticipant& participant,
-    bool& mixable) {
+bool AudioConferenceMixerImpl::MixabilityStatus(
+    const MixerParticipant& participant) const {
     CriticalSectionScoped cs(_cbCrit.get());
-    mixable = IsParticipantInList(participant, &_participantList);
-    return 0;
+    return IsParticipantInList(participant, _participantList);
 }
 
 int32_t AudioConferenceMixerImpl::SetAnonymousMixabilityStatus(
-    MixerParticipant& participant, const bool anonymous) {
+    MixerParticipant* participant, bool anonymous) {
     CriticalSectionScoped cs(_cbCrit.get());
-    if(IsParticipantInList(participant, &_additionalParticipantList)) {
+    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;
         }
@@ skipping 11 matching lines @@
             _id,
             "participant must be registered before turning it into anonymous");
         // Setting anonymous status is only possible if MixerParticipant is
         // already registered.
         return -1;
     }
     return AddParticipantToList(participant, &_additionalParticipantList) ?
         0 : -1;
 }
 
-int32_t AudioConferenceMixerImpl::AnonymousMixabilityStatus(
-    MixerParticipant& participant, bool& mixable) {
+bool AudioConferenceMixerImpl::AnonymousMixabilityStatus(
+    const MixerParticipant& participant) const {
     CriticalSectionScoped cs(_cbCrit.get());
-    mixable = IsParticipantInList(participant,
-                                  &_additionalParticipantList);
-    return 0;
+    return IsParticipantInList(participant, _additionalParticipantList);
 }
 
 int32_t AudioConferenceMixerImpl::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 AudioConferenceMixerImpl::GetLowestMixingFrequency() {
+int32_t AudioConferenceMixerImpl::GetLowestMixingFrequency() const {
     const int participantListFrequency =
-        GetLowestMixingFrequencyFromList(&_participantList);
+        GetLowestMixingFrequencyFromList(_participantList);
     const int anonymousListFrequency =
-        GetLowestMixingFrequencyFromList(&_additionalParticipantList);
+        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 AudioConferenceMixerImpl::GetLowestMixingFrequencyFromList(
-    MixerParticipantList* mixList) {
+    const MixerParticipantList& mixList) const {
     int32_t highestFreq = 8000;
-    for (MixerParticipantList::iterator iter = mixList->begin();
-         iter != mixList->end();
+    for (MixerParticipantList::const_iterator iter = mixList.begin();
+         iter != mixList.end();
          ++iter) {
         const int32_t neededFrequency = (*iter)->NeededFrequency(_id);
         if(neededFrequency > highestFreq) {
             highestFreq = neededFrequency;
         }
     }
     return highestFreq;
 }
 
 void AudioConferenceMixerImpl::UpdateToMix(
     AudioFrameList* mixList,
     AudioFrameList* rampOutList,
     std::map<int, MixerParticipant*>* mixParticipantList,
-    size_t& maxAudioFrameCounter) {
+    size_t* maxAudioFrameCounter) const {
     WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
                  "UpdateToMix(mixList,rampOutList,mixParticipantList,%d)",
-                 maxAudioFrameCounter);
+                 *maxAudioFrameCounter);
     const size_t mixListStartSize = mixList->size();
     AudioFrameList activeList;
     // Struct needed by the passive lists to keep track of which AudioFrame
     // belongs to which MixerParticipant.
     ParticipantFramePairList passiveWasNotMixedList;
     ParticipantFramePairList passiveWasMixedList;
-    for (MixerParticipantList::iterator participant = _participantList.begin();
-         participant != _participantList.end();
+    for (MixerParticipantList::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 >
+        bool mustAddToPassiveList = (*maxAudioFrameCounter >
                                     (activeList.size() +
                                      passiveWasMixedList.size() +
                                      passiveWasNotMixedList.size()));
 
         bool wasMixed = false;
-        (*participant)->_mixHistory->WasMixed(wasMixed);
+        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;
 
-        if((*participant)->GetAudioFrame(_id,*audioFrame) != 0) {
+        if((*participant)->GetAudioFrame(_id, audioFrame) != 0) {
             WEBRTC_TRACE(kTraceWarning, kTraceAudioMixerServer, _id,
                          "failed to GetAudioFrame() from participant");
             _audioFramePool->PushMemory(audioFrame);
             continue;
         }
         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) {
                 RampIn(*audioFrame);
             }
 
-            if(activeList.size() >= maxAudioFrameCounter) {
+            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;
                 CalculateEnergy(*audioFrame);
                 uint32_t lowestEnergy = audioFrame->energy_;
 
                 bool found_replace_item = false;
                 for (AudioFrameList::iterator iter = activeList.begin();
                      iter != activeList.end();
                      ++iter) {
                     CalculateEnergy(**iter);
                     if((*iter)->energy_ < lowestEnergy) {
                         replaceItem = iter;
                         lowestEnergy = (*iter)->energy_;
                         found_replace_item = true;
                     }
                 }
                 if(found_replace_item) {
                     AudioFrame* replaceFrame = *replaceItem;
 
                     bool replaceWasMixed = false;
-                    std::map<int, MixerParticipant*>::iterator it =
+                    std::map<int, MixerParticipant*>::const_iterator it =
                         mixParticipantList->find(replaceFrame->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());
-                    it->second->_mixHistory->WasMixed(replaceWasMixed);
+                    replaceWasMixed = it->second->_mixHistory->WasMixed();
 
                     mixParticipantList->erase(replaceFrame->id_);
                     activeList.erase(replaceItem);
 
                     activeList.push_front(audioFrame);
                     (*mixParticipantList)[audioFrame->id_] = *participant;
                     assert(mixParticipantList->size() <=
                            kMaximumAmountOfMixedParticipants);
 
                     if (replaceWasMixed) {
@@ skipping 30 matching lines @@
                 RampIn(*audioFrame);
                 ParticipantFramePair* pair = new ParticipantFramePair;
                 pair->audioFrame  = audioFrame;
                 pair->participant = *participant;
                 passiveWasNotMixedList.push_back(pair);
             } else {
                 _audioFramePool->PushMemory(audioFrame);
             }
         }
     }
-    assert(activeList.size() <= maxAudioFrameCounter);
+    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::iterator iter = activeList.begin();
+    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 (ParticipantFramePairList::iterator iter = passiveWasMixedList.begin();
-         iter != passiveWasMixedList.end();
+    for (ParticipantFramePairList::const_iterator
+        iter = passiveWasMixedList.begin(); iter != passiveWasMixedList.end();
          ++iter) {
-        if(mixList->size() < maxAudioFrameCounter + mixListStartSize) {
+        if(mixList->size() < *maxAudioFrameCounter + mixListStartSize) {
             mixList->push_back((*iter)->audioFrame);
             (*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 (ParticipantFramePairList::iterator iter =
+    for (ParticipantFramePairList::const_iterator iter =
              passiveWasNotMixedList.begin();
          iter != passiveWasNotMixedList.end();
          ++iter) {
-        if(mixList->size() <  maxAudioFrameCounter + mixListStartSize) {
+        if(mixList->size() <  *maxAudioFrameCounter + mixListStartSize) {
           mixList->push_back((*iter)->audioFrame);
             (*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();
+    assert(*maxAudioFrameCounter + mixListStartSize >= mixList->size());
+    *maxAudioFrameCounter += mixListStartSize - mixList->size();
 }
 
 void AudioConferenceMixerImpl::GetAdditionalAudio(
-    AudioFrameList* additionalFramesList) {
+    AudioFrameList* additionalFramesList) const {
     WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
                  "GetAdditionalAudio(additionalFramesList)");
     // The GetAudioFrame() 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.
     MixerParticipantList additionalParticipantList;
     additionalParticipantList.insert(additionalParticipantList.begin(),
                                      _additionalParticipantList.begin(),
                                      _additionalParticipantList.end());
 
-    for (MixerParticipantList::iterator participant =
+    for (MixerParticipantList::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;
-        if((*participant)->GetAudioFrame(_id, *audioFrame) != 0) {
+        if((*participant)->GetAudioFrame(_id, audioFrame) != 0) {
             WEBRTC_TRACE(kTraceWarning, kTraceAudioMixerServer, _id,
                          "failed to GetAudioFrame() 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(audioFrame);
     }
 }
 
 void AudioConferenceMixerImpl::UpdateMixedStatus(
-    std::map<int, MixerParticipant*>& mixedParticipantsMap) {
+    const std::map<int, MixerParticipant*>& 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 (MixerParticipantList::iterator participant = _participantList.begin();
-         participant != _participantList.end();
+    for (MixerParticipantList::const_iterator
+        participant =_participantList.begin();
+        participant != _participantList.end();
          ++participant) {
         bool isMixed = false;
-        for (std::map<int, MixerParticipant*>::iterator it =
+        for (std::map<int, MixerParticipant*>::const_iterator it =
                  mixedParticipantsMap.begin();
              it != mixedParticipantsMap.end();
              ++it) {
           if (it->second == *participant) {
             isMixed = true;
             break;
           }
         }
         (*participant)->_mixHistory->SetIsMixed(isMixed);
     }
 }
 
 void AudioConferenceMixerImpl::ClearAudioFrameList(
-    AudioFrameList* audioFrameList) {
+    AudioFrameList* audioFrameList) const {
     WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
                  "ClearAudioFrameList(audioFrameList)");
     for (AudioFrameList::iterator iter = audioFrameList->begin();
          iter != audioFrameList->end();
          ++iter) {
         _audioFramePool->PushMemory(*iter);
     }
     audioFrameList->clear();
 }
 
 void AudioConferenceMixerImpl::UpdateVADPositiveParticipants(
-    AudioFrameList* mixList) {
+    AudioFrameList* mixList) const {
     WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
                  "UpdateVADPositiveParticipants(mixList)");
 
-    for (AudioFrameList::iterator iter = mixList->begin();
+    for (AudioFrameList::const_iterator iter = mixList->begin();
          iter != mixList->end();
          ++iter) {
         CalculateEnergy(**iter);
     }
 }
 
 bool AudioConferenceMixerImpl::IsParticipantInList(
-    MixerParticipant& participant,
-    MixerParticipantList* participantList) const {
+    const MixerParticipant& participant,
+    const MixerParticipantList& participantList) const {
     WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
                  "IsParticipantInList(participant,participantList)");
-    for (MixerParticipantList::const_iterator iter = participantList->begin();
-         iter != participantList->end();
+    for (MixerParticipantList::const_iterator iter = participantList.begin();
+         iter != participantList.end();
          ++iter) {
         if(&participant == *iter) {
             return true;
         }
     }
     return false;
 }
 
 bool AudioConferenceMixerImpl::AddParticipantToList(
-    MixerParticipant& participant,
-    MixerParticipantList* participantList) {
+    MixerParticipant* participant,
+    MixerParticipantList* participantList) const {
     WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
                  "AddParticipantToList(participant, participantList)");
-    participantList->push_back(&participant);
+    participantList->push_back(participant);
     // Make sure that the mixed status is correct for new MixerParticipant.
-    participant._mixHistory->ResetMixedStatus();
+    participant->_mixHistory->ResetMixedStatus();
     return true;
 }
 
 bool AudioConferenceMixerImpl::RemoveParticipantFromList(
-    MixerParticipant& participant,
-    MixerParticipantList* participantList) {
+    MixerParticipant* participant,
+    MixerParticipantList* participantList) const {
     WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
                  "RemoveParticipantFromList(participant, participantList)");
     for (MixerParticipantList::iterator iter = participantList->begin();
          iter != participantList->end();
          ++iter) {
-        if(*iter == &participant) {
+        if(*iter == participant) {
             participantList->erase(iter);
             // Participant is no longer mixed, reset to default.
-            participant._mixHistory->ResetMixedStatus();
+            participant->_mixHistory->ResetMixedStatus();
             return true;
         }
     }
     return false;
 }
 
 int32_t AudioConferenceMixerImpl::MixFromList(
-    AudioFrame& mixedAudio,
-    const AudioFrameList* audioFrameList) {
+    AudioFrame* mixedAudio,
+    const AudioFrameList& audioFrameList) const {
     WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
                  "MixFromList(mixedAudio, audioFrameList)");
-    if(audioFrameList->empty()) return 0;
+    if(audioFrameList.empty()) return 0;
 
     uint32_t position = 0;
 
     if (_numMixedParticipants == 1) {
-      mixedAudio.timestamp_ = audioFrameList->front()->timestamp_;
-      mixedAudio.elapsed_time_ms_ = audioFrameList->front()->elapsed_time_ms_;
+      mixedAudio->timestamp_ = audioFrameList.front()->timestamp_;
+      mixedAudio->elapsed_time_ms_ = audioFrameList.front()->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;
+      mixedAudio->timestamp_ = 0;
+      mixedAudio->elapsed_time_ms_ = -1;
     }
 
-    for (AudioFrameList::const_iterator iter = audioFrameList->begin();
-         iter != audioFrameList->end();
+    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;
         }
-        MixFrames(&mixedAudio, (*iter), use_limiter_);
+        MixFrames(mixedAudio, (*iter), use_limiter_);
 
         position++;
     }
 
     return 0;
 }
 
 // TODO(andrew): consolidate this function with MixFromList.
 int32_t AudioConferenceMixerImpl::MixAnonomouslyFromList(
-    AudioFrame& mixedAudio,
-    const AudioFrameList* audioFrameList) {
+    AudioFrame* mixedAudio,
+    const AudioFrameList& audioFrameList) const {
     WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, _id,
                  "MixAnonomouslyFromList(mixedAudio, audioFrameList)");
 
-    if(audioFrameList->empty()) return 0;
+    if(audioFrameList.empty()) return 0;
 
-    for (AudioFrameList::const_iterator iter = audioFrameList->begin();
-         iter != audioFrameList->end();
+    for (AudioFrameList::const_iterator iter = audioFrameList.begin();
+         iter != audioFrameList.end();
          ++iter) {
-        MixFrames(&mixedAudio, *iter, use_limiter_);
+        MixFrames(mixedAudio, *iter, use_limiter_);
     }
     return 0;
 }
 
-bool AudioConferenceMixerImpl::LimitMixedAudio(AudioFrame& mixedAudio) {
+bool AudioConferenceMixerImpl::LimitMixedAudio(AudioFrame* mixedAudio) const {
     if (!use_limiter_) {
       return true;
     }
 
     // Smoothly limit the mixed frame.
-    const int error = _limiter->ProcessStream(&mixedAudio);
+    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;
+    *mixedAudio += *mixedAudio;
 
     if(error != _limiter->kNoError) {
         WEBRTC_TRACE(kTraceError, kTraceAudioMixerServer, _id,
                      "Error from AudioProcessing: %d", error);
         assert(false);
         return false;
     }
     return true;
 }
 }  // namespace webrtc