Simplifications of the mixing algorithm.

webrtc/modules/audio_mixer/audio_mixer_impl.h

Index: webrtc/modules/audio_mixer/audio_mixer_impl.h
diff --git a/webrtc/modules/audio_mixer/audio_mixer_impl.h b/webrtc/modules/audio_mixer/audio_mixer_impl.h
index 6f612ca9abea0ca713efefd23611965ed0080d27..ac4af639b83c5c6dbea8df18d82163566a82d147 100644
--- a/webrtc/modules/audio_mixer/audio_mixer_impl.h
+++ b/webrtc/modules/audio_mixer/audio_mixer_impl.h
@@ -26,13 +26,7 @@ namespace webrtc {
 class AudioProcessing;
 class CriticalSectionWrapper;
 
-struct FrameAndMuteInfo {
-  FrameAndMuteInfo(AudioFrame* f, bool m) : frame(f), muted(m) {}
-  AudioFrame* frame;
-  bool muted;
-};
-
-typedef std::list<FrameAndMuteInfo> AudioFrameList;

[aleloi, 2016/08/31 11:34:29]

Mixing structure is a little simplified. Mute information is only used
inside of Get*AnonymousAudio. Muted frames are filtered out one step
earlier. Therefore a |muted| field is no longer needed here, and the
FrameAndMuteInfo struct can be replaced by a single frame.

+typedef std::list<AudioFrame*> AudioFrameList;

[ivoc, 2016/08/31 15:01:06]

I think list is in many cases less efficient than vector (mostly due to
caching), are we sure that list is the right choice here? If you're interested
there's an interesting talk by Bjarne Stroustrup on the topic:
https://www.youtube.com/watch?v=YQs6IC-vgmo

[aleloi, 2016/08/31 15:25:34]

Will watch!

I think the right way is to make a performance test with lots of participants
and see what performs better. In addition: our typical use case should be a
small number of participants, so we may want the structure that performs best at
small sizes.

The list has been here since the beginning. I thought it was because of the
removals in SetMixedStatus(..., false). But maybe vectors are better anyway.

[aleloi, 2016/09/01 13:20:43]

Got convinced by watching. Changed to vector.

 typedef std::list<MixerAudioSource*> MixerAudioSourceList;
 
 // Cheshire cat implementation of MixerAudioSource's non virtual functions.
@@ -86,11 +80,10 @@ class AudioMixerImpl : public AudioMixer {
   int32_t SetOutputFrequency(const Frequency& frequency);
   Frequency OutputFrequency() const;
 
-  // Compute what audio sources to mix from audio_source_list_. Ramp in
-  // and out. Update mixed status. maxAudioFrameCounter specifies how
-  // many participants are allowed to be mixed.
-  AudioFrameList UpdateToMix(size_t maxAudioFrameCounter) const
-      EXCLUSIVE_LOCKS_REQUIRED(crit_);
+  // Compute what audio sources to mix from audio_source_list_. Ramp
+  // in and out. Update mixed status. Mixes up to
+  // kMaximumAmountOfMixedAudioSources audio sources.
+  AudioFrameList GetNonAnonymousAudio() const EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
   // Return the lowest mixing frequency that can be used without having to
   // downsample any audio.
@@ -98,9 +91,9 @@ class AudioMixerImpl : public AudioMixer {
   int32_t GetLowestMixingFrequencyFromList(
       const MixerAudioSourceList& mixList) const;
 
-  // Return the AudioFrames that should be mixed anonymously.
-  void GetAdditionalAudio(AudioFrameList* additionalFramesList) const
-      EXCLUSIVE_LOCKS_REQUIRED(crit_);

[aleloi, 2016/08/31 11:34:29]

Made naming and signature more consistent between the Get*Audio
methods.

+  // Return the AudioFrames that should be mixed anonymously. Ramp in
+  // and out. Update mixed status.
+  AudioFrameList GetAnonymousAudio() const EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
   // This function returns true if it finds the MixerAudioSource in the
   // specified list of MixerAudioSources.
@@ -120,12 +113,6 @@ class AudioMixerImpl : public AudioMixer {
                              int32_t id,
                              bool use_limiter);
 
-  // Mix the AudioFrames stored in audioFrameList into mixedAudio. No
-  // record will be kept of this mix (e.g. the corresponding MixerAudioSources
-  // will not be marked as IsMixed()
-  int32_t MixAnonomouslyFromList(AudioFrame* mixedAudio,
-                                 const AudioFrameList& audioFrameList) const;
-

[aleloi, 2016/08/31 11:34:29]

Merged with MixFromList

   bool LimitMixedAudio(AudioFrame* mixedAudio) const;
 
   // Output level functions for VoEVolumeControl.