AudioMixer interface cleanup suggestions

webrtc/modules/audio_mixer/audio_mixer_impl.cc

Index: webrtc/modules/audio_mixer/audio_mixer_impl.cc
diff --git a/webrtc/modules/audio_mixer/audio_mixer_impl.cc b/webrtc/modules/audio_mixer/audio_mixer_impl.cc
index 44e04fa32d4aa6de25d5297b0cdc74154f1368ca..57a6e44f36d32f22e33784ebd7359204ab3ebbc7 100644
--- a/webrtc/modules/audio_mixer/audio_mixer_impl.cc
+++ b/webrtc/modules/audio_mixer/audio_mixer_impl.cc
@@ -23,11 +23,14 @@ namespace {
 
 class SourceFrame {
  public:
+  // !!!: Style guide is against abbreviations. Plus these don't make sense. 'p'
+  // for MixerAudioSource?
   SourceFrame(MixerAudioSource* p, AudioFrame* a, bool m, bool was_mixed_before)
       : audio_source_(p),
         audio_frame_(a),
         muted_(m),
         was_mixed_before_(was_mixed_before) {
+    // !!!: Here would be a good place to check pointers aren't null.
     if (!muted_) {
       energy_ = NewMixerCalculateEnergy(*a);
     }
@@ -44,6 +47,7 @@ class SourceFrame {
         energy_(energy),
         was_mixed_before_(was_mixed_before) {}
 
+  // !!!: Capital S here.
   // a.shouldMixBefore(b) is used to select mixer participants.
   bool shouldMixBefore(const SourceFrame& other) const {
     if (muted_ != other.muted_) {
@@ -60,6 +64,7 @@ class SourceFrame {
     return energy_ > other.energy_;
   }
 
+  // !!!: You should have accessors for these, so that you can e.g. check that
   MixerAudioSource* audio_source_;
   AudioFrame* audio_frame_;
   bool muted_;
@@ -67,6 +72,7 @@ class SourceFrame {
   bool was_mixed_before_;
 };
 
+// !!!: The term is usually "Downmix".
 // Remixes a frame between stereo and mono.
 void RemixFrame(AudioFrame* frame, size_t number_of_channels) {
   RTC_DCHECK(number_of_channels == 1 || number_of_channels == 2);
@@ -97,8 +103,10 @@ int32_t MixFromList(AudioFrame* mixed_audio,
                     const AudioFrameList& audio_frame_list,
                     int32_t id,
                     bool use_limiter) {
+  // !!!: Don't use WEBRTC_TRACE in new code
   WEBRTC_TRACE(kTraceStream, kTraceAudioMixerServer, id,
                "MixFromList(mixed_audio, audio_frame_list)");
+  // !!!: Consistently use {} for one-liners, or don't.
   if (audio_frame_list.empty())
     return 0;
 
@@ -198,6 +206,7 @@ void AudioMixerImpl::Mix(int sample_rate,
   }
 
   if (OutputFrequency() != sample_rate) {
+    // !!!: Dangerous cast!
     SetOutputFrequency(static_cast<Frequency>(sample_rate));
   }