Mixing audio with different latency requirements

media/base/audio_renderer_mixer.cc

Index: media/base/audio_renderer_mixer.cc
diff --git a/media/base/audio_renderer_mixer.cc b/media/base/audio_renderer_mixer.cc
index 008fcce793320af352ff80ab17ff51c8ea17cff3..93d8c751472d81cc4c65ac31bb46cba49fc3d501 100644
--- a/media/base/audio_renderer_mixer.cc
+++ b/media/base/audio_renderer_mixer.cc
@@ -10,20 +10,55 @@
 #include "base/bind_helpers.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
 
 namespace media {
 
 enum { kPauseDelaySeconds = 10 };
 
+// Tracks the maximum value of a counter and logs it into a UMA histogram upon
+// each increase of the maximum. NOT thread-safe, make sure it is used under
+// lock.
+class AudioRendererMixer::UMAMaxValueTracker {
+ public:
+  UMAMaxValueTracker(const UmaLogCallback& log_callback)
+      : log_callback_(log_callback), count_(0), max_count_(0) {}
+
+  ~UMAMaxValueTracker() {}
+
+  // Increments the counter, updates the maximum.
+  void Increment() {
+    ++count_;
+    if (max_count_ < count_) {
+      max_count_ = count_;
+      log_callback_.Run(max_count_);
+    }
+  }
+
+  // Decrements the counter.
+  void Decrement() {
+    DCHECK_GE(count_, 0);
+    --count_;
+  }
+
+ private:
+  const UmaLogCallback log_callback_;
+  int count_;
+  int max_count_;
+  DISALLOW_COPY_AND_ASSIGN(UMAMaxValueTracker);
+};
+
 AudioRendererMixer::AudioRendererMixer(const AudioParameters& output_params,
-                                       scoped_refptr<AudioRendererSink> sink)
+                                       scoped_refptr<AudioRendererSink> sink,
+                                       const UmaLogCallback& log_callback)
     : output_params_(output_params),
       audio_sink_(std::move(sink)),
       master_converter_(output_params, output_params, true),
       pause_delay_(base::TimeDelta::FromSeconds(kPauseDelaySeconds)),
       last_play_time_(base::TimeTicks::Now()),
       // Initialize |playing_| to true since Start() results in an auto-play.
-      playing_(true) {
+      playing_(true),
+      input_count_tracker_(new UMAMaxValueTracker(log_callback)) {
   DCHECK(audio_sink_);
   audio_sink_->Initialize(output_params, this);
   audio_sink_->Start();
@@ -70,6 +105,8 @@ void AudioRendererMixer::AddMixerInput(const AudioParameters& input_params,
     }
     converter->second->AddInput(input);
   }
+
+  input_count_tracker_->Increment();
 }
 
 void AudioRendererMixer::RemoveMixerInput(
@@ -91,6 +128,8 @@ void AudioRendererMixer::RemoveMixerInput(
       converters_.erase(converter);
     }
   }
+
+  input_count_tracker_->Decrement();
 }
 
 void AudioRendererMixer::AddErrorCallback(const base::Closure& error_cb) {