Mixing audio with different latency requirements

media/base/audio_renderer_mixer.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/base/audio_renderer_mixer.h"
 
 #include <cmath>
 
 #include "base/bind.h"
 #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

[DaleCurtis, 2016/06/29 17:08:55]

Feels like there should be some UMA built in for this, but don't have a better
suggestion.

+// 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();
 }
 
 AudioRendererMixer::~AudioRendererMixer() {
   // AudioRendererSink must be stopped before mixer is destructed.
   audio_sink_->Stop();
 
   // Ensure that all mixer inputs have removed themselves prior to destruction.
@@ skipping 26 matching lines @@
                                      // size requests, disabling FIFO.
                                      new LoopbackAudioConverter(
                                          input_params, output_params_, true))));
       converter = result.first;
 
       // Add newly-created resampler as an input to the master mixer.
       master_converter_.AddInput(converter->second.get());
     }
     converter->second->AddInput(input);
   }
+
+  input_count_tracker_->Increment();
 }
 
 void AudioRendererMixer::RemoveMixerInput(
     const AudioParameters& input_params,
     AudioConverter::InputCallback* input) {
   base::AutoLock auto_lock(lock_);
 
   int input_sample_rate = input_params.sample_rate();
   if (is_master_sample_rate(input_sample_rate)) {
     master_converter_.RemoveInput(input);
   } else {
     AudioConvertersMap::iterator converter =
         converters_.find(input_sample_rate);
     DCHECK(converter != converters_.end());
     converter->second->RemoveInput(input);
     if (converter->second->empty()) {
       // Remove converter when it's empty.
       master_converter_.RemoveInput(converter->second.get());
       converters_.erase(converter);
     }
   }
+
+  input_count_tracker_->Decrement();
 }
 
 void AudioRendererMixer::AddErrorCallback(const base::Closure& error_cb) {
   base::AutoLock auto_lock(lock_);
   error_callbacks_.push_back(error_cb);
 }
 
 void AudioRendererMixer::RemoveErrorCallback(const base::Closure& error_cb) {
   base::AutoLock auto_lock(lock_);
   for (ErrorCallbackList::iterator it = error_callbacks_.begin();
@@ skipping 39 matching lines @@
 }
 
 void AudioRendererMixer::OnRenderError() {
   // Call each mixer input and signal an error.
   base::AutoLock auto_lock(lock_);
   for (const auto& cb : error_callbacks_)
     cb.Run();
 }
 
 }  // namespace media