Enable renderer side mixing behind a flag.

content/renderer/media/audio_renderer_mixer_manager.cc

Index: content/renderer/media/audio_renderer_mixer_manager.cc
diff --git a/content/renderer/media/audio_renderer_mixer_manager.cc b/content/renderer/media/audio_renderer_mixer_manager.cc
new file mode 100644
index 0000000000000000000000000000000000000000..03e638e7799dafc54074c53e6c8da9800a72fc19
--- /dev/null
+++ b/content/renderer/media/audio_renderer_mixer_manager.cc
@@ -0,0 +1,73 @@
+// 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 "content/renderer/media/audio_renderer_mixer_manager.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "content/renderer/media/audio_device_factory.h"
+#include "media/base/audio_renderer_mixer.h"
+#include "media/base/audio_renderer_mixer_input.h"
+
+namespace content {
+
+AudioRendererMixerManager::AudioRendererMixerManager(int hardware_sample_rate,
+                                                     int hardware_buffer_size)
+    : hardware_sample_rate_(hardware_sample_rate),
+      hardware_buffer_size_(hardware_buffer_size) {
+}
+
+AudioRendererMixerManager::~AudioRendererMixerManager() {
+  DCHECK(mixers_.empty());
+}
+
+media::AudioRendererMixerInput* AudioRendererMixerManager::CreateInput() {
+  return new media::AudioRendererMixerInput(
+      base::Bind(
+          &AudioRendererMixerManager::GetMixer, base::Unretained(this)),
+      base::Bind(
+          &AudioRendererMixerManager::RemoveMixer, base::Unretained(this)));
+}
+
+media::AudioRendererMixer* AudioRendererMixerManager::GetMixer(
+    const media::AudioParameters& params) {
+  base::AutoLock auto_lock(mixers_lock_);
+
+  AudioRendererMixerMap::iterator it = mixers_.find(params);
+  if (it != mixers_.end()) {
+    it->second.ref_count++;
+    return it->second.mixer;
+  }
+
+  // Create output parameters based on the audio hardware configuration for
+  // passing on to the output sink.  Force to 16-bit output for now since we
+  // know that works well for WebAudio and WebRTC.
+  media::AudioParameters output_params(
+      media::AudioParameters::AUDIO_PCM_LOW_LATENCY, params.channel_layout(),
+      hardware_sample_rate_, 16, hardware_buffer_size_);
+
+  media::AudioRendererMixer* mixer = new media::AudioRendererMixer(
+      params, output_params, AudioDeviceFactory::Create());
+
+  AudioRendererMixerReference mixer_reference = { mixer, 1 };
+  mixers_[params] = mixer_reference;
+  return mixer;
+}
+
+void AudioRendererMixerManager::RemoveMixer(
+    const media::AudioParameters& params) {
+  base::AutoLock auto_lock(mixers_lock_);
+
+  AudioRendererMixerMap::iterator it = mixers_.find(params);
+  DCHECK(it != mixers_.end());
+
+  // Only remove the mixer if AudioRendererMixerManager is the last owner.
+  it->second.ref_count--;
+  if (it->second.ref_count == 0) {
+    delete it->second.mixer;
+    mixers_.erase(it);
+  }
+}
+
+}  // namespace content