Implement runtime audio post-processing pipeline. See go/cast_audio.json

chromecast/media/cma/backend/alsa/post_processors/governor_shlib.cc

+// Copyright 2017 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 <memory>
+#include <string>
+
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/values.h"
+#include "chromecast/base/serializers.h"
+#include "chromecast/media/cma/backend/alsa/slew_volume.h"
+#include "chromecast/public/media/audio_post_processor_shlib.h"
+
+namespace chromecast {
+namespace media {
+
+namespace {
+const int kNoSampleRate = -1;
+
+// Configuration strings:
+const char kOnsetVolumeKey[] = "onset_volume";
+const char kClampMultiplierKey[] = "clamp_multiplier";
+
+}  // namespace
+
+// Provides a flat reduction in output volume if the input volume is above a
+// given threshold.
+// Used to protect speakers at high output levels
+// while providing dyanmic range at low output level.
+// The configuration string for this plugin is:
+//  {"onset_volume": |VOLUME_TO_CLAMP|, "clamp_multiplier": |CLAMP_MULTIPLIER|}
+// Input volumes > |VOLUME_TO_CLAMP| will be attenuated by |CLAMP_MULTIPLIER|.
+class Governor : public AudioPostProcessor {
+ public:
+  Governor(const std::string& config, int channels);
+  ~Governor() override;
+
+  bool SetSampleRate(int sample_rate) override;
+  int ProcessFrames(uint8_t* data, int frames, float volume) override;
+  int GetRingingTimeInFrames() override;
+
+ private:
+  float GetGovernorMultiplier();
+
+  int channels_;
+  int sample_rate_;
+  float volume_;
+  double onset_volume_;
+  double clamp_multiplier_;
+  SlewVolume governor_;
+  DISALLOW_COPY_AND_ASSIGN(Governor);
+};
+
+Governor::Governor(const std::string& config, int channels)
+    : channels_(channels), sample_rate_(kNoSampleRate), volume_(1.0) {
+  auto config_dict = base::DictionaryValue::From(DeserializeFromJson(config));
+  CHECK(config_dict) << "Governor config is not valid json: " << config;
+  CHECK(config_dict->GetDouble(kOnsetVolumeKey, &onset_volume_));
+  CHECK(config_dict->GetDouble(kClampMultiplierKey, &clamp_multiplier_));
+  DCHECK_EQ(channels_, 2);
+  governor_.SetVolume(1.0);
+  LOG(INFO) << "Created a governor: onset_volume = " << onset_volume_
+            << ", clamp_multiplier = " << clamp_multiplier_;
+}
+
+Governor::~Governor() = default;
+
+bool Governor::SetSampleRate(int sample_rate) {
+  sample_rate_ = sample_rate;
+  governor_.SetSampleRate(sample_rate);

[wzhong, 2017/03/27 14:23:43]

return governor_.SetSampleRate(sample_rate);

[bshaya, 2017/03/27 21:00:26]

SlewVolume::SetSampleRate has void return type but Governor::SetSampleRate
returns bool.

+  return true;
+}
+
+int Governor::ProcessFrames(uint8_t* data, int frames, float volume) {
+  if (volume != volume_) {
+    volume_ = volume;
+    governor_.SetVolume(GetGovernorMultiplier());
+  }
+
+  governor_.ProcessInterleaved(reinterpret_cast<int32_t*>(data), frames);
+  return 0;  // No delay in this pipeline.

[wzhong, 2017/03/27 14:23:43]

return governor_.ProcessInterleaved(reinterpret_cast<int32_t*>(data), frames);

[bshaya, 2017/03/27 21:00:26]

SlewVolume::ProcessInterleaved returns bool indicating error, but
AudioPostProcessor::ProcessFrames returns int number of frames of delay.

+}
+
+int Governor::GetRingingTimeInFrames() {
+  return 0;
+}
+
+float Governor::GetGovernorMultiplier() {
+  if (volume_ >= onset_volume_) {
+    return clamp_multiplier_;
+  }
+  return 1.0;
+}
+
+}  // namespace media
+}  // namespace chromecast
+
+chromecast::media::AudioPostProcessor* AudioPostProcessorShlib_Create(
+    const std::string& config,
+    int channels) {
+  return static_cast<chromecast::media::AudioPostProcessor*>(
+      new chromecast::media::Governor(config, channels));
+}