Add a simple, safe gain PostProcessor.

chromecast/media/cma/backend/alsa/volume_map.cc

Index: chromecast/media/cma/backend/alsa/volume_map.cc
diff --git a/chromecast/media/cma/backend/alsa/volume_map.cc b/chromecast/media/cma/backend/alsa/volume_map.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a8c3f34765d4c37df33e0d329908449a43520657
--- /dev/null
+++ b/chromecast/media/cma/backend/alsa/volume_map.cc
@@ -0,0 +1,123 @@
+// 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 "chromecast/media/cma/backend/alsa/volume_map.h"
+
+#include "base/files/file_path.h"
+#include "base/files/file_util.h"
+#include "base/logging.h"
+#include "base/values.h"
+#include "chromecast/base/serializers.h"
+#include "chromecast/media/cma/backend/alsa/cast_audio_json.h"
+
+namespace chromecast {
+namespace media {
+
+namespace {
+constexpr char kKeyVolumeMap[] = "volume_map";
+constexpr char kKeyLevel[] = "level";
+constexpr char kKeyDb[] = "db";
+constexpr float kMinDbFS = -120.0f;
+
+}  // namespace
+
+VolumeMap::VolumeMap() {
+  auto cast_audio_config =
+      DeserializeJsonFromFile(base::FilePath(kCastAudioJsonFilePath));
+  const base::DictionaryValue* cast_audio_dict;
+  if (!cast_audio_config ||
+      !cast_audio_config->GetAsDictionary(&cast_audio_dict)) {
+    LOG(WARNING) << "No cast audio config found; using default volume map.";
+    UseDefaultVolumeMap();
+    return;
+  }
+
+  const base::ListValue* volume_map_list;
+  if (!cast_audio_dict->GetList(kKeyVolumeMap, &volume_map_list)) {
+    LOG(WARNING) << "No volume map found; using default volume map.";
+    UseDefaultVolumeMap();
+    return;
+  }
+
+  double prev_level = -1.0;
+  for (size_t i = 0; i < volume_map_list->GetSize(); ++i) {
+    const base::DictionaryValue* volume_map_entry;
+    CHECK(volume_map_list->GetDictionary(i, &volume_map_entry));
+
+    double level;
+    CHECK(volume_map_entry->GetDouble(kKeyLevel, &level));
+    CHECK_GE(level, 0.0);
+    CHECK_LE(level, 1.0);
+    CHECK_GT(level, prev_level);
+    prev_level = level;
+
+    double db;
+    CHECK(volume_map_entry->GetDouble(kKeyDb, &db));
+    CHECK_LE(db, 0.0);
+    if (level == 1.0) {
+      CHECK_EQ(db, 0.0);
+    }
+
+    volume_map_.push_back({level, db});
+  }
+
+  if (volume_map_.empty()) {
+    LOG(FATAL) << "No entries in volume map.";
+    return;
+  }
+
+  if (volume_map_[0].level > 0.0) {
+    volume_map_.insert(volume_map_.begin(), {0.0, kMinDbFS});
+  }
+
+  if (volume_map_.rbegin()->level < 1.0) {
+    volume_map_.push_back({1.0, 0.0});
+  }
+}
+
+VolumeMap::~VolumeMap() = default;
+
+float VolumeMap::VolumeToDbFS(float volume) {
+  if (volume <= volume_map_[0].level) {
+    return volume_map_[0].db;
+  }
+  for (size_t i = 1; i < volume_map_.size(); ++i) {
+    if (volume < volume_map_[i].level) {
+      const float x_range = volume_map_[i].level - volume_map_[i - 1].level;
+      const float y_range = volume_map_[i].db - volume_map_[i - 1].db;
+      const float x_pos = volume - volume_map_[i - 1].level;
+
+      return volume_map_[i - 1].db + x_pos * y_range / x_range;
+    }
+  }
+  return volume_map_[volume_map_.size() - 1].db;
+}
+
+float VolumeMap::DbFSToVolume(float db) {
+  if (db <= volume_map_[0].db) {
+    return volume_map_[0].level;
+  }
+  for (size_t i = 1; i < volume_map_.size(); ++i) {
+    if (db < volume_map_[i].db) {
+      const float x_range = volume_map_[i].db - volume_map_[i - 1].db;
+      const float y_range = volume_map_[i].level - volume_map_[i - 1].level;
+      const float x_pos = db - volume_map_[i - 1].db;
+
+      return volume_map_[i - 1].level + x_pos * y_range / x_range;
+    }
+  }
+  return volume_map_[volume_map_.size() - 1].level;
+}
+
+// static
+void VolumeMap::UseDefaultVolumeMap() {
+  volume_map_ = {{0.0f, kMinDbFS},
+                 {0.01f, -58.0f},
+                 {0.090909f, -48.0f},
+                 {0.818182f, -8.0f},
+                 {1.0f, 0.0f}};
+}
+
+}  // namespace media
+}  // namespace chromecast