[Chromecast] Correct libcast_governor behavior.

chromecast/media/cma/backend/alsa/post_processors/governor.h

+// 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.
+
+#ifndef CHROMECAST_MEDIA_CMA_BACKEND_ALSA_POST_PROCESSORS_GOVERNOR_H_
+#define CHROMECAST_MEDIA_CMA_BACKEND_ALSA_POST_PROCESSORS_GOVERNOR_H_
+
+#include <memory>
+#include <vector>
+
+#include "base/macros.h"
+#include "chromecast/media/cma/backend/alsa/slew_volume.h"
+#include "chromecast/public/media/audio_post_processor_shlib.h"
+
+namespace chromecast {
+namespace media {
+
+// 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 dynamic 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;
+
+  // AudioPostProcessor implementation:
+  bool SetSampleRate(int sample_rate) override;
+  int ProcessFrames(const std::vector<float*>& data,
+                    int frames,
+                    float volume) override;
+  int GetRingingTimeInFrames() override;
+
+  void SetSlewTimeMsForTest(int slew_time_ms);
+
+ private:
+  float GetGovernorMultiplier();
+
+  int channels_;
+  int sample_rate_;
+  float volume_;
+  double onset_volume_;
+  double clamp_multiplier_;
+  SlewVolume slew_volume_;
+
+  DISALLOW_COPY_AND_ASSIGN(Governor);
+};
+
+}  // namespace media
+}  // namespace chromecast
+
+#endif  // CHROMECAST_MEDIA_CMA_BACKEND_ALSA_POST_PROCESSORS_GOVERNOR_H_