[Chromecast] Add new volume control API to CastMediaShlib

chromecast/public/volume_control.h

Index: chromecast/public/volume_control.h
diff --git a/chromecast/public/volume_control.h b/chromecast/public/volume_control.h
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+++ b/chromecast/public/volume_control.h
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+// 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_PUBLIC_VOLUME_CONTROL_H_
+#define CHROMECAST_PUBLIC_VOLUME_CONTROL_H_
+
+#include <string>
+#include <vector>
+
+#include "chromecast_export.h"
+
+namespace chromecast {
+namespace media {
+
+// Audio content types for volume control. Each content type has a separate
+// volume and mute state.
+enum class AudioContentType {
+  kMedia,          // Normal audio playback; also used for system sound effects.
+  kAlarm,          // Alarm sounds.
+  kCommunication,  // Voice communication, eg assistant TTS.
+};
+
+// Observer for volume/mute state changes. This is useful to detect volume
+// changes that occur outside of cast_shell. Add/RemoveVolumeObserver() must not
+// be called synchronously from OnVolumeChange() or OnMuteChange().
+class VolumeObserver {
+ public:
+  // Called whenever the volume changes for a given stream |type|. May be called
+  // on an arbitrary thread.
+  virtual void OnVolumeChange(AudioContentType type, float new_volume) = 0;
+
+  // Called whenever the mute state changes for a given stream |type|. May be
+  // called on an arbitrary thread.
+  virtual void OnMuteChange(AudioContentType type, bool new_muted) = 0;
+
+ protected:
+  virtual ~VolumeObserver() = default;
+};
+
+// Volume control is initialized once when cast_shell starts up, and finalized
+// on shutdown. Revoking resources has no effect on volume control. All volume
+// control methods are called on the same thread that calls Initialize().
+class CHROMECAST_EXPORT VolumeControl {
+ public:
+  // Initializes platform-specific volume control. Only called when volume
+  // control is in an uninitialized state. The implementation of this method
+  // should load previously set volume and mute states from persistent storage,
+  // so that the volume and mute are preserved across reboots.
+  static void Initialize(const std::vector<std::string>& argv)
+      __attribute__((__weak__));
+
+  // Tears down platform-specific volume control and returns to the
+  // uninitialized state.
+  static void Finalize() __attribute__((__weak__));
+
+  // Adds a volume observer.
+  static void AddVolumeObserver(VolumeObserver* observer)
+      __attribute__((__weak__));
+  // Removes a volume observer. After this is called, the implementation must
+  // not call any more methods on the observer.
+  static void RemoveVolumeObserver(VolumeObserver* observer)
+      __attribute__((__weak__));
+
+  // Gets/sets the output volume for a given audio stream |type|. The volume
+  // |level| is in the range [0.0, 1.0].
+  static float GetVolume(AudioContentType type) __attribute__((__weak__));
+  static void SetVolume(AudioContentType type, float level)
+      __attribute__((__weak__));
+
+  // Gets/sets the mute state for a given audio stream |type|.
+  static bool IsMuted(AudioContentType type) __attribute__((__weak__));
+  static void SetMuted(AudioContentType type, bool muted)
+      __attribute__((__weak__));
+
+  // Limits the output volume for a given stream |type| to no more than |limit|.
+  // This does not affect the logical volume for the stream type; the volume
+  // returned by GetVolume() should not change, and no OnVolumeChange() event
+  // should be sent to observers.
+  static void SetOutputLimit(AudioContentType type, float limit)
+      __attribute__((__weak__));
+
+  // Converts a volume level in the range [0.0, 1.0] to/from a volume in dB.
+  // The volume in dB should be full-scale (so a volume level of 1.0 would be
+  // 0.0 dBFS, and any lower volume level would be negative).
+  // May be called from multiple processes.
+  static float VolumeToDbFS(float volume) __attribute__((__weak__));
+  static float DbFSToVolume(float dbfs) __attribute__((__weak__));
+};
+
+}  // namespace media
+}  // namespace chromecast
+
+#endif  // CHROMECAST_PUBLIC_VOLUME_CONTROL_H_