Android CarAudio

一、CarAudio介绍

Android Automotive OS (AAOS) 是在核心 Android 音频堆栈的基础之上打造而成，以支持用作车辆信息娱乐系统的用例。AAOS 负责实现信息娱乐声音（即媒体、导航和通讯声音），但不直接负责具有严格可用性和计时要求的铃声和警告。虽然 AAOS 提供了信号和机制来帮助车辆管理音频，但最终还是由车辆来决定应为驾驶员和乘客播放什么声音，从而确保对保障安全至关重要的声音和监管声音能被确切听到，而不会中断。

当 Android 管理车辆的媒体体验时，应通过应用来代表外部媒体来源（例如电台调谐器），这类应用可以处理该来源的音频焦点和媒体键事件。

汽车音频系统可以处理以下声音和声音流：

二、CarAudio相关接口

ICarVolumeCallback

Binder interface to callback the volume key events.

用于回调音量键事件的绑定程序接口。

ICarVolumeCallback代码位于：

packages/services/Car/service/src/com/android/car/audio/ICarVolumeCallback.aidl

ICarVolumeCallback的定义：

interface ICarVolumeCallback {
    void onGroupVolumeChanged(int zoneId, int groupId, int flags);
    void onGroupMuteChanged(int zoneId, int groupId, int flags);
    void onMasterMuteChanged(int zoneId, int flags);
}

AudioControlWrapper

AudioControlWrapper wraps IAudioControl HAL interface, handling version specific support so that the rest of CarAudioService doesn't need to know about it.

AudioControlWrapper包装了IAudioControl HAL接口，处理特定于版本的支持，因此CarAudioService的其余部分不需要知道它。

AudioControlWrapper代码位于：

packages/services/Car/service/src/com/android/car/audio/hal/AudioControlWrapper.java

AudioControlWrapper的定义：

public interface AudioControlWrapper {}

AudioControlWrapper方法：

void unregisterFocusListener()：关闭在音频控制 HAL 上注册的焦点侦听器。
boolean supportsFeature(@AudioControlFeature int feature)：指示 HAL 是否可以支持指定的功能。
void registerFocusListener(HalFocusListener focusListener)：向 IAudioControl 注册 HAL 音频焦点请求的侦听器。
void registerAudioGainCallback(@NonNull HalAudioGainCallback gainCallback)：使用 IAudioControl 注册 HAL 音频增益更改通知的回调。
void unregisterAudioGainCallback()：关闭在音频控制 HAL 上注册的音频增益回调。
void onAudioFocusChange(@AttributeUsage int usage, int zoneId, int focusChange)：通知 HAL 已发出的请求的音频焦点更改。
void dump(IndentingPrintWriter writer)：dumps the current state of the AudioControlWrapper
void setFadeTowardFront(float value)：Sets the fade for the vehicle.
void setBalanceTowardRight(float value)：Sets the balance value for the vehicle.
void onDevicesToDuckChange(@NonNull List<CarDuckingInfo> carDuckingInfos)：Notifies HAL of changes in usages holding focus and the corresponding ducking changes for a given zone.
void onDevicesToMuteChange(@NonNull List<MutingInfo> carZonesMutingInfo)：Notifies HAL of changes in muting changes for all audio zones.
void linkToDeath(@Nullable AudioControlDeathRecipient deathRecipient)：Registers recipient to be notified if AudioControl HAL service dies.
 void unlinkToDeath()：Unregisters recipient for AudioControl HAL service death.

HalFocusListener

Framework focus listener interface to abstract away the specific HAL version

Framework 焦点侦听器接口，用于抽象出特定的 HAL 版本。

HalFocusListener代码位于：

packages/services/Car/service/src/com/android/car/audio/hal/HalFocusListener.java

HalFocusListener的定义：

public interface HalFocusListener{
    void requestAudioFocus(@AttributeUsage int usage, int zoneId, int focusGain);
    void abandonAudioFocus(@AttributeUsage int usage, int zoneId);
}

三、CarAudio相关类

CarAudioManager

CarAudioManager是Android Automotive OS中提供的一个与车载音频相关的管理类，用于管理应用程序与车载音频的交互，CarAudioManager扩展了AudioManager的功能，同时增加了一些针对车载音频使用场景的特殊功能。

CarAudioManager代码位于：

packages/services/Car/car-lib/src/android/car/media/CarAudioManager.java

CarAudioManager的定义：

public final class CarAudioManager implements CarManagerBase {}

AudioManagerHelper

AudioManagerHelper 代码位于：

packages/services/Car/car-builtin-lib/src/android/car/builtin/media/AudioManagerHelper.Java

AudioManagerHelper 的定义：

public final class AudioManagerHelper {}

CarAudioSettings

CarAudioSettings在Automotive OS系统中用于管理车载音频设置，其主要功能是控制车载系统的音量设置，以及配置提升和通知的音频设置。

CarAudioSettings代码位于：

packages/services/Car/car-lib/src/android/car/audio/CarAudioSettings.java

CarAudioSettings的定义：

public class CarAudioSettings {}

CarAudioService

CarAudioService是Android Automotive OS系统中提供的一个服务，类似于AudioService，它管理整个车载音频系统，包括音频路由控制、音频设备管理、音量控制、焦点管理、车载媒体播放管理等。CarAudioService提供了对车辆音频系统功能和状态的控制，为车载音频应用提供便利，并支持多个应用程序同时执行音频任务。

CarAudioService代码位于：

packages/services/Car/service/src/com/android/car/audio/audioCarAudioService.java

CarAudioService的定义：

public class CarAudioService extends ICarAudio.Stub implements CarServiceBase {}

CarAudioContext

CarAudioContext在Android Automotive OS系统中用于管理车载音频场景相关的设置。在Android Auto中，可以通过它来管理不同的音频场景，例如导航、车载电话、媒体等，CarAudioContext包含的音频场景如下：

static final int MUSIC = 1：Music playback

static final int NAVIGATION = 2：Navigation directions

static final int VOICE_COMMAND = 3：Voice command session

static final int CALL_RING = 4：Voice call ringing

static final int CALL = 5：Voice call

static final int ALARM = 6：Alarm sound from Android

static final int NOTIFICATION = 7：Notifications

static final int SYSTEM_SOUND = 8：System sounds

static final int EMERGENCY = 9：Emergency related sounds such as collision warnings

static final int SAFETY = 10：Safety sounds such as obstacle detection when backing up or when changing lanes

static final int VEHICLE_STATUS = 11：Vehicle Status related sounds such as check engine light or seat belt chimes

static final int ANNOUNCEMENT = 12：Announcement such as traffic announcements

CarAudioContext代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioContext.java

CarAudioContext的定义：

public final class CarAudioContext {}

CarVolume

CarVolume在Android Automotive OS系统中用于管理车载音量设置。在Android Auto中，可以通过它来控制车载音量，包括媒体音频、通话音量、通知音量等。同时，CarVolume还提供了一组API，用于处理车辆速度和声音关联的特殊需求。

CarVolume代码位于：

packages/services/Car/service/src/com/android/car/audio/CarVolume.java

CarVolume的定义：

final class CarVolume {}

CarVolumeGroup

A class encapsulates a volume group in car.

CarVolumeGroup 代码位于：

packages/services/Car/service/src/com/android/car/audio/CarVolumeGroup.java

CarVolumeGroup 的定义：

final class CarVolumeGroup {}

CarVolumeGroupMuting

CarVolumeGroup代码位于：

packages/services/Car/service/src/com/android/car/audio/CarVolumeGroup.java

CarVolumeGroup的定义：

final class CarVolumeGroupMuting {}

CarAudioPolicyVolumeCallback

继承于AudioPolicy.AudioPolicyVolumeCallback，用于接收与Volume更改相关的事件的回调类。

CarAudioPolicyVolumeCallback 代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioPolicyVolumeCallback.java

CarAudioPolicyVolumeCallback 的定义：

final class CarAudioPolicyVolumeCallback extends AudioPolicy.AudioPolicyVolumeCallback{
    public void onVolumeAdjustment(int adjustment)
}

CarVolumeCallbackHandler

Manages callbacks for changes in car volume.

CarVolumeCallbackHandler代码位于：

packages/services/Car/service/src/com/android/car/audio/CarVolumeCallbackHandler.java

CarVolumeCallbackHandler的定义：

class CarVolumeCallbackHandler {}

CarAudioZone

CarAudioZone在Android Automotive OS系统中用于描述车载音频区域并提供音频设置。一个汽车通常有多个音频输出区域，例如，前排和后排，左侧和右侧等。CarAudioZone可以描述这些不同的音频区域，并提供相应的音频设置。

CarAudioZone代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioZone.java

CarAudioZone的定义：

class CarAudioZone{}

CarAudioZonesValidator

汽车音频区域验证器

CarAudioZonesValidator代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioZonesValidator.java

CarAudioZonesValidator的定义：

class CarAudioZonesValidator{}

CarAudioZonesHelper

A helper class loads all audio zones from the configuration XML file.

帮助程序类从配置 XML 文件加载所有音频区域。

CarAudioZonesHelper代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioZonesHelper.java

CarAudioZonesHelper的定义：

class CarAudioZonesHelper {}

CarAudioZonesHelperLegacy

A helper class loads volume groups from car_volume_groups.xml configuration into one zone.

帮助程序类将volume groups 从car_volume_groups.xml配置加载到一个区域中。

CarAudioZonesHelperLegacy代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioZonesHelperLegacy.java

CarAudioZonesHelperLegacy的定义：

class CarAudioZonesHelperLegacy {}

CarZonesAudioFocus

Manages audio focus on a per zone basis.

基于每个区域管理音频焦点。

CarZonesAudioFocus代码位于：

packages/services/Car/service/src/com/android/car/audio/CarZonesAudioFocus.java

CarZonesAudioFocus的定义：

final class CarZonesAudioFocus extends AudioPolicy.AudioPolicyFocusListener {}

CarAudioFocus

CarAudioFocus在Android Automotive OS系统中用于控制车载音频角度相关设置。

CarAudioFocus代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioFocus.java

CarAudioFocus的定义：

class CarAudioFocus extends AudioPolicy.AudioPolicyFocusListener {}

FocusInteraction

FocusInteraction is responsible for evaluating how incoming focus requests should be handled based on pre-defined interaction behaviors for each incoming {AudioContext} in relation to a {AudioContext} that is currently holding focus.

负责根据与当前持有焦点的 {AudioContext} 相关的每个传入 {AudioContext} 的预定义交互行为，评估如何处理传入的焦点请求。

FocusInteraction代码位于：

packages/services/Car/service/src/com/android/car/audio/FocusInteraction.java

FocusInteraction的定义：

final class FocusInteraction {}

FocusEntry

FocusEntry代码位于：

packages/services/Car/service/src/com/android/car/audio/FocusEntry.java

FocusEntry的定义：

final class FocusEntry {}

CarDucking

CarDucking代码位于：

packages/services/Car/service/src/com/android/car/audio/CarDucking.java

CarDucking的定义：

final class CarDucking implements CarFocusCallback {}

CarDuckingInfo

Ducking information for a given car audio zone based on its focus state.

CarDuckingInfo代码位于：

packages/services/Car/service/src/com/android/car/audio/CarDuckingInfo.java

CarDuckingInfo的定义：

public final class CarDuckingInfo {}

CarDuckingUtils

CarDuckingUtils代码位于：

packages/services/Car/service/src/com/android/car/audio/CarDuckingUtils.java

CarDuckingUtils的定义：

final class CarDuckingUtils {}

CarAudioDeviceInfo

A helper class wraps {@link AudioDeviceInfo}, and helps get/set the gain on a specific port in terms of millibels.

Note to the reader. For whatever reason, it seems that AudioGain contains only configuration information (min/max/step, etc) while the AudioGainConfig class contains the actual currently active gain value(s).

CarAudioDeviceInfo在Android Automotive OS系统中用于提供车载媒体系统和音频外设设备的信息。

CarAudioDeviceInfo代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioDeviceInfo.java

CarAudioDeviceInfo的定义：

class CarAudioDeviceInfo {}

CarAudioDynamicRouting

CarAudioDynamicRouting在Android Automotive OS系统中用于动态控制车载音频的路由。

CarAudioDynamicRouting代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioDynamicRouting.java

CarAudioDynamicRouting的定义：

final class CarAudioDynamicRouting {}

CarAudioGainConfigInfo

CarAudioGainConfigInfo在Android Automotive OS系统中用于描述音频输入/输出通道的增益配置信息。

CarAudioGainConfigInfo代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioGainConfigInfo.java

CarAudioGainConfigInfo的定义：

public class CarAudioGainConfigInfo {}

CarAudioGainMonitor

Provides audio gain callback registration helpers and implements AudioGain listener business logic.

提供音频增益回调注册帮助程序，实现音频增益监听器业务逻辑。

CarAudioGainMonitor代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioGainMonitor.java

CarAudioGainMonit

final class CarAudioGainMonitor {}

CarHalAudioUtils

Car HAL audio Utils

CarHalAudioUtils代码位于：

packages/services/Car/service/src/com/android/car/audio/CarHalAudioUtils.java

CarHalAudioUtils的定义：

public final class CarHalAudioUtils {}

CarAudioPlaybackCallback

CarAudioPlaybackCallback是在Android Automotive OS系统中用于音频播放事件的回调接口。

CarAudioPlaybackCallback代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioPlaybackCallback.java

CarAudioPlaybackCallback的定义：

final class CarAudioPlaybackCallback extends AudioManager.AudioPlaybackCallback {}

CarAudioPowerListener

CarAudioPowerListener代码位于：

packages/services/Car/service/src/com/android/car/audio/CarAudioPowerListener.java

CarAudioPowerListener的定义：

class CarAudioPowerListener {}

CarAudioPatchHandle

CarAudioPatchHandle是在Android Automotive OS系统中用于表示音频路径的句柄。

CarAudioPatchHandle代码位于：

packages/services/Car/service/src/com/android/car/media/CarAudioPatchHandle.java

CarAudioPatchHandle的定义：

public final class CarAudioPatchHandle implements Parcelable {}

AudioControlFactory

Factory for constructing wrappers around IAudioControl HAL instances.

用于围绕 IAudioControl HAL 实例构造包装器的工厂。

AudioControlFactory代码位于：

packages/services/Car/service/src/com/android/car/audio/hal/AudioControlFactory.java

AudioControlFactory的定义：

public final class AudioControlFactory {}

HalAudioFocus

Manages focus requests from the HAL on a per-zone per-usage basis.

基于每个区域的每次使用量管理 HAL 的焦点请求

HalAudioFocus代码位于：

packages/services/Car/service/src/com/android/car/audio/hal/HalAudioFocus.java

HalAudioFocus的定义：

public final class HalAudioFocus implements HalFocusListener {
    private final class HalAudioFocusRequest {
}

AudioControlWrapperAidl

AudioControlWrapperV1

AudioControlWrapperV2

Wrapper for AIDL interface for AudioControl HAL.

Wrapper for IAudioControl@1.0.

Wrapper for IAudioControl@2.0.

AudioControlWrapper代码位于：

packages/services/Car/service/src/com/android/car/audio/hal/AudioControlWrapperAidl.java

packages/services/Car/service/src/com/android/car/audio/hal/AudioControlWrapperV1.java

packages/services/Car/service/src/com/android/car/audio/hal/AudioControlWrapperV2.java

AudioControlWrapper的定义：

public final class AudioControlWrapperAidl implements AudioControlWrapper {
    private static final class FocusListenerWrapper extends IFocusListener.Stub {}
    private static final class AudioGainCallbackWrapper extends IAudioGainCallback.Stub {}
}
public final class AudioControlWrapperV1 implements AudioControlWrapper {}
public final class AudioControlWrapperV2 implements AudioControlWrapper {}