Android P的音频架构(二)

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已于 2022-07-04 14:03:20 修改 · 4.6k 阅读

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#android p #音频策略 #audio_policy_configuration

于 2019-04-15 16:46:24 首次发布

深入探讨AndroidP的音频策略，包括AudioPolicyService的工作原理，音频设备管理，路由策略及音量控制。分析audio_policy_configuration.xml配置文件的结构与解析过程。

Android P的音频策略分析

本文主要讲解AudioPolicy部分，对音频策略流程的分析，音频策略代码在frameworks\av\services\audiopolicy中。

相关定义：
frameworks/base/media/java/android/media/AudioSystem.java

AudioPolicyService

AudioPolicyService是Android音频系统的两大服务之一，路径为：frameworks\av\services\audiopolicy\service\AudioPolicyService.cpp

AudioPolicyService主要完成以下任务：

JAVA应用层通过JNI，经由IAudioPolicyService接口，访问AudioPolicyService提供的服务
输入输出设备的连接状态
系统的路由策略（strategy）的切换
音量参数的设置

AudioPolicyService详细说明：

AudioPolicyService同时也继承了AudioPolicyClientInterface类，他有一个AudioPolicyInterface类的成员指针mAudioPolicyManager，实际上就是指向了AudioPolicyManager；
AudioPolicyManager类继承了AudioPolicyInterface类以便向AudioPolicyService提供服务，反过来同时还有一个AudioPolicyClientInterface指针，该指针在构造函数中被初始化，指向了AudioPolicyService，实际上，AudioPolicyService是通过成员指针mAudioPolicyManager访问AudioPolicyManager，而AudioPolicyManager则通过AudioPolicyClientInterface（mpClientInterface）访问AudioPolicyService；
AudioPolicyService有一个内部线程类AudioCommandThread，顾名思义，所有的命令（音量控制，输入、输出的切换等）最终都会在该线程中排队执行；

AudioPolicyService的很大一部分管理工作都是在AudioPolicyManager中完成的。包括音量管理，路由策略（strategy）管理，输入输出设备管理。下面我们重点看一下AudioPolicyManager.cpp文件

AudioPolicyManager

AudioPolicyManager主要完成了路由策略管理和输入输出设备的管理，其路径为：frameworks\av\services\audiopolicy\managerdefault\AudioPolicyManager.cpp

一、输入输出设备管理

Audio系统中定义了一些输入输出设备，定义在文件audio-base.h中，该文件路径为：system\media\audio\include\system\audio-base.h

定义如下：

enum {
   
   
    AUDIO_DEVICE_NONE                          = 0x0u,
    AUDIO_DEVICE_BIT_IN                        = 0x80000000u,
    AUDIO_DEVICE_BIT_DEFAULT                   = 0x40000000u,

    AUDIO_DEVICE_OUT_EARPIECE                  = 0x1u,		//听筒
    AUDIO_DEVICE_OUT_SPEAKER                   = 0x2u,		//扬声器
    AUDIO_DEVICE_OUT_WIRED_HEADSET             = 0x4u,		//带话筒的耳机
    AUDIO_DEVICE_OUT_WIRED_HEADPHONE           = 0x8u,		//不带话筒的耳机
    AUDIO_DEVICE_OUT_BLUETOOTH_SCO             = 0x10u,		//蓝牙，面向连接（SCO）方式，主要用于语音传输
    AUDIO_DEVICE_OUT_BLUETOOTH_SCO_HEADSET     = 0x20u,		//蓝牙耳机，带话筒
    AUDIO_DEVICE_OUT_BLUETOOTH_SCO_CARKIT      = 0x40u,		//蓝牙车载设备
    AUDIO_DEVICE_OUT_BLUETOOTH_A2DP            = 0x80u,		//蓝牙立体声
    AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES = 0x100u,	//蓝牙立体声音耳机
    AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER    = 0x200u,	//蓝牙扬声器
    AUDIO_DEVICE_OUT_AUX_DIGITAL               = 0x400u,	//Aux
    AUDIO_DEVICE_OUT_HDMI                      = 0x400u,      // OUT_AUX_DIGITAL
    AUDIO_DEVICE_OUT_ANLG_DOCK_HEADSET         = 0x800u,
    AUDIO_DEVICE_OUT_DGTL_DOCK_HEADSET         = 0x1000u,
    AUDIO_DEVICE_OUT_USB_ACCESSORY             = 0x2000u,
    AUDIO_DEVICE_OUT_USB_DEVICE                = 0x4000u,
    AUDIO_DEVICE_OUT_REMOTE_SUBMIX             = 0x8000u,
    AUDIO_DEVICE_OUT_TELEPHONY_TX              = 0x10000u,
    AUDIO_DEVICE_OUT_LINE                      = 0x20000u,
    AUDIO_DEVICE_OUT_HDMI_ARC                  = 0x40000u,
    AUDIO_DEVICE_OUT_SPDIF                     = 0x80000u,
    AUDIO_DEVICE_OUT_FM                        = 0x100000u,
    AUDIO_DEVICE_OUT_AUX_LINE                  = 0x200000u,
    AUDIO_DEVICE_OUT_SPEAKER_SAFE              = 0x400000u,
    AUDIO_DEVICE_OUT_IP                        = 0x800000u,
    AUDIO_DEVICE_OUT_BUS                       = 0x1000000u,
    AUDIO_DEVICE_OUT_PROXY                     = 0x2000000u,
    AUDIO_DEVICE_OUT_USB_HEADSET               = 0x4000000u,
    AUDIO_DEVICE_OUT_HEARING_AID               = 0x8000000u,
    AUDIO_DEVICE_OUT_ECHO_CANCELLER            = 0x10000000u,
    AUDIO_DEVICE_OUT_DEFAULT                   = 0x40000000u, // BIT_DEFAULT

    AUDIO_DEVICE_IN_COMMUNICATION              = 0x80000001u, // BIT_IN | 0x1
    AUDIO_DEVICE_IN_AMBIENT                    = 0x80000002u, // BIT_IN | 0x2
    AUDIO_DEVICE_IN_BUILTIN_MIC                = 0x80000004u, // BIT_IN | 0x4
    AUDIO_DEVICE_IN_BLUETOOTH_SCO_HEADSET      = 0x80000008u, // BIT_IN | 0x8
    AUDIO_DEVICE_IN_WIRED_HEADSET              = 0x80000010u, // BIT_IN | 0x10
    AUDIO_DEVICE_IN_AUX_DIGITAL                = 0x80000020u, // BIT_IN | 0x20
    AUDIO_DEVICE_IN_HDMI                       = 0x80000020u, // IN_AUX_DIGITAL
    AUDIO_DEVICE_IN_VOICE_CALL                 = 0x80000040u, // BIT_IN | 0x40
    AUDIO_DEVICE_IN_TELEPHONY_RX               = 0x80000040u, // IN_VOICE_CALL
    AUDIO_DEVICE_IN_BACK_MIC                   = 0x80000080u, // BIT_IN | 0x80
    AUDIO_DEVICE_IN_REMOTE_SUBMIX              = 0x80000100u, // BIT_IN | 0x100
    AUDIO_DEVICE_IN_ANLG_DOCK_HEADSET          = 0x80000200u, // BIT_IN | 0x200
    AUDIO_DEVICE_IN_DGTL_DOCK_HEADSET          = 0x80000400u, // BIT_IN | 0x400
    AUDIO_DEVICE_IN_USB_ACCESSORY              = 0x80000800u, // BIT_IN | 0x800
    AUDIO_DEVICE_IN_USB_DEVICE                 = 0x80001000u, // BIT_IN | 0x1000
    AUDIO_DEVICE_IN_FM_TUNER                   = 0x80002000u, // BIT_IN | 0x2000
    AUDIO_DEVICE_IN_TV_TUNER                   = 0x80004000u, // BIT_IN | 0x4000
    AUDIO_DEVICE_IN_LINE                       = 0x80008000u, // BIT_IN | 0x8000
    AUDIO_DEVICE_IN_SPDIF                      = 0x80010000u, // BIT_IN | 0x10000
    AUDIO_DEVICE_IN_BLUETOOTH_A2DP             = 0x80020000u, // BIT_IN | 0x20000
    AUDIO_DEVICE_IN_LOOPBACK                   = 0x80040000u, // BIT_IN | 0x40000
    AUDIO_DEVICE_IN_IP