Android(安卓)Audio 分析

一、架构

二、MediaServer初始化

所有的media服务都在进程mediaserver里。其代码在framework/base/media/mediaserver/main_mediaserver.cpp中。初始化过程如下。

1. 先初始化AudioFlinger

其初始化通过AudioFlinger的父类BindService创建唯一的AudioFlinger实例。

2. 然后初始化MediaPlayerService和CameraService

3. 最后初始化AudioPolicyService

三、 AudioFlinger分析

AudioFlinger负责管理每个音轨AudioTrack及RecordTrack，主音量控制，每种声音流的属性设置，设备控制，音效控制。

四、 AudioPolicyService分析

AudioPolicyService用于声音策略管理

客户端代码在framework/base/media/libmedia/AudioSystem.cpp中，其实该客户端只是监测AudioPolicyService是否死亡（binderDied)。真正的客户端为BpAudioPolicyService类，在framework/base/media/libmedia/IAudioPolicyService.cpp中。

接口

 1 adjustVolume 2 adjustSuggestedStreamVolume 3 adjustStreamVolume 4 setStreamVolume 5 setStreamSolo 6 setStreamMute 7 getStreamVolume 8 getStreamMaxVolume 9 setRingerMode10 getRingerMode11 setVibrateSetting12 getVibrateSetting13 shouldVibrate14 setMode15 getMode16 playSoundEffect17 playSoundEffectVolume18 loadSoundEffects19 unloadSoundEffects20 reloadAudioSettings21 setSpeakerphoneOn22 isSpeakerphoneOn23 setBluetoothScoOn24 isBluetoothScoOn25 requestAudioFocus26 abandonAudioFocus27 unregisterAudioFocusClient28 registerMediaButtonEventReceiver29 unregisterMediaButtonEventReceiver30 startBluetoothSco31 stopBluetoothSco

服务端代码在framework/base/services/audioflinger/AudioPolicyService.cpp中，实现了AudioPolicyService本地代码及服务内部使用的AudioPolicyClientInterface接口，该接口被AudioPolicyManager调用。

 1 openOutput 2 openDuplicateOutput 3 closeOutput 4 suspendOutput 5 restoreOutput 6 openInput 7 loseInput 8 setStreamVolume 9 setStreamOutput10 setParameters11 getParameters12 startTone13 stopTone14 setVoiceVolume15 moveEffects

AudioPolicyService会启动两个AudioCommandThread类的线程mTonePlaybackThread和mAudioCommandThread，然后构造AudioPolicyManager的实例mpPolicyManager。基本上所有的服务接口都会在检查权限后调用mpPolicyManager的相应实现。

mTonePlaybackThread用户播放通话中的通知音

mAudioCommandThread用于设置AudioFlinger的一些设置(为什么使用AudioCommandThread，然后调用AudioSystem中接口控制AudioFlinger?)

五、 AudioManager分析

1. 音频焦点转

1 requestAudioFocus         请求焦点2 abandonAudioFocus         放弃焦点

requestAudioFocus的第一参数是Listener,可以是下面枚举的后三个值

第二个参数是当前流类型

最后一个参数可以是以下的前三个值

1 AUDIOFOCUS_GAIN 1 2 AUDIOFOCUS_GAIN_TRANSIENT 23 AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK = 3;4 AUDIOFOCUS_LOSS = -1 * AUDIOFOCUS_GAIN;5 AUDIOFOCUS_LOSS_TRANSIENT = -1 * AUDIOFOCUS_GAIN_TRANSIENT;6 AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK =7  -1 * AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK;

六、 AudioPolicyManager分析

流类型stream_type(在 AudioSystem中定义)

TYPE                          VALUE                                STRATEGYDEFAULT(->MUSIC)                -1                             STRATEGY_MEDIA(0)VOICE_CALL                       0                             STRATEGY_PHONE(1)SYSTEM                           1                             STRATEGY_MEDIA(0)RING                             2                             STRATEGY_SONIFICATION(2)MUSIC                            3                             STRATEGY_MEDIA(0)ALARM                            4                             STRATEGY_SONIFICATION(2)NOTIFICATION                     5                             STRATEGY_SONIFICATION(2)BLUETOOTH_SCO                    6                             STRATEGY_PHONE(1)// Sounds that cannot be muted by user and must be routed to speakerENFORCED_AUDIBLE                 7                             STRATEGY_SONIFICATION(2)DTMF                             8                             STRATEGY_DTMF(3)TTS                              9                             STRATEGY_MEDIA(0)HDMI                             10  MV的自定义类型              STRATEGY_MEDIA(0)FM                               11  MV的自定义类型              STRATEGY_MEDIA(0)

音频状态audio_mode(在 AudioSystem中定义)

1  enum audio_mode {2  MODE_INVALID = -2,3  MODE_CURRENT = -1,4  MODE_NORMAL = 0,5  MODE_RINGTONE,6  MODE_IN_CALL,7  MODE_IN_COMMUNICATION,8  NUM_MODES  // not a valid entry, denotes end-of-list9  };

策略类型routing_strategy:

STRATEGY_MEDIA             0STRATEGY_PHONE             1STRATEGY_SONIFICATION      2STRATEGY_DTMF              3

设备类型audio_devices：

 1 enum audio_devices { 2  // output devices 3  DEVICE_OUT_EARPIECE = 0x1, 4  DEVICE_OUT_SPEAKER = 0x2, 5  DEVICE_OUT_WIRED_HEADSET = 0x4, 6  DEVICE_OUT_WIRED_HEADPHONE = 0x8, 7  DEVICE_OUT_BLUETOOTH_SCO = 0x10, 8  DEVICE_OUT_BLUETOOTH_SCO_HEADSET = 0x20, 9  DEVICE_OUT_BLUETOOTH_SCO_CARKIT = 0x40,10  DEVICE_OUT_BLUETOOTH_A2DP = 0x80,11  DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES = 0x100,12  DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER = 0x200,13  DEVICE_OUT_AUX_DIGITAL = 0x400,14  DEVICE_OUT_DEFAULT = 0x8000,15  DEVICE_OUT_ALL = (DEVICE_OUT_EARPIECE | DEVICE_OUT_SPEAKER | DEVICE_OUT_WIRED_HEADSET |16  DEVICE_OUT_WIRED_HEADPHONE | DEVICE_OUT_BLUETOOTH_SCO | DEVICE_OUT_BLUETOOTH_SCO_HEADSET |17  DEVICE_OUT_BLUETOOTH_SCO_CARKIT | DEVICE_OUT_BLUETOOTH_A2DP | DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES |18  DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER | DEVICE_OUT_AUX_DIGITAL | DEVICE_OUT_DEFAULT),19  DEVICE_OUT_ALL_A2DP = (DEVICE_OUT_BLUETOOTH_A2DP | DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES |20  DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER),21 22  // input devices23  DEVICE_IN_COMMUNICATION = 0x10000,24  DEVICE_IN_AMBIENT = 0x20000,25  DEVICE_IN_BUILTIN_MIC = 0x40000,26  DEVICE_IN_BLUETOOTH_SCO_HEADSET = 0x80000,27  DEVICE_IN_WIRED_HEADSET = 0x100000,28  DEVICE_IN_AUX_DIGITAL = 0x200000,29  DEVICE_IN_VOICE_CALL = 0x400000,30  DEVICE_IN_BACK_MIC = 0x800000,31  DEVICE_IN_DEFAULT = 0x80000000,32 33  DEVICE_IN_ALL = (DEVICE_IN_COMMUNICATION | DEVICE_IN_AMBIENT | DEVICE_IN_BUILTIN_MIC |34  DEVICE_IN_BLUETOOTH_SCO_HEADSET | DEVICE_IN_WIRED_HEADSET | DEVICE_IN_AUX_DIGITAL |35  DEVICE_IN_VOICE_CALL | DEVICE_IN_BACK_MIC | DEVICE_IN_DEFAULT)36  };

流程分析：

1.音量控制

initStreamVolumesetStreamVolumeIndexsetPhoneState

2.播放控制

入口函数

 1 startOutput 2  3 getStrategy 4  5 getDeviceForStrategy 6  7 setOutputDevice 8  9 applyStreamVolume10 11 checkAndSetVolume

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