AudioSystem

概述

    AudioSystem是声音系统的抽象，它为AudioService提供接口，具体实现透过JNI调用C++层的AudioSystem。

static常量定义

Audio类型

• 该组变量对应Settings.System.VOLUME_SETTINGS和attrs.xml

Audio状态

错误信息

• 该组变量对应libs/android_runtime/android_media_AudioSystem.cpp的定义

• 以下常量对应AudioSystem.cpp中的定义

输出设备

输入设备

JNI接口

• AudioSystem的JNI接口定义在frameworks/base/core/jni/android_media_AudioSystem.cpp中

static JNINativeMethod gMethods[] = {
    {"setParameters",        "(Ljava/lang/String;)I", (void *)android_media_AudioSystem_setParameters},
    {"getParameters",        "(Ljava/lang/String;)Ljava/lang/String;", (void *)android_media_AudioSystem_getParameters},
    {"muteMicrophone",      "(Z)I",     (void *)android_media_AudioSystem_muteMicrophone},
    {"isMicrophoneMuted",   "()Z",      (void *)android_media_AudioSystem_isMicrophoneMuted},
    {"isStreamActive",      "(I)Z",     (void *)android_media_AudioSystem_isStreamActive},
    {"setDeviceConnectionState", "(IILjava/lang/String;)I", (void *)android_media_AudioSystem_setDeviceConnectionState},
    {"getDeviceConnectionState", "(ILjava/lang/String;)I",  (void *)android_media_AudioSystem_getDeviceConnectionState},
    {"setPhoneState",       "(I)I",     (void *)android_media_AudioSystem_setPhoneState},
    {"setRingerMode",       "(II)I",    (void *)android_media_AudioSystem_setRingerMode},
    {"setForceUse",         "(II)I",    (void *)android_media_AudioSystem_setForceUse},
    {"getForceUse",         "(I)I",     (void *)android_media_AudioSystem_getForceUse},
    {"initStreamVolume",    "(III)I",   (void *)android_media_AudioSystem_initStreamVolume},
    {"setStreamVolumeIndex","(II)I",    (void *)android_media_AudioSystem_setStreamVolumeIndex},
    {"getStreamVolumeIndex","(I)I",     (void *)android_media_AudioSystem_getStreamVolumeIndex}
};

AudioSystem(C++层)

• AudioSystem主要是调用IAudioFlinger接口实现具体的功能，这里主要关注两个Binder的回调：
  • AudioSystem::AudioFlingerClient：连接AudioFlinger服务的回调。
    • 当Binder断开时会调用binderDied。
    • 当io配置变化时，会调用ioConfigChanged，如AudioFlinger初始化时。
  • AudioSystem::AudioPolicyServiceClient：连接AudioPolicyService服务的回调，当Binder断开时会调用该回调。

AudioSystem::AudioFlingerClient

class AudioFlingerClient: public IBinder::DeathRecipient, public BnAudioFlingerClient
{
public:
    AudioFlingerClient() {
    }

    // Binder通知
    virtual void binderDied(const wp<IBinder>& who);

    // 输入和输出的配置变更时被调用
    virtual void ioConfigChanged(int event, int ioHandle, void *param2);
};

AudioSystem::AudioPolicyServiceClient

class AudioPolicyServiceClient: public IBinder::DeathRecipient
{
public:
    AudioPolicyServiceClient() {
    }

    // Binder通知
    virtual void binderDied(const wp<IBinder>& who);
};