Android 音频源码分析——AudioTrack设备选择_android audio的例子 audiotrack和audiorecorder

Android 音频源码分析——AndroidRecord录音（一）
Android 音频源码分析——AndroidRecord录音（二）
Android 音频源码分析——AndroidRecord音频数据传输流程
Android 音频源码分析——audioserver启动
Android 音频源码分析——AudioFlinger
Android 音频源码分析——AudioTrack设备选择

基于Andorid9.0源码

以AudioTrack为例，梳理下输出设备选择流程。

音频设备选择的影响因素：

1. AudioAttributes 声音流类型
2. setForceUse 设置
3. setPreferredDevice设置 （AudioRecord、AudioTrack、MediaRecorder、MediaPlayer）
4. 等。。。。待研究

一、大多数情况输出设备选择

直接从AudioTrack.cpp 开始。

AudioTrack构造器  
》AudioTrack::set(){
   }
》AudioTrack::createTrack_l()
》audioFlinger->createTrack(input, output, &status);
》AudioFlinger::createTrack()
》AudioSystem::getOutputForAttr()
》AudioPolicyService::getOutputForAttr()
》AudioPolicyManager::getOutputForAttr()
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status_t AudioPolicyManager::getOutputForAttr(const audio_attributes_t *attr,
                                              audio_io_handle_t *output,
                                              audio_session_t session,
                                              audio_stream_type_t *stream,
                                              uid_t uid,
                                              const audio_config_t *config,
                                              audio_output_flags_t *flags,
                                              audio_port_handle_t *selectedDeviceId,
                                              audio_port_handle_t *portId)
{
   
    //获取stream type
    *stream = streamTypefromAttributesInt(&attributes)
    
    routing_strategy strategy = (routing_strategy) getStrategyForAttr(&attributes)
        
    audio_devices_t device = getDeviceForStrategy(strategy, false /*fromCache*/);
    
    *output = getOutputForDevice(device, session, *stream, config, flags);    
}
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1. 通过AudioAttribute中的flags和usage获取对应的Stream type;
2. AudioAttribute usage属性映射到strategy;
3. 通过strategy 选择device类型;
4. 选择音频设备、音频通路；

1. 获取stream type

通过flags和usage映射到 stream type

audio_stream_type_t AudioPolicyManager::streamTypefromAttributesInt(const audio_attributes_t *attr)
{
   
    // flags to stream type mapping
    if ((attr->flags & AUDIO_FLAG_AUDIBILITY_ENFORCED) == AUDIO_FLAG_AUDIBILITY_ENFORCED) {
   
        return AUDIO_STREAM_ENFORCED_AUDIBLE;
    }
    if ((attr->flags & AUDIO_FLAG_SCO) == AUDIO_FLAG_SCO) {
   
        return AUDIO_STREAM_BLUETOOTH_SCO;
    }
    if ((attr->flags & AUDIO_FLAG_BEACON) == AUDIO_FLAG_BEACON) {
   
        return AUDIO_STREAM_TTS;
    }
    // usage to stream type mapping
    switch (attr->usage) {
   
    case AUDIO_USAGE_MEDIA:
    case AUDIO_USAGE_GAME:
    case AUDIO_USAGE_ASSISTANT:
    case AUDIO_USAGE_ASSISTANCE_NAVIGATION_GUIDANCE:
        return AUDIO_STREAM_MUSIC;
    case AUDIO_USAGE_ASSISTANCE_ACCESSIBILITY:
        return AUDIO_STREAM_ACCESSIBILITY;
    case AUDIO_USAGE_ASSISTANCE_SONIFICATION:
        return AUDIO_STREAM_SYSTEM;
    case AUDIO_USAGE_VOICE_COMMUNICATION:
        return AUDIO_STREAM_VOICE_CALL;
    case AUDIO_USAGE_VOICE_COMMUNICATION_SIGNALLING:
        return AUDIO_STREAM_DTMF;
    case AUDIO_USAGE_ALARM:
        return AUDIO_STREAM_ALARM;
    case AUDIO_USAGE_NOTIFICATION_TELEPHONY_RINGTONE:
        return AUDIO_STREAM_RING;
    case AUDIO_USAGE_NOTIFICATION:
    case AUDIO_USAGE_NOTIFICATION_COMMUNICATION_REQUEST:
    case AUDIO_USAGE_NOTIFICATION_COMMUNICATION_INSTANT:
    case AUDIO_USAGE_NOTIFICATION_COMMUNICATION_DELAYED:
    case AUDIO_USAGE_NOTIFICATION_EVENT:
        return AUDIO_STREAM_NOTIFICATION;
    case AUDIO_USAGE_UNKNOWN:
    default:
        return AUDIO_STREAM_MUSIC;
    }
}
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2. 获取strategy

getStrategyForAttr会调到Engine的getStrategyForUsage函数

routing_strategy Engine::getStrategyForUsage(audio_usage_t usage)
{
   
    // usage to strategy mapping
    switch (usage) {
   
    case AUDIO_USAGE_ASSISTANCE_ACCESSIBILITY:
        return STRATEGY_ACCESSIBILITY;
    case AUDIO_USAGE_MEDIA:
    case AUDIO_USAGE_GAME:
    case AUDIO_USAGE_ASSISTANT:
    case AUDIO_USAGE_ASSISTANCE_NAVIGATION_GUIDANCE:
    case AUDIO_USAGE_ASSISTANCE_SONIFICATION:
        return STRATEGY_MEDIA;
    case AUDIO_USAGE_VOICE_COMMUNICATION:
        return STRATEGY_PHONE;
    case AUDIO_USAGE_VOICE_COMMUNICATION_SIGNALLING:
        return STRATEGY_DTMF;
    case AUDIO_USAGE_ALARM:
    case AUDIO_USAGE_NOTIFICATION_TELEPHONY_RINGTONE:
        return STRATEGY_SONIFICATION;
    case AUDIO_USAGE_NOTIFICATION:
    case AUDIO_USAGE_NOTIFICATION_COMMUNICATION_REQUEST:
    case AUDIO_USAGE_NOTIFICATION_COMMUNICATION_INSTANT:
    case AUDIO_USAGE_NOTIFICATION_COMMUNICATION_DELAYED:
    case AUDIO_USAGE_NOTIFICATION_EVENT:
        return STRATEGY_SONIFICATION_RESPECTFUL;
    case AUDIO_USAGE_UNKNOWN:
    default:
        return STRATEGY_MEDIA;
    }
}
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AudioAttribute usage属性映射到strategy。

3. 获取设备类型

audio_devices_t AudioPolic