Android Audio 音频路由

一、在 AudioPolicyService 中，选择音频路由时会从当前音频流的类型获取音频的路由策略：

/frameworks/av/services/audiopolicy/managerdefault/AudioPolicyManager.cpp

routing_strategy AudioPolicyManager::getStrategy(audio_stream_type_t stream) const
{ALOG_ASSERT(stream != AUDIO_STREAM_PATCH,"getStrategy() called for AUDIO_STREAM_PATCH");return mEngine->getStrategyForStream(stream);
}

/frameworks/av/services/audiopolicy/enginedefault/src/Engine.cpp

routing_strategy Engine::getStrategyForStream(audio_stream_type_t stream)
{// stream to strategy mappingswitch (stream) {case AUDIO_STREAM_VOICE_CALL:case AUDIO_STREAM_BLUETOOTH_SCO:return STRATEGY_PHONE;case AUDIO_STREAM_RING:case AUDIO_STREAM_ALARM:return STRATEGY_SONIFICATION;case AUDIO_STREAM_NOTIFICATION:return STRATEGY_SONIFICATION_RESPECTFUL;case AUDIO_STREAM_DTMF:return STRATEGY_DTMF;default:ALOGE("unknown stream type %d", stream);case AUDIO_STREAM_SYSTEM:// NOTE: SYSTEM stream uses MEDIA strategy because muting music and switching outputs// while key clicks are played produces a poor resultcase AUDIO_STREAM_MUSIC:return STRATEGY_MEDIA;case AUDIO_STREAM_ENFORCED_AUDIBLE:return STRATEGY_ENFORCED_AUDIBLE;case AUDIO_STREAM_TTS:return STRATEGY_TRANSMITTED_THROUGH_SPEAKER;case AUDIO_STREAM_ACCESSIBILITY:return STRATEGY_ACCESSIBILITY;case AUDIO_STREAM_REROUTING:return STRATEGY_REROUTING;}
}

音频策略枚举：

enum routing_strategy {STRATEGY_MEDIA, // 媒体策略STRATEGY_PHONE, // 电话策略STRATEGY_SONIFICATION, // 通知策略STRATEGY_SONIFICATION_RESPECTFUL,STRATEGY_DTMF, // DTMF 策略STRATEGY_ENFORCED_AUDIBLE, // 强制输出策略STRATEGY_TRANSMITTED_THROUGH_SPEAKER,STRATEGY_ACCESSIBILITY,STRATEGY_REROUTING,NUM_STRATEGIES
};

二、获取到音频路由策略类型后，通过调用 getDeviceForStrategy() 选择最终的输出设备

/frameworks/av/services/audiopolicy/enginedefault/src/Engine.cpp

audio_devices_t Engine::getDeviceForStrategy(routing_strategy strategy) const
{DeviceVector availableOutputDevices = mApmObserver->getAvailableOutputDevices();DeviceVector availableInputDevices = mApmObserver->getAvailableInputDevices();const SwAudioOutputCollection &outputs = mApmObserver->getOutputs();return getDeviceForStrategyInt(strategy, availableOutputDevices,availableInputDevices, outputs, (uint32_t)AUDIO_DEVICE_NONE);
}

audio_devices_t Engine::getDeviceForStrategyInt(routing_strategy strategy,DeviceVector availableOutputDevices,DeviceVector availableInputDevices,const SwAudioOutputCollection &outputs,uint32_t outputDeviceTypesToIgnore) const
{uint32_t device = AUDIO_DEVICE_NONE;uint32_t availableOutputDevicesType =availableOutputDevices.types() & ~outputDeviceTypesToIgnore;switch (strategy) {... ...case STRATEGY_MEDIA: {uint32_t device2 = AUDIO_DEVICE_NONE;if (strategy != STRATEGY_SONIFICATION) {// no sonification on remote submix (e.g. WFD)if (availableOutputDevices.getDevice(AUDIO_DEVICE_OUT_REMOTE_SUBMIX,String8("0")) != 0) {device2 = availableOutputDevices.types() & AUDIO_DEVICE_OUT_REMOTE_SUBMIX;}}if (isInCall() && (strategy == STRATEGY_MEDIA)) {device = getDeviceForStrategyInt(STRATEGY_PHONE, availableOutputDevices, availableInputDevices, outputs,outputDeviceTypesToIgnore);break;}if (device2 == AUDIO_DEVICE_NONE) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_HEARING_AID;}if ((device2 == AUDIO_DEVICE_NONE) &&(mForceUse[AUDIO_POLICY_FORCE_FOR_MEDIA] != AUDIO_POLICY_FORCE_NO_BT_A2DP) &&outputs.isA2dpSupported()) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_BLUETOOTH_A2DP;if (device2 == AUDIO_DEVICE_NONE) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES;}if (device2 == AUDIO_DEVICE_NONE) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER;}}if ((device2 == AUDIO_DEVICE_NONE) &&(mForceUse[AUDIO_POLICY_FORCE_FOR_MEDIA] == AUDIO_POLICY_FORCE_SPEAKER)) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_SPEAKER;}if (device2 == AUDIO_DEVICE_NONE) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_WIRED_HEADPHONE;}if (device2 == AUDIO_DEVICE_NONE) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_LINE;}if (device2 == AUDIO_DEVICE_NONE) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_WIRED_HEADSET;}if (device2 == AUDIO_DEVICE_NONE) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_USB_HEADSET;}if (device2 == AUDIO_DEVICE_NONE) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_USB_ACCESSORY;}if (device2 == AUDIO_DEVICE_NONE) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_USB_DEVICE;}if (device2 == AUDIO_DEVICE_NONE) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_DGTL_DOCK_HEADSET;}if ((device2 == AUDIO_DEVICE_NONE) && (strategy != STRATEGY_SONIFICATION)) {// no sonification on aux digital (e.g. HDMI)device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_AUX_DIGITAL;}if ((device2 == AUDIO_DEVICE_NONE) &&(mForceUse[AUDIO_POLICY_FORCE_FOR_DOCK] == AUDIO_POLICY_FORCE_ANALOG_DOCK)) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_ANLG_DOCK_HEADSET;}if (device2 == AUDIO_DEVICE_NONE) {device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_SPEAKER;}int device3 = AUDIO_DEVICE_NONE;if (strategy == STRATEGY_MEDIA) {// ARC, SPDIF and AUX_LINE can co-exist with others.device3 = availableOutputDevicesType & AUDIO_DEVICE_OUT_HDMI_ARC;device3 |= (availableOutputDevicesType & AUDIO_DEVICE_OUT_SPDIF);device3 |= (availableOutputDevicesType & AUDIO_DEVICE_OUT_AUX_LINE);}device2 |= device3;// device is DEVICE_OUT_SPEAKER if we come from case STRATEGY_SONIFICATION or// STRATEGY_ENFORCED_AUDIBLE, AUDIO_DEVICE_NONE otherwisedevice |= device2;// If hdmi system audio mode is on, remove speaker out of output list.if ((strategy == STRATEGY_MEDIA) &&(mForceUse[AUDIO_POLICY_FORCE_FOR_HDMI_SYSTEM_AUDIO] ==AUDIO_POLICY_FORCE_HDMI_SYSTEM_AUDIO_ENFORCED)) {device &= ~AUDIO_DEVICE_OUT_SPEAKER;}// for STRATEGY_SONIFICATION:// if SPEAKER was selected, and SPEAKER_SAFE is available, use SPEAKER_SAFE insteadif ((strategy == STRATEGY_SONIFICATION) &&(device & AUDIO_DEVICE_OUT_SPEAKER) &&(availableOutputDevicesType & AUDIO_DEVICE_OUT_SPEAKER_SAFE)) {device |= AUDIO_DEVICE_OUT_SPEAKER_SAFE;device &= ~AUDIO_DEVICE_OUT_SPEAKER;}} break;... ...
}

通过判断音频设备是否连接，及相关优先级进行添加设备或移除设备，这里可以通过自定义去完成音频输出的优先级。

常见设备的定义：

/system/media/audio/include/system/audio-base.h

enum {AUDIO_DEVICE_NONE                          = 0x0u,AUDIO_DEVICE_BIT_IN                        = 0x80000000u,AUDIO_DEVICE_BIT_DEFAULT                   = 0x40000000u,AUDIO_DEVICE_OUT_EARPIECE                  = 0x1u,AUDIO_DEVICE_OUT_SPEAKER                   = 0x2u,AUDIO_DEVICE_OUT_WIRED_HEADSET             = 0x4u,AUDIO_DEVICE_OUT_WIRED_HEADPHONE           = 0x8u,AUDIO_DEVICE_OUT_BLUETOOTH_SCO             = 0x10u,AUDIO_DEVICE_OUT_BLUETOOTH_SCO_HEADSET     = 0x20u,AUDIO_DEVICE_OUT_BLUETOOTH_SCO_CARKIT      = 0x40u,AUDIO_DEVICE_OUT_BLUETOOTH_A2DP            = 0x80u,AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES = 0x100u,AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER    = 0x200u,AUDIO_DEVICE_OUT_AUX_DIGITAL               = 0x400u,AUDIO_DEVICE_OUT_HDMI                      = 0x400u,      // OUT_AUX_DIGITALAUDIO_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_DEFAULTAUDIO_DEVICE_IN_COMMUNICATION              = 0x80000001u, // BIT_IN | 0x1AUDIO_DEVICE_IN_AMBIENT                    = 0x80000002u, // BIT_IN | 0x2AUDIO_DEVICE_IN_BUILTIN_MIC                = 0x80000004u, // BIT_IN | 0x4AUDIO_DEVICE_IN_BLUETOOTH_SCO_HEADSET      = 0x80000008u, // BIT_IN | 0x8AUDIO_DEVICE_IN_WIRED_HEADSET              = 0x80000010u, // BIT_IN | 0x10AUDIO_DEVICE_IN_AUX_DIGITAL                = 0x80000020u, // BIT_IN | 0x20AUDIO_DEVICE_IN_HDMI                       = 0x80000020u, // IN_AUX_DIGITALAUDIO_DEVICE_IN_VOICE_CALL                 = 0x80000040u, // BIT_IN | 0x40AUDIO_DEVICE_IN_TELEPHONY_RX               = 0x80000040u, // IN_VOICE_CALLAUDIO_DEVICE_IN_BACK_MIC                   = 0x80000080u, // BIT_IN | 0x80AUDIO_DEVICE_IN_REMOTE_SUBMIX              = 0x80000100u, // BIT_IN | 0x100AUDIO_DEVICE_IN_ANLG_DOCK_HEADSET          = 0x80000200u, // BIT_IN | 0x200AUDIO_DEVICE_IN_DGTL_DOCK_HEADSET          = 0x80000400u, // BIT_IN | 0x400AUDIO_DEVICE_IN_USB_ACCESSORY              = 0x80000800u, // BIT_IN | 0x800AUDIO_DEVICE_IN_USB_DEVICE                 = 0x80001000u, // BIT_IN | 0x1000AUDIO_DEVICE_IN_FM_TUNER                   = 0x80002000u, // BIT_IN | 0x2000AUDIO_DEVICE_IN_TV_TUNER                   = 0x80004000u, // BIT_IN | 0x4000AUDIO_DEVICE_IN_LINE                       = 0x80008000u, // BIT_IN | 0x8000AUDIO_DEVICE_IN_SPDIF                      = 0x80010000u, // BIT_IN | 0x10000AUDIO_DEVICE_IN_BLUETOOTH_A2DP             = 0x80020000u, // BIT_IN | 0x20000AUDIO_DEVICE_IN_LOOPBACK                   = 0x80040000u, // BIT_IN | 0x40000AUDIO_DEVICE_IN_IP                         = 0x80080000u, // BIT_IN | 0x80000AUDIO_DEVICE_IN_BUS                        = 0x80100000u, // BIT_IN | 0x100000AUDIO_DEVICE_IN_PROXY                      = 0x81000000u, // BIT_IN | 0x1000000AUDIO_DEVICE_IN_USB_HEADSET                = 0x82000000u, // BIT_IN | 0x2000000AUDIO_DEVICE_IN_BLUETOOTH_BLE              = 0x84000000u, // BIT_IN | 0x4000000AUDIO_DEVICE_IN_DEFAULT                    = 0xC0000000u, // BIT_IN | BIT_DEFAULT
};

音频输入类似，Android 9.0源码为例，不同版本会存在差异

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