AudioTrack最终会调用AudioPolicyManager::getOutput();

frameworks\av\services\audiopolicy\managerdefault\AudioPolicyManager.cppaudio_io_handle_t AudioPolicyManager::getOutput(audio_stream_type_t stream,                                                uint32_t samplingRate,                                                audio_format_t format,                                                audio_channel_mask_t channelMask,                                                audio_output_flags_t flags,                                                const audio_offload_info_t *offloadInfo){    //APM_AudioPolicyManager: getOutput() device 2, stream 1, samplingRate 0, format 0, channelMask 3, flags 0    // stream = 1, AUDIO_STREAM_SYSTEM, 得到的strategy = STRATEGY_MEDIA    routing_strategy strategy = getStrategy(stream);    // AUDIO_DEVICE_NONE & AUDIO_DEVICE_OUT_SPEAKER    audio_devices_t device = getDeviceForStrategy(strategy, false /*fromCache*/);    //APM_AudioPolicyManager: getOutput() device 2, stream 1, samplingRate 0, format 0, channelMask 3, flags 0    ALOGV("getOutput() device %d, stream %d, samplingRate %d, format %x, channelMask %x, flags %x",          device, stream, samplingRate, format, channelMask, flags);    ALOGE("Liutao getOutput() device %d, stream %d, samplingRate %d, format %x, channelMask %x, flags %x",          device, stream, samplingRate, format, channelMask, flags);    return getOutputForDevice(device, AUDIO_SESSION_ALLOCATE, stream, samplingRate, format,                              channelMask, flags, offloadInfo);}

根据stream获取strategy

StreamType指PCM的生成类型。是播放电影产生的？还是通话产生的？

STRATEGY指针对某一中stream,该采用的策略。在策略里面，会根据其他信息来具体选定某一个具体的Audio Devices

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);}// 不同的stream类型对应的stragegy，播放音乐，系统铃声，stream = 1, AUDIO_STREAM_SYSTEM = 1,frameworks\av\services\audiopolicy\enginedefault\src\Engine.cpprouting_strategy Engine::getStrategyForStream(audio_stream_type_t stream){    // stream to strategy mapping    switch (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 result    case 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;    }}frameworks\av\services\audiopolicy\common\include\RoutingStrategy.henum routing_strategy {    STRATEGY_MEDIA,    STRATEGY_PHONE,    STRATEGY_SONIFICATION,    STRATEGY_SONIFICATION_RESPECTFUL,    STRATEGY_DTMF,    STRATEGY_ENFORCED_AUDIBLE,    STRATEGY_TRANSMITTED_THROUGH_SPEAKER,    STRATEGY_ACCESSIBILITY,    STRATEGY_REROUTING,    NUM_STRATEGIES};// STREAM类型定义typedef enum {    AUDIO_STREAM_DEFAULT = -1, // (-1)    AUDIO_STREAM_MIN = 0,    AUDIO_STREAM_VOICE_CALL = 0,    AUDIO_STREAM_SYSTEM = 1,    AUDIO_STREAM_RING = 2,    AUDIO_STREAM_MUSIC = 3,    AUDIO_STREAM_ALARM = 4,    AUDIO_STREAM_NOTIFICATION = 5,    AUDIO_STREAM_BLUETOOTH_SCO = 6,    AUDIO_STREAM_ENFORCED_AUDIBLE = 7,    AUDIO_STREAM_DTMF = 8,    AUDIO_STREAM_TTS = 9,    AUDIO_STREAM_ACCESSIBILITY = 10,    AUDIO_STREAM_REROUTING = 11,    AUDIO_STREAM_PATCH = 12,    AUDIO_STREAM_PUBLIC_CNT = 11, // (ACCESSIBILITY + 1)    AUDIO_STREAM_FOR_POLICY_CNT = 12, // PATCH    AUDIO_STREAM_CNT = 13, // (PATCH + 1)} audio_stream_type_t;

根据Strategy获取device

audio_devices_t AudioPolicyManager::getDeviceForStrategy(routing_strategy strategy,                                                         bool fromCache){    // Routing    // see if we have an explicit route    // scan the whole RouteMap, for each entry, convert the stream type to a strategy    // (getStrategy(stream)).    // if the strategy from the stream type in the RouteMap is the same as the argument above,    // and activity count is non-zero and the device in the route descriptor is available    // then select this device.    for (size_t routeIndex = 0; routeIndex < mOutputRoutes.size(); routeIndex++) {        sp
    
      route = mOutputRoutes.valueAt(routeIndex);        routing_strategy routeStrategy = getStrategy(route->mStreamType);        // 判断输入的STRAGEGY是否在系统支持的mOutputRoutes列表里面        if ((routeStrategy == strategy) && route->isActive() &&                (mAvailableOutputDevices.indexOf(route->mDeviceDescriptor) >= 0)) {            return route->mDeviceDescriptor->type();        }    }    if (fromCache) {        ALOGVV("getDeviceForStrategy() from cache strategy %d, device %x",              strategy, mDeviceForStrategy[strategy]);        return mDeviceForStrategy[strategy];    }    // 传入的stragegy = STRATEGY_MEDIA    return mEngine->getDeviceForStrategy(strategy);}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);}frameworks\av\services\audiopolicy\enginedefault\src\Engine.cppaudio_devices_t Engine::getDeviceForStrategyInt(routing_strategy strategy,                                                DeviceVector availableOutputDevices,                                                DeviceVector availableInputDevices,                                                const SwAudioOutputCollection &outputs) const{    uint32_t device = AUDIO_DEVICE_NONE;    uint32_t availableOutputDevicesType = availableOutputDevices.types();    bool isFmA2dpConcurrencyOn = property_get_bool("vendor.fm.a2dp.conc.disabled", false);    // Do not support a2dp device when FM is active based on concurrency property    if (isFmA2dpConcurrencyOn && (availableOutputDevicesType & AUDIO_DEVICE_OUT_FM)) {        ALOGV("FM a2dp concurrency is set, not considering a2dp for device selection");        availableOutputDevicesType = availableOutputDevicesType & ~AUDIO_DEVICE_OUT_ALL_A2DP;    }// 传入的stragegy = STRATEGY_MEDIA = 0    switch (strategy) {    // FIXME: STRATEGY_REROUTING follow STRATEGY_MEDIA for now    case STRATEGY_REROUTING:    case STRATEGY_MEDIA: {        uint32_t device2 = AUDIO_DEVICE_NONE;        // 是否在打电话        if (isInCall() && (device == AUDIO_DEVICE_NONE)) {            // when in call, get the device for Phone strategy            device = getDeviceForStrategy(STRATEGY_PHONE);            break;        }        if (strategy != STRATEGY_SONIFICATION) {            // no sonification on remote submix (e.g. WFD)            // 查看是否有远程设备            if (availableOutputDevices.getDevice(AUDIO_DEVICE_OUT_REMOTE_SUBMIX,                                                 String8("0")) != 0) {                device2 = availableOutputDevices.types() & AUDIO_DEVICE_OUT_REMOTE_SUBMIX;            }        }        // 打电话, 并且播放音乐还有系统铃声时的处理        if (isInCall() && (strategy == STRATEGY_MEDIA)) {            device = getDeviceForStrategyInt(                    STRATEGY_PHONE, availableOutputDevices, availableInputDevices, outputs);            break;        }        // 蓝牙耳机        if ((device2 == AUDIO_DEVICE_NONE) &&                (mForceUse[AUDIO_POLICY_FORCE_FOR_MEDIA] != AUDIO_POLICY_FORCE_NO_BT_A2DP) &&                (outputs.isA2dpOnPrimary() || (outputs.getA2dpOutput() != 0))) {            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;            }        }        // SPEAKER        if ((device2 == AUDIO_DEVICE_NONE) &&            (mForceUse[AUDIO_POLICY_FORCE_FOR_MEDIA] == AUDIO_POLICY_FORCE_SPEAKER)) {            device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_SPEAKER;        }        // 听筒        if (device2 == AUDIO_DEVICE_NONE) {            device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_WIRED_HEADPHONE;        }        if (device2 == AUDIO_DEVICE_NONE) {            device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_LINE;        }        // 有线耳机        if (device2 == AUDIO_DEVICE_NONE) {            device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_WIRED_HEADSET;        }        // USB耳机        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) &&                (device == AUDIO_DEVICE_NONE)) {            // no sonification on aux digital (e.g. HDMI)            device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_AUX_DIGITAL;        }        if ((device2 == AUDIO_DEVICE_NONE) && (strategy != STRATEGY_SONIFICATION) &&                (mForceUse[AUDIO_POLICY_FORCE_FOR_DOCK] == AUDIO_POLICY_FORCE_ANALOG_DOCK)) {            device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_ANLG_DOCK_HEADSET;        }        if ((device2 == AUDIO_DEVICE_NONE) && (strategy != STRATEGY_SONIFICATION) &&                (device == AUDIO_DEVICE_NONE)) {            // no sonification on WFD sink            device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_PROXY;        }        if (device2 == AUDIO_DEVICE_NONE) {            device2 = availableOutputDevicesType & AUDIO_DEVICE_OUT_SPEAKER;        }        int device3 = AUDIO_DEVICE_NONE;        // 几个设备同时输出        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 otherwise        device |= 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 instead        if ((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;    default:        ALOGW("getDeviceForStrategy() unknown strategy: %d", strategy);        break;    }    if (device == AUDIO_DEVICE_NONE) {        ALOGV("getDeviceForStrategy() no device found for strategy %d", strategy);        device = mApmObserver->getDefaultOutputDevice()->type();        ALOGE_IF(device == AUDIO_DEVICE_NONE,                 "getDeviceForStrategy() no default device defined");    }    ALOGVV("getDeviceForStrategy() strategy %d, device %x", strategy, device);    return device;}
    

为设备选择的输出通道

// APM_AudioPolicyManager: getOutput() device 2, stream 1, samplingRate 0, format 0, channelMask 3, flags 0

audio_io_handle_t AudioPolicyManager::getOutputForDevice(        audio_devices_t device,        audio_session_t session,        audio_stream_type_t stream,        uint32_t samplingRate,        audio_format_t format,        audio_channel_mask_t channelMask,        audio_output_flags_t flags,        const audio_offload_info_t *offloadInfo)hardware\qcom\audio\hal\msm8916\platform.cstatic int msm_device_to_be_id_internal_codec [][NO_COLS] = {       {AUDIO_DEVICE_OUT_EARPIECE                       ,       34},       {AUDIO_DEVICE_OUT_SPEAKER                        ,       34},       {AUDIO_DEVICE_OUT_WIRED_HEADSET                  ,       34},       {AUDIO_DEVICE_OUT_WIRED_HEADPHONE                ,       34},       {AUDIO_DEVICE_OUT_BLUETOOTH_SCO                  ,       11},       {AUDIO_DEVICE_OUT_BLUETOOTH_SCO_HEADSET          ,       11},       {AUDIO_DEVICE_OUT_BLUETOOTH_SCO_CARKIT           ,       11},       {AUDIO_DEVICE_OUT_BLUETOOTH_A2DP                 ,       -1},       {AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES      ,       -1},       {AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER         ,       -1},       {AUDIO_DEVICE_OUT_AUX_DIGITAL                    ,       4},       {AUDIO_DEVICE_OUT_ANLG_DOCK_HEADSET              ,       9},       {AUDIO_DEVICE_OUT_DGTL_DOCK_HEADSET              ,       9},       {AUDIO_DEVICE_OUT_USB_ACCESSORY                  ,       -1},       {AUDIO_DEVICE_OUT_USB_DEVICE                     ,       -1},       {AUDIO_DEVICE_OUT_USB_HEADSET                    ,       -1},       {AUDIO_DEVICE_OUT_REMOTE_SUBMIX                  ,       9},       {AUDIO_DEVICE_OUT_PROXY                          ,       9},       {AUDIO_DEVICE_OUT_FM                             ,       7},       {AUDIO_DEVICE_OUT_FM_TX                          ,       8},       {AUDIO_DEVICE_OUT_ALL                            ,      -1},       {AUDIO_DEVICE_NONE                               ,      -1},       {AUDIO_DEVICE_OUT_DEFAULT                        ,      -1},};static int msm_device_to_be_id_external_codec [][NO_COLS] = {       {AUDIO_DEVICE_OUT_EARPIECE                       ,       2},       {AUDIO_DEVICE_OUT_SPEAKER                        ,       2},       {AUDIO_DEVICE_OUT_WIRED_HEADSET                  ,       41},       {AUDIO_DEVICE_OUT_WIRED_HEADPHONE                ,       41},       {AUDIO_DEVICE_OUT_BLUETOOTH_SCO                  ,       11},       {AUDIO_DEVICE_OUT_BLUETOOTH_SCO_HEADSET          ,       11},       {AUDIO_DEVICE_OUT_BLUETOOTH_SCO_CARKIT           ,       11},       {AUDIO_DEVICE_OUT_BLUETOOTH_A2DP                 ,       -1},       {AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES      ,       -1},       {AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER         ,       -1},       {AUDIO_DEVICE_OUT_AUX_DIGITAL                    ,       4},       {AUDIO_DEVICE_OUT_ANLG_DOCK_HEADSET              ,       9},       {AUDIO_DEVICE_OUT_DGTL_DOCK_HEADSET              ,       9},       {AUDIO_DEVICE_OUT_USB_ACCESSORY                  ,       -1},       {AUDIO_DEVICE_OUT_USB_DEVICE                     ,       -1},       {AUDIO_DEVICE_OUT_USB_HEADSET                    ,       -1},       {AUDIO_DEVICE_OUT_REMOTE_SUBMIX                  ,       9},       {AUDIO_DEVICE_OUT_PROXY                          ,       9},       {AUDIO_DEVICE_OUT_FM                             ,       7},       {AUDIO_DEVICE_OUT_FM_TX                          ,       8},       {AUDIO_DEVICE_OUT_ALL                            ,      -1},       {AUDIO_DEVICE_NONE                               ,      -1},       {AUDIO_DEVICE_OUT_DEFAULT                        ,      -1},};