(总结)音频输出设备的获取流程
文章目录
- 1 AudioTrack创建时获取output
- 2 getOutputForAttr函数内的获取流程
- 2.1 attr的获取
- 2.2 attr -> strategy
- 2.3 strategy -> device
- 2.3 device -> output
- outputdevice的定义
本文根据zhuyong006的音频输出设备是如何决定的文章进行总结。
1 AudioTrack创建时获取output
AudioTrack的函数调用情况如下：
AudioTrack::AudioTrack|- AudioTrack::set|- AudioTrack::createTrack_l|- AudioSystem::getOutputForAttr
其中AudioSystem::getOutputForAttr()函数根据attr获取output。
2 getOutputForAttr函数内的获取流程
attr -> strategy -> device -> output
2.1 attr的获取
我们从使用的地方往上推，看看attr是从哪里获取的，参考下上面的函数调用flow。
//AudioTrack.cpp
status_t AudioTrack::createTrack_l()
{//attr源于mAttributes audio_attributes_t *attr = (mStreamType == AUDIO_STREAM_DEFAULT) ? &mAttributes : NULL;status = AudioSystem::getOutputForAttr(attr, &output,mSessionId, &streamType, mClientUid,&config,mFlags, &mRoutedDeviceId, &mPortId);
}//AudioTrack.h
class AudioTrack : public AudioSystem::AudioDeviceCallback
{audio_attributes_t mAttributes;
}status_t AudioTrack::set(audio_stream_type_t streamType,uint32_t sampleRate,audio_format_t format,audio_channel_mask_t channelMask,size_t frameCount,audio_output_flags_t flags,callback_t cbf,void* user,int32_t notificationFrames,const sp<IMemory>& sharedBuffer,bool threadCanCallJava,audio_session_t sessionId,transfer_type transferType,const audio_offload_info_t *offloadInfo,uid_t uid,pid_t pid,const audio_attributes_t* pAttributes,//这里bool doNotReconnect, //默认值float maxRequiredSpeed) //默认值
{if (pAttributes == NULL) {//······} else {// stream type shouldn't be looked at, this track has audio attributesmemcpy(&mAttributes, pAttributes, sizeof(audio_attributes_t));//处理attrmStreamType = AUDIO_STREAM_DEFAULT;if ((mAttributes.flags & AUDIO_FLAG_HW_AV_SYNC) != 0) {flags = (audio_output_flags_t)(flags | AUDIO_OUTPUT_FLAG_HW_AV_SYNC);}if ((mAttributes.flags & AUDIO_FLAG_LOW_LATENCY) != 0) {flags = (audio_output_flags_t) (flags | AUDIO_OUTPUT_FLAG_FAST);}// check deep buffer after flags have been modified aboveif (flags == AUDIO_OUTPUT_FLAG_NONE && (mAttributes.flags & AUDIO_FLAG_DEEP_BUFFER) != 0) {flags = AUDIO_OUTPUT_FLAG_DEEP_BUFFER;}}
}AudioTrack::AudioTrack(audio_stream_type_t streamType,uint32_t sampleRate,audio_format_t format,audio_channel_mask_t channelMask,const sp<IMemory>& sharedBuffer,audio_output_flags_t flags,callback_t cbf,void* user,int32_t notificationFrames,audio_session_t sessionId,transfer_type transferType,const audio_offload_info_t *offloadInfo,uid_t uid,pid_t pid,const audio_attributes_t* pAttributes, //herebool doNotReconnect,float maxRequiredSpeed): mStatus(NO_INIT),mState(STATE_STOPPED),mPreviousPriority(ANDROID_PRIORITY_NORMAL),mPreviousSchedulingGroup(SP_DEFAULT),mPausedPosition(0),mSelectedDeviceId(AUDIO_PORT_HANDLE_NONE),mPauseTimeRealUs(0),mPortId(AUDIO_PORT_HANDLE_NONE),mTrackOffloaded(false)
{mStatus = set(streamType, sampleRate, format, channelMask,0 /*frameCount*/, flags, cbf, user, notificationFrames,sharedBuffer, false /*threadCanCallJava*/, sessionId, transferType, offloadInfo,uid, pid, pAttributes, doNotReconnect, maxRequiredSpeed);
}createTrack_l函数中，判断mStreamType是否为默认值AUDIO_STREAM_DEFAULT，是的话就把mAttributes赋给attr。
createTrack_l()函数没有入参，推断这个mAttributes应该是AudioTrack的成员变量。看来下头文件，确实是，那么再往上看。
set函数中发现是将传入的参数pAttributes按照audio_attributes_t类型赋值给mAttributes。再追踪下构造函数。
构造函数中发现是传入参数，那么确定了attr是由创建audiotrack的时候赋值的，推断应该是应用层传下来，以soundpool为例看下出处。
//soundpool.cpp
void SoundChannel::play(const sp<Sample>& sample, int nextChannelID, float leftVolume,float rightVolume, int priority, int loop, float rate)
{newTrack = new AudioTrack(streamType, sampleRate, sample->format(),channelMask, frameCount, AUDIO_OUTPUT_FLAG_FAST, callback, userData,bufferFrames, AUDIO_SESSION_ALLOCATE, AudioTrack::TRANSFER_DEFAULT,NULL /*offloadInfo*/, -1 /*uid*/, -1 /*pid*/, mSoundPool->attributes());
}//soundpool.cpp
class SoundPool {const audio_attributes_t* attributes() { return &mAttributes; }audio_attributes_t mAttributes;
}
最后一个参数就是attr的由来。（ps：最后两个参数可不写，因为设了默认值）
attributes()函数是soundpool的成员函数，只是获取其成员变量mAttributes。
看下soundpool的构造函数
//audio.h
typedef struct {audio_content_type_t content_type;audio_usage_t usage;audio_source_t source;audio_flags_mask_t flags;char tags[AUDIO_ATTRIBUTES_TAGS_MAX_SIZE]; /* UTF8 */
} audio_attributes_t;//SoundPool.cpp
SoundPool::SoundPool(int maxChannels, const audio_attributes_t* pAttributes)memcpy(&mAttributes, pAttributes, sizeof(audio_attributes_t));
}
SoundPool构造函数中将传入的参数pAttributes赋值给成员变量mAttributes。
好的，就追踪到这里，soundpool的创建应该是应用层的，那么确定了，应用层传下attr。
2.2 attr -> strategy
createTrack_l的函数调用flow
AudioTrack::createTrack_l|- AudioSystem::getOutputForAttr|- AudioPolicyService::getOutputForAttr|- AudioPolicyManager::getOutputForAttr|- getStrategyForAttr|- getDeviceForStrategy|- AudioPolicyManager::getOutputForDevice
createTrack_l中的AudioSystem::getOutputForAttr最终调用到AudioPolicyManager::getOutputForAttr，调用流程可以参考的我另一篇文章：Android获取音频输出getOutput和设置
接下来，我们从getStrategyForAttr看起。
- getStrategyForAttr在getOutputForAttr中被调用：
//AudioPolicyManager.cpp
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strategyrouting_strategy strategy = (routing_strategy) getStrategyForAttr(&attributes);//获取device类型audio_devices_t device = getDeviceForStrategy(strategy, false /*fromCache*/);//获取output*output = getOutputForDevice(device, session, *stream,config->sample_rate, config->format, config->channel_mask,flags, &config->offload_info);
}//routingstrategy.h
enum 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
};
头文件中看到了音频路径策略是enum类型，有这几种，最常见的是STRATEGY_MEDIA。
- getStrategyForAttr的函数定义
//AudioPolicyManager.cpp
uint32_t AudioPolicyManager::getStrategyForAttr(const audio_attributes_t *attr) {// flags to strategy mappingif ((attr->flags & AUDIO_FLAG_BEACON) == AUDIO_FLAG_BEACON) {return (uint32_t) STRATEGY_TRANSMITTED_THROUGH_SPEAKER;}if ((attr->flags & AUDIO_FLAG_AUDIBILITY_ENFORCED) == AUDIO_FLAG_AUDIBILITY_ENFORCED) {return (uint32_t) STRATEGY_ENFORCED_AUDIBLE;}// usage to strategy mappingreturn static_cast<uint32_t>(mEngine->getStrategyForUsage(attr->usage));
}
具体调用就不找了，这篇文章写的很好。参考文章
2.3 strategy -> device
- 调用
//audio.h
typedef uint32_t audio_devices_t;//AudioPolicyManager.cpp
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)
{audio_devices_t device = getDeviceForStrategy(strategy, false /*fromCache*/);
}
注意一下，audio_devices_t变量的类型是uint32_t，这里的device只是设备类型，不是真的device。
- getDeviceForStrategy函数定义
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<SessionRoute> route = mOutputRoutes.valueAt(routeIndex);routing_strategy routeStrategy = getStrategy(route->mStreamType);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];}#if 0return mEngine->getDeviceForStrategy(strategy);#else
/* OEM 20171027 Jack W Lu, Add Audio Policy Setting {*/audio_devices_t device2;char project_id[PROPERTY_VALUE_MAX];device2 = mEngine->getDeviceForStrategy(strategy);// property_get("ro.product.model", project_id, "");if(userManualAudioPolicy != 0){ALOGE("enforce User Strategy : %d", userManualAudioPolicy);enforceUserStrategy(device2, userManualAudioPolicy);}ALOGV("proj=%s, device2 = %d", project_id, device2);return device2;#endif
/* OEM 20171027 Jack W Lu, Add Audio Policy Setting }*/
}//AudioPolicyManager.h
//头文件中定义了该数组
audio_devices_t mDeviceForStrategy[NUM_STRATEGIES];//初始化mDeviceForStrategy数组
void AudioPolicyManager::updateDevicesAndOutputs()
{for (int i = 0; i < NUM_STRATEGIES; i++) {mDeviceForStrategy[i] = getDeviceForStrategy((routing_strategy)i, false /*fromCache*/);}mPreviousOutputs = mOutputs;
}
getDeviceForStrategy函数就是遍历了mDeviceForStrategy数组，通过strategy获取需要的device。
mDeviceForStrategy的初始化函数被调用我没有查，有空再细看
总结：这里只需要知道通过strategy获取了device 类型。
具体的函数调用查看参考文章。
2.3 device -> output
这个部分可以参考我的文章：Android获取音频输出getOutput和设置
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)
{//······non_direct_output:if ((flags & AUDIO_OUTPUT_FLAG_HW_AV_SYNC) != 0) {return AUDIO_IO_HANDLE_NONE;}if (audio_is_linear_pcm(format)) {SortedVector<audio_io_handle_t> outputs = getOutputsForDevice(device, mOutputs);flags = (audio_output_flags_t)(flags & ~AUDIO_OUTPUT_FLAG_DIRECT);output = selectOutput(outputs, flags, format);}return output;
}
这里有两种情况
- 重新打开output，参考我的文章
- audiopolicymanager构造函数中打开了outputs中选择一个合适的output
选择方法：
传入的device有对应的outputs表（这些outputs支持该类型的device），根据flags音频标识获取output。
总结：有device类型获取output
outputdevice的定义
audiopolicymanager构造函数中解析了config文件，config文件中包含了特定output下的设备信息，具体的device调用之后再看。
本文本就是对这篇文章的总结，写的比较简单，建议结合该文章进行理解。
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