音轨|制定者_Android音频源码分析——AudioFlinger

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Android 音频源码分析——AndroidRecord录音&＃xff08;一&＃xff09;
Android 音频源码分析——AndroidRecord录音&＃xff08;二&＃xff09;
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

源码基于Android9.0

混音&＃xff1a;把多种来源的声音&＃xff0c;整合至一个立体音轨或单音轨中。

AudioFlinger和AudioPolicyService是音频中的两大服务&＃xff0c;这里先整理下AudioFlinger。

AudioPolicyService时策略制定者&＃xff0c;不和AudioHal直接交互&＃xff1b;而AudioFlinger是策略执行者&＃xff0c;与AudioHal层进行交互。

简介

AudioFlinger运行在audioserver进程中&＃xff0c;是一个音频服务。主要职责&＃xff1a;

1. 音频数据接收和转发&＃xff0c;录音时从HAL层获取音频数据&＃xff0c;转给客户端&＃xff1b;播放时从客户端获取数据&＃xff0c;并发送给HAL层。
2. 音频数据处理&＃xff0c;包括数据格式转换、声道数转换、重采样、混音、音效、变速、音量等。
3. 执行AudioFlinger的策略。

与HAL层通信

framework层hidl相关代码目录&＃xff1a; frameworks/av/media/libaudiohal

hal层hidl相关代码&＃xff1a; hardware/interfaces/audio

 AudioFlinger通过hidl接口的方式调用hal层服务。有上一篇文章可知&＃xff0c;启动AudioPolicyService时&＃xff0c;会加载音频配置文件&＃xff0c;然后根据配置加载HAL module。后续可以调用hal接口进行其他交互&＃xff08;设备选择、通路、读写数据等&＃xff09;。

AudioPolicyService并不直接于Hal层交互&＃xff0c;而是由AudioFlinger和Hal通信&＃xff0c;这里看看AudioFlinger加载音频模块。

1 加载Module

audio_module_handle_t AudioFlinger::loadHwModule(const char *name)

if (name &＃61;&＃61; NULL)
return AUDIO_MODULE_HANDLE_NONE;

if (!settingsAllowed())
return AUDIO_MODULE_HANDLE_NONE;

Mutex::Autolock _l(mLock);
return loadHwModule_l(name);

// loadHwModule_l() must be called with AudioFlinger::mLock held
audio_module_handle_t AudioFlinger::loadHwModule_l(const char *name)

sp<DeviceHalInterface> dev;
int rc &＃61; mDevicesFactoryHal->openDevice(name, &dev);
//......
audio_module_handle_t handle &＃61; (audio_module_handle_t) nextUniqueId(AUDIO_UNIQUE_ID_USE_MODULE);
mAudioHwDevs.add(handle, new AudioHwDevice(handle, name, dev, flags));
return handle;



加载hal层module,mAudioHwDevs保存handle 和AudioHwDevice.

接着看mDevicesFactoryHal->openDevice流程

mDevicesFactoryHal->openDevice(name, &dev);
>>DevicesFactoryHalHybrid::openDevice
>>
status_t DevicesFactoryHalHidl::openDevice(const char *name, sp<DeviceHalInterface> *device)
if (mDevicesFactory &＃61;&＃61; 0) return NO_INIT;
IDevicesFactory::Device hidlDevice;
status_t status &＃61; nameFromHal(name, &hidlDevice);
if (status !&＃61; OK) return status;
Result retval &＃61; Result::NOT_INITIALIZED;
Return<void> ret &＃61; mDevicesFactory->openDevice(
hidlDevice,
[&](Result r, const sp<IDevice>& result)
retval &＃61; r;
if (retval &＃61;&＃61; Result::OK)
*device &＃61; new DeviceHalHidl(result);

);
if (ret.isOk())
if (retval &＃61;&＃61; Result::OK) return OK;
else if (retval &＃61;&＃61; Result::INVALID_ARGUMENTS) return BAD_VALUE;
else return NO_INIT;

return FAILED_TRANSACTION;



1. nameFromHal通过name获取Device类型&＃xff1a;IDevicesFactory::Device::PRIMARY、IDevicesFactory::Device::A2DP、IDevicesFactory::Device::USB、IDevicesFactory::Device::R_SUBMIX等&＃xff1b;
2. mDevicesFactory->openDevice通过hidl跨进程调用接口

hardware/interfaces/audio/core/all-versions/default/include/core/all-version/DevicesFactory.impl.h

Return<void> DevicesFactory::openDevice(IDevicesFactory::Device device, openDevice_cb _hidl_cb)
switch (device)
case IDevicesFactory::Device::PRIMARY:
return openDevice<PrimaryDevice>(AUDIO_HARDWARE_MODULE_ID_PRIMARY, _hidl_cb);
case IDevicesFactory::Device::A2DP:
return openDevice(AUDIO_HARDWARE_MODULE_ID_A2DP, _hidl_cb);
case IDevicesFactory::Device::USB:
return openDevice(AUDIO_HARDWARE_MODULE_ID_USB, _hidl_cb);
case IDevicesFactory::Device::R_SUBMIX:
return openDevice(AUDIO_HARDWARE_MODULE_ID_REMOTE_SUBMIX, _hidl_cb);
case IDevicesFactory::Device::STUB:
return openDevice(AUDIO_HARDWARE_MODULE_ID_STUB, _hidl_cb);

_hidl_cb(Result::INVALID_ARGUMENTS, nullptr);
return Void();

int DevicesFactory::loadAudioInterface(const char* if_name, audio_hw_device_t** dev)
const hw_module_t* mod;
int rc;
rc &＃61; hw_get_module_by_class(AUDIO_HARDWARE_MODULE_ID, if_name, &mod);
if (rc)
ALOGE("%s couldn&＃39;t load audio hw module %s.%s (%s)", __func__, AUDIO_HARDWARE_MODULE_ID,
if_name, strerror(-rc));
goto out;

rc &＃61; audio_hw_device_open(mod, dev);
if (rc)
ALOGE("%s couldn&＃39;t open audio hw device in %s.%s (%s)", __func__, AUDIO_HARDWARE_MODULE_ID,
if_name, strerror(-rc));
goto out;

if ((*dev)->common.version < AUDIO_DEVICE_API_VERSION_MIN)
ALOGE("%s wrong audio hw device version %04x", __func__, (*dev)->common.version);
rc &＃61; -EINVAL;
audio_hw_device_close(*dev);
goto out;

return OK;
out:
*dev &＃61; NULL;
return rc;



1. hw_get_module_by_class动态链接 hal 库&＃xff0c;如&＃xff1a;audio.primary.default.so、audio.a2dp.default.so、audio.usb.default.so
2. audio_hw_device_open对应module method->open函数

2 open stream

这里看看加载后的openOutput流程

status_t AudioFlinger::openOutput(audio_module_handle_t module,
audio_io_handle_t *output,
audio_config_t *config,
audio_devices_t *devices,
const String8& address,
uint32_t *latencyMs,
audio_output_flags_t flags)

if (devices &＃61;&＃61; NULL || *devices &＃61;&＃61; AUDIO_DEVICE_NONE)
return BAD_VALUE;

Mutex::Autolock _l(mLock);
sp<ThreadBase> thread &＃61; openOutput_l(module, output, config, *devices, address, flags);
//......
return NO_INIT;

sp<AudioFlinger::ThreadBase> AudioFlinger::openOutput_l(audio_module_handle_t module,
audio_io_handle_t *output,
audio_config_t *config,
audio_devices_t devices,
const String8& address,
audio_output_flags_t flags)

AudioHwDevice *outHwDev &＃61; findSuitableHwDev_l(module, devices);
//......
AudioStreamOut *outputStream &＃61; NULL;
status_t status &＃61; outHwDev->openOutputStream(
&outputStream,
*output,
devices,
flags,
config,
address.string());
mHardwareStatus &＃61; AUDIO_HW_IDLE;
if (status &＃61;&＃61; NO_ERROR)
if (flags & AUDIO_OUTPUT_FLAG_MMAP_NOIRQ)
sp<MmapPlaybackThread> thread &＃61;
new MmapPlaybackThread(this, *output, outHwDev, outputStream,
devices, AUDIO_DEVICE_NONE, mSystemReady);
mMmapThreads.add(*output, thread);
return thread;
else
sp<PlaybackThread> thread;
if (flags & AUDIO_OUTPUT_FLAG_COMPRESS_OFFLOAD)
thread &＃61; new OffloadThread(this, outputStream, *output, devices, mSystemReady);
else if ((flags & AUDIO_OUTPUT_FLAG_DIRECT)
|| !isValidPcmSinkFormat(config->format)
|| !isValidPcmSinkChannelMask(config->channel_mask))
thread &＃61; new DirectOutputThread(this, outputStream, *output, devices, mSystemReady);
else
thread &＃61; new MixerThread(this, outputStream, *output, devices, mSystemReady);

mPlaybackThreads.add(*output, thread);
return thread;


return 0;



1. findSuitableHwDev_l找寻对应的AudioHwDevice&＃xff1b;
2. openOutputStream打开输出Stream&＃xff0c;这里会调用到hal层 adev_open_output_stream中&＃xff0c;这里就不分析了&＃xff1b;
3. 根据flags创建不同的通路线程&＃xff1b;
4. 将线程添加到mPlaybackThreads&＃xff1b;

openinput 流程就先不分析了。

与APP通信

App和AudioFlinger间音频数据则通过共享内存的方式进行传输。

如下图AudioRecord的数据传输&＃xff1a;

如下图AudioTrack的数据传输&＃xff1a;

AudioFlinger是一个binder服务&＃xff0c;app中的native层可以通过获取其binder服务从而进行交互。

如下示例&＃xff1a;

const sp<IAudioFlinger>& audioFlinger &＃61; AudioSystem::get_audio_flinger();
record &＃61; audioFlinger->createRecord(input,
output,
&status);