基于Android 9.0
1.概述
在《Android 音频子系统--03：从开机到audioserver启动》章节中，分析的audioserver启动过程中，audioserver的main()方法中会启动音频框架中两大服务：AudioFlinger和AudioPolicyService，这章将继续从启动AudioPolicyService服务开始，分析AudioPolicyService相关的流程。
根据上面的思维导图，主要是对AudioPolicyService启动的分析，涉及从AudioPolicyService启动流程到 AudioPolicyManager流程和AudioPolicyManager详细分析流程（加载配置文件，loadHwModule，openOutput，这里涉及的AudioFlinger相关操作在下一节中详细分析其流程）。
2.从AudioPolicyService启动流程到AudioPolicyManager
AudioPolicyService的启动是在main_audioserver.cpp中实现，代码如下：
// frameworks/av/media/audioserver/main_audioserver.cpp
int main(int argc __unused, char **argv)
{
// ......
android::hardware::configureRpcThreadpool(4, false /*callerWillJoin*/);
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm = defaultServiceManager();
ALOGI("ServiceManager: %p", sm.get());
AudioFlinger::instantiate(); // 启动AudioFlinger
AudioPolicyService::instantiate(); // 启动AudioPolicyService
// .....
}
这里AudioFlinger服务先启动，之后AudioPolicyService启动就可以直接使用AudioFlinger服务了。此处专注分析AudioPolicyService::instantiate()的实现，AudioFlinger和AudioPolicyService等几个服务都统一继承于Binder服务类代码如下：
// frameworks/native/include/binder/BinderService.h
static void instantiate() { publish(); }
继续分析publish，代码如下：
// frameworks/native/libs/binder/include/binder/BinderService.h
static status_t publish(bool allowIsolated = false,
int dumpFlags = IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT) {
sp<IServiceManager> sm(defaultServiceManager());
return sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated,
dumpFlags);//注册服务到servicemanager中
}
这里会创建 一个AudioPolicyService，并将该服务注册到service_manager 中。创建服务会执行AudioPolicyService的构造器，代码如下：
// frameworks/av/services/audiopolicy/service/AudioPolicyService.cpp
AudioPolicyService::AudioPolicyService()
: BnAudioPolicyService(), mpAudioPolicyDev(NULL), mpAudioPolicy(NULL),
mAudioPolicyManager(NULL), mAudioPolicyClient(NULL), mPhoneState(AUDIO_MODE_INVALID)
{
}
主要是一些变量的初始化，AudioPolicyService由BnAudioPolicyService继承到RefBase.cpp，在第一次引用时会执行onFirstRef()，这个函数很重要，派生类可以重载这个函数，完成一些初始化工作，代码如下：
// frameworks/av/services/audiopolicy/service/AudioPolicyService.cpp
void AudioPolicyService::onFirstRef()
{
{
Mutex::Autolock _l(mLock);
// 创建3个线程：
// 线程1：用于执行tone播放命令
// start tone playback thread
mTonePlaybackThread = new AudioCommandThread(String8("ApmTone"), this);
// 线程2：用于执行audio命令
// start audio commands thread
mAudioCommandThread = new AudioCommandThread(String8("ApmAudio"), this);
//线程3：用于执行输出命令
// start output activity command thread
mOutputCommandThread = new AudioCommandThread(String8("ApmOutput"), this);
//AudioFlinger客户端实现，调用AudioFlinger的一些服务
mAudioPolicyClient = new AudioPolicyClient(this);
// 创建AudioPolicyManager
mAudioPolicyManager = createAudioPolicyManager(mAudioPolicyClient);
}
// load audio processing modules
sp<AudioPolicyEffects>audioPolicyEffects = new AudioPolicyEffects();
{
Mutex::Autolock _l(mLock);
mAudioPolicyEffects = audioPolicyEffects;
}
mUidPolicy = new UidPolicy(this);
mUidPolicy->registerSelf();
}
这里主要关注createAudioPolicyManager的实现，代码如下：
// frameworks/av/services/audiopolicy/manager/AudioPolicyFactory.cpp
extern "C" AudioPolicyInterface* createAudioPolicyManager(
AudioPolicyClientInterface *clientInterface)
{
return new AudioPolicyManager(clientInterface);
}
接下来继续分析AudioPolicyManager的实现。
3.AudioPolicyManager详细分析
AudioPolicyManager的代码实现如下：
// frameworks/av/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
AudioPolicyManager::AudioPolicyManager(AudioPolicyClientInterface *clientInterface)
: AudioPolicyManager(clientInterface, false /*forTesting*/)
{
//关键点1：解析配置文件
loadConfig();
initialize();
}
下面看一下loadConfig()方法的具体实现：
// frameworks/av/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
void AudioPolicyManager::loadConfig() {
/*
系统会首先加载vendor/etc目录下的configure文件，再加载system/etc目录下的configure文件。
若这两者加载都发生错误的话，系统会加载default配置文件，并命名为primary module，从这可以看
出，音频系统中一定必须存在的module就是primary了。
*/
if (deserializeAudioPolicyXmlConfig(getConfig()) != NO_ERROR) {
ALOGE("could not load audio policy configuration file, setting defaults");
getConfig().setDefault();
}
}
loadConfig加载音频配置文件audio_policy_configuration.xml，对其中的配置项进行解析。再来看一下initialize()方法：
// frameworks/av/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
status_t AudioPolicyManager::initialize() {
// ...
// 省略部分代码
// ...
// mAvailableOutputDevices and mAvailableInputDevices now contain all attached devices
// open all output streams needed to access attached devices
audio_devices_t outputDeviceTypes = mAvailableOutputDevices.types();
audio_devices_t inputDeviceTypes = mAvailableInputDevices.types() & ~AUDIO_DEVICE_BIT_IN;
// 这里的mHwModules就是上面解析配置文件得到信息(primary,a2dp,usb,r_submix)
for (const auto& hwModule : mHwModulesAll) {
//关键点2，使用AudioFlinger加载audio policy硬件抽象库
hwModule->setHandle(mpClientInterface->loadHwModule(hwModule->getName()));
if (hwModule->getHandle() == AUDIO_MODULE_HANDLE_NONE) {
ALOGW("could not open HW module %s", hwModule->getName());
continue;
}
mHwModules.push_back(hwModule);
// open all output streams needed to access attached devices
// except for direct output streams that are only opened when they are actually
// required by an app.
// This also validates mAvailableOutputDevices list
//获取每个音频输出路径的配置
for (const auto& outProfile : hwModule->getOutputProfiles()) {
if (!outProfile->canOpenNewIo()) {
ALOGE("Invalid Output profile max open count %u for profile %s",
outProfile->maxOpenCount, outProfile->getTagName().c_str());
continue;
}
if (!outProfile->hasSupportedDevices()) {
ALOGW("Output profile contains no device on module %s", hwModule->getName());
continue;
}
if ((outProfile->getFlags() & AUDIO_OUTPUT_FLAG_TTS) != 0) {
mTtsOutputAvailable = true;
}
if ((outProfile->getFlags() & AUDIO_OUTPUT_FLAG_DIRECT) != 0) {
continue;
}
const DeviceVector &supportedDevices = outProfile->getSupportedDevices();
DeviceVector availProfileDevices = supportedDevices.filter(mAvailableOutputDevices);
sp<DeviceDescriptor> supportedDevice = 0;
if (supportedDevices.contains(mDefaultOutputDevice)) {
supportedDevice = mDefaultOutputDevice;
} else {
// choose first device present in profile's SupportedDevices also part of
// mAvailableOutputDevices.
if (availProfileDevices.isEmpty()) {
continue;
}
supportedDevice = availProfileDevices.itemAt(0);
}
if (!mAvailableOutputDevices.contains(supportedDevice)) {
continue;
}
//通过outProfile构建SwAudioOutputDescriptor类型的变量outputDesc
sp<SwAudioOutputDescriptor> outputDesc = new SwAudioOutputDescriptor(outProfile,
mpClientInterface);
audio_io_handle_t output = AUDIO_IO_HANDLE_NONE;
//关键点3：openOutput
status_t status = outputDesc->open(nullptr, DeviceVector(supportedDevice),
AUDIO_STREAM_DEFAULT,
AUDIO_OUTPUT_FLAG_NONE, &output);
if (status != NO_ERROR) {
ALOGW("Cannot open output stream for devices %s on hw module %s",
supportedDevice->toString().c_str(), hwModule->getName());
continue;
}
for (const auto &device : availProfileDevices) {
// give a valid ID to an attached device once confirmed it is reachable
if (!device->isAttached()) {
device->attach(hwModule);
}
}
if (mPrimaryOutput == 0 &&
outProfile->getFlags() & AUDIO_OUTPUT_FLAG_PRIMARY) {
mPrimaryOutput = outputDesc;
}
/*保存输出设备描述符对象outputDesc到mOutputs，表示已经打开的Output
*这样以后就可以根据一个整数output 找到对应的thread和outputDesc
*/
addOutput(output, outputDesc);
//设置输出设备
setOutputDevices(outputDesc,
DeviceVector(supportedDevice),
true,
0,
NULL);
}
// 省略：input类似操作
// Silence ALOGV statements
property_set("log.tag." LOG_TAG, "D");
//更新输出设备
updateDevicesAndOutputs();
return status;
}
这里主要分析 3个关键点：解析配置文件，loadHwModule和打开output。
3.1 解析配置文件
上面代码中通过deserializeAudioPolicyXmlConfig()方法去解析配置文件，解析结果保存在AudioPolicyConfig对象中。下面看一下这个方法的实现：
// frameworks/av/services/audiopolicy/managerdefault/AudioPolicyManager.cpp
// 配置文件路径：根据这个先后顺序查找，前面的成功后，后面的不再继续
static const char *kConfigLocationList[] =
{"/odm/etc", "/vendor/etc/audio", "/vendor/etc", "/system/etc"};
static const int kConfigLocationListSize =
(sizeof(kConfigLocationList) / sizeof(kConfigLocationList[0]));
static status_t deserializeAudioPolicyXmlConfig(AudioPolicyConfig &config) {
char audioPolicyXmlConfigFile[AUDIO_POLICY_XML_CONFIG_FILE_PATH_MAX_LENGTH];
std::vector<const char*> fileNames;
status_t ret;
if (property_get_bool("ro.bluetooth.a2dp_offload.supported", false)) {
if (property_get_bool("persist.bluetooth.bluetooth_audio_hal.disabled", false) &&
property_get_bool("persist.bluetooth.a2dp_offload.disabled", false)) {
// Both BluetoothAudio@2.0 and BluetoothA2dp@1.0 (Offlaod) are disabled, and uses
// the legacy hardware module for A2DP and hearing aid.
fileNames.push_back(AUDIO_POLICY_BLUETOOTH_LEGACY_HAL_XML_CONFIG_FILE_NAME);
} else if (property_get_bool("persist.bluetooth.a2dp_offload.disabled", false)) {
// A2DP offload supported but disabled: try to use special XML file
fileNames.push_back(AUDIO_POLICY_A2DP_OFFLOAD_DISABLED_XML_CONFIG_FILE_NAME);
}
} else if (property_get_bool("persist.bluetooth.bluetooth_audio_hal.disabled", false)) {
fileNames.push_back(AUDIO_POLICY_BLUETOOTH_LEGACY_HAL_XML_CONFIG_FILE_NAME);
}
fileNames.push_back(AUDIO_POLICY_XML_CONFIG_FILE_NAME);
for (const char* fileName : fileNames) {
for (int i = 0; i < kConfigLocationListSize; i++) {
snprintf(audioPolicyXmlConfigFile, sizeof(audioPolicyXmlConfigFile),
"%s/%s", kConfigLocationList[i], fileName);
// 根据文件解析
ret = deserializeAudioPolicyFile(audioPolicyXmlConfigFile, &config);
if (ret == NO_ERROR) {
config.setSource(audioPolicyXmlConfigFile);
return ret;
}
}
}
return ret;
}
这里本质上是解析一个文件audio_policy_configuration.xml，这个文件的构造如下：
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<audioPolicyConfiguration version="1.0" xmlns:xi="http://www.w3.org/2001/XInclude">
<!-- version section contains a “version” tag in the form “major.minor” e.g version=”1.0” -->
<!-- Global configuration Decalaration -->
<globalConfiguration speaker_drc_enabled="true"/>
<modules>
<!-- Primary Audio HAL -->
<!-- 一个module对应厂家提供一个so文件 -->
<module name="primary" halVersion="3.0">
<attachedDevices>
<item>Speaker</item>
<item>Built-In Mic</item>
<item>Built-In Back Mic</item>
</attachedDevices>
<defaultOutputDevice>Speaker</defaultOutputDevice>
<mixPorts>
<mixPort name="primary output" role="source" flags="AUDIO_OUTPUT_FLAG_PRIMARY">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
</mixPort>
<mixPort name="deep_buffer" role="source"
flags="AUDIO_OUTPUT_FLAG_DEEP_BUFFER">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
</mixPort>
<mixPort name="compressed_offload" role="source"
flags="AUDIO_OUTPUT_FLAG_DIRECT|AUDIO_OUTPUT_FLAG_COMPRESS_OFFLOAD|AUDIO_OUTPUT_FLAG_NON_BLOCKING">
<profile name="" format="AUDIO_FORMAT_MP3"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_OUT_STEREO,AUDIO_CHANNEL_OUT_MONO"/>
<profile name="" format="AUDIO_FORMAT_AAC"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_OUT_STEREO,AUDIO_CHANNEL_OUT_MONO"/>
<profile name="" format="AUDIO_FORMAT_AAC_LC"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_OUT_STEREO,AUDIO_CHANNEL_OUT_MONO"/>
</mixPort>
<mixPort name="voice_tx" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_OUT_MONO"/>
</mixPort>
<mixPort name="primary input" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_IN_MONO,AUDIO_CHANNEL_IN_STEREO,AUDIO_CHANNEL_IN_FRONT_BACK"/>
</mixPort>
<mixPort name="voice_rx" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_IN_MONO"/>
</mixPort>
</mixPorts>
<devicePorts>
<!-- Output devices declaration, i.e. Sink DEVICE PORT -->
<devicePort tagName="Earpiece" type="AUDIO_DEVICE_OUT_EARPIECE" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_IN_MONO"/>
</devicePort>
<devicePort tagName="Speaker" role="sink" type="AUDIO_DEVICE_OUT_SPEAKER" address="">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
<gains>
<gain name="gain_1" mode="AUDIO_GAIN_MODE_JOINT"
minValueMB="-8400"
maxValueMB="4000"
defaultValueMB="0"
stepValueMB="100"/>
</gains>
</devicePort>
<devicePort tagName="Wired Headset" type="AUDIO_DEVICE_OUT_WIRED_HEADSET" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
</devicePort>
<devicePort tagName="Wired Headphones" type="AUDIO_DEVICE_OUT_WIRED_HEADPHONE" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/>
</devicePort>
<devicePort tagName="BT SCO" type="AUDIO_DEVICE_OUT_BLUETOOTH_SCO" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_OUT_MONO"/>
</devicePort>
<devicePort tagName="BT SCO Headset" type="AUDIO_DEVICE_OUT_BLUETOOTH_SCO_HEADSET" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_OUT_MONO"/>
</devicePort>
<devicePort tagName="BT SCO Car Kit" type="AUDIO_DEVICE_OUT_BLUETOOTH_SCO_CARKIT" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_OUT_MONO"/>
</devicePort>
<devicePort tagName="Telephony Tx" type="AUDIO_DEVICE_OUT_TELEPHONY_TX" role="sink">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_OUT_MONO"/>
</devicePort>
<devicePort tagName="Built-In Mic" type="AUDIO_DEVICE_IN_BUILTIN_MIC" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_IN_MONO,AUDIO_CHANNEL_IN_STEREO,AUDIO_CHANNEL_IN_FRONT_BACK"/>
</devicePort>
<devicePort tagName="Built-In Back Mic" type="AUDIO_DEVICE_IN_BACK_MIC" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_IN_MONO,AUDIO_CHANNEL_IN_STEREO,AUDIO_CHANNEL_IN_FRONT_BACK"/>
</devicePort>
<devicePort tagName="Wired Headset Mic" type="AUDIO_DEVICE_IN_WIRED_HEADSET" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,11025,12000,16000,22050,24000,32000,44100,48000"
channelMasks="AUDIO_CHANNEL_IN_MONO,AUDIO_CHANNEL_IN_STEREO,AUDIO_CHANNEL_IN_FRONT_BACK"/>
</devicePort>
<devicePort tagName="BT SCO Headset Mic" type="AUDIO_DEVICE_IN_BLUETOOTH_SCO_HEADSET" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_IN_MONO"/>
</devicePort>
<devicePort tagName="Telephony Rx" type="AUDIO_DEVICE_IN_TELEPHONY_RX" role="source">
<profile name="" format="AUDIO_FORMAT_PCM_16_BIT"
samplingRates="8000,16000" channelMasks="AUDIO_CHANNEL_IN_MONO"/>
</devicePort>
</devicePorts>
<!-- route declaration, i.e. list all available sources for a given sink -->
<routes>
<route type="mix" sink="Earpiece"
sources="primary output,deep_buffer,BT SCO Headset Mic"/>
<route type="mix" sink="Speaker"
sources="primary output,deep_buffer,compressed_offload,BT SCO Headset Mic,Telephony Rx"/>
<route type="mix" sink="Wired Headset"
sources="primary output,deep_buffer,compressed_offload,BT SCO Headset Mic,Telephony Rx"/>
<route type="mix" sink="Wired Headphones"
sources="primary output,deep_buffer,compressed_offload,BT SCO Headset Mic,Telephony Rx"/>
<route type="mix" sink="primary input"
sources="Built-In Mic,Built-In Back Mic,Wired Headset Mic,BT SCO Headset Mic"/>
<route type="mix" sink="Telephony Tx"
sources="Built-In Mic,Built-In Back Mic,Wired Headset Mic,BT SCO Headset Mic, voice_tx"/>
<route type="mix" sink="voice_rx"
sources="Telephony Rx"/>
</routes>
</module>
<!-- A2dp Input Audio HAL -->
<xi:include href="a2dp_in_audio_policy_configuration.xml"/>
<!-- Usb Audio HAL -->
<xi:include href="usb_audio_policy_configuration.xml"/>
<!-- Remote Submix Audio HAL -->
<xi:include href="r_submix_audio_policy_configuration.xml"/>
<!-- Bluetooth Audio HAL -->
<xi:include href="bluetooth_audio_policy_configuration.xml"/>
<!-- MSD Audio HAL (optional) -->
<xi:include href="msd_audio_policy_configuration.xml"/>
</modules>
<!-- End of Modules section -->
<!-- Volume section:
IMPORTANT NOTE: Volume tables have been moved to engine configuration.
Keep it here for legacy.
Engine will fallback on these files if none are provided by engine.
-->
<xi:include href="audio_policy_volumes.xml"/>
<xi:include href="default_volume_tables.xml"/>
<!-- End of Volume section -->
<!-- Surround Sound configuration -->
<xi:include href="surround_sound_configuration_5_0.xml"/>
<!-- End of Surround Sound configuration -->
</audioPolicyConfiguration>
总结下，这部分代码主要是加载解析/vendor/etc/audio_policy_configuration.xml或/system/etc/audio_policy_configuration.xml。具体解析过程后续单独章节分析。
3.2 loadHwModule的实现
AudioPolicyManager初始化过程中调用的initialize()方法，会通过loadHwModule()方法加载audio policy硬件抽象库，如下代码：
hwModule->setHandle(mpClientInterface->loadHwModule(hwModule->getName()));
最后调用到AudioFlinger的loadHwModule方法，它的代码实现如下：
// frameworks/av/services/audiopolicy/service/AudioPolicyClientImpl.cpp
audio_module_handle_t AudioPolicyService::AudioPolicyClient::loadHwModule(const char *name)
{
sp<IAudioFlinger> af = AudioSystem::get_audio_flinger();
if (af == 0) {
ALOGW("%s: could not get AudioFlinger", __func__);
return AUDIO_MODULE_HANDLE_NONE;
}
return af->loadHwModule(name);
}
这里最后调用了AudioFlinger的loadHwModule方法。后续章节对后续流程进行分析。
3.3 open的实现
outputDesc->open，调用SwAudioOutputDescriptor::open()方法，代码实现如下：
// frameworks/av/services/audiopolicy/common/managerdefinitions/src/AudioOutputDescriptor.cpp
status_t SwAudioOutputDescriptor::open(const audio_config_t *config,
const DeviceVector &devices,
audio_stream_type_t stream,
audio_output_flags_t flags,
audio_io_handle_t *output)
{
mDevices = devices;
const String8& address = devices.getFirstValidAddress();
audio_devices_t device = devices.types();
audio_config_t lConfig;
if (config == nullptr) {
lConfig = AUDIO_CONFIG_INITIALIZER;
lConfig.sample_rate = mSamplingRate;
lConfig.channel_mask = mChannelMask;
lConfig.format = mFormat;
} else {
lConfig = *config;
}
// if the selected profile is offloaded and no offload info was specified,
// create a default one
if ((mProfile->getFlags() & AUDIO_OUTPUT_FLAG_COMPRESS_OFFLOAD) &&
lConfig.offload_info.format == AUDIO_FORMAT_DEFAULT) {
flags = (audio_output_flags_t)(flags | AUDIO_OUTPUT_FLAG_COMPRESS_OFFLOAD);
lConfig.offload_info = AUDIO_INFO_INITIALIZER;
lConfig.offload_info.sample_rate = lConfig.sample_rate;
lConfig.offload_info.channel_mask = lConfig.channel_mask;
lConfig.offload_info.format = lConfig.format;
lConfig.offload_info.stream_type = stream;
lConfig.offload_info.duration_us = -1;
lConfig.offload_info.has_video = true; // conservative
lConfig.offload_info.is_streaming = true; // likely
}
mFlags = (audio_output_flags_t)(mFlags | flags);
ALOGV("opening output for device %s profile %p name %s",
mDevices.toString().c_str(), mProfile.get(), mProfile->getName().string());
status_t status = mClientInterface->openOutput(mProfile->getModuleHandle(),
output,
&lConfig,
&device,
address,
&mLatency,
mFlags);
LOG_ALWAYS_FATAL_IF(mDevices.types() != device,
"%s openOutput returned device %08x when given device %08x",
__FUNCTION__, mDevices.types(), device);
if (status == NO_ERROR) {
LOG_ALWAYS_FATAL_IF(*output == AUDIO_IO_HANDLE_NONE,
"%s openOutput returned output handle %d for device %08x",
__FUNCTION__, *output, device);
mSamplingRate = lConfig.sample_rate;
mChannelMask = lConfig.channel_mask;
mFormat = lConfig.format;
mId = AudioPort::getNextUniqueId();
mIoHandle = *output;
mProfile->curOpenCount++;
}
return status;
}
调用到mpClientInterface->openOutput，最后调用的是AudioFlinger的openOutput方法，它的代码实现如下：
// frameworks/av/services/audiopolicy/service/AudioPolicyClientImpl.cpp
status_t AudioPolicyService::AudioPolicyClient::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)
{
sp<IAudioFlinger> af = AudioSystem::get_audio_flinger();
if (af == 0) {
ALOGW("%s: could not get AudioFlinger", __func__);
return PERMISSION_DENIED;
}
return af->openOutput(module, output, config, devices, address, latencyMs, flags);
}
这里最后调用了AudioFlinger的output (这里最后会创建一个MixerThread线程与对应的output相关联，之后应用程序就可以把数据传递给线程了，进而传递给硬件设备了)。
