Android Audioflinger

一：录制audioflinger层和audiorecord。

音频系统的对外接口是AudioRecord,它通过iBinder来远程调用Audioflinger的openRecorder函数。AudioRecord构造函数如下：

1：AudioRecord

AudioRecord::AudioRecord(

int streamType,

uint32_t sampleRate,

int format,

int channelCount,

int frameCount,

uint32_t flags,

callback_t cbf,

void* user,

int notificationFrames)

: mStatus(NO_INIT)

{

log_wj("ENTER IN::--%s---%s---\n",__FILE__,__FUNCTION__);

mStatus = set(streamType, sampleRate, format, channelCount,

frameCount, flags, cbf, user, notificationFrames);

}

调用：

status_t AudioRecord::set(int streamType,

uint32_t sampleRate,

int format,

int channelCount,

int frameCount,

uint32_t flags,

callback_t cbf,

void* user,

int notificationFrames,

bool threadCanCallJava)

{

const sp& audioFlinger = AudioSystem::get_audio_flinger();

//获取缓存大小，间接调用我们修改过该函数（经过三次调用中转），返回值为//channelCount*320

AudioSystem::getInputBufferSize(sampleRate, format, channelCount, &inputBuffSizeInBytes)；

//远程调用audioFlinger的openrecord函数，openRecord相当于audioflinger为audioRecord

//开辟相应的服务窗口

sp record = audioFlinger->openRecord(getpid(), streamType,

sampleRate, format,

channelCount,

frameCount,

((uint16_t)flags) << 16,

&status);

//创建一个线程用来处理

mClientRecordThread = new ClientRecordThread(*this, threadCanCallJava);

}

AudioRecord相当于一个代理，它的线程是用来处理其它客户的请求。

2：AudioFlinger

sp AudioFlinger::openRecord(

pid_t pid,

int streamType,

uint32_t sampleRate,

int format,

int channelCount,

int frameCount,

uint32_t flags,

status_t *status)

{

// AudioRecord线程

if (mAudioRecordThread == 0) {

LOGE("Audio record thread not started");

lStatus = NO_INIT;

goto Exit;

}

// add client to list

{ // scope for mLock

Mutex::Autolock _l(mLock);

wclient = mClients.valueFor(pid);

if (wclient != NULL) {

client = wclient.promote();

} else {

client = new Client(this, pid);

mClients.add(pid, client);

}

// create new record track. The record track uses one track in mHardwareMixerThread by //convention.

//生成一个recordTrack用来作为数据的中转（audioflinger与audiorecord之间）。

//他们使用audio_track_cblk_t数据结构来传输数据。

recordTrack = new MixerThread::RecordTrack(mHardwareMixerThread, client, streamType, sampleRate, format, channelCount, frameCount, flags);

if (recordTrack->getCblk() == NULL) {

recordTrack.clear();

lStatus = NO_MEMORY;

goto Exit;

}

// return to handle to client------我们的audiorecord。

recordHandle = new RecordHandle(recordTrack);

}

AudioRecord和AudioFlinger操作的都是RecordTrack实例，AudioRecord通过它的执行控制操作（start/stop）和读取操作（read）。Audiorecord的start/stop操作可以理解为一个开关，控制的是AudiorecordThread的运行与否。

Audioflinger则负责从音频设备读取数据放置到

audio_track_cblk_t数据结构中。

二：硬件抽象层