概述
我们日常在处理音频录制的时候，大部分情况下都是使用AudioRecord录制原始的PCM数据，但是音频相关的处理通常都是在native层进行的，今天笔者要记录一下在native层通过OpenSL ES来完成音频的录制。
配置权限
动态权限的申请这里不赘述
<uses-permission android:name="android.permission.RECORD_AUDIO"/>
导入OpenSL ES库
CMake方式：CMakeList.txt中加入
target_link_libraries(native-lib OpenSLES)
NDK Build方式：在Android.mk文件添加选项
LOCAL_LDLIBS = -lOpenSLES
源代码中引入头文件
#include <SLES/OpenSLES.h>
#include <SLES/OpenSLES_Android.h>
录制流程分析
image
开始录制
SL_API SLresult SLAPIENTRY slCreateEngine(
SLObjectItf *pEngine, //对象地址，用于传出对象
SLuint32 numOptions, //配置参数数量
const SLEngineOption *pEngineOptions, //配置参数，为枚举数组
SLuint32 numInterfaces, //支持的接口数量
const SLInterfaceID *pInterfaceIds, //具体的要支持的接口，是枚举的数组
const SLboolean *pInterfaceRequired //具体的要支持的接口是开放的还是关闭的，也是一个数组，这三个参数长度是一致的
);
void OpenSLESRecorder::StartRecord(const char *pcmPath, int sampleRate, int channels, int bitRate) {
//打开输出文件
pcmFile = fopen(pcmPath, "w");
recordBuffer = new RecordBuffer(RECORDER_FRAMES * 2);
//1. 调用全局方法创建一个引擎对象(OpenSL ES唯一入口)
SLresult result = slCreateEngine(&engineObject, 0, NULL, 0, NULL, NULL);
if (SL_RESULT_SUCCESS != result) {
return;
}
//2. 实例化这个对象
result = (*engineObject)->Realize(engineObject, SL_BOOLEAN_FALSE);
if (SL_RESULT_SUCCESS != result) {
return;
}
//3. 从这个对象里面获取引擎接口
result = (*engineObject)->GetInterface(engineObject, SL_IID_ENGINE, &engineEngine);
if (SL_RESULT_SUCCESS != result) {
return;
}
//4. 设置IO设备(麦克风)
SLDataLocator_IODevice ioDevice = {
SL_DATALOCATOR_IODEVICE, //类型
SL_IODEVICE_AUDIOINPUT, //device类型 选择了音频输入类型
SL_DEFAULTDEVICEID_AUDIOINPUT, //deviceID
NULL //device实例
};
SLDataSource dataSource = {
&ioDevice, //SLDataLocator_IODevice配置输入
NULL //输入格式,采集的并不需要
};
//5. 设置输出buffer队列
SLDataLocator_AndroidSimpleBufferQueue buffer_queue = {
SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE, //类型 这里只能是这个常量
2 //buffer的数量
};
//6. 设置输出数据的格式
SLDataFormat_PCM pcmFormat = {
SL_DATAFORMAT_PCM, //输出PCM格式的数据
(SLuint32) channels, //输出的声道数量
SL_SAMPLINGRATE_44_1, //输出的采样频率，这里是44100Hz
SL_PCMSAMPLEFORMAT_FIXED_16, //输出的采样格式，这里是16bit
SL_PCMSAMPLEFORMAT_FIXED_16, //一般来说，跟随上一个参数
SL_SPEAKER_FRONT_LEFT |
SL_SPEAKER_FRONT_RIGHT, //双声道配置，如果单声道可以用 SL_SPEAKER_FRONT_CENTER
SL_BYTEORDER_LITTLEENDIAN //PCM数据的大小端排列
};
SLDataSink audioSink = {
&buffer_queue, //SLDataFormat_PCM配置输出
&pcmFormat //输出数据格式
};
SLAndroidSimpleBufferQueueItf recorderBufferQueue; //Buffer接口
//7. 创建录制的对象
const SLInterfaceID id[1] = {SL_IID_ANDROIDSIMPLEBUFFERQUEUE};
const SLboolean req[1] = {SL_BOOLEAN_TRUE};
result = (*engineEngine)->CreateAudioRecorder(engineEngine, //引擎接口
&recorderObject, //录制对象地址，用于传出对象
&dataSource, //输入配置
&audioSink, //输出配置
1, //支持的接口数量
id, //具体的要支持的接口
req //具体的要支持的接口是开放的还是关闭的
);
if (SL_RESULT_SUCCESS != result) {
return;
}
//8. 实例化这个录制对象
result = (*recorderObject)->Realize(recorderObject, SL_BOOLEAN_FALSE);
if (SL_RESULT_SUCCESS != result) {
return;
}
//9. 获取录制接口
(*recorderObject)->GetInterface(recorderObject, SL_IID_RECORD, &recorderRecorder);
//10. 获取Buffer接口
(*recorderObject)->GetInterface(recorderObject, SL_IID_ANDROIDSIMPLEBUFFERQUEUE,
&recorderBufferQueue);
finished = false;
result = (*recorderBufferQueue)->Enqueue(recorderBufferQueue, recordBuffer->getRecordBuffer(),
recorderSize);
if (SL_RESULT_SUCCESS != result) {
return;
}
result = (*recorderBufferQueue)->RegisterCallback(recorderBufferQueue, RecordCallback,
this);
if (SL_RESULT_SUCCESS != result) {
return;
}
//11. 开始录音
(*recorderRecorder)->SetRecordState(recorderRecorder, SL_RECORDSTATE_RECORDING);
}
停止录制
void OpenSLESRecorder::StopRecord() {
if (NULL != recorderRecorder) {
finished = true;
}
}
回调函数
static void RecordCallback(SLAndroidSimpleBufferQueueItf bufferQueue, void *context) {
LOGI("录制大小: %d", recorderSize);
OpenSLESRecorder *recorder = (OpenSLESRecorder *) context;
if (NULL != recorder->recordBuffer) {
fwrite(recorder->recordBuffer->getNowBuffer(), 1, recorderSize, recorder->pcmFile);
}
if (recorder->finished) {
(*recorder->recorderRecorder)->SetRecordState(recorder->recorderRecorder,
SL_RECORDSTATE_STOPPED);
//刷新缓冲区后，关闭流
fclose(recorder->pcmFile);
//释放内存
delete recorder->recordBuffer;
recorder->recordBuffer = NULL;
LOGI("停止录音");
} else {
(*bufferQueue)->Enqueue(bufferQueue, recorder->recordBuffer->getRecordBuffer(),
recorderSize);
}
}
小结
如果参考官方的例子，整个过程并不算复杂，笔者也是参考官方的例子进行操作实践
image
项目地址：audio-opensles
https://github.com/byhook/ffmpeg4android
参考
https://github.com/googlesamples/android-ndk/tree/master/native-audio
https://developer.android.com/ndk/guides/audio/opensl/getting-started
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