音视频开发技术（23） OpenSL 录制及播放 PCM 音频数据
目录
- Android OpenSL 录制 PCM 音频数据
- Android OpenSL ES播放PCM 数据
音视频开发知识点路线图：
一、Android OpenSL 录制 PCM 音频数据
开发准备
1.在Android studo下面建立工程，在使用OpenSL ES的API之前，首先需要引入CMakeLists.txt里面添加依赖库和链接库，代码如下：
find_library( # Sets the name of the path variable.
log-lib
android
# Specifies the name of the NDK library that
# you want CMake to locate.
log )
# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.
target_link_libraries( # Specifies the target library.
native-lib
OpenSLES
android
# Links the target library to the log library
# included in the NDK.
${log-lib} )2.同时添加静态库依赖的c++文件
add_library( # Sets the name of the library.
native-lib
# Sets the library as a shared library.
SHARED
native-lib.cpp
)OpenSL ES 录制 PCM 音频数据流程主要有如下：
1、 新建native-lib.cpp文件，然后引入头文件
#include <SLES/OpenSLES.h>
#include <SLES/OpenSLES_Android.h>声明SLObjectItf接口类型的引擎接口对象engineObject，而后用方法slCreateEngine建立一个引擎接口对象；建立好引擎接口对象后，须要用SLObjectItf的Realize方法来实现engineObject；最后用SLObjectItf的GetInterface方法来初始化SLEngnineItf对象实例。如：
//引擎接口
static SLObjectItf engineObject = NULL;
//引擎对象
static SLEngineItf engineEngine;
void createEngine()
SLresult result;
result = slCreateEngine(&engineObject, 0, NULL, 0, NULL, NULL);
result = (*engineObject)->Realize(engineObject, SL_BOOLEAN_FALSE);
result = (*engineObject)->GetInterface(engineObject, SL_IID_ENGINE, &engineEngine);
}2、设置IO设备麦克风，设置buffer队列，设置录制规格。
/**
* 设置IO设备（麦克风）
SLDataLocator_IODevice loc_dev = {SL_DATALOCATOR_IODEVICE, SL_IODEVICE_AUDIOINPUT,
SL_DEFAULTDEVICEID_AUDIOINPUT, NULL};
SLDataSource audioSrc = {&loc_dev, NULL};
* 设置buffer队列
SLDataLocator_AndroidSimpleBufferQueue loc_bq = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE, 2};
* 设置录制规格：PCM、2声道、44100HZ、16bit
SLDataFormat_PCM format_pcm = {SL_DATAFORMAT_PCM, 2, SL_SAMPLINGRATE_44_1,
SL_PCMSAMPLEFORMAT_FIXED_16, SL_PCMSAMPLEFORMAT_FIXED_16,
SL_SPEAKER_FRONT_LEFT | SL_SPEAKER_FRONT_RIGHT, SL_BYTEORDER_LITTLEENDIAN};
SLDataSink audioSnk = {&loc_bq, &format_pcm};
const SLInterfaceID id[1] = {SL_IID_ANDROIDSIMPLEBUFFERQUEUE};
const SLboolean req[1] = {SL_BOOLEAN_TRUE};3、创建录音器
/**
* 创建录制器
result = (*engineEngine)->CreateAudioRecorder(engineEngine, &recorderObject, &audioSrc,
&audioSnk, 1, id, req);
if (SL_RESULT_SUCCESS != result) {
return;
result = (*recorderObject)->Realize(recorderObject, SL_BOOLEAN_FALSE);
if (SL_RESULT_SUCCESS != result) {
return;
result = (*recorderObject)->GetInterface(recorderObject, SL_IID_RECORD, &recorderRecord);
result = (*recorderObject)->GetInterface(recorderObject, SL_IID_ANDROIDSIMPLEBUFFERQUEUE,
&recorderBufferQueue);
finished = false;
result = (*recorderBufferQueue)->Enqueue(recorderBufferQueue, recordBuffer->getRecordBuffer(),
recorderSize);
result = (*recorderBufferQueue)->RegisterCallback(recorderBufferQueue, bqRecorderCallback, NULL);4、设置回调函数
result = (*recorderBufferQueue)->RegisterCallback(recorderBufferQueue, bqRecorderCallback, NULL);
void bqRecorderCallback(SLAndroidSimpleBufferQueueItf bq, void *context)
// for streaming recording, here we would call Enqueue to give recorder the next buffer to fill
// but instead, this is a one-time buffer so we stop recording
fwrite(recordBuffer->getNowBuffer(), 1, recorderSize, inputPcmFile);
if(finished)
(*recorderRecord)->SetRecordState(recorderRecord, SL_RECORDSTATE_STOPPED);
fclose(inputPcmFile);
} else{
(*recorderBufferQueue)->Enqueue(recorderBufferQueue, recordBuffer->getRecordBuffer(),
recorderSize);
}5、开始录音
/**
* 开始录音
(*recorderRecord)->SetRecordState(recorderRecord, SL_RECORDSTATE_RECORDING);通过上面五个步骤就完成了Android OpenGL ES录制pcm功能。
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二、Android OpenSL ES播放PCM 数据
OpenSL ES 的开发流程主要有如下：
1、 新建native-lib.cpp文件，然后引入头文件
#include <SLES/OpenSLES.h>
#include <SLES/OpenSLES_Android.h>和录制pcm数据一样，声明SLObjectItf接口类型的引擎接口对象engineObject，而后用方法slCreateEngine建立一个引擎接口对象；建立好引擎接口对象后，须要用SLObjectItf的Realize方法来实现engineObject；最后用SLObjectItf的GetInterface方法来初始化SLEngnineItf对象实例。如：
// 引擎接口
SLObjectItf engineObject = NULL;
//引擎对象
SLEngineItf engineEngine = NULL;
void createEngine()
SLresult result;
result = slCreateEngine(&engineObject, 0, NULL, 0, NULL, NULL);
result = (*engineObject)->Realize(engineObject, SL_BOOLEAN_FALSE);
result = (*engineObject)->GetInterface(engineObject, SL_IID_ENGINE, &engineEngine);
}2.创建混音器
//第二步，创建混音器
const SLInterfaceID mids[1] = {SL_IID_ENVIRONMENTALREVERB};
const SLboolean mreq[1] = {SL_BOOLEAN_FALSE};
result = (*engineEngine)->CreateOutputMix(engineEngine, &outputMixObject, 1, mids, mreq);
(void)result;
result = (*outputMixObject)->Realize(outputMixObject, SL_BOOLEAN_FALSE);
(void)result;
result = (*outputMixObject)->GetInterface(outputMixObject, SL_IID_ENVIRONMENTALREVERB, &outputMixEnvironmentalReverb);
if (SL_RESULT_SUCCESS == result) {
result = (*outputMixEnvironmentalReverb)->SetEnvironmentalReverbProperties(
outputMixEnvironmentalReverb, &reverbSettings);
(void)result;
SLDataLocator_OutputMix outputMix = {SL_DATALOCATOR_OUTPUTMIX, outputMixObject};
SLDataSink audioSnk = {&outputMix, NULL};3.设置pcm格式的频率位数等信息并建立播放器
// 第三步，配置PCM格式信息
SLDataLocator_AndroidSimpleBufferQueue android_queue={SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE,2};
SLDataFormat_PCM pcm={
SL_DATAFORMAT_PCM,//播放pcm格式的数据
2,//2个声道（立体声）
SL_SAMPLINGRATE_44_1,//44100hz的频率
SL_PCMSAMPLEFORMAT_FIXED_16,//位数 16位
SL_PCMSAMPLEFORMAT_FIXED_16,//和位数一致就行
SL_SPEAKER_FRONT_LEFT | SL_SPEAKER_FRONT_RIGHT,//立体声（前左前右）
SL_BYTEORDER_LITTLEENDIAN//结束标志
SLDataSource slDataSource = {&android_queue, &pcm};
const SLInterfaceID ids[3] = {SL_IID_BUFFERQUEUE, SL_IID_EFFECTSEND, SL_IID_VOLUME};
const SLboolean req[3] = {SL_BOOLEAN_TRUE, SL_BOOLEAN_TRUE, SL_BOOLEAN_TRUE};
result = (*engineEngine)->CreateAudioPlayer(engineEngine, &pcmPlayerObject, &slDataSource, &audioSnk, 3, ids, req);
//初始化播放器
(*pcmPlayerObject)->Realize(pcmPlayerObject, SL_BOOLEAN_FALSE);
// 得到接口后调用 获取Player接口
(*pcmPlayerObject)->GetInterface(pcmPlayerObject, SL_IID_PLAY, &pcmPlayerPlay);4.设置缓冲队列，音量设置和回调函数
// 注册回调缓冲区 获取缓冲队列接口
(*pcmPlayerObject)->GetInterface(pcmPlayerObject, SL_IID_BUFFERQUEUE, &pcmBufferQueue);
//缓冲接口回调
(*pcmBufferQueue)->RegisterCallback(pcmBufferQueue, pcmBufferCallBack, NULL);
// 获取音量接口
(*pcmPlayerObject)->GetInterface(pcmPlayerObject, SL_IID_VOLUME, &pcmPlayerVolume);缓存队列回调函数
void pcmBufferCallBack(SLAndroidSimpleBufferQueueItf bf, void * context)
//assert(NULL == context);
getPcmData(&buffer);
// for streaming playback, replace this test by logic to find and fill the next buffer
if (NULL != buffer) {
SLresult result;
// enqueue another buffer
result = (*pcmBufferQueue)->Enqueue(pcmBufferQueue, buffer, 44100 * 2 * 2);
// the most likely other result is SL_RESULT_BUFFER_INSUFFICIENT,
// which for this code example would indicate a programming error