OpenSL ES

OpenSL ES 是无授权费、跨平台、针对嵌入式系统精心优化的硬件音频加速API。该库都允许使用C或C ++来实现高性能，低延迟的音频操作。
Android的OpenSL ES库同样位于NDK的platforms文件夹内。关于OpenSL ES的使用可以进入ndk-sample查看native-audio工程:https://github.com/googlesamples/android-ndk/blob/master/native-audio/app/src/main/cpp/native-audio-jni.c
OpenSL ES的开发流程主要有如下7个步骤：
1、创建接口对象
2、设置混音器
3、创建播放器
4、设置播放回调函数
5、设置播放状态
6、启动回调函数
7、释放
1、创建引擎与接口
SLresult result;
// 创建引擎 SLObjectItf engineObject
result = slCreateEngine(&engineObject, 0, NULL, 0, NULL, NULL);
if (SL_RESULT_SUCCESS != result) {
return;
}
// 初始化引擎
result = (engineObject)->Realize(engineObject, SL_BOOLEAN_FALSE);
if (SL_RESULT_SUCCESS != result) {
return;
}
// 获取引擎接口SLEngineItf engineInterface
result = (engineObject)->GetInterface(engineObject, SL_IID_ENGINE,
&engineInterface);
if (SL_RESULT_SUCCESS != result) {
return;
}

2、设置混音器
// 创建混音器SLObjectItf outputMixObject
result = (engineInterface)->CreateOutputMix(engineInterface, &outputMixObject, 0,
0, 0);
if (SL_RESULT_SUCCESS != result) {
return;
}
// 初始化混音器outputMixObject
result = (outputMixObject)->Realize(outputMixObject, SL_BOOLEAN_FALSE);
if (SL_RESULT_SUCCESS != result) {
return;
}

//不启用混响可以不用获取接口
// 获得混音器接口
//result = (*outputMixObject)->GetInterface(outputMixObject, SL_IID_ENVIRONMENTALREVERB,
 //                                         &outputMixEnvironmentalReverb);
//if (SL_RESULT_SUCCESS == result) {
    //设置混响 ： 默认。
    //SL_I3DL2_ENVIRONMENT_PRESET_ROOM: 室内
    //SL_I3DL2_ENVIRONMENT_PRESET_AUDITORIUM : 礼堂 等
    //const SLEnvironmentalReverbSettings settings = SL_I3DL2_ENVIRONMENT_PRESET_DEFAULT;
    //(*outputMixEnvironmentalReverb)->SetEnvironmentalReverbProperties(
     //       outputMixEnvironmentalReverb, &settings);
//}

3、创建播放器
/**

配置输入声音信息
*/
//创建buffer缓冲类型的队列 2个队列
SLDataLocator_AndroidSimpleBufferQueue android_queue = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE,2};
//pcm数据格式
SLDataFormat_PCM 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};

//数据源将上述配置信息放到这个数据源中
SLDataSource slDataSource = {&android_queue, &pcm};

//设置混音器
SLDataLocator_OutputMix outputMix = {SL_DATALOCATOR_OUTPUTMIX, outputMixObject};
SLDataSink audioSnk = {&outputMix, NULL};
//需要的接口
const SLInterfaceID ids[1] = {SL_IID_BUFFERQUEUE};
const SLboolean req[1] = {SL_BOOLEAN_TRUE};
//创建播放器
(engineInterface)->CreateAudioPlayer(engineInterface, &bqPlayerObject, &slDataSource,
&audioSnk, 1,
ids, req);
//初始化播放器
(bqPlayerObject)->Realize(bqPlayerObject, SL_BOOLEAN_FALSE);

// 得到接口后调用获取Player接口
(*bqPlayerObject)->GetInterface(bqPlayerObject, SL_IID_PLAY, &bqPlayerInterface);

4、设置播放回调
//获取播放器队列接口
(bqPlayerObject)->GetInterface(bqPlayerObject, SL_IID_BUFFERQUEUE,
&bqPlayerBufferQueue);
//设置回调
(bqPlayerBufferQueue)->RegisterCallback(bqPlayerBufferQueue, bqPlayerCallback, this);

5、设置播放状态
// 设置播放状态
(*bqPlayerInterface)->SetPlayState(bqPlayerInterface, SL_PLAYSTATE_PLAYING);

6、启动回调函数
bqPlayerCallback(bqPlayerBufferQueue, this);

7、释放
//设置停止状态
if (bqPlayerInterface) {
(bqPlayerInterface)->SetPlayState(bqPlayerInterface, SL_PLAYSTATE_STOPPED);
bqPlayerInterface = 0;
}
//销毁播放器
if (bqPlayerObject) {
(bqPlayerObject)->Destroy(bqPlayerObject);
bqPlayerObject = 0;
bqPlayerBufferQueue = 0;
}
//销毁混音器
if (outputMixObject) {
(outputMixObject)->Destroy(outputMixObject);
outputMixObject = 0;
}
//销毁引擎
if (engineObject) {
(engineObject)->Destroy(engineObject);
engineObject = 0;
engineInterface = 0;
}

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