Android通过OpenSL ES播放音频套路详解

我的视频课程（基础）：《（NDK）FFmpeg打造Android万能音频播放器》

我的视频课程（进阶）：《（NDK）FFmpeg打造Android视频播放器》

我的视频课程（编码直播推流）：《Android视频编码和直播推流》

我的视频课程（C++ OpenGL）：《Android C++ OpenGL教程》

先定个小目标

通过本篇博客，我们会很容易的使用Android底层库OpenSL ES来播放音频文件（包括assets、uri和pcm）。

一、首先OpenSL ES是什么？

OpenSL ES (Open Sound Library for Embedded Systems)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。它为嵌入式移动多媒体设备上的本地应用程序开发者提供标准化, 高性能,低响应时间的音频功能实现方法，并实现软/硬件音频性能的直接跨平台部署，降低执行难度，促进高级音频市场的发展。——摘自百度百科。

简单来说OpenSL ES是一个嵌入式跨平台免费的音频处理库。

二、OpenSL ES库在哪里？

Android的OpenSL ES库是在NDK的platforms文件夹对应android平台先相应cpu类型里面，如：

三、OpenSL ES开发流程和重要接口

通过分析android-ndk中native-audio的代码，发现了用OpenSL ES来开发应用也是有套路(规律)可寻的：

3.1、OpenSL ES的开发流程主要有如下6个步骤：

1、创建接口对象

2、设置混音器

3、创建播放器（录音器）

4、设置缓冲队列和回调函数

5、设置播放状态

6、启动回调函数

其中4和6是播放PCM等数据格式的音频是需要用到的。

3.2、OpenSL ES中最重要的接口类SLObjectItf

通过SLObjectItf接口类我们可以创建所需要的各种类型的类接口，比如：

创建引擎接口对象：SLObjectItf engineObject

创建混音器接口对象：SLObjectItf outputMixObject

创建播放器接口对象：SLObjectItf playerObject

以上等等都是通过SLObjectItf来创建的，知道了这个规则后，看源代码就会轻松很多了

3.3、利用SLObjectItf来创建具体的接口对象实例

OpenSL ES中也有具体的接口类，比如（引擎：SLEngineItf，播放器：SLPlayItf，声音控制器：SLVolumeItf等等）。

3.4、创建引擎并实现它

OpenSL ES中开始的第一步都是声明SLObjectItf接口类型的引擎接口对象engineObject，然后用方法slCreateEngine创建一个引擎接口对象；创建好引擎接口对象后，需要用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：

SLObjectItf engineObject = NULL;//用SLObjectItf声明引擎接口对象
SLEngineItf engineEngine = NULL;//声明具体的引擎对象实例void createEngine()
{SLresult result;//返回结果result = slCreateEngine(&engineObject, 0, NULL, 0, NULL, NULL);//第一步创建引擎result = (*engineObject)->Realize(engineObject, SL_BOOLEAN_FALSE);//实现（Realize）engineObject接口对象result = (*engineObject)->GetInterface(engineObject, SL_IID_ENGINE, &engineEngine);//通过engineObject的GetInterface方法初始化engineEngine
}

3.4、利用引擎对象创建其他接口对象

其他接口对象（SLObjectItf outputMixObject，SLObjectItf playerObject）等都是用引擎接口对象创建的（具体的接口对象需要的参数这里就说了，可参照ndk例子里面的），如：

//混音器
SLObjectItf outputMixObject = NULL;//用SLObjectItf创建混音器接口对象
SLEnvironmentalReverbItf outputMixEnvironmentalReverb = NULL;创建具体的混音器对象实例result = (*engineEngine)->CreateOutputMix(engineEngine, &outputMixObject, 1, mids, mreq);//利用引擎接口对象创建混音器接口对象
result = (*outputMixObject)->Realize(outputMixObject, SL_BOOLEAN_FALSE);//实现（Realize）混音器接口对象
result = (*outputMixObject)->GetInterface(outputMixObject, SL_IID_ENVIRONMENTALREVERB, &outputMixEnvironmentalReverb);//利用混音器接口对象初始化具体混音器实例//播放器
SLObjectItf playerObject = NULL;//用SLObjectItf创建播放器接口对象
SLPlayItf playerPlay = NULL;//创建具体的播放器对象实例result = (*engineEngine)->CreateAudioPlayer(engineEngine, &playerObject, &audioSrc, &audioSnk, 3, ids, req);//利用引擎接口对象创建播放器接口对象
result = (*playerObject)->Realize(playerObject, SL_BOOLEAN_FALSE);//实现（Realize）播放器接口对象
result = (*playerObject)->GetInterface(playerObject, SL_IID_PLAY, &playerPlay);//初始化具体的播放器对象实例

3.6、最后就是使用创建好的具体对象实例来实现具体的功能。

四、具体列子

首先导入OpenSL ES和其他必须的库

target_link_libraries( # Specifies the target library.openslaudioywl5320OpenSLESandroid# Links the target library to the log library# included in the NDK.${log-lib} )

4.1、播放assets文件

第一步：创建引擎

第二步：创建混音器

第三步：创建播放器

第四步：设置播放状态

JNIEXPORT void JNICALL
Java_com_ywl5320_openslaudio_MainActivity_playAudioByOpenSL_1assets(JNIEnv *env, jobject instance, jobject assetManager, jstring filename) {release();const char *utf8 = (*env)->GetStringUTFChars(env, filename, NULL);// use asset manager to open asset by filenameAAssetManager* mgr = AAssetManager_fromJava(env, assetManager);AAsset* asset = AAssetManager_open(mgr, utf8, AASSET_MODE_UNKNOWN);(*env)->ReleaseStringUTFChars(env, filename, utf8);// open asset as file descriptoroff_t start, length;int fd = AAsset_openFileDescriptor(asset, &start, &length);AAsset_close(asset);SLresult result;//第一步，创建引擎createEngine();//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;}//第三步，设置播放器参数和创建播放器// 1、 配置 audio sourceSLDataLocator_AndroidFD loc_fd = {SL_DATALOCATOR_ANDROIDFD, fd, start, length};SLDataFormat_MIME format_mime = {SL_DATAFORMAT_MIME, NULL, SL_CONTAINERTYPE_UNSPECIFIED};SLDataSource audioSrc = {&loc_fd, &format_mime};// 2、 配置 audio sinkSLDataLocator_OutputMix loc_outmix = {SL_DATALOCATOR_OUTPUTMIX, outputMixObject};SLDataSink audioSnk = {&loc_outmix, NULL};// 创建播放器const SLInterfaceID ids[3] = {SL_IID_SEEK, SL_IID_MUTESOLO, SL_IID_VOLUME};const SLboolean req[3] = {SL_BOOLEAN_TRUE, SL_BOOLEAN_TRUE, SL_BOOLEAN_TRUE};result = (*engineEngine)->CreateAudioPlayer(engineEngine, &fdPlayerObject, &audioSrc, &audioSnk, 3, ids, req);(void)result;// 实现播放器result = (*fdPlayerObject)->Realize(fdPlayerObject, SL_BOOLEAN_FALSE);(void)result;// 得到播放器接口result = (*fdPlayerObject)->GetInterface(fdPlayerObject, SL_IID_PLAY, &fdPlayerPlay);(void)result;// 得到声音控制接口result = (*fdPlayerObject)->GetInterface(fdPlayerObject, SL_IID_VOLUME, &fdPlayerVolume);(void)result;//第四步，设置播放状态if (NULL != fdPlayerPlay) {result = (*fdPlayerPlay)->SetPlayState(fdPlayerPlay, SL_PLAYSTATE_PLAYING);(void)result;}//设置播放音量 （100 * -50：静音 ）(*fdPlayerVolume)->SetVolumeLevel(fdPlayerVolume, 20 * -50);}

4.2、播放Uri连接

第一步：创建引擎

第二步：创建混音器

第三步：创建播放器

第四步：设置播放状态

JNIEXPORT void JNICALL
Java_com_ywl5320_openslaudio_MainActivity_playAudioByOpenSL_1uri(JNIEnv *env, jobject instance, jstring uri) {SLresult result;release();// convert Java string to UTF-8const char *utf8 = (*env)->GetStringUTFChars(env, uri, NULL);//第一步，创建引擎createEngine();//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;}//第三步，设置播放器参数和创建播放器// configure audio source// (requires the INTERNET permission depending on the uri parameter)SLDataLocator_URI loc_uri = {SL_DATALOCATOR_URI, (SLchar *) utf8};SLDataFormat_MIME format_mime = {SL_DATAFORMAT_MIME, NULL, SL_CONTAINERTYPE_UNSPECIFIED};SLDataSource audioSrc = {&loc_uri, &format_mime};// configure audio sinkSLDataLocator_OutputMix loc_outmix = {SL_DATALOCATOR_OUTPUTMIX, outputMixObject};SLDataSink audioSnk = {&loc_outmix, NULL};// create audio playerconst SLInterfaceID ids[3] = {SL_IID_SEEK, SL_IID_MUTESOLO, SL_IID_VOLUME};const SLboolean req[3] = {SL_BOOLEAN_TRUE, SL_BOOLEAN_TRUE, SL_BOOLEAN_TRUE};result = (*engineEngine)->CreateAudioPlayer(engineEngine, &uriPlayerObject, &audioSrc, &audioSnk, 3, ids, req);(void)result;// release the Java string and UTF-8(*env)->ReleaseStringUTFChars(env, uri, utf8);// realize the playerresult = (*uriPlayerObject)->Realize(uriPlayerObject, SL_BOOLEAN_FALSE);// this will always succeed on Android, but we check result for portability to other platformsif (SL_RESULT_SUCCESS != result) {(*uriPlayerObject)->Destroy(uriPlayerObject);uriPlayerObject = NULL;return;}// get the play interfaceresult = (*uriPlayerObject)->GetInterface(uriPlayerObject, SL_IID_PLAY, &uriPlayerPlay);(void)result;// get the volume interfaceresult = (*uriPlayerObject)->GetInterface(uriPlayerObject, SL_IID_VOLUME, &uriPlayerVolume);(void)result;
//第四步，设置播放状态if (NULL != uriPlayerPlay) {// set the player's stateresult = (*uriPlayerPlay)->SetPlayState(uriPlayerPlay, SL_PLAYSTATE_PLAYING);(void)result;}//设置播放音量 （100 * -50：静音 ）
//    (*uriPlayerVolume)->SetVolumeLevel(uriPlayerVolume, 0 * -50);
}

4.3、播放pcm文件（集成到ffmpeg时，也是播放ffmpeg转换成的pcm格式的数据），这里为了模拟是直接读取的pcm格式的音频文件。
4.3.1、创建播放器和混音器

//第一步，创建引擎createEngine();//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};

4.3.2、设置pcm格式的频率位数等信息并创建播放器

// 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);

4.3.3、设置缓冲队列和回调函数

//    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);

回调函数：

void * pcmBufferCallBack(SLAndroidBufferQueueItf bf, void * context)
{//assert(NULL == context);getPcmData(&buffer);// for streaming playback, replace this test by logic to find and fill the next bufferif (NULL != buffer) {SLresult result;// enqueue another bufferresult = (*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}
}

读取pcm格式的文件：

void getPcmData(void **pcm)
{while(!feof(pcmFile)){fread(out_buffer, 44100 * 2 * 2, 1, pcmFile);if(out_buffer == NULL){LOGI("%s", "read end");break;} else{LOGI("%s", "reading");}*pcm = out_buffer;break;}
}

4.3.4、设置播放状态并手动开始调用回调函数

//    获取播放状态接口(*pcmPlayerPlay)->SetPlayState(pcmPlayerPlay, SL_PLAYSTATE_PLAYING);//    主动调用回调函数开始工作pcmBufferCallBack(pcmBufferQueue, NULL);

注意：在回调函数中result = (*pcmBufferQueue)->Enqueue(pcmBufferQueue, buffer, 44100 * 2 * 2);，最后的“44100*2*2”是buffer的大小，因为我这里是指定了没读取一次就从pcm文件中读取了“44100*2*2”个字节，所以可以正常播放，如果是利用ffmpeg来获取pcm数据源，那么实际大小要根据每个AVframe的具体大小来定，这样才能正常播放出声音！！！（44100 * 2 * 2 表示：44100是频率HZ，2是立体声双通道，2是采用的16位采样即2个字节，所以总的字节数就是：44100 * 2 * 2）

好的，以上就是android利用OpenSL ES来播放音频的过程，不知各位看官是否明白了，文末提供源码和音频文件的下载。好了，开始双十一的枪枪抢吧~

GitHub：Android_OpenSl_Audio