1、OpenSL ES介紹

OpenSL ES (Open Sound Library for Embedded Systems)是無授權(quán)費(fèi)饭玲、跨平臺、針對嵌入式系統(tǒng)精心優(yōu)化的硬件音頻加速API叁执。它為嵌入式移動多媒體設(shè)備上的本地應(yīng)用程序開發(fā)者提供標(biāo)準(zhǔn)化, 高性能,低響應(yīng)時間的音頻功能實(shí)現(xiàn)方法茄厘，并實(shí)現(xiàn)軟/硬件音頻性能的直接跨平臺部署，降低執(zhí)行難度谈宛，促進(jìn)高級音頻市場的發(fā)展蚕断。簡單來說OpenSL ES是一個嵌入式跨平臺免費(fèi)的音頻處理庫。

2入挣、OpenSL ES開發(fā)流程

OpenSL ES 的開發(fā)流程主要有如下6個步驟：

1亿乳、 創(chuàng)建接口對象

2、設(shè)置混音器

3径筏、創(chuàng)建播放器（錄音器）

4葛假、設(shè)置緩沖隊(duì)列和回調(diào)函數(shù)

5、設(shè)置播放狀態(tài)

6滋恬、啟動回調(diào)函數(shù)

注明：其中第4步和第6步是OpenSL ES 播放PCM等數(shù)據(jù)格式的音頻是需要用到的

在使用OpenSL ES的API之前聊训，需要引入OpenSL ES的頭文件:

#include <SLES/OpenSLES.h>
#include <SLES/OpenSLES_Android.h>

由于是在Native層使用該特性，如果是ndk開發(fā)的話恢氯，需要在Android.mk中增加鏈接選項(xiàng)带斑，以便在鏈接階段使用到系統(tǒng)系統(tǒng)的OpenSL ES的so庫：

LOCAL_LDLIBS += -lOepnSLES

如果是Cmake開發(fā)的話，需要在CmakeLists.txt中添加鏈接選項(xiàng)：

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

我們知道OpenSL ES提供的是基于C語言的API勋拟，但是它是基于對象和接口的方式提供的勋磕，會采用面向?qū)ο蟮乃枷腴_發(fā)API。因此我們先來了解一下OpenSL ES中對象和接口的概念：

• 對象：對象是對一組資源及其狀態(tài)的抽象敢靡，每個對象都有一個在其創(chuàng)建時指定的類型挂滓，類型決定了對象可以執(zhí)行的任務(wù)集，對象有點(diǎn)類似于C++中類的概念啸胧。
• 接口：接口是對象提供的一組特征的抽象赶站，這些抽象會為開發(fā)者提供一組方法以及每個接口的類型功能，在代碼中纺念，接口的類型由接口ID來標(biāo)識贝椿。
  需要重點(diǎn)理解的是，一個對象在代碼中其實(shí)是沒有實(shí)際的表示形式的陷谱，可以通過接口來改變對象的狀態(tài)以及使用對象提供的功能烙博。對象有可以有一個或者多個接口的實(shí)例，但是接口實(shí)例肯定只屬于一個對象。

如果明白了OpenSL ES 中對象和接口的概念习勤，那么下面我們就繼續(xù)看看，在代碼中是如何使用它們的焙格。

上面我們也提到過图毕，對象是沒有實(shí)際的代碼表示形式的，對象的創(chuàng)建也是通過接口來完成的眷唉。通過獲取對象的方法來獲取出對象予颤，進(jìn)而可以訪問對象的其他的接口方法或者改變對象的狀態(tài)，下面是使用對象和接口的相關(guān)說明冬阳。

2.1蛤虐、OpenSL ES 開發(fā)最重要的接口類 SLObjectItf

通過SLObjectItf接口類我們可以創(chuàng)建所需要的各種類型的類接口，比如：

• 創(chuàng)建引擎接口對象：SLObjectItf engineObject
• 創(chuàng)建混音器接口對象：SLObjectItf outputMixObject
• 創(chuàng)建播放器接口對象：SLObjectItf playerObject

2.2肝陪、SLObjectItf 創(chuàng)建的具體的接口對象實(shí)例

OpenSL ES中也有具體的接口類驳庭，比如（引擎：SLEngineItf，播放器：SLPlayItf氯窍，聲音控制器：SLVolumeItf等等）饲常。

2.3、創(chuàng)建引擎并實(shí)現(xiàn)

OpenSL ES創(chuàng)建引擎步驟：

• 聲明SLObjectItf接口類型的引擎接口對象engineObject狼讨；
• 然后用方法slCreateEngine創(chuàng)建一個引擎接口對象贝淤；
• 創(chuàng)建好引擎接口對象后，需要用SLObjectItf的Realize方法來實(shí)現(xiàn)engineObject政供；
• 最后用SLObjectItf的GetInterface方法來初始化SLEngnineItf對象實(shí)例播聪。如：

SLObjectItf engineObject = NULL;//用SLObjectItf聲明引擎接口對象
SLEngineItf engineEngine = NULL;//聲明具體的引擎對象實(shí)例

slCreateEngine(&engineObject,0,0,0,0,0);//第一步創(chuàng)建引擎
(*engineObject)->Realize(engineObject,SL_BOOLEAN_FALSE);//實(shí)現(xiàn)（Realize）engineObject接口對象
(*engineObject)->GetInterface(engineObject,SL_IID_ENGINE,&engineEngine);//通過engineObject的GetInterface方法初始化engineEngine

2.4、利用引擎對象創(chuàng)建其他接口對象

其他接口對象（我們要播放pcm文件布隔，就要創(chuàng)建混音器接口對象（SLObjectItf outputMixObject）离陶、播放器接口對象（SLObjectItf playerObject））等都是用引擎接口對象創(chuàng)建的（具體的接口對象需要的參數(shù)這里就說了，可參照ndk例子里面的）衅檀，如：

//混音器
SLObjectItf outputMixObject = NULL;//用SLObjectItf創(chuàng)建混音器接口對象
SLEnvironmentalReverbItf outputMixEnvironmentalReverb = NULL;//創(chuàng)建具體的混音器對象實(shí)例
 
(*engineEngine)->CreateOutputMix(engineEngine, &outputMixObject, 1, mids, mreq);//利用引擎接口對象創(chuàng)建混音器接口對象
(*outputMixObject)->Realize(outputMixObject, SL_BOOLEAN_FALSE);//實(shí)現(xiàn)（Realize）混音器接口對象
result = (*outputMixObject)->GetInterface(outputMixObject, SL_IID_ENVIRONMENTALREVERB, &outputMixEnvironmentalReverb);//利用混音器接口對象初始化具體混音器實(shí)例
 
//播放器
SLObjectItf playerObject = NULL;//用SLObjectItf創(chuàng)建播放器接口對象
SLPlayItf playerPlay = NULL;//創(chuàng)建具體的播放器對象實(shí)例
 
(*engineEngine)->CreateAudioPlayer(engineEngine, &playerObject, &audioSrc, &audioSnk, 3, ids, req);//利用引擎接口對象創(chuàng)建播放器接口對象
(*playerObject)->Realize(playerObject, SL_BOOLEAN_FALSE);//實(shí)現(xiàn)（Realize）播放器接口對象
(*playerObject)->GetInterface(playerObject, SL_IID_PLAY, &playerPlay);//初始化具體的播放器對象實(shí)例

3枕磁、Android OpenSL ES播放pcm文件

3.1、創(chuàng)建支持C++的Android Studio項(xiàng)目

3.2术吝、編寫Android Studio項(xiàng)目的Java代碼

3.2.1计济、布局文件

activity_main.xml

• 一個輸入框：要播放的pcm文件
• 一個按鈕：播放控制

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <EditText
        android:id="@+id/etUrl"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Charlie Puth - Look At Me Now.pcm"/>

    <Button
        android:id="@+id/btnPlay"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="play"
        android:text="播放"/>
</LinearLayout>

3.2.2、Android文件
MainActivity.java

public class MainActivity extends AppCompatActivity {

    String BASE_PATH = Environment.getExternalStorageDirectory().getPath();
    private EditText etUrl;
    private Button btnPlay;
    static {
        System.loadLibrary("native-lib");
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        etUrl = (EditText) findViewById(R.id.etUrl);
        btnPlay = (Button) findViewById(R.id.btnPlay);
    }

    public native void palyPcm(String url);

    public void play(View view) {
        String path = BASE_PATH + "/" + etUrl.getText().toString();
        Log.d("ZJF",path);
        palyPcm(path);
    }
}

3.3排苍、編寫jni代碼

按照OpenSL ES開發(fā)流程我們分為6個步驟沦寂！

3.3.1、創(chuàng)建接口對象

SLObjectItf engineObject = NULL;//用SLObjectItf聲明引擎接口對象
SLEngineItf engineEngine = NULL;//聲明具體的引擎對象實(shí)例
 // 1淘衙、創(chuàng)建一個引擎：三部曲 slCreateEngine->Realize->GetInterface
slCreateEngine(&engineObject,0,0,0,0,0);//第一步創(chuàng)建引擎
(*engineObject)->Realize(engineObject,SL_BOOLEAN_FALSE);//第二步實(shí)現(xiàn)（Realize）engineObject接口對象
(*engineObject)->GetInterface(engineObject,SL_IID_ENGINE,&engineEngine);//第三部通過engineObject的GetInterface方法初始化engineEngine

3.3.2传藏、設(shè)置混音器

SLObjectItf outputMixObject = NULL;//用SLObjectItf創(chuàng)建混音器接口對象
SLEnvironmentalReverbItf outputMixEnvReb = NULL;//創(chuàng)建具體的混音器對象實(shí)例
SLEnvironmentalReverbSettings reverbSettings = SL_I3DL2_ENVIRONMENT_PRESET_STONECORRIDOR;

// 2、設(shè)置混音器：創(chuàng)建混音器引擎->設(shè)置混音器屬性
const SLInterfaceID mids[1] = {SL_IID_ENVIRONMENTALREVERB};
const SLboolean mrep[1] = {SL_BOOLEAN_FALSE};

(*engineEngine)->CreateOutputMix(engineEngine,&outputMixObject,1,mids,mrep);
(*outputMixObject)->Realize(outputMixObject,SL_BOOLEAN_FALSE);
(*outputMixObject)->GetInterface(outputMixObject,SL_IID_ENVIRONMENTALREVERB,&outputMixEnvReb);
(*outputMixEnvReb)->SetEnvironmentalReverbProperties(outputMixEnvReb,&reverbSettings);

3.3.3、創(chuàng)建播放器

SLObjectItf pcmPlayerObject = NULL;
SLPlayItf pcmPlayerPlay = NULL;

// 3毯侦、創(chuàng)建播放器
SLDataLocator_AndroidSimpleBufferQueue android_queue = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE,2};//一個隊(duì)列
SLDataFormat_PCM format_pcm = {//設(shè)置PCM播放時的屬性
        SL_DATAFORMAT_PCM,//播放pcm格式的數(shù)據(jù)
        2,//2個聲道（立體聲）
        SL_SAMPLINGRATE_44_1,//44100hz的頻率
        SL_PCMSAMPLEFORMAT_FIXED_16,//位數(shù) 16位
        SL_PCMSAMPLEFORMAT_FIXED_16,//和位數(shù)一致就行
        SL_SPEAKER_FRONT_LEFT | SL_SPEAKER_FRONT_RIGHT,//立體聲（前左前右）
        SL_BYTEORDER_LITTLEENDIAN//結(jié)束標(biāo)志
};
SLDataSource slDataSource ={&android_queue,&format_pcm};

SLDataLocator_OutputMix outputMix = {SL_DATALOCATOR_OUTPUTMIX,outputMixObject};
SLDataSink audioSink = {&outputMix,NULL};

const SLInterfaceID ids[1] = {SL_IID_BUFFERQUEUE};
const SLboolean req[1] = {SL_BOOLEAN_TRUE};
(*engineEngine)->CreateAudioPlayer(engineEngine,&pcmPlayerObject,&slDataSource,&audioSink,1,ids,req);
(*pcmPlayerObject)->Realize(pcmPlayerObject,SL_BOOLEAN_FALSE);
(*pcmPlayerObject)->GetInterface(pcmPlayerObject,SL_IID_PLAY,&pcmPlayerPlay);

3.3.4哭靖、設(shè)置緩沖隊(duì)列和回調(diào)函數(shù)

SLAndroidSimpleBufferQueueItf pcmBufferQueue = NULL;
//回調(diào)方法
void pcmBufferCallback(SLAndroidSimpleBufferQueueItf bf,void *context){
    int size = getPcmData(&buffer);
    if (buffer != NULL){
        (*pcmBufferQueue)->Enqueue(pcmBufferQueue,buffer,size);
    }
}
/*
*獲取pcm文件的數(shù)據(jù)
**/

FILE *pcmFile;//待播放的文件路徑
void *buffer;//保存pcm數(shù)據(jù)，整個文件的侈离，不斷的從out_buffer中讀取出來
uint8_t *out_buffer;//保存從pcm文件中每秒讀取出來的pcm數(shù)據(jù)

int getPcmData(void **pcm){
    int size = 0;
    while (!feof(pcmFile)){
        size = fread(out_buffer,1,44100 * 2 * 2,pcmFile);
        if (out_buffer == NULL) {
            LOGD("READ ENG...");
            break;
        } else {
            LOGD("READING...");
        }
        *pcm = out_buffer;
        break;
    }
    return size;
}


//4试幽、設(shè)置緩沖隊(duì)列和回調(diào)函數(shù)
(*pcmPlayerObject)->GetInterface(pcmPlayerObject,SL_IID_BUFFERQUEUE,&pcmBufferQueue);
(*pcmBufferQueue)->RegisterCallback(pcmBufferQueue,pcmBufferCallback,NULL);

3.3.5、設(shè)置播放狀態(tài)

//5卦碾、設(shè)置播放狀態(tài)
(*pcmPlayerPlay)->SetPlayState(pcmPlayerPlay,SL_PLAYSTATE_PLAYING);

3.3.6铺坞、啟動回調(diào)函數(shù)

//啟動回調(diào)函數(shù)
pcmBufferCallback(pcmBufferQueue,NULL);

3.3.6、jni源碼

#include <jni.h>
#include <string>
#include <android/log.h>
#include <SLES/OpenSLES.h>
#include <SLES/OpenSLES_Android.h>

extern "C" {
    #define LOGD(FORMAT,...) __android_log_print(ANDROID_LOG_DEBUG,"zjf",FORMAT,##__VA_ARGS__);
    #define LOGE(FORMAT,...) __android_log_print(ANDROID_LOG_ERROR,"zjf",FORMAT,##__VA_ARGS__);
};

/**
 *  1洲胖、創(chuàng)建接口對象

    2济榨、設(shè)置混音器

    3、創(chuàng)建播放器（錄音器）

    4绿映、設(shè)置緩沖隊(duì)列和回調(diào)函數(shù)

    5擒滑、設(shè)置播放狀態(tài)

    6、啟動回調(diào)函數(shù)

 */

SLObjectItf engineObject = NULL;
SLEngineItf engineEngine = NULL;

SLObjectItf outputMixObject = NULL;
SLEnvironmentalReverbItf outputMixEnvReb = NULL;
SLEnvironmentalReverbSettings reverbSettings = SL_I3DL2_ENVIRONMENT_PRESET_STONECORRIDOR;

SLObjectItf pcmPlayerObject = NULL;
SLPlayItf pcmPlayerPlay = NULL;

SLAndroidSimpleBufferQueueItf pcmBufferQueue = NULL;


FILE *pcmFile;
void *buffer;
uint8_t *out_buffer;


int getPcmData(void **pcm){
    int size = 0;
    while (!feof(pcmFile)){
        size = fread(out_buffer,1,44100 * 2 * 2,pcmFile);
        if (out_buffer == NULL) {
            LOGD("READ ENG...");
            break;
        } else {
            LOGD("READING...");
        }
        *pcm = out_buffer;
        break;
    }
    return size;
}

void pcmBufferCallback(SLAndroidSimpleBufferQueueItf bf,void *context){
    int size = getPcmData(&buffer);
    if (buffer != NULL){
        (*pcmBufferQueue)->Enqueue(pcmBufferQueue,buffer,size);
    }
}
extern "C"
JNIEXPORT void JNICALL
Java_com_example_zjf_androidopenslaudio_MainActivity_palyPcm(JNIEnv *env, jobject instance,
                                                             jstring url_) {
    const char *url = env->GetStringUTFChars(url_, 0);

    pcmFile = fopen(url,"r");
    if (pcmFile == NULL) {
        LOGE("打不開文件 url === %s",url);
        return;
    }

    out_buffer = (uint8_t *)malloc(44100 * 2 * 2);
    // 1叉弦、創(chuàng)建一個引擎：三部曲 slCreateEngine->Realize->GetInterface
    slCreateEngine(&engineObject,0,0,0,0,0);
    (*engineObject)->Realize(engineObject,SL_BOOLEAN_FALSE);
    (*engineObject)->GetInterface(engineObject,SL_IID_ENGINE,&engineEngine);


    // 2橘忱、設(shè)置混音器：創(chuàng)建混音器引擎->設(shè)置混音器屬性
    const SLInterfaceID mids[1] = {SL_IID_ENVIRONMENTALREVERB};
    const SLboolean mrep[1] = {SL_BOOLEAN_FALSE};

    (*engineEngine)->CreateOutputMix(engineEngine,&outputMixObject,1,mids,mrep);
    (*outputMixObject)->Realize(outputMixObject,SL_BOOLEAN_FALSE);
    (*outputMixObject)->GetInterface(outputMixObject,SL_IID_ENVIRONMENTALREVERB,&outputMixEnvReb);

    (*outputMixEnvReb)->SetEnvironmentalReverbProperties(outputMixEnvReb,&reverbSettings);


    // 3、創(chuàng)建播放器
    SLDataLocator_AndroidSimpleBufferQueue android_queue = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE,2};//一個隊(duì)列
    SLDataFormat_PCM format_pcm = {//設(shè)置PCM播放時的屬性
            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
    };
    SLDataSource slDataSource ={&android_queue,&format_pcm};

    SLDataLocator_OutputMix outputMix = {SL_DATALOCATOR_OUTPUTMIX,outputMixObject};
    SLDataSink audioSink = {&outputMix,NULL};

    const SLInterfaceID ids[1] = {SL_IID_BUFFERQUEUE};
    const SLboolean req[1] = {SL_BOOLEAN_TRUE};
    (*engineEngine)->CreateAudioPlayer(engineEngine,&pcmPlayerObject,&slDataSource,&audioSink,1,ids,req);
    (*pcmPlayerObject)->Realize(pcmPlayerObject,SL_BOOLEAN_FALSE);
    (*pcmPlayerObject)->GetInterface(pcmPlayerObject,SL_IID_PLAY,&pcmPlayerPlay);


    //4卸奉、設(shè)置緩沖隊(duì)列和回調(diào)函數(shù)
    (*pcmPlayerObject)->GetInterface(pcmPlayerObject,SL_IID_BUFFERQUEUE,&pcmBufferQueue);
    (*pcmBufferQueue)->RegisterCallback(pcmBufferQueue,pcmBufferCallback,NULL);


    //5钝诚、設(shè)置播放狀態(tài)
    (*pcmPlayerPlay)->SetPlayState(pcmPlayerPlay,SL_PLAYSTATE_PLAYING);

    pcmBufferCallback(pcmBufferQueue,NULL);


    env->ReleaseStringUTFChars(url_, url);
}

4、遇到的問題

01-03 12:36:32.545 30764-30764/com.example.zjf.androidopenslaudio D/ZJF: /storage/emulated/0/Charlie Puth - Look At Me Now.pcm
01-03 12:36:32.565 30764-30764/com.example.zjf.androidopenslaudio E/libOpenSLES: pAudioSrc: data format 2 not allowed
01-03 12:36:32.565 30764-30764/com.example.zjf.androidopenslaudio W/libOpenSLES: Leaving Engine::CreateAudioPlayer (SL_RESULT_CONTENT_UNSUPPORTED)
01-03 12:36:32.565 30764-30764/com.example.zjf.androidopenslaudio A/libc: Fatal signal 11 (SIGSEGV), code 1, fault addr 0x0 in tid 30764 (roidopenslaudio)

創(chuàng)建播放器時：

SLDataLocator_AndroidBufferQueue android_queue = {SL_DATALOCATOR_ANDROIDBUFFERQUEUE,2};//一個隊(duì)列

改為：

SLDataLocator_AndroidSimpleBufferQueue android_queue = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE,2};//一個隊(duì)列

源碼：https://github.com/Xiaoben336/AndroidOpenSLAudio