Android 音视频深入 十三 OpenSL ES 制作音乐播放器，能暂停和调整音量（附源码下载）

项目地址
https://github.com/979451341/OpenSLAudio 

OpenSL ES 是基于NDK也就是c语言的底层开发音频的公开API，通过使用它能够做到标准化, 高性能,低响应时间的音频功能实现方法。

这次是使用OpenSL ES来做一个音乐播放器，它能够播放m4a、mp3文件，并能够暂停和调整音量

播放音乐需要做一些步骤

1.创建声音引擎

首先创建声音引擎的对象接口 
    result = slCreateEngine(&engineObject, 0, NULL, 0, NULL, NULL);

然后实现它
    result = (*engineObject)->Realize(engineObject, SL_BOOLEAN_FALSE);

从声音引擎的对象中抓取声音引擎
    result = (*engineObject)->GetInterface(engineObject, SL_IID_ENGINE, &engineEngine);

创建"输出混音器"
    result = (*engineEngine)->CreateOutputMix(engineEngine, &outputMixObject, 1, ids, req);

实现输出混合音
    result = (*outputMixObject)->Realize(outputMixObject, SL_BOOLEAN_FALSE);

2.创建声音播放器

创建和实现播放器

    // realize the player
    result = (*bqPlayerObject)->Realize(bqPlayerObject, SL_BOOLEAN_FALSE);
    assert(SL_RESULT_SUCCESS == result);
    (void)result;

    // get the play interface
    result = (*bqPlayerObject)->GetInterface(bqPlayerObject, SL_IID_PLAY, &bqPlayerPlay);
    assert(SL_RESULT_SUCCESS == result);
    (void)result;

3.设置播放缓冲

数据格式配置

    SLDataFormat_PCM format_pcm = {SL_DATAFORMAT_PCM, 1, SL_SAMPLINGRATE_8,
                                   SL_PCMSAMPLEFORMAT_FIXED_16, SL_PCMSAMPLEFORMAT_FIXED_16,
                                   SL_SPEAKER_FRONT_CENTER, SL_BYTEORDER_LITTLEENDIAN};

数据定位器 就是定位要播放声音数据的存放位置，分为4种：内存位置，输入/输出设备位置，缓冲区队列位置，和midi缓冲区队列位置。

数据定位器配置

    SLDataLocator_AndroidSimpleBufferQueue loc_bufq = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE, 2};

得到了缓存队列接口，并注册

    // get the buffer queue interface
    result = (*bqPlayerObject)->GetInterface(bqPlayerObject, SL_IID_BUFFERQUEUE,
                                             &bqPlayerBufferQueue);
    assert(SL_RESULT_SUCCESS == result);
    (void)result;

    // register callback on the buffer queue
    result = (*bqPlayerBufferQueue)->RegisterCallback(bqPlayerBufferQueue, bqPlayerCallback, NULL);
    assert(SL_RESULT_SUCCESS == result);
    (void)result;

4.获得其他接口用来控制播放

得到声音特效接口

    // get the effect send interface
    result = (*bqPlayerObject)->GetInterface(bqPlayerObject, SL_IID_EFFECTSEND,
                                             &bqPlayerEffectSend);
    assert(SL_RESULT_SUCCESS == result);
    (void)result;

得到音量接口

    // get the volume interface
    result = (*bqPlayerObject)->GetInterface(bqPlayerObject, SL_IID_VOLUME, &bqPlayerVolume);
    assert(SL_RESULT_SUCCESS == result);
    (void)result;

    // set the player's state to playing
    result = (*bqPlayerPlay)->SetPlayState(bqPlayerPlay, SL_PLAYSTATE_PLAYING);
    assert(SL_RESULT_SUCCESS == result);
    (void)result;

5.提供播放数据

打开音乐文件

    // convert Java string to UTF-8
    const char *utf8 = (*env)->GetStringUTFChars(env, filename, NULL);
    assert(NULL != utf8);

    // use asset manager to open asset by filename
    AAssetManager* mgr = AAssetManager_fromJava(env, assetManager);
    assert(NULL != mgr);
    AAsset* asset = AAssetManager_open(mgr, utf8, AASSET_MODE_UNKNOWN);

    // release the Java string and UTF-8
    (*env)->ReleaseStringUTFChars(env, filename, utf8);

    // the asset might not be found
    if (NULL == asset) {
        return JNI_FALSE;
    }

    // open asset as file descriptor
    off_t start, length;
    int fd = AAsset_openFileDescriptor(asset, &start, &length);
    assert(0 <= fd);
    AAsset_close(asset);

设置播放数据

    SLDataLocator_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};

6.播放音乐

播放音乐只需要通过播放接口改变播放状态就可以了,暂停也是，停止也是，但是暂停必须之前的播放缓存做了才行，否则那暂停就相当于停止了

        result = (*fdPlayerPlay)->SetPlayState(fdPlayerPlay, isPlaying ?
                                                             SL_PLAYSTATE_PLAYING : SL_PLAYSTATE_PAUSED);

7.调解音量

SLVolumeItf getVolume()
{
    if (fdPlayerVolume != NULL)
        return fdPlayerVolume;
    else
        return bqPlayerVolume;
}

void Java_com_ywl5320_openslaudio_MainActivity_setVolumeAudioPlayer(JNIEnv* env, jclass clazz,
                                                                      jint millibel)
{
    SLresult result;
    SLVolumeItf volumeItf = getVolume();
    if (NULL != volumeItf) {
        result = (*volumeItf)->SetVolumeLevel(volumeItf, millibel);
        assert(SL_RESULT_SUCCESS == result);
        (void)result;
    }
}

8.释放资源

关闭app时释放占用资源

void Java_com_ywl5320_openslaudio_MainActivity_shutdown(JNIEnv* env, jclass clazz)
{

    // destroy buffer queue audio player object, and invalidate all associated interfaces
    if (bqPlayerObject != NULL) {
        (*bqPlayerObject)->Destroy(bqPlayerObject);
        bqPlayerObject = NULL;
        bqPlayerPlay = NULL;
        bqPlayerBufferQueue = NULL;
        bqPlayerEffectSend = NULL;
        bqPlayerMuteSolo = NULL;
        bqPlayerVolume = NULL;
    }

    // destroy file descriptor audio player object, and invalidate all associated interfaces
    if (fdPlayerObject != NULL) {
        (*fdPlayerObject)->Destroy(fdPlayerObject);
        fdPlayerObject = NULL;
        fdPlayerPlay = NULL;
        fdPlayerSeek = NULL;
        fdPlayerMuteSolo = NULL;
        fdPlayerVolume = NULL;
    }



    // destroy output mix object, and invalidate all associated interfaces
    if (outputMixObject != NULL) {
        (*outputMixObject)->Destroy(outputMixObject);
        outputMixObject = NULL;
        outputMixEnvironmentalReverb = NULL;
    }

    // destroy engine object, and invalidate all associated interfaces
    if (engineObject != NULL) {
        (*engineObject)->Destroy(engineObject);
        engineObject = NULL;
        engineEngine = NULL;
    }

}

参考文章
http://blog.csdn.net/u013898698/article/details/72822595

http://blog.csdn.net/ywl5320/article/details/78503768