Android 音視頻深入 十三 OpenSL ES 製作音樂播放器，能暫停和調整音量（附源碼下載）

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

OpenSL ES 是基於NDK也就是c語言的底層開發音頻的公開API，通過使用它能夠做到標準化, 高性能,低響應時間的音頻功能實現方法。

這次是使用OpenSL ES來做一個音樂播放器，它能夠播放m4a、mp3文件，並能夠暫停和調整音量

播放音樂需要做一些步驟
1.創建聲音引擎

首先創建聲音引擎的對象接口
result = slCreateEngine(&engineObject, 0, NULL, 0, NULL, NULL);

然後實現它
result = (*engineObject)->Realize(engineObject, SL_BOOLEAN_FALSE);

從聲音引擎的對象中抓取聲音引擎
result = (*engineObject)->GetInterface(engineObject, SL_IID_ENGINE, &engineEngine);

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

實現輸出混合音
result = (*outputMixObject)->Realize(outputMixObject, SL_BOOLEAN_FALSE);

2.創建聲音播放器

創建和實現播放器

// 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.設置播放緩衝

數據格式配置

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};

數據定位器 就是定位要播放聲音數據的存放位置，分爲4種：內存位置，輸入/輸出設備位置，緩衝區隊列位置，和midi緩衝區隊列位置。
數據定位器配置

SLDataLocator_AndroidSimpleBufferQueue loc_bufq = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE, 2};

得到了緩存隊列接口，並註冊

// 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.獲得其他接口用來控制播放

得到聲音特效接口

// 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.提供播放數據

打開音樂文件

// 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);

設置播放數據

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.播放音樂

播放音樂只需要通過播放接口改變播放狀態就可以了,暫停也是，停止也是，但是暫停必須之前的播放緩存做了才行，否則那暫停就相當於停止了

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

7.調解音量

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.釋放資源

關閉app時釋放佔用資源

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;
}

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

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