【Android音视频】OpenSL ES音频播放示例一

本文将实现一个使用OpenSL ES来播放assets目录下mp3歌曲的demo（实际推荐大家使用oboe库）。

Android NDK之高性能音频https://developer.android.google.cn/ndk/guides/audio/opensl/getting-started

Oboe is a C++ library that makes it easy to build high-performance audio apps on Android.https://github.com/google/oboe NDK 软件包中包括 Khronos Group 开发的 OpenSL ES™ 1.0.1 API 规范的 Android 专用实现。利用这个库，不论您是编写合成器、数字音频工作站、卡拉 OK 应用、游戏还是其他实时应用，都可以使用 C 或 C++ 实现高性能、低延迟的音频。

OpenSL ES™ 标准与 Android Java 框架中的 MediaPlayer 和 MediaRecorder API 提供类似的音频功能。

OpenSL ES API 可以帮助您开发和提升应用的音频性能。

标准 OpenSL ES 头文件 和 允许音频输入和输出。 和 中提供了其他 Android 专用功能。

OpenSL ES编程简述https://developer.android.google.cn/ndk/guides/audio/opensl/opensl-prog-notes

---

PlayerX.c

#include 
#include 
#include 
#include 

#include 
#include 

#include 
#include 
#include 

该示例将包含4个简单的接口

• 引擎初始化（学习 SLObjectItf，SLEngineItf）
• 创建播放器（学习 SLPlayItf）
• 切换播放状态
• 回收资源

static SLObjectItf engineObject = NULL;
static SLEngineItf engineEngine = NULL;

static SLObjectItf outputMixObject = NULL;
static SLEnvironmentalReverbItf outputMixEnvironmentalReverb = NULL;

JNIEXPORT void JNICALL
Java_tao_h_playerx_MainActivity_createEngine(JNIEnv *env, jclass clazz) {
    SLresult result = slCreateEngine(&engineObject, 0, NULL, 0, NULL, NULL);
    assert(SL_RESULT_SUCCESS == result);
    (void) result;

    result = (*engineObject)->Realize(engineObject, SL_BOOLEAN_FALSE);
    assert(SL_RESULT_SUCCESS == result);
    (void) result;

    result = (*engineObject)->GetInterface(engineObject, SL_IID_ENGINE, &engineEngine);
    assert(SL_RESULT_SUCCESS == result);
    (void) result;

    const SLInterfaceID ids[1] = {SL_IID_ENVIRONMENTALREVERB};
    const SLboolean req[1] = {SL_BOOLEAN_FALSE};
    result = (*engineEngine)->CreateOutputMix(engineEngine, &outputMixObject, 1, ids, req);
    assert(SL_RESULT_SUCCESS == result);
    (void) result;

    result = (*outputMixObject)->Realize(outputMixObject, SL_BOOLEAN_FALSE);
    assert(SL_RESULT_SUCCESS == result);
    (void) result;

    result = (*outputMixObject)->GetInterface(outputMixObject, SL_IID_ENVIRONMENTALREVERB,
                                              &outputMixEnvironmentalReverb);
    const SLEnvironmentalReverbSettings reverbSettings = SL_I3DL2_ENVIRONMENT_PRESET_STONECORRIDOR;
    if (result == SL_RESULT_SUCCESS) {
        result = (*outputMixEnvironmentalReverb)->SetEnvironmentalReverbProperties(
                outputMixEnvironmentalReverb, &reverbSettings);
        (void) result;
    }
}

 （void）result 只是用于忽略编译警告

---

创建基于FD的音频播放器

static SLObjectItf fdPlayerObject = NULL;
static SLPlayItf fdPlayerPlay = NULL;
static SLSeekItf fdPlayerSeek = NULL;

JNIEXPORT jboolean JNICALL
Java_tao_h_playerx_MainActivity_createAssetAudioPlayer(JNIEnv *env, jclass clazz,
                                                       jobject asset_manager, jstring file_name) {
    SLresult result;

    const char *utf8 = (*env)->GetStringUTFChars(env, file_name, NULL);
    assert(NULL != utf8);

    AAssetManager *mgr = AAssetManager_fromJava(env, asset_manager);
    assert(NULL != mgr);
    AAsset *asset = AAssetManager_open(mgr, utf8, AASSET_MODE_UNKNOWN);

    (*env)->ReleaseStringUTFChars(env, file_name, utf8);

    if (asset == NULL) {
        return JNI_FALSE;
    }

    off_t start, length;
    int fd = AAsset_openFileDescriptor(asset, &start, &length);
    assert(0 <= fd);
    AAsset_close(asset);

    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};

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

    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,
                                                &audioSink, 3, ids, req);
    assert(SL_RESULT_SUCCESS == result);
    (void) result;

    result = (*fdPlayerObject)->Realize(fdPlayerObject, SL_BOOLEAN_FALSE);
    assert(SL_RESULT_SUCCESS == result);
    (void) result;

    result = (*fdPlayerObject)->GetInterface(fdPlayerObject, SL_IID_PLAY, &fdPlayerPlay);
    assert(SL_RESULT_SUCCESS == result);
    (void) result;

    result = (*fdPlayerObject)->GetInterface(fdPlayerObject, SL_IID_SEEK, &fdPlayerSeek);
    assert(SL_RESULT_SUCCESS == result);
    (void) result;

    result = (*fdPlayerSeek)->SetLoop(fdPlayerSeek, SL_BOOLEAN_TRUE, 0, SL_TIME_UNKNOWN);
    assert(SL_RESULT_SUCCESS == result);
    (void) result;

    return JNI_TRUE;
}

设置播放状态

JNIEXPORT void JNICALL
Java_tao_h_playerx_MainActivity_setPlayingAssetAudioPlayer(JNIEnv *env, jclass clazz,
                                                           jboolean is_playing) {
    SLresult result;

    if (NULL != fdPlayerPlay) {
        result = (*fdPlayerPlay)->SetPlayState(fdPlayerPlay, is_playing ? SL_PLAYSTATE_PLAYING
                                                                        : SL_PLAYSTATE_PAUSED);
        assert(SL_RESULT_SUCCESS == result);
        (void) result;
    }
}

 回收资源（务必按照与创建时相反的顺序进行资源释放）

JNIEXPORT void JNICALL
Java_tao_h_playerx_MainActivity_shutdown(JNIEnv *env, jclass clazz) {
    if (fdPlayerObject != NULL) {
        (*fdPlayerObject)->Destroy(fdPlayerObject);
        fdPlayerPlay = NULL;
        fdPlayerSeek = NULL;
    }

    if (outputMixObject != NULL) {
        (*outputMixObject)->Destroy(outputMixObject);
        outputMixObject = NULL;
        outputMixEnvironmentalReverb = NULL;
    }

    if (engineObject != NULL) {
        (*engineObject)->Destroy(engineObject);
        engineObject = NULL;
        engineEngine = NULL;
    }
}

---

 创建简单的页面来进行播放，布局就不放上来了

public class MainActivity extends AppCompatActivity {

    static {
        System.loadLibrary("PlayerX");
    }

    private AssetManager mAssetManager;
    private boolean isPlayingAsset = false;

    public static native void createEngine();

    public static native boolean createAssetAudioPlayer(AssetManager assetManager, String fileName);

    public static native void setPlayingAssetAudioPlayer(boolean isPlaying);

    public static native void shutdown();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mAssetManager = getAssets();

        createEngine();

        findViewById(R.id.asset_song).setOnClickListener(new View.OnClickListener() {
            boolean created = false;

            @Override
            public void onClick(View v) {
                if (!created) {
                    created = createAssetAudioPlayer(mAssetManager, "Legend Of Heroes.mp3");
                }

                if (created) {
                    isPlayingAsset = !isPlayingAsset;
                    setPlayingAssetAudioPlayer(isPlayingAsset);
                }
            }
        });
    }

    @Override
    protected void onDestroy() {
        shutdown();
        super.onDestroy();
    }
}

---

CMakeLists.txt

cmake_minimum_required(VERSION 3.4.1)

project("PlayerX")

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c99 -Wall")

add_library(PlayerX
        SHARED
        PlayerX.c)

target_link_libraries(PlayerX
        android
        log
        OpenSLES)