OpenSL ES: 利用OpenSL ES播放一个存在于SDcard上的PCM文件

native-lib.cpp

#include <jni.h>
#include <string>

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

#include <android/log.h>

#define LOGD(FORMAT,...) __android_log_print(ANDROID_LOG_ERROR,"xp.chen",FORMAT,##__VA_ARGS__);

void bufferQueueCallback(SLAndroidSimpleBufferQueueItf bufferQueue, void *pContext) {
    static FILE *fp = NULL;
    static char *buf = NULL;
    if (!buf) {
        buf = new char[*];
    }
    if (!fp) {
        fp = fopen("/sdcard/test.pcm", "rb");
    }
    if (!fp) return;
    if (feof(fp) == ) {
        int len = fread(buf, , , fp);
        if (len > )
            (*bufferQueue)->Enqueue(bufferQueue, buf, len);
    }
}

extern "C" JNIEXPORT jstring JNICALL
Java_com_yongdaimi_android_androidapitest_OpenSLESApiUseDemoActivity_stringFromJNI(JNIEnv* env, jobject object)
{
    std::string hello = "Hello from C++";

    SLresult re;
    SLObjectItf engineObject;
    SLEngineItf slAudioEngine;

    // 1. Create and init audio engine
    re = slCreateEngine(&engineObject, , NULL, , NULL, NULL);
    if (re != SL_RESULT_SUCCESS) {
        LOGD("slCreateEngine() failed");
    }
    re = (*engineObject)->Realize(engineObject, SL_BOOLEAN_FALSE);
    if (re != SL_RESULT_SUCCESS) {
        LOGD("engineObject Realize failed");
    }
    re = (*engineObject)->GetInterface(engineObject, SL_IID_ENGINE, &slAudioEngine);
    if (re != SL_RESULT_SUCCESS) {
        LOGD("engineObject GetInterface SL_IID_ENGINE failed");
    }

    // 2. Set output mix
    SLObjectItf outputMix;
    re = (*slAudioEngine)->CreateOutputMix(slAudioEngine, &outputMix, , NULL, NULL);
    if (re != SL_RESULT_SUCCESS) {
        LOGD("CreateOutputMix() failed");
    }
    re = (*outputMix)->Realize(outputMix, SL_BOOLEAN_FALSE);
    if (re != SL_RESULT_SUCCESS) {
        LOGD("outputMix Realize failed");
    }

    // 3. Configuring the input data source
    SLDataLocator_AndroidSimpleBufferQueue inputBuffQueueLocator = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE, };
    SLDataFormat_PCM input_format_pcm = {
            SL_DATAFORMAT_PCM,                              // <<< 输入的音频格式,PCM
            ,                                              // <<< 输入的声道数，2(立体声)
            SL_SAMPLINGRATE_44_1,                           // <<< 输入的采样率，44100hz
            SL_PCMSAMPLEFORMAT_FIXED_16,                    // <<< 输入的采样位数，16bit
            SL_PCMSAMPLEFORMAT_FIXED_16,                    // <<< 容器大小，同上
            SL_SPEAKER_FRONT_LEFT|SL_SPEAKER_FRONT_RIGHT,   // <<< 声道标记，这里使用左前声道和右前声道
            SL_BYTEORDER_LITTLEENDIAN                       // <<< 输入的字节序,小端
    };
    SLDataSource dataSource = {&inputBuffQueueLocator, &input_format_pcm};

    SLDataLocator_OutputMix outputMixLocator = {SL_DATALOCATOR_OUTPUTMIX, outputMix};
    SLDataSink dataSink = {&outputMixLocator, };

    // 4. Create Audio Player
    SLObjectItf audioPlayer;
    SLAndroidSimpleBufferQueueItf pcmBufferQueue;
    SLPlayItf playInterface;
    SLInterfaceID audioPlayerInterfaceIDs[] = {SL_IID_ANDROIDSIMPLEBUFFERQUEUE};
    SLboolean audioPlayerInterfaceRequired[] = {SL_BOOLEAN_TRUE};

    re = (*slAudioEngine)->CreateAudioPlayer(slAudioEngine, &audioPlayer, &dataSource, &dataSink, , audioPlayerInterfaceIDs, audioPlayerInterfaceRequired);
    if (re != SL_RESULT_SUCCESS) {
        LOGD("CreateAudioPlayer() failed");
    }
    re = (*audioPlayer)->Realize(audioPlayer, SL_BOOLEAN_FALSE);
    if (re != SL_RESULT_SUCCESS) {
        LOGD("AudioPlayer Realize failed");
    }
    re = (*audioPlayer)->GetInterface(audioPlayer, SL_IID_PLAY, &playInterface);
    if (re != SL_RESULT_SUCCESS) {
        LOGD("AudioPlayer GetInterface SL_IID_PLAY failed");
    }
    re = (*audioPlayer)->GetInterface(audioPlayer, SL_IID_BUFFERQUEUE, &pcmBufferQueue);
    if (re != SL_RESULT_SUCCESS) {
        LOGD("AudioPlayer GetInterface SL_IID_BUFFERQUEUE failed");
    }

    (*pcmBufferQueue)->RegisterCallback(pcmBufferQueue, bufferQueueCallback, NULL);
    (*playInterface)->SetPlayState(playInterface, SL_PLAYSTATE_PLAYING);

    // Start queue callback
    (*pcmBufferQueue)->Enqueue(pcmBufferQueue, "", );
    return env->NewStringUTF(hello.c_str());
}

代码中的一些概念补充：

1.结构体中的 numInterfaces ， pInterfaceIds ， pInterfaceRequired ，这里以创建播放器所调用的 CreateAudioPlayer 函数为例说明：

SLresult (*CreateAudioPlayer) (
        SLEngineItf self,
        SLObjectItf * pPlayer,
        SLDataSource *pAudioSrc,
        SLDataSink *pAudioSnk,
        SLuint32 numInterfaces,
        const SLInterfaceID * pInterfaceIds,
        const SLboolean * pInterfaceRequired
    );

各参数含义如下：

• SLEngineItf C语言不像C++,没有this指针,只能通过每次调用SLEngineItf的方法的时候手动传入
• SLObjectItf 用于保存创建出来的AudioPlayerObject
• SLDataSource 输入数据源的信息
• SLDataSink 输出的信息
• numInterfaces 与下面的SLInterfaceID和SLboolean配合使用,用于标记SLInterfaceID数组和SLboolean数组的大小
• SLInterfaceID 这里需要传入一个数组,指定创建的AudioPlayerObject需要包含哪些Interface
• SLboolean 这里也是一个数组,用来标记每个需要包含的Interface在AudioPlayerObject不支持的情况下,是不是需要在创建AudioPlayerObject时返回失败。

最后的三个参数用于指定AudioPlayerObject需要包含哪些Interface,如果不包含是不是要直接创建失败。之前也提到过，并不是每个系统上都实现了 OpenSL ES 为 Object 定义的所有 Interface，所以在获取 Interface 的时候需要做一些选择和判断，如果创建成功的话我们就能使用AudioPlayerObject的GetInterface方法获取到这些Interface了。

2. DataSouce和DataSink

OpenSL ES 里面，这两个结构体均是作为创建 Media Object 对象时的参数而存在的，data source 代表着输入源的信息，即数据从哪儿来、输入的数据参数是怎样的；而 data sink 则代表着输出的信息，即数据输出到哪儿、以什么样的参数来输出。