android系统使用FFmpeng集成OpenSL音频录制和播放

一、背景

二、方案

三、代码实现

[3.1 初始化OpenSL](#3.1 初始化OpenSL)

[3.2 设置播放回掉](#3.2 设置播放回掉)

[3.3 使用FFmpeg计算出转换后的样本数目](#3.3 使用FFmpeg计算出转换后的样本数目)

一、背景

FFmpeg不能够操作Android的硬件设备，所以要在Android系统上面播放音频的话需要另找办法

二、方案

Android 环境下音频播放通常有两种方式------ AudioTrack 和 OpenSLES。AudioTrack 本身是Java实现，另外一种实现方式就是OpenSL ES 播放音频。

三、代码实现

3.1 初始化OpenSL

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void AudioChannel::initOpenSL() {
    //创建引擎
    SLresult result;
    // 创建引擎engineObject
    result = slCreateEngine(&engineObject, 0, NULL, 0, NULL, NULL);
    if (SL_RESULT_SUCCESS != result) {
        return;
    }
    // 初始化引擎engineObject
    result = (*engineObject)->Realize(engineObject, SL_BOOLEAN_FALSE);
    if (SL_RESULT_SUCCESS != result) {
        return;
    }
    // 获取引擎接口engineEngine
    result = (*engineObject)->GetInterface(engineObject, SL_IID_ENGINE,
                                           &engineInterface);
    if (SL_RESULT_SUCCESS != result) {
        return;
    }

    // 创建混音器outputMixObject
    result = (*engineInterface)->CreateOutputMix(engineInterface, &outputMixObject, 0, 0, 0);
    if (SL_RESULT_SUCCESS != result) {
        return;
    }

    // 初始化混音器outputMixObject
    result = (*outputMixObject)->Realize(outputMixObject, SL_BOOLEAN_FALSE);
    if (SL_RESULT_SUCCESS != result) {
        return;
    }


    /**
     * 配置输入声音信息
     */
    //创建buffer缓冲类型的队列 2个队列
    SLDataLocator_AndroidSimpleBufferQueue android_queue = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE,
                                                            2};
    //pcm数据格式
    SLDataFormat_PCM pcm = {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};

    //数据源 将上述配置信息放到这个数据源中
    SLDataSource slDataSource = {&android_queue, &pcm};


    //设置混音器
    SLDataLocator_OutputMix outputMix = {SL_DATALOCATOR_OUTPUTMIX, outputMixObject};
    SLDataSink audioSnk = {&outputMix, NULL};
    //需要的接口
    const SLInterfaceID ids[1] = {SL_IID_BUFFERQUEUE};
    const SLboolean req[1] = {SL_BOOLEAN_TRUE};
    //创建播放器
    (*engineInterface)->CreateAudioPlayer(engineInterface, &bqPlayerObject, &slDataSource,
                                          &audioSnk, 1,
                                          ids, req);
    //初始化播放器
    (*bqPlayerObject)->Realize(bqPlayerObject, SL_BOOLEAN_FALSE);

//    得到接口后调用  获取Player接口
    (*bqPlayerObject)->GetInterface(bqPlayerObject, SL_IID_PLAY, &bqPlayerInterface);

//    获得播放器接口
    (*bqPlayerObject)->GetInterface(bqPlayerObject, SL_IID_BUFFERQUEUE,
                                    &bqPlayerBufferQueue);
    //设置回调
    (*bqPlayerBufferQueue)->RegisterCallback(bqPlayerBufferQueue, bqPlayerCallback, this);
//    设置播放状态
    (*bqPlayerInterface)->SetPlayState(bqPlayerInterface, SL_PLAYSTATE_PLAYING);

    bqPlayerCallback(bqPlayerBufferQueue, this);
}

3.2 设置播放回掉

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//第一次主动调用在调用线程
//之后在新线程中回调
void bqPlayerCallback(SLAndroidSimpleBufferQueueItf bq, void *context) {
    AudioChannel *audioChannel = static_cast<AudioChannel *>(context);
    int datalen = audioChannel->getPcm();
    if (datalen > 0) {
        (*bq)->Enqueue(bq, audioChannel->buffer, datalen);
    }
}

3.3 使用FFmpeg计算出转换后的样本数目

复制代码

uint64_t dst_nb_samples = av_rescale_rnd(
                swr_get_delay(swr_ctx, frame->sample_rate) + frame->nb_samples,
                out_sample_rate,
                frame->sample_rate,
                AV_ROUND_UP);
        // 转换，返回值为转换后的sample个数
        int nb = swr_convert(swr_ctx, &buffer, dst_nb_samples,
                             (const uint8_t **) frame->data, frame->nb_samples);
        //转换后多少数据
        data_size = nb * out_channels * out_samplesize;
        //音频的时间
        clock = frame->best_effort_timestamp * av_q2d(time_base);
        if (javaCallHelper) {
            javaCallHelper->onProgress(THREAD_CHILD, clock);
        }