使用ffmpeg将pcm格式音频转化为mp3格式音频

void AudioCode::ENcode(AVCodecContext *cdc_ctx, AVFrame *frame, AVPacket *pkt){
    int ret=0;
    /* send the frame for encoding */
    ret = avcodec_send_frame(cdc_ctx, frame);
    if (ret < 0) {
        qDebug() << "Error sending the frame to the encoder\n";
        return;
    }

    /* read all the available output packets (in general there may be any
         * number of them */
    while (ret >= 0) {
        ret = avcodec_receive_packet(cdc_ctx, pkt);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
            continue;
        else if (ret < 0) {
            qDebug() << "Error encoding audio frame\n";
            continue;
        }

        socket->writeDatagram((char *)pkt->data,pkt->size,QHostAddress(m_strTargetIP),m_iTargetPort);
        if(mp3OutFILE.isOpen())
            mp3OutFILE.write((char *)pkt->data,pkt->size);
        av_packet_unref(pkt);

    }

    return;
}

void AudioCode::PCM2MP3(){

    AVFormatContext *fmtCtx = nullptr;
    AVCodecContext *codecCtx =nullptr;
    const AVCodec *codec = nullptr;
    AVFrame *frame = nullptr;
    AVPacket *pkt = nullptr;

    fmtCtx = avformat_alloc_context();
    frame = av_frame_alloc();
    pkt = av_packet_alloc();

    //==========Output information============
    //查找编码器
    codec = avcodec_find_encoder(AV_CODEC_ID_MP3);
    if(codec==nullptr){
        qInfo() <<"Cannot find audio encoder.\n";
    }

    codecCtx = avcodec_alloc_context3(codec);
    codecCtx->bit_rate = 64000;
    codecCtx->sample_fmt = AV_SAMPLE_FMT_S16P;
    if (!check_sample_fmt(codec, codecCtx->sample_fmt)) {
        qInfo() << "Encoder does not support sample format %s",
                av_get_sample_fmt_name(codecCtx->sample_fmt);
        exit(1);
    }
    codecCtx->sample_rate = Samplerate;
    codecCtx->ch_layout =AV_CHANNEL_LAYOUT_STEREO;

    //打开编码器
    if(avcodec_open2(codecCtx,codec,nullptr) < 0)
        qInfo() << "Open encode error!";

    frame->nb_samples = codecCtx->frame_size;
    frame->format = codecCtx->sample_fmt;
    av_channel_layout_copy(&frame->ch_layout, &codecCtx->ch_layout);

    qInfo() << "start init swr";
    // MP3数不支持AV_SAMPLE_FMT_S16解码，所以将数据转化为AV_SAMPLE_FMT_S16P
    struct SwrContext *swrContext = swr_alloc();
    swr_alloc_set_opts2(&swrContext,
                        &codecCtx->ch_layout,
                        AV_SAMPLE_FMT_S16P,
                        Samplerate,
                        &codecCtx->ch_layout,
                        AV_SAMPLE_FMT_S16,// PCM源文件的采样格式
                        Samplerate,0,nullptr);

    // 重采样初始化
    swr_init(swrContext);
    qInfo() << "end init swr";

    /* 分配空间 */
    uint8_t **convert_data = static_cast<uint8_t**>(calloc(2, static_cast<int>(sizeof(convert_data))));
    av_samples_alloc(convert_data,nullptr,2,codecCtx->frame_size,
                     codecCtx->sample_fmt,0);

    uint8_t *frameBuf = static_cast<uint8_t *>(av_malloc(sizeof(uint8_t *)));
    int length = av_samples_get_buffer_size(nullptr, codecCtx->ch_layout.nb_channels, codecCtx->frame_size, codecCtx->sample_fmt, 1);
    int readsize = length / (codecCtx->ch_layout.nb_channels * av_get_bytes_per_sample(codecCtx->sample_fmt));

    //存储所有数据
    QByteArray arrayAll;
    qInfo() << "start encode";
    while(che){
        //输入一帧数据的长度 4608 ，使用qt从系统中读取一定长度的音频
        QByteArray array = audioDevice->read(length);
        //使用length有杂音，不使用length会丢失最后几帧数据
        arrayAll += array;

        if(arrayAll.size() > length)
        {
            //对数据进行处理，方便后面音频编码
            array = arrayAll.left(length);
            arrayAll.remove(0,length);

            //读PCM：特意注意读取的长度，否则可能出现转码之后声音变快或者变慢
            frameBuf = reinterpret_cast<uint8_t *>(array.data()) ;
            const uint8_t *tmpframe = frameBuf;
            swr_convert(swrContext,
                        convert_data,codecCtx->frame_size,
                        &tmpframe,readsize);
            //输出一帧数据的长度
            //双通道赋值（输出的AAC为双通道）
            frame->data[0] = convert_data[0];
            frame->data[1] = convert_data[1];

            ENcode(codecCtx,frame,pkt);
        }
    }
    qInfo() << "end encode";
    ENcode(codecCtx,nullptr,pkt);
    swr_free(&swrContext);
    avcodec_free_context(&codecCtx);
    av_free(frame);
    avio_close(fmtCtx->pb);
    avformat_free_context(fmtCtx);
    return;
}