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1. 初始化    AVCodecContext         *m_avctx;    AVCodec                      *m_codec;    /* Init ffmpeg log */    ffmpeg_log_callback pcb_log = libffmpeg_log_callback;    av_log_set_level(AV_LOG_DEBUG);    av_log_set_flags(AV_LOG_SKIP_REPEATED);    av_log_set_callback(pcb_log);    printf("Current ffmpeg log_level = %d\n", av_log_get_level());    /* Open the encoder. */    m_codec = avcodec_find_encoder(AV_CODEC_ID_AAC);    if (!m_codec){        printf("Codec not found\n");        exit(1);    }        m_avctx = avcodec_alloc_context3(m_codec);    if (!m_avctx) {        printf("Could not allocate audio codec context\n");        exit(1);    }    m_avctx->codec_type = AVMEDIA_TYPE_AUDIO;    m_avctx->codec_id = AV_CODEC_ID_AAC;    m_avctx->bit_rate = m_audio_bitrate;    m_avctx->sample_fmt = AV_SAMPLE_FMT_FLTP;      if (!check_sample_fmt(m_codec, m_avctx->sample_fmt)) {        printf("Encoder does not support sample format %s",                av_get_sample_fmt_name(m_avctx->sample_fmt));        exit(1);    }    m_avctx->sample_rate = m_audio_clock_rate;    m_avctx->channels    = m_audio_channel_num;    m_avctx->channel_layout =         (m_audio_channel_num == 1) ? AV_CH_LAYOUT_MONO : AV_CH_LAYOUT_STEREO;    m_avctx->time_base = (AVRational){1, m_avctx->sample_rate};        /* open it */    if (avcodec_open2(m_avctx, m_codec, NULL) < 0) {        printf("Could not open codec\n");        exit(1);    }2. 调用NOTE: 1. 这里只举了个简单的例子， PCM数据是用伪码实现的；2. PCM的数据格式要和编码器相匹配，     即 编码器要求是：　AV_SAMPLE_FMT_S16，则输入的PCM数据也要是 AV_SAMPLE_FMT_S16    通常，ffmpeg原生的AAC编码器 ：  AV_SAMPLE_FMT_FLT              libfaac                               :  AV_SAMPLE_FMT_S16              libfdk-aac                          :   AV_SAMPLE_FTM_FLTP              for (int i = 0 ;  i <  XXX; i++) {    /* Encode by Using ffmpeg-4.0  */        AVPacket *pkt;    AVFrame  *frame;    uint16_t *samples;    pkt = av_packet_alloc();    if (!pkt) {        printf("could not allocate the packet\n");        exit(1);    }    /* frame containing input raw audio */    frame = av_frame_alloc();    if (!frame) {        printf("Could not allocate audio frame\n");        exit(1);    }    frame->nb_samples     = m_avctx->frame_size;    frame->format         = m_avctx->sample_fmt;    frame->channel_layout = m_avctx->channel_layout;    /* allocate the data buffers */    ret = av_frame_get_buffer(frame, 0);    if (ret < 0) {        printf("Could not allocate audio data buffers\n");        exit(1);    }    /* make sure the frame is writable -- makes a copy if the encoder     * kept a reference internally */    ret = av_frame_make_writable(frame);    if (ret < 0){        exit(1);    }    samples = (uint16_t*)frame->data[0];        /* 复制一帧待编码的PCM数据 */    int   in_pcm_buffer_size = 1024;     uint8_t  *in_pcm_buffer;  // 输入的数据    memcpy(samples, in_pcm_buffer, in_pcm_buffer_size);        /* send the frame for encoding */    ret = avcodec_send_frame(m_avctx, frame);    if (ret < 0) {        printf("Error sending the frame to the encoder\n");        exit(1);    }    ret = avcodec_receive_packet(m_avctx, pkt);    if (ret == AVERROR(EAGAIN) ){        printf("Encoding audio frame again! \n");    } else if (ret == AVERROR_EOF) {        printf("Encoding audio frame EOF! \n");    } else if (ret < 0) {        printf("Error encoding audio frame\n");        exit(1);    }    /* 将编码后的数据输出*/    if (pkt->size > 0){        memcpy(aac_buf, pkt->data, pkt->size);        aac_size = pkt->size;    }        av_packet_unref(pkt);    av_frame_free(&frame);    av_packet_free(&pkt);}/* 资源释放 */    if (m_avctx) {        avcodec_close(m_avctx);        av_free(m_avctx);        m_avctx = NULL;    }

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