C语言实现将MP3转为g711或者pcm，并通过rtmp推流

将MP3转为G711或PCM可以使用FFmpeg库来实现。FFmpeg是一个开源的多媒体处理库，支持多种格式的音视频文件的转换和处理。以下是使用FFmpeg库进行MP3转G711的示例代码：

#include <stdio.h>
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswresample/swresample.h>

int main(int argc, char* argv[]) {
    // 注册所有的编解码器和格式器
    av_register_all();
    // 打开输入文件
    AVFormatContext* pFormatCtx = NULL;
    if (avformat_open_input(&pFormatCtx, argv[1], NULL, NULL) != 0) {
        printf("Could not open input file.\n");
        return -1;
    }
    // 查找音频流信息
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {
        printf("Could not find stream information.\n");
        return -1;
    }
    // 查找音频流
    int audioStreamIndex = -1;
    for (int i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
            audioStreamIndex = i;
            break;
        }
    }
    if (audioStreamIndex == -1) {
        printf("Could not find audio stream.\n");
        return -1;
    }
    // 获取音频流解码器
    AVCodec* pCodec = avcodec_find_decoder(pFormatCtx->streams[audioStreamIndex]->codecpar->codec_id);
    if (!pCodec) {
        printf("Could not find audio codec.\n");
        return -1;
    }
    AVCodecContext* pCodecCtx = avcodec_alloc_context3(pCodec);
    if (!pCodecCtx) {
        printf("Could not allocate codec context.\n");
        return -1;
    }
    if (avcodec_parameters_to_context(pCodecCtx, pFormatCtx->streams[audioStreamIndex]->codecpar) < 0) {
        printf("Could not copy codec parameters.\n");
        return -1;
    }
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {
        printf("Could not open codec.\n");
        return -1;
    }
    // 初始化重采样器
    SwrContext* pSwrCtx = swr_alloc_set_opts(NULL, pCodecCtx->channel_layout, AV_SAMPLE_FMT_S16, pCodecCtx->sample_rate,
                                             pCodecCtx->channel_layout, pCodecCtx->sample_fmt, pCodecCtx->sample_rate, 0, NULL);
    if (!pSwrCtx) {
        printf("Could not allocate resampler context.\n");
        return -1;
    }
    if (swr_init(pSwrCtx) < 0) {
        printf("Could not initialize resampler.\n");
        return -1;
    }
    // 打开输出文件
    FILE* pFile = fopen(argv[2], "wb");
    if (!pFile) {
        printf("Could not open output file.\n");
        return -1;
    }
    // 解码并转换音频数据
    AVPacket packet;
    AVFrame* pFrame = av_frame_alloc();
    while (av_read_frame(pFormatCtx, &packet) >= 0) {
        if (packet.stream_index == audioStreamIndex) {
            int ret = avcodec_send_packet(pCodecCtx, &packet);
            if (ret < 0) {
                printf("Error sending a packet for decoding.\n");
                break;
            }
            while (ret >= 0) {
                ret = avcodec_receive_frame(pCodecCtx, pFrame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    break;
                } else if (ret < 0) {
                    printf("Error during decoding.\n");
                    break;
                }
                // 转换音频数据
                uint8_t* outBuffer = NULL;
                int outBufferSize = av_samples_get_buffer_size(NULL, pCodecCtx->channels, pFrame->nb_samples, AV_SAMPLE_FMT_S16, 1);
                av_samples_alloc(&outBuffer, NULL, pCodecCtx->channels, pFrame->nb_samples, AV_SAMPLE_FMT_S16, 1);
                swr_convert(pSwrCtx, &outBuffer, pFrame->nb_samples, (const uint8_t**)pFrame->data, pFrame->nb_samples);
                // 将转换后的音频数据写入输出文件
                fwrite(outBuffer, 1, outBufferSize, pFile);
                av_freep(&outBuffer);
            }
        }
        av_packet_unref(&packet);
    }
    // 释放资源
    fclose(pFile);
    swr_free(&pSwrCtx);
    avcodec_free_context(&pCodecCtx);
    avformat_close_input(&pFormatCtx);
    avformat_free_context(pFormatCtx);
    av_frame_free(&pFrame);
    return 0;
}

以上代码将MP3文件转为PCM格式，并将PCM数据写入文件。

将PCM数据通过RTMP推流可以使用librtmp库来实现。librtmp是一个开源的RTMP客户端库，支持RTMP协议的各种操作。以下是使用librtmp库进行RTMP推流的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <librtmp/rtmp.h>

int main(int argc, char* argv[]) {
    // 打开RTMP连接
    RTMP* pRTMP = RTMP_Alloc();
    if (!pRTMP) {
        printf("Could not allocate RTMP object.\n");
        return -1;
    }
    if (!RTMP_Init(pRTMP)) {
        printf("Could not initialize RTMP.\n");
        RTMP_Free(pRTMP);
        return -1;
    }
    if (!RTMP_SetupURL(pRTMP, argv[1])) {
        printf("Could not setup RTMP URL.\n");
        RTMP_Free(pRTMP);
        return -1;
    }
    RTMP_EnableWrite(pRTMP);
    if (!RTMP_Connect(pRTMP, NULL)) {
        printf("Could not connect to RTMP server.\n");
        RTMP_Free(pRTMP);
        return -1;
    }
    if (!RTMP_ConnectStream(pRTMP, 0)) {
        printf("Could not connect to RTMP stream.\n");
        RTMP_Free(pRTMP);
        return -1;
    }
    // 打开PCM文件
    FILE* pFile = fopen(argv[2], "rb");
    if (!pFile) {
        printf("Could not open PCM file.\n");
        RTMP_Free(pRTMP);
        return -1;
    }
    // 推流
    char* pBuffer = (char*)malloc(1024 * 1024);
    while (!feof(pFile)) {
        int bytesRead = fread(pBuffer, 1, 1024 * 1024, pFile);
        if (bytesRead <= 0) {
            break;
        }
        RTMP_Write(pRTMP, pBuffer, bytesRead);
    }
    free(pBuffer);
    // 释放资源
    fclose(pFile);
    RTMP_Close(pRTMP);
    RTMP_Free(pRTMP);
    return 0;
}

以上代码将PCM数据通过RTMP推流到指定的RTMP服务器。