写一份ffmpeg推流代码

ffmpeg是一个开源的多媒体框架，可以对音频和视频进行编解码、转码和推流等操作。下面是一份使用ffmpeg推流的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <libavformat/avformat.h>
#include <libavutil/opt.h>

int main(int argc, char **argv) {
    AVFormatContext *fmt_ctx = NULL;
    AVOutputFormat *fmt = NULL;
    AVStream *video_st = NULL;
    AVCodecContext *codec_ctx = NULL;
    AVCodec *codec = NULL;
    AVDictionary *options = NULL;
    int ret, i;
    const char *stream_url = "rtmp://example.com/live/stream";

    // Initialize libavformat
    av_register_all();
    avformat_network_init();

    // Open output URL
    if ((ret = avformat_alloc_output_context2(&fmt_ctx, NULL, "flv", stream_url)) < 0) {
        fprintf(stderr, "Could not allocate output context: %s\n", av_err2str(ret));
        exit(1);
    }

    fmt = fmt_ctx->oformat;

    // Add video stream to output context
    video_st = avformat_new_stream(fmt_ctx, NULL);
    if (!video_st) {
        fprintf(stderr, "Could not create video stream\n");
        exit(1);
    }

    codec = avcodec_find_encoder(fmt->video_codec);
    if (!codec) {
        fprintf(stderr, "Could not find encoder for '%s'\n", avcodec_get_name(fmt->video_codec));
        exit(1);
    }

    codec_ctx = avcodec_alloc_context3(codec);
    if (!codec_ctx) {
        fprintf(stderr, "Could not allocate codec context\n");
        exit(1);
    }

    // Set codec parameters
    codec_ctx->codec_id = fmt->video_codec;
    codec_ctx->bit_rate = 400000;
    codec_ctx->width = 640;
    codec_ctx->height = 480;
    codec_ctx->time_base = (AVRational){1, 25};
    codec_ctx->gop_size = 10;
    codec_ctx->pix_fmt = AV_PIX_FMT_YUV420P;

    // Set codec options
    av_opt_set(codec_ctx->priv_data, "preset", "fast", 0);

    // Open codec
    if ((ret = avcodec_open2(codec_ctx, codec, &options)) < 0) {
        fprintf(stderr, "Could not open codec: %s\n", av_err2str(ret));
        exit(1);
    }

    // Set stream parameters
    video_st->codecpar->codec_id = fmt->video_codec;
    video_st->codecpar->bit_rate = 400000;
    video_st->codecpar->width = 640;
    video_st->codecpar->height = 480;
    video_st->codecpar->format = codec_ctx->pix_fmt;
    video_st->time_base = codec_ctx->time_base;

    // Allocate output buffer
    ret = avformat_write_header(fmt_ctx, &options);
    if (ret < 0) {
        fprintf(stderr, "Could not write header: %s\n", av_err2str(ret));
        exit(1);
    }

    // Start streaming
    for (i = 0; i < 10000; i++) {
        AVFrame *frame = av_frame_alloc();
        if (!frame) {
            fprintf(stderr, "Could not allocate frame\n");
            exit(1);
        }

        // Fill frame with data