写一个C++使用ffmpeg实现rtsp推流本地摄像头的代码

以下是一个使用FFmpeg实现本地摄像头实时推流到RTSP服务器的C代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <libavutil/opt.h>
#include <libavformat/avformat.h>
#include <libavutil/mathematics.h>
#include <libavdevice/avdevice.h>
#include <libavcodec/avcodec.h>

#define STREAM_DURATION 60.0
#define STREAM_FRAME_RATE 25 /* 25 images/s */
#define STREAM_PIX_FMT AV_PIX_FMT_YUV420P /* default pix_fmt */

int main(int argc, char **argv)
{
    AVFormatContext *pFormatCtx = NULL;
    AVOutputFormat *pOutputFmt = NULL;
    AVStream *pStream = NULL;
    AVCodecContext *pCodecCtx = NULL;
    AVCodec *pCodec = NULL;
    AVDictionary *options = NULL;
    AVFrame *pFrame = NULL;
    int ret, i, x, y;
    int frame_count = 0, video_outbuf_size;
    FILE *f = NULL;

    /* Initialize libavcodec, and register all codecs and formats. */
    av_register_all();
    avdevice_register_all();

    /* Open video input device */
    AVInputFormat *inputFmt = av_find_input_format("video4linux2");
    if ((ret = avformat_open_input(&pFormatCtx, "/dev/video0", inputFmt, NULL)) < 0) {
        fprintf(stderr, "Could not open input device\n");
        return ret;
    }

    /* Retrieve stream information */
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {
        fprintf(stderr, "Could not find stream information\n");
        return -1;
    }

    /* Find the first video stream */
    for (i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            pStream = pFormatCtx->streams[i];
            break;
        }
    }

    if (!pStream) {
        fprintf(stderr, "Could not find video stream\n");
        return -1;
    }

    /* Open output URL */
    if ((ret = avformat_alloc_output_context2(&pFormatCtx, NULL, "rtsp", "rtsp://localhost:8554/test")) < 0) {
        fprintf(stderr, "Could not allocate output context\n");
        return ret;
    }

    pOutputFmt = pFormatCtx->oformat;

    /* Add the video stream using the default format codec */
    pCodec = avcodec_find_encoder(pOutputFmt->video_codec);
    if (!pCodec) {
        fprintf(stderr, "Codec not found\n");
        return -1;
    }

    pCodecCtx = avcodec_alloc_context3(pCodec);
    if (!pCodecCtx) {
        fprintf(stderr, "Could not allocate codec context\n");
        return -1;
    }

    /* Set stream parameters */
    pCodecCtx->codec_id = pOutputFmt->video_codec;
    pCodecCtx->codec_type = AVMEDIA_TYPE_VIDEO;
    pCodecCtx->bit_rate = 400000;
    pCodecCtx->width = pStream->codecpar->width;
    pCodecCtx->height = pStream->codecpar->height;
    pCodecCtx->time_base = (AVRational){1, STREAM_FRAME_RATE};
    pCodecCtx->pix_fmt = STREAM_PIX_FMT;

    /* Set the encoder's options */
    av_dict_set(&options, "preset