给我写一份ffmpeg读取rtsp的代码

好的，以下是一份使用FFmpeg读取RTSP流的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <libavutil/avutil.h>
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>

int main(int argc, char *argv[]) {
    AVFormatContext *format_ctx = NULL;
    AVCodecContext *codec_ctx = NULL;
    AVCodec *codec = NULL;
    AVPacket packet;
    int video_stream_index = -1;
    int ret;

    if (argc < 2) {
        printf("Usage: %s rtsp_url\n", argv[0]);
        return 1;
    }

    av_register_all();

    // 打开输入流
    if ((ret = avformat_open_input(&format_ctx, argv[1], NULL, NULL)) < 0) {
        printf("Could not open input stream.\n");
        return 1;
    }

    // 查找视频流
    if ((ret = avformat_find_stream_info(format_ctx, NULL)) < 0) {
        printf("Could not find stream info.\n");
        return 1;
    }

    // 打印视频信息
    av_dump_format(format_ctx, 0, argv[1], 0);

    // 查找视频流索引
    for (int i = 0; i < format_ctx->nb_streams; i++) {
        if (format_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            video_stream_index = i;
            break;
        }
    }

    if (video_stream_index == -1) {
        printf("Could not find video stream.\n");
        return 1;
    }

    // 获取视频解码器
    codec = avcodec_find_decoder(format_ctx->streams[video_stream_index]->codecpar->codec_id);
    if (codec == NULL) {
        printf("Could not find video decoder.\n");
        return 1;
    }

    // 打开视频解码器
    codec_ctx = avcodec_alloc_context3(codec);
    if (codec_ctx == NULL) {
        printf("Could not allocate codec context.\n");
        return 1;
    }
    if ((ret = avcodec_parameters_to_context(codec_ctx, format_ctx->streams[video_stream_index]->codecpar)) < 0) {
        printf("Could not copy codec parameters to codec context.\n");
        return 1;
    }
    if ((ret = avcodec_open2(codec_ctx, codec, NULL)) < 0) {
        printf("Could not open codec.\n");
        return 1;
    }

    // 读取视频流
    while (1) {
        if ((ret = av_read_frame(format_ctx, &packet)) < 0) {
            printf("Could not read frame.\n");
            break;
        }

        // 解码视频帧
        if (packet.stream_index == video_stream_index) {
            AVFrame *frame = av_frame_alloc();
            if (frame == NULL) {
                printf("Could not allocate video frame.\n");
                break;
            }
            ret = avcodec_send_packet(codec_ctx, &packet);
            if (ret < 0) {
                printf("Error sending a packet for decoding.\n");
                break;
            }
            while (ret >= 0) {
                ret = avcodec_receive_frame(codec_ctx, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    break;
                } else if (ret < 0