编写一个基于ffmpeg的读取rtsp流的例程

好的，我可以回答这个问题。以下是一个基于ffmpeg的读取rtsp流的例程：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <libavformat/avformat.h>
#include <libavutil/imgutils.h>
#include <libswscale/swscale.h>

int main(int argc, char *argv[]) {
    AVFormatContext *fmt_ctx = NULL;
    AVCodecContext *codec_ctx = NULL;
    AVCodec *codec = NULL;
    AVPacket pkt;
    AVFrame *frame = NULL;
    struct SwsContext *sws_ctx = NULL;
    int video_stream_index = -1;
    int ret = ;

    if (argc < 2) {
        fprintf(stderr, "Usage: %s <rtsp url>\n", argv[]);
        return 1;
    }

    av_register_all();

    if (avformat_open_input(&fmt_ctx, argv[1], NULL, NULL) < ) {
        fprintf(stderr, "Could not open input file '%s'\n", argv[1]);
        return 1;
    }

    if (avformat_find_stream_info(fmt_ctx, NULL) < ) {
        fprintf(stderr, "Could not find stream information\n");
        return 1;
    }

    av_dump_format(fmt_ctx, , argv[1], );

    for (int i = ; i < fmt_ctx->nb_streams; i++) {
        if (fmt_ctx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            video_stream_index = i;
            break;
        }
    }

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

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

    ret = avcodec_parameters_to_context(codec_ctx, fmt_ctx->streams[video_stream_index]->codecpar);
    if (ret < ) {
        fprintf(stderr, "Could not copy codec parameters to codec context\n");
        return 1;
    }

    codec = avcodec_find_decoder(codec_ctx->codec_id);
    if (!codec) {
        fprintf(stderr, "Unsupported codec\n");
        return 1;
    }

    ret = avcodec_open2(codec_ctx, codec, NULL);
    if (ret < ) {
        fprintf(stderr, "Could not open codec\n");
        return 1;
    }

    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Could not allocate frame\n");
        return 1;
    }

    sws_ctx = sws_getContext(codec_ctx->width, codec_ctx->height, codec_ctx->pix_fmt,
                             codec_ctx->width, codec_ctx->height, AV_PIX_FMT_RGB24,
                             SWS_BILINEAR, NULL, NULL, NULL);
    if (!sws_ctx) {
        fprintf(stderr, "Could not initialize sws context\n");
        return 1;
    }

    while (av_read_frame(fmt_ctx, &pkt) >= ) {
        if (pkt.stream_index == video_stream_index) {
            ret = avcodec_send_packet(codec_ctx, &pkt);
            if (ret < ) {
                fprintf(stderr, "Error sending packet to decoder\n");
                break;
            }

            while (ret >= ) {
                ret = avcodec_receive_frame(codec_ctx, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    break;
                } else if (ret < ) {
                    fprintf(stderr, "Error receiving frame from decoder\n");
                    break;
                }

                sws_scale(sws_ctx, frame->data, frame->linesize, , codec_ctx->height,
                          frame->data, frame->linesize);

                // Do something with the RGB24 frame here

                av_frame_unref(frame);
            }
        }

        av_packet_unref(&pkt);
    }

    avformat_close_input(&fmt_ctx);
    avcodec_free_context(&codec_ctx);
    av_frame_free(&frame);
    sws_freeContext(sws_ctx);

    return ;
}

这个例程使用了ffmpeg库来读取rtsp流，并将视频帧转换为RGB24格式。你可以在`// Do something with the RGB24 frame here`处添加你自己的代码来处理视频帧。