ffmpeg 获取 rtsp 视频流 c++ 代码实现

以下是获取 RTSP 视频流并转换为 OpenCV Mat 格式的 C++ 代码示例，需要使用 FFmpeg 库：

#include <opencv2/opencv.hpp>
extern "C" {
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libswscale/swscale.h>
}

int main(int argc, char* argv[])
{
    AVFormatContext* pFormatCtx = nullptr;
    AVCodecContext* pCodecCtx = nullptr;
    AVCodec* pCodec = nullptr;
    AVFrame* pFrame = nullptr;
    AVPacket* packet = nullptr;
    struct SwsContext* img_convert_ctx = nullptr;

    av_register_all();
    avformat_network_init();

    // 填写 RTSP 地址
    const char* url = "rtsp://example.com/stream";

    if (avformat_open_input(&pFormatCtx, url, nullptr, nullptr) != 0) {
        std::cerr << "Failed to open input stream." << std::endl;
        return -1;
    }

    if (avformat_find_stream_info(pFormatCtx, nullptr) < 0) {
        std::cerr << "Failed to find stream information." << std::endl;
        return -1;
    }

    // 找到视频流
    int videoIndex = -1;
    for (int i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            videoIndex = i;
            break;
        }
    }
    if (videoIndex == -1) {
        std::cerr << "Failed to find video stream." << std::endl;
        return -1;
    }

    // 获取视频解码器
    pCodecCtx = avcodec_alloc_context3(nullptr);
    avcodec_parameters_to_context(pCodecCtx, pFormatCtx->streams[videoIndex]->codecpar);
    pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
    if (pCodec == nullptr) {
        std::cerr << "Failed to find codec." << std::endl;
        return -1;
    }
    if (avcodec_open2(pCodecCtx, pCodec, nullptr) < 0) {
        std::cerr << "Failed to open codec." << std::endl;
        return -1;
    }

    // 分配内存
    pFrame = av_frame_alloc();
    packet = av_packet_alloc();

    // 初始化转换器
    img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
        pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_BGR24, SWS_BICUBIC, nullptr, nullptr, nullptr);

    while (av_read_frame(pFormatCtx, packet) >= 0) {
        if (packet->stream_index != videoIndex) {
            av_packet_unref(packet);
            continue;
        }

        // 解码
        int ret = avcodec_send_packet(pCodecCtx, packet);
        if (ret < 0) {
            std::cerr << "Error sending a packet for decoding." << std::endl;
            break;
        }
        while (ret >= 0) {
            ret = avcodec_receive_frame(pCodecCtx, pFrame);
            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                break;
            }
            else if (ret < 0) {
                std::cerr << "Error during decoding." << std::endl;
                break;
            }

            // 转换为 OpenCV Mat 格式
            cv::Mat frame(pFrame->height, pFrame->width, CV_8UC3);
            sws_scale(img_convert_ctx, pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
                frame.data, frame.step);

            // 显示图像
            cv::imshow("Frame", frame);
            cv::waitKey(1);

            av_frame_unref(pFrame);
        }
        av_packet_unref(packet);
    }

    // 释放资源
    av_packet_free(&packet);
    av_frame_free(&pFrame);
    avcodec_close(pCodecCtx);
    avcodec_free_context(&pCodecCtx);
    avformat_close_input(&pFormatCtx);
    sws_freeContext(img_convert_ctx);

    return 0;
}

需要注意的是，该代码示例仅适用于单个 RTSP 视频流的情况。如果需要同时处理多个 RTSP 视频流，需要使用多线程或多进程来实现。