参考了这位大佬的方法用自己的视频跑ORB_SLAM3（密码：eu2t）

  1. 在ORB_SLAM3\Examples\Monocular下新建myvideo.yaml和myvideo.cpp，视频文件也放到这。
  2. 在myvideo.yaml中添加内容：
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    %YAML:1.0

    #--------------------------------------------------------------------------------------------
    # Camera Parameters. Adjust them!
    #--------------------------------------------------------------------------------------------
    Camera.type: "PinHole"

    # Camera calibration and distortion parameters (OpenCV) 
    Camera.fx: 614.3472290039062
    Camera.fy: 613.3615112304688
    Camera.cx: 314.36767578125
    Camera.cy: 239.8182830810547

    Camera.k1: 0.0
    Camera.k2: 0.0
    Camera.p1: 0.0
    Camera.p2: 0.0
    Camera.k3: 0.0

    # Camera frames per second 
    Camera.fps: 30.0

    # Color order of the images (0: BGR, 1: RGB. It is ignored if images are grayscale)
    Camera.RGB: 1

    # Camera resolution
    Camera.width: 1920
    Camera.height: 1080

    #--------------------------------------------------------------------------------------------
    # ORB Parameters
    #--------------------------------------------------------------------------------------------

    # ORB Extractor: Number of features per image
    ORBextractor.nFeatures: 1000

    # ORB Extractor: Scale factor between levels in the scale pyramid 	
    ORBextractor.scaleFactor: 1.2

    # ORB Extractor: Number of levels in the scale pyramid	
    ORBextractor.nLevels: 8

    # ORB Extractor: Fast threshold
    # Image is divided in a grid. At each cell FAST are extracted imposing a minimum response.
    # Firstly we impose iniThFAST. If no corners are detected we impose a lower value minThFAST
    # You can lower these values if your images have low contrast			
    ORBextractor.iniThFAST: 20
    ORBextractor.minThFAST: 7

    #--------------------------------------------------------------------------------------------
    # Viewer Parameters
    #--------------------------------------------------------------------------------------------
    Viewer.KeyFrameSize: 0.05
    Viewer.KeyFrameLineWidth: 5
    Viewer.GraphLineWidth: 0.9
    Viewer.PointSize:2
    Viewer.CameraSize: 0.08
    Viewer.CameraLineWidth: 3
    Viewer.ViewpointX: 0
    Viewer.ViewpointY: -0.7
    Viewer.ViewpointZ: -1.8
    Viewer.ViewpointF: 500
  3. 在myvideo.cpp中添加内容：
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    //
    // Created by xiang on 11/29/17.
    //

    // 该文件将打开给定的视频文件，并将图像传递给ORB-SLAM2进行定位

    // 需要opencv
    #include <opencv2/opencv.hpp>

    // ORB-SLAM的系统接口
    #include "System.h"

    #include <string>
    #include <chrono>   // for time stamp
    #include <iostream>

    using namespace std;

    // 参数文件与字典文件
    // 如果你系统上的路径不同，请修改它
    // 第二个路径建议用相对路径
    string parameterFile = "./myvideo.yaml";
    string vocFile = "../../Vocabulary/ORBvoc.txt";

    // 视频文件，修改的话需要和你的视频名字一起改
    string videoFile = "./video.mp4";

    int main(int argc, char **argv) {

        // 声明 ORB-SLAM3 系统
        ORB_SLAM3::System SLAM(vocFile, parameterFile, ORB_SLAM3::System::MONOCULAR, true);

        // 获取视频图像
        cv::VideoCapture cap(videoFile);    // change to 1 if you want to use USB camera.

        // 记录系统时间
        auto start = chrono::system_clock::now();

        while (1) {
            cv::Mat frame;
            cap >> frame;   // 读取相机数据
            if ( frame.data == nullptr )
                break;

            // rescale because image is too large
            cv::Mat frame_resized;
            cv::resize(frame, frame_resized, cv::Size(640,480));

            auto now = chrono::system_clock::now();
            auto timestamp = chrono::duration_cast<chrono::milliseconds>(now - start);
            SLAM.TrackMonocular(frame_resized, double(timestamp.count())/1000.0);
            cv::waitKey(30);
        }

        SLAM.Shutdown();
        return 0;
    }
  4. 修改ORB_SLAM3的CMakeLists.txt，在最后添加：
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    add_executable(myvideo Examples/Monocular/myvideo.cpp)
    target_link_libraries(myvideo ${PROJECT_NAME})
  5. 运行ORB_SLAM3
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    cd ORB_SLAM3
    chmod +x build.sh
    ./build.sh
    不知道为什么myvideo文件生成在了ORB_SLAM3\Examples_old\Stereo-Inertial下，复制到ORB_SLAM3\Examples\Monocular下就行
    之后再运行它：
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    cp Examples_old/Stereo-Inertial/myvideo Examples/Monocular/myvideo
    ./myvideo
  6. 效果