opencv(c++)读取rtsp视频流并保存帧为jpg图片

本想简单写个demo程序，读取摄像头的rtsp视频流，将最新帧保存为jpg图片传给AI程序进行识别，结果网上针对linux下c++版读取视频流保存图片的资料，凌乱且各种错误。现将踩坑后成功执行的流程和代码整理出来，供有需之人参考。

1.linux下配置opencv开发环境

1. 安装必要的库
   [compiler] sudo apt-get install build-essential
   [required] sudo apt-get install cmake git libgtk2.0-dev pkg-config libavcodec-dev libavformat-dev libswscale-dev
   [optional] sudo apt-get install python-dev python-numpy libtbb2 libtbb-dev libjpeg-dev libpng-dev libtiff-dev libjasper-dev libdc1394-22-dev
2. 下载opencv源码
   https://opencv.org/，这里下载最新的opencv-4.2.0.zip。
3. 编译源码，并安装
   解压后进入opencv-4.2.0目录，mkdir build，进入build目录，然后执行

cmake -D CMAKE_BUILD_TYPE=Release -D CMAKE_INSTALL_PREFIX=/usr/local ..

make # 开始编译，等待编译完成

sudo make install # 安装

2.读取视频流并保存图片

编写demo文件，包含opencv_demo.cpp、CMakeLists.txt两个文件。
1. CMakeLists.txt内容

cmake_minimum_required(VERSION 2.8)
add_definitions(-std=c++11)
project(demo)
find_package(OpenCV REQUIRED)
include_directories(${OpenCV_INCLUDE_DIRS})
add_executable(demo opencv_demo.cpp)
target_link_libraries(demo ${OpenCV_LIBS})

2. opencv_demo.cpp

#include 
#include 
#include 
#include 

using namespace std;
using namespace cv;

void Video_to_Image(Mat& frame);

int main()
{
    //string filename = "Wildlife.wmv";
    string filename = "rtsp://admin:[email protected]/ch1/stream1";
    Mat frame;
    VideoCapture cap;
    cap.open(filename);
    if (!cap.isOpened()) {
        cerr << "ERROR! Unable to open camera\n";
        return -1;
    }

    //--- GRAB AND WRITE LOOP
    cout << "Start grabbing" << endl
        << "Press any key to terminate" << endl;
    time_t start_time = time(NULL);
    for (;;)
    {
        // wait for a new frame from camera and store it into 'frame'
        cap.read(frame);
        // check if we succeeded
        if (frame.empty()) {
            cerr << "ERROR! blank frame grabbed\n";
            break;
        }
        // show live and wait for a key with timeout long enough to show images
        imshow("Live", frame);

        // 每隔2s保存图片
        time_t end_time = time(NULL);
        if ((end_time - start_time) >=2)
        {
            cout << "2s capture" << endl;
            Video_to_Image(frame);
            start_time = time(NULL);
        }

        if (waitKey(5) >= 0)
            break;
    }
    cap.release();

    return 0;
}

void Video_to_Image(Mat& frame)
{

    char image_name[PATH_MAX];
    sprintf(image_name, "%s%s", "test_image", ".jpg");
    imwrite(image_name, frame);

}

3. 编译执行

cmake .
make
./demo

test_image.jpg

imshow("Live", frame)