在 OpenCV 3 中我们使用 CV_FOURCC 来标识 codec1，例如：
writer.open("image.jpg", CV_FOURCC('M', 'J', 'P', 'G'), fps, size);
在这行代码中，我们给 cv::VideoWriter writer 的存储目标文件命名为 image.jpg，采用 MJPG 的 codec（此处MJPG 是 motion jpeg 的缩写），并输入相应的每秒帧数和视屏镜头的尺寸。
遗憾的是，在 OpenCV 4 (4.5.4-dev) 中， CV_FOURCC 已经被 VideoWriter 的函数 fourcc 所取代2。如果我们继续采用宏 CV_FOURCC 的话，编译时会报错：
error: ‘CV_FOURCC’ was not declared in this scope
下面我们给出 OpenCV4 中 fourcc 的一个简单用法：
writer.open("image.jpg", cv::VideoWriter::fourcc('M', 'J', 'P', 'G'), fps, size);
为了更好的展示 fourcc 的标准用法，以及如何在 OpenCV 4 中存储视频，下面我们给出有关如何存储视频的一个完整示例3：
1 #include <opencv2/core.hpp> 2 #include <opencv2/videoio.hpp> 3 #include <opencv2/highgui.hpp> 4 #include <iostream> 5 #include <stdio.h> 6 using namespace cv; 7 using namespace std; 8 int main(int, char**) 9 { 10 Mat src; 11 // use default camera as video source 12 VideoCapture cap(0); 13 // check if we succeeded 14 if (!cap.isOpened()) { 15 cerr << "ERROR! Unable to open camera\n"; 16 return -1; 17 } 18 // get one frame from camera to know frame size and type 19 cap >> src; 20 // check if we succeeded 21 if (src.empty()) { 22 cerr << "ERROR! blank frame grabbed\n"; 23 return -1; 24 } 25 bool isColor = (src.type() == CV_8UC3); 26 //--- INITIALIZE VIDEOWRITER 27 VideoWriter writer; 28 int codec = VideoWriter::fourcc('M', 'J', 'P', 'G'); // select desired codec (must be available at runtime) 29 double fps = 25.0; // framerate of the created video stream 30 string filename = "./live.avi"; // name of the output video file 31 writer.open(filename, codec, fps, src.size(), isColor); 32 // check if we succeeded 33 if (!writer.isOpened()) { 34 cerr << "Could not open the output video file for write\n"; 35 return -1; 36 } 37 //--- GRAB AND WRITE LOOP 38 cout << "Writing videofile: " << filename << endl 39 << "Press any key to terminate" << endl; 40 for (;;) 41 { 42 // check if we succeeded 43 if (!cap.read(src)) { 44 cerr << "ERROR! blank frame grabbed\n"; 45 break; 46 } 47 // encode the frame into the videofile stream 48 writer.write(src); 49 // show live and wait for a key with timeout long enough to show images 50 imshow("Live", src); 51 if (waitKey(5) >= 0) 52 break; 53 } 54 // the videofile will be closed and released automatically in VideoWriter destructor 55 return 0; 56 }
出处：
1. Learning OpenCV 3. Example 02-11. Adrian Kaehler, Gary Bradski.
2. https://docs.opencv.org/4.x/dd/d9e/classcv_1_1VideoWriter.html#afec93f94dc6c0b3e28f4dd153bc5a7f0
3. https://docs.opencv.org/4.x/df/d94/samples_2cpp_2videowriter_basic_8cpp-example.html#a5