写video 需要用到 VideoWriter 

视频文件可看作一个容器

视频的类型由视频文件的后缀名来指定

Due to this OpenCV for video containers supports only the avi extension, its first version. A direct limitation of this is that you cannot save a video file larger than 2 GB. Furthermore you can only create and expand a single video track inside the container. No audio or other track editing support here.

Code

#include "stdafx.h"#include <iostream> // for standard I/O#include <string>   // for strings#include <opencv2/core/core.hpp>        // Basic OpenCV structures (cv::Mat)#include <opencv2/highgui/highgui.hpp>  // Video writeusing namespace std;using namespace cv;static void help(){	cout		<< "------------------------------------------------------------------------------" << endl		<< "This program shows how to write video files."                                   << endl		<< "You can extract the R or G or B color channel of the input video."              << endl		<< "Usage:"                                                                         << endl		<< "./video-write inputvideoName [ R | G | B] [Y | N]"                              << endl		<< "------------------------------------------------------------------------------" << endl		<< endl;}int main(int argc, char *argv[]){	help();	if (argc != 4)	{		cout << "Not enough parameters" << endl;		return -1;	}	const string source      = argv[1];           // the source file name	const bool askOutputType = argv[3][0] ==‘Y‘;  // If false it will use the inputs codec type	VideoCapture inputVideo(source);              // Open input	if (!inputVideo.isOpened())	{		cout  << "Could not open the input video: " << source << endl;		return -1;	}	string::size_type pAt = source.find_last_of(‘.‘);                  // Find extension point	const string NAME = source.substr(0, pAt) + argv[2][0] + ".avi";   // Form the new name with container	int ex = static_cast<int>(inputVideo.get(CV_CAP_PROP_FOURCC));     // Get Codec Type- Int form	// Transform from int to char via Bitwise operators	char EXT[] = {(char)(ex & 0XFF) , (char)((ex & 0XFF00) >> 8),(char)((ex & 0XFF0000) >> 16),(char)((ex & 0XFF000000) >> 24), 0};	Size S = Size((int) inputVideo.get(CV_CAP_PROP_FRAME_WIDTH),    // Acquire input size		(int) inputVideo.get(CV_CAP_PROP_FRAME_HEIGHT));	VideoWriter outputVideo;                                        // Open the output	if (askOutputType)		outputVideo.open(NAME, ex=-1, inputVideo.get(CV_CAP_PROP_FPS), S, true);	else		outputVideo.open(NAME, ex, inputVideo.get(CV_CAP_PROP_FPS), S, true);	if (!outputVideo.isOpened())	{		cout  << "Could not open the output video for write: " << source << endl;		return -1;	}	cout << "Input frame resolution: Width=" << S.width << "  Height=" << S.height		<< " of nr#: " << inputVideo.get(CV_CAP_PROP_FRAME_COUNT) << endl;	cout << "Input codec type: " << EXT << endl;	int channel = 2; // Select the channel to save	switch(argv[2][0])	{	case ‘R‘ : channel = 2; break;	case ‘G‘ : channel = 1; break;	case ‘B‘ : channel = 0; break;	}	Mat src, res;	vector<Mat> spl;	for(;;) //Show the image captured in the window and repeat	{		inputVideo >> src;              // read		if (src.empty()) break;         // check if at end		split(src, spl);                // process - extract only the correct channel		for (int i =0; i < 3; ++i)			if (i != channel)				spl[i] = Mat::zeros(S, spl[0].type());		merge(spl, res);	// 仅单通道不能构成图像，需要将其他通道置零，merge		//outputVideo.write(res); //save or		outputVideo << res;	}	cout << "Finished writing" << endl;	return 0;}

OpenCV Tutorials —— Creating a video with OpenCV