c++OpenCV操作mp4

注意：

读取mp4文件时，需要把opencv_videoio_ffmpeg动态库dll文件拷贝到可执行程序exe所在目录，

否则读取mp4文件时，读取的视频为空，宽高等参数都为0。

比如：

opencv_videoio_ffmpeg454_64.dll

读取视频保存mp4：

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

int main(int argc, const char ** argv){
		cv::String base_dir = "d:/data/shanghai/2019-09-21";

		cv::String video_id = "011400.mp4";
		cv::String video_save = "011400_save.mp4";

		double beg_, end_;
		double freq = cv::getTickFrequency();

		cv::String input_video = base_dir  + "/" + video_id;
		cv::VideoCapture input_stream(input_video);

		float frame_width = input_stream.get(cv::CAP_PROP_FRAME_WIDTH);
		float frame_height = input_stream.get(cv::CAP_PROP_FR