"Opencv2" Operation of the video

Opencv2 , provides two video operation related classes,videocapture and videowriter, of course, there are corresponding constructors.

For videocapture, there are several operation functions:

Open (const string &filename)// opening video file

Open (int device)// turn on camera, device is serial number

Isopened ()// determine if the video file or camera is open and its return value is bool type

Release ()// close video file or webcam

Grab ()// Gets the video or camera next frame, if successful, returns TRUE, and its function type is bool type.

Retrieve (mat& image, int channel= ())// decodes a frame image that has just been acquired and assigns it to Image, the return value of this function is also bool type.

Read (mat& image)// gets, decodes, and reads the next frame of the video. In OpenCV , it overloads the function with the ">>" operator, which is the video >> image

Get (int propid)// return properties of the video

Propid values are different, the returned properties are also different. when propid takes the following values:

Cv_cap_prop_pos_msec the location of the current video file in milliseconds or timestamps

Cv_cap_prop_pos_frames capturing index with 0 -start video frame decoding

Cv_cap_prop_pos_avi_ratio Video relative position,0 for start,1 for end

Cv_cap_prop_frame_width The width of the video frame picture

Cv_cap_prop_frame_height The height of the video frame picture

Cv_cap_prop_fps Frame rate

CV_CAP_PROP_FOURCC Four-character code for video

total number of frames in Cv_cap_prop_frame_count video

picture format for Cv_cap_prop_format video

Cv_cap_prop_mode back-end specific values indicate the current capture mode

The following properties are only valid in camera mode:

Cv_cap_prop_brightness The brightness of the image

Cv_cap_prop_contrast Image Contrast Ratio

saturation of the cv_cap_prop_saturation image

chroma of Cv_cap_prop_hue image

exposure of cv_cap_prop_exposure images

Cv_cap_prop_convert_rgb whether the image is converted to an RGB type

Set (int propid)// Sets the property with the same value as the get function for the parameter

For Videowriter, there are several operation functions:

Open (const string &filename, int FourCC, double fps, Size framesize, color = True)

Several of the above parameters have been described above.

Isopened ()// with the front is a meaning

This function is also overloaded in the write (const mat& image)//opencv, with the operator <<

The following section of the program, the function of the program is to make a segment of the video smaller, that is, the original 1024*780 video, into 320*280, in order to use a few video operation functions, So some places can be greatly simplified or modified I have not modified, in order to show the use of various functions.

#include "opencv2/objdetect/objdetect.hpp" #include "opencv2/highgui/highgui.hpp" #include "opencv2/imgproc/ Imgproc.hpp "#include <opencv2/opencv.hpp> #include <iostream> #include <stdio.h>using namespace std ; using namespace Cv;int main (int argc, const char** argv) {Mat frame; Videocapture video;   Videowriter newvideo;double FourCC, fps, width, height;video.open ("25.avi"); Open Video FOURCC = Video.get (CV_CAP_PROP_FOURCC); fps = Video.get (cv_cap_prop_fps); width = Video.get (cv_cap_prop_frame_width); height = Video.get (cv_cap_prop_frame_  HEIGHT); Get some parameters for the video//create a new video Markvideo.open ("Markvideo10.avi", FourCC, fps); if (video.isopened () &&  Markvideo.isopened ()) {while (true) {video >> frame;  Read each frame of the video resize (frame, frame, Size (320, 280)); Zoom out every frame of the video if (!frame.empty ()) {Markvideo << frame;//each frame is written into a new video}else{printf ("-(!) No captured Frame--break! "); break;} if (char) waitkey (1) = = ' C ') {video.release (); Markvideo.release (); break;}}} return 0;}

"Opencv2" Operation of the video