HarishGadade

Video Reversing

In openCV, video capturing and playing video in reverse way is very easy. First we need to install openCV on your machine.

For Windows Operating system:

pip install opencv-python

For Linux Operating System:

sudo apt-get install python-opencv

OpenCv library can be used to perform multiple operations on videos. Let’s try to do something interesting using CV2. Take a video as input and play it in a reverse mode by breaking the video into frame by frame and simultaneously store that frame in the list. After getting list of frames we perform iteration over the frames. For playing video in reverse mode, we need only to iterate reverse in the list of frames. Use reverse method of the list for reversing the order of frames in the list.

To play video in reverse direction, use following steps

Step 1: We import OpenCv library named cv2.
Step 2: Take a video as input data.
Step 3: First we break the video into a number of frames and store all these frames in a list.
Step 4: When we are getting all the frames then we shall apply iteration method.
Step 5: Here we apply iteration for reversing the list.
Step 6: Use the reverse() method for reversing the order of the frames in the list.

Detailed Steps

Step-I:

Import CV2 library

import cv2

Step-II:

Take a video as input data. videoCapture method of cv2 return video object and Pass absolute address of video file .

cap = cv2.VideoCapture("canny.mp4")

First we break the video into a number of frames and store all these frames in a list. Read method of video object will return a tuple with 1st element denotes whether the frame was read successfully or not, 2nd element is the actual frame.

Step-III:

So, Grab the current frame.

check , vid = cap.read()

Step-IV:

Initialize a counter variable for counting frames.

counter = 0

Also, Initialize the value of check variable.

# Initialization
check = True
frame_list = []

If reached the end of the video then we got False value of check.

Step-V:

Keep looping untill we got False value of check.

#Write frames into the current folder
while(check == True): 
     # imwrite method of cv2 saves the  
    # image to the specified format. 
    cv2.imwrite("frame%d.jpg" %counter , vid) 
    check , vid = cap.read() 
      
    # Add each frame in the list by 
    # using append method of the List 
    frame_list.append(vid) 
      
    # increment the counter by 1 
    counter += 1

last value in the frame_list is None because when video reaches to the end then false value store in check variable and None value is store in vide variable.

Step-VI:

Remove the last value from the frame_list by using pop method of List

frame_list.pop()

Step-VII:

Looping in the List of frames.

# Save frames in current folder
for frame in frame_list:      
    # show the frame. 
    cv2.imshow("Frame" , frame) 
    # waitkey method to stoping the frame 
    # for some time. q key is presses, 
    # stop the loop 
    if cv2.waitKey(25) and 0xFF == ord("q"): 
        break

Step-VIII:

Release method of video object clean the input video.

cap.release()

Step-IX:

Close any open windows.

cv2.destroyAllWindows()

Step-X:

Reverse the order of the element present in the list by using reverse method of the List.

frame_list.reverse()

for frame in frame_list: 
    cv2.imshow("Frame" , frame) 
    if cv2.waitKey(25) and 0xFF == ord("q"): 
        break
  
cap.release() 
cv2.destroyAllWindows()

Example: Program for Playing a video in reverse mode using OpenCV

# import cv2 library 
import cv2 
cap = cv2.VideoCapture("canny.mp4") 
  
check , vid = cap.read() 
  
counter = 0
  
check = True
  
frame_list = [] 
  
while(check == True): 
    cv2.imwrite("frame%d.jpg" %counter , vid) 
    check , vid = cap.read() 
    frame_list.append(vid)       
    counter += 1
  
frame_list.pop() 
for frame in frame_list:   
    cv2.imshow("Frame" , frame) 
    if cv2.waitKey(25) and 0xFF == ord("q"): 
        break
      
cap.release() 
cv2.destroyAllWindows() 
   
frame_list.reverse() 
for frame in frame_list: 
    cv2.imshow("Frame" , frame) 
    if cv2.waitKey(25) and 0xFF == ord("q"): 
        break
  
cap.release() 
cv2.destroyAllWindows()

Output:

In output, all the video frames will be stored in current folder and will play the wideo in reverse direction. Note that, for this program, create separate folder and save above program in newly created folder.

Image Processing