# import the opencv library 
import cv2
  
  
# define a video capture object 
camera = cv2.VideoCapture(0) 
camera.set(cv2.CAP_PROP_FPS, 20.0)
if not camera.isOpened():
    print("Cannot open camera")
    exit()

queue = [(False, None)] * 100
 
# Define the codec and create VideoWriter object
fourcc = cv2.VideoWriter_fourcc(*'mp4v')
#out = cv2.VideoWriter('output.mp4', fourcc, 20.0, (int(camera.get(3)),int(camera.get(4))))
 
idx = 0
offset = 0
while(True): 
      
    # Capture the video frame 
    # by frame 
    ret, frame = camera.read() 

    frame = cv2.flip(frame, 1)

    #recod the frame
    #out.write(frame)
    queue[idx] = ret, frame

    showo, fr = queue[(idx - offset) % len(queue)]
    if showo:
        cv2.imshow('vid', fr)
      
    # the 'q' button is set as the  quitting button you may use any  desired button of your choice 
    key = cv2.waitKey(1) & 0xFF
    if key == ord('q'): 
        break

    if key == ord('a'):
        offset += 1
    if key == ord('d'):
        offset -= 1

    idx = (idx + 1) % len(queue)
  
# After the loop release the cap object 
camera.release()
#out.release()
# Destroy all the windows 
cv2.destroyAllWindows()