Working with Video in opencv

read_video_from_file.py

import numpy as np
import cv2 as cv

cap = cv.VideoCapture('vid.mp4')

while cap.isOpened():
    ret, frame = cap.read()

    # if frame is read correctly ret is True
    if not ret:
        print("Can't receive frame (stream end?). Exiting ...")
        break

    gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
    cv.imshow('frame', gray)
    if cv.waitKey(1) == ord('q'):
        break

cap.release()
cv.destroyAllWindows()

read_video_from_webcam.py

import numpy as np
import cv2 as cv
import sys

cap = cv.VideoCapture(0)
if not cap.isOpened():
    sys.exit("Cannot open camera")

while True:
    # capture frame-by-frame
    ret, frame = cap.read()

    # if frame is read correctly ret is True
    if not ret:
        print("Can't receive frame (stream end?). Exiting ...")
        break

    # Convert frame to gray
    gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)

    # Display the resulting frame
    cv.imshow('frame', gray)
    if cv.waitKey(1) == ord('q'):
        break

# When everything done, release the capture
cap.release()
cv.destroyAllWindows()

write_video_from_webcam.py

import numpy as np
import cv2 as cv

cap = cv.VideoCapture(0)

# Define codec by specifying four character code
fourcc = cv.VideoWriter_fourcc(*'XVID')
out = cv.VideoWriter('output.avi', fourcc, 20.0, (640, 480))

while cap.isOpened():
    ret, frame = cap.read()
    if not ret:
        print("Can't receive frame (stream end?). Exiting ...")
        break

    frame = cv.flip(frame, 0)

    # write the flipped frame
    out.write(frame)

    cv.imshow('frame', frame)
    if cv.waitKey(1) == ord('q'):
        break

# Release everything if job is finished
cap.release()
out.release()
cv.destroyAllWindows()