face_detection.py

import cv2

# Load the cascade
face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')

# To capture video from webcam. 
cap = cv2.VideoCapture(0)
# To use a video file as input 
# cap = cv2.VideoCapture('filename.mp4')

tick = 0

while True:
	# Read the frame
	_, img = cap.read()

	if (tick % 20) == 0:
		# Convert to grayscale
		gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

		# Detect the faces
		faces = face_cascade.detectMultiScale(gray, 1.1, 4)

		# Draw the rectangle around each face
		for (x, y, w, h) in faces:
			cv2.rectangle(img, (x, y), (x+w, y+h), (255, 0, 0), 2)

	tick += 1

	# Display
	cv2.imshow('img', img)

	# Stop if escape key is pressed
	k = cv2.waitKey(30) & 0xff

	if k==27:
		break

# Release the VideoCapture object
cap.release()