Python: take screenshot from video

问题

The idea is that, user should be able to load a video from their local machine and tell the program to take a screenshot from the video every 5sec or 30sec. Is there any library to help me with this task? Any idea from how to proceed would be helpful.

回答1:

install opencv-python (which is an unofficial pre-built OpenCV package for Python) by issuing the following command:

pip install opencv-python

# Importing all necessary libraries
import cv2
import os
import time

# Read the video from specified path
cam = cv2.VideoCapture("C:/Users/User/Desktop/videoplayback.mp4")

try:

    # creating a folder named data
    if not os.path.exists('data'):
        os.makedirs('data')

    # if not created then raise error
except OSError:
    print('Error: Creating directory of data')

# frame
currentframe = 0

while (True):
    time.sleep(5) # take schreenshot every 5 seconds
    # reading from frame
    ret, frame = cam.read()

    if ret:
        # if video is still left continue creating images
        name = './data/frame' + str(currentframe) + '.jpg'
        print('Creating...' + name)

        # writing the extracted images
        cv2.imwrite(name, frame)

        # increasing counter so that it will
        # show how many frames are created
        currentframe += 1
    else:
        break

# Release all space and windows once done
cam.release()
cv2.destroyAllWindows()

回答2:

the above answer is partially right but time.sleep here does not help at all but rather it makes the process slower. however, if you want to take a screenshot at a certain time of a video you need to understand that every time you do "ret, frame = cam.read()" it reads the next frame of the video. every second in a video has a number of frames depends on the video. you get that number using:

  frame_per_second = cam.get(cv2.CAP_PROP_FPS) 

so if you need to take a screenshot of the 3rd second you can keep the iteration as is in the above answer and just add

  if currentframe == (3*frame_per_second):  
      cv2.imwrite(name, frame)

this will take a screenshot of the first frame in the 3rd second.

回答3:

To add on data_sniffer's answer. I would recommend using round (Math function) on frame_per_second when checking as if the frame rate is a decimal number then it will go into an infinite loop.

回答4:

#ncica & Data_sniffer solution remake
import cv2
import os
import time

step = 10
frames_count = 3
cam = cv2.VideoCapture('video/example.MP4')

currentframe = 0
frame_per_second = cam.get(cv2.CAP_PROP_FPS) 
frames_captured = 0

while (True):
    ret, frame = cam.read()
    if ret:
        if currentframe > (step*frame_per_second):  
            currentframe = 0
            name = 'photo/frame' + str(frames_captured) + '.jpg'
            print(name)
            cv2.imwrite(name, frame)            
            frames_captured+=1
            if frames_captured>frames_count-1:
                ret = False
        currentframe += 1           
    if ret==False:
        break
cam.release()
cv2.destroyAllWindows()

来源：https://stackoverflow.com/questions/57791203/python-take-screenshot-from-video