OpenCV/Python: read specific frame using VideoCapture

Question

Is there a way to get a specific frame using VideoCapture() method?

My current code is:

import numpy as np
import cv2

cap = cv2.VideoCaptur         


        

Answer 1

Set a specific frame

From the documentation of the VideoCaptureProperties (docs) is possible to see that the way to set the frame in the VideoCapture is:

frame = 30
cap.set(cv2.CAP_PROP_POS_FRAMES, frame)

Notice that you don't have to pass to the function frame - 1 because, as the documentation says, the flag CAP_PROP_POS_FRAMES rapresent the "0-based index of the frame to be decoded/captured next".

Concluding a full example where i want to read a frame at each second is:

import cv2

cap = cv2.VideoCapture('video.avi')

# Get the frames per second
fps = cap.get(cv2.CAP_PROP_FPS) 

# Get the total numer of frames in the video.
frame_count = cap.get(cv2.CAP_PROP_FRAME_COUNT)

frame_number = 0
cap.set(cv2.CAP_PROP_POS_FRAMES, frame_number) # optional
success, image = cap.read()

while success and frame_number <= frame_count:

    # do stuff

    frame_number += fps
    cap.set(cv2.CAP_PROP_POS_FRAMES, frame_number)
    success, image = cap.read()

Set a specific time

In the documentation linked above is possible to see that the way to set a specific time in the VideoCapture is:

milliseconds = 1000
cap.set(cv2.CAP_PROP_POS_MSEC, milliseconds)

And like before a full example that read a frame each second che be achieved in this way:

import cv2

cap = cv2.VideoCapture('video.avi')

# Get the frames per second
fps = cap.get(cv2.CAP_PROP_FPS) 

# Get the total numer of frames in the video.
frame_count = cap.get(cv2.CAP_PROP_FRAME_COUNT)

# Calculate the duration of the video in seconds
duration = frame_count / fps

second = 0
cap.set(cv2.CAP_PROP_POS_MSEC, second * 1000) # optional
success, image = cap.read()

while success and second <= duration:

    # do stuff

    second += 1
    cap.set(cv2.CAP_PROP_POS_MSEC, second * 1000)
    success, image = cap.read()