Getting specific frames from VideoCapture opencv in python

Question

I have the following code, which continuously fetches all the frames from a video by using VideoCapture library in opencv in python:

import cv2

def frame_capture:
        cap = cv2.VideoCapture("video.mp4")
        while not cap.isOpened():
                cap = cv2.VideoCapture("video.mp4")
                cv2.waitKey(1000)
                print "Wait for the header"

        pos_frame = cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES)
        while True:
                flag, frame = cap.read()
                if flag:
                        # The frame is ready and already captured
                        cv2.imshow('video', frame)
                        pos_frame = cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES)
                        print str(pos_frame)+" frames"
                else:
                        # The next frame is not ready, so we try to read it again
                        cap.set(cv2.cv.CV_CAP_PROP_POS_FRAMES, pos_frame-1)
                        print "frame is not ready"
                        # It is better to wait for a while for the next frame to be ready
                        cv2.waitKey(1000)

                if cv2.waitKey(10) == 27:
                        break
                if cap.get(cv2.cv.CV_CAP_PROP_POS_FRAMES) == cap.get(cv2.cv.CV_CAP_PROP_FRAME_COUNT):
                        # If the number of captured frames is equal to the total number of frames,
                        # we stop
                        break

But I want to grab a specific frame in a specific timestamp in the video.

How can I achieve this?

set the position using CV_CAP_PROP_POS_MSEC , and then grab the frame — Miki
– Miki, Commented Nov 4, 2015 at 14:01
I would presume it would be similar to: frame = cap.get(CV_CAP_PROP_POS_MSEC(10)). Although this may be a more difficult problem than this — GPPK
– GPPK, Commented Nov 4, 2015 at 15:14
@GPPK it should be more like cap.set(CV_CAP_PROP_POS_MSEC, 123) frame = cap.read(). All if set works properly as you mentioned — Miki
– Miki, Commented Nov 4, 2015 at 15:53

DomTomCat · Accepted Answer · 2023-05-05 08:29:00Z

41

You can use set() function of VideoCapture.

You can calculate total frames:

cap = cv2.VideoCapture("video.mp4")
total_frames = cap.get(cv2.CAP_PROP_FRAME_COUNT)

Here 7 is the prop-Id. You can find more here http://docs.opencv.org/2.4/modules/highgui/doc/reading_and_writing_images_and_video.html

After that you can set the frame number, suppose i want to extract 100th frame

cap.set(cv2.CAP_PROP_FRAME_COUNT, 100)
ret, frame = cap.read()
cv2.imwrite("path_where_to_save_image", frame)

edited May 5, 2023 at 8:29

DomTomCat

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answered Jul 14, 2016 at 7:35

Abhishek Sachan

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5 Comments

SomethingSomething Over a year ago

Nice! I'd specify that 7 is the ordinal value of CV_CAP_PROP_FRAME_COUNT and that 1 is the ordinal value of CV_CAP_PROP_POS_FRAMES - so what you're doing here is, you're actually moving the "frame reader" to the offset of the 100th frame, and then you read the "next" one, that is the 101st frame

June Wang Over a year ago

is there a way to set the number of frames to be extracted?

Jacob Lawrence Over a year ago

what if the frames are recieved from a web cam. Does this take effect

Jabba Over a year ago

The magic number 7 is actually the constant cv2.CAP_PROP_FRAME_COUNT, i.e. total_frames = cap.get(cv2.CAP_PROP_FRAME_COUNT) .

Apostolos Over a year ago

Doesn't work for me. I get empty frames (NP array full of zeros) whatever video file and whatever count I use. Any idea why?

Apostolos · Accepted Answer · 2024-02-25 09:26:38Z

8

this is my first post so please don't rip into me if I don't follow protocol completely. I just wanted to respond to June Wang just in case she didn't figure out how to set the number of frames to be extracted, or in case anyone else stumbles upon this thread with that question:

The solution is the good ol' for loop:

    vid = cv2.VideoCapture(video_path)
    for i in range(start_frame, start_frame+how_many_frames_you_want):
        vid.set(1, i)
        ret, still = vid.read()
        cv2.imwrite(f'{video_path}_frame{i}.jpg', still)

edited Feb 25, 2024 at 9:26

Apostolos

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answered Mar 28, 2020 at 1:35

Eric De Luna

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3 Comments

Nick Over a year ago

Welcome to SO. Explaining how your code answers the question is always a good thing.

mikey Over a year ago

For me, this just print the same image for each number in range

Apostolos Over a year ago

Nice. Only that the range you were using was wrong. (range(start_frame, how_many_frames_you_want). I corrected it

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