How to get frame from video by its index via OpenCV and Python?

Question

I need to access frames from video by the frame index. So far I used code like this:

video = cv2.VideoCapture(video_path)
status, frame = video.read()

The code reads the first frame. If I use the code repeatedly I will get next frames. But how I can access directly any frame by its index?

In other words, if I want second frame, how can I access directly the second frame without calling read() two times?

similar to stackoverflow.com/questions/70292873/…

NDAYISABA Charles
– NDAYISABA Charles

2023-08-22 14:58:12 +00:00
Commented Aug 22, 2023 at 14:58 — NDAYISABA Charles
– NDAYISABA Charles, Commented Aug 22, 2023 at 14:58

matousc · Accepted Answer · 2017-09-07 17:14:39Z

33

Use VideoCapture::set() with CAP_PROP_POS_FRAMES property id to set the position of the frame to be read.

myFrameNumber = 50
cap = cv2.VideoCapture("video.mp4")

# get total number of frames
totalFrames = cap.get(cv2.CAP_PROP_FRAME_COUNT)

# check for valid frame number
if myFrameNumber >= 0 & myFrameNumber <= totalFrames:
    # set frame position
    cap.set(cv2.CAP_PROP_POS_FRAMES,myFrameNumber)

while True:
    ret, frame = cap.read()
    cv2.imshow("Video", frame)
    if cv2.waitKey(20) & 0xFF == ord('q'):
        break

cv2.destroyAllWindows()

edited Sep 7, 2017 at 17:14

matousc

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answered Sep 7, 2017 at 16:38

zindarod

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6 Comments

msch Over a year ago

cap.set(1, myFrameNumber) is required for python 3

Volkov Maxim Over a year ago

Thanks, @zindarod for the help! It's also recommended to add cap.release() before cv2.destroyAllWindows()

Peter Over a year ago

This method can lead to incorrect results - see github.com/opencv/opencv/issues/9053 . Basically opencv can't do reliable random access

Paul Jurczak Over a year ago

@Peter Thank you for pointing this out. Do you know if subsequent frames produced by calls to read() will be consecutive?

Peter Over a year ago

Yes, I believe so - though I have had the experience of getting None returned partway through a video, only to get a frame on the next call to read() ... So I'm not sure what that means. All solutions are bad though as far as I know. pyav works but is slow decord is fast but eats way to much memory on long videos.

|

Sanaa · Accepted Answer · 2019-11-21 02:34:58Z

2

import os
folder= 'frames'
os.mkdir(folder)
import cv2
vidcap = cv2.VideoCapture('four.mp4')
def getFrame(sec):
    vidcap.set(cv2.CAP_PROP_POS_MSEC,sec*1000)
    hasFrames,image = vidcap.read()
    if hasFrames:
        cv2.imwrite("image"+str(count)+".jpg", image)     # save frame as JPG file
    return hasFrames
sec = 0
frameRate = 0.5 #//it will capture image in each 0.5 second
count=1
success = getFrame(sec)
while success:
    count = count + 1
    sec = sec + frameRate
    sec = round(sec, 2)
    success = getFrame(sec)

answered Nov 21, 2019 at 2:34

Sanaa

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