How to read a specific frame to a specific frame from video using opencv?

Question

I want to read from a specific frame to a specific frame in a video. For example , my video consists of 150 frames, but I want to read the video from frame 5th to frame 134th in that video. Is it possible?

Answer 1

First you have to read your video and store it into a multi-dimensional numpy array. Afterwards you can slice the numpy array according to your requirements

See https://stackoverflow.com/a/42166299/4141279 on how to read a video into a numpy array.

Slicing is then done by:

buf[4:134] # assuming buf is your numpy array from the previous step

You could also drop all the unnecessary frames during initial creation of the numpy array if you have memory limitations.

idx = 0
while (fc < frameCount  and ret):
    ret, tmp = cap.read()
    if fc in range(4, 135):
        buf[idx] = tmp
        idx += 1
    fc += 1

Answer 2

I would do something like this :

This probably uses less opencv than you want, but I personally believe that ffmpeg is more adapted to this kind of operation

import cv2
from moviepy.video.io.ffmpeg_tools import ffmpeg_extract_subclip

def get_framerate(video)->float:
    """ this function was made to extract the framerate from a video"""
    # Find OpenCV version
    (major_ver, minor_ver, subminor_ver) = (cv2.__version__).split('.')
    if int(major_ver)  < 3 :
        return video.get(cv2.cv.CV_CAP_PROP_FPS)
    else :
        return = video.get(cv2.CAP_PROP_FPS)

if __name__ == "__main__":
    # get start frame
    videoName = input("Path of the video file ?")
    video = cv2.VideoCapture(videoName);
    fps = get_framerate(video)
    frame_start = int(input("Starting frame ?\n"))
    ts_start = frame_start / fps
    frame_end = int(input("Ending frame ?\n"))
    ts_end = frame_end / fps
    ffmpeg_extract_subclip(frameName, ts_start, ts_end, targetname="output.mp4")

source 1 : an openCV guide

source 2 : another question on stack overflow