How to get frame from video by its index via OpenC

问题:

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?

回答1:

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()

回答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)