如何使用 OpenCV 更改视频中的单个帧？

Question

I have a video that I built using OpenCV VideoWriter.

I want to change a specific frame with a different one. Is there a way to do it without rebuilding the entire video?

Answer 1

I am changing the third frame by making all pixels to zeros.

import numpy as np
import cv2

cap = cv2.VideoCapture(0)
fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('output.avi',fourcc, 20.0, (640,480))

frame_number = -1

while(True):
    frame_number += 1
    ret, frame = cap.read()
    if frame_number == 3:  # if frame is the third frame than replace it with blank drame
      change_frame_with = np.zeros_like(frame)
      frame = change_frame_with
    out.write(frame)

    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    cv2.imshow('frame',gray)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
out.release()
cv2.destroyAllWindows()

If you do not want to go through all the frames again:

import numpy as np
import cv2

cap = cv2.VideoCapture(0)
fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter('output.avi',fourcc, 20.0, (640,480))

frame_number = -1

while(True):
    frame_number += 1
    ret, frame = cap.read()
    if frame_number == 3:  # if frame is the third frame than replace it with blank drame
      change_frame_with = np.zeros_like(frame)
      frame = change_frame_with
      out.write(frame)
      break                # add a break here
    else:
      out.write(frame)

    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    cv2.imshow('frame',gray)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
out.release()
cv2.destroyAllWindows()

• But the above solution will not write all the other frames after 3 to the whole new video

Answer 2

This might help you :)

import cv2 as cv
vid = cv.VideoCapture('input.mp4')
total_frames = last_frame_number =  vid.get(cv.CAP_PROP_FRAME_COUNT)

fourcc = cv.VideoWriter_fourcc(*'avc1')
writer = cv.VideoWriter("output.mp4", apiPreference=0,fourcc=fourcc,fps=video_fps[0], frameSize=(width, height))

frame_number = -1

while(True):
 frame_number += 1
 vid.set(1,frame_number)
 ret, frame = vid.read()
 if not ret  or frame_number >= last_frame_number: break
 # check these two lines first
 if frame_number == changeable_frame_number :
   frame = new_img_to_be_inserted
 writer.write(frame)

 # frame = np.asarray(frame)
 gray = cv.cvtColor(frame, cv.IMREAD_COLOR)
 # cv.imshow('frame',gray)
 if cv.waitKey(1) & 0xFF == ord('q'):
    break

vid.release()
writer.release()
cv.destroyAllWindows()