Why the frame2video function doesn't work?

Question

I write a function in PyQt5 in order to all frames in one directory can convert to a single video. My code is :

import os

import cv2
import numpy as np
from PIL import Image


def frame2video(im_dir, video_dir, fps):
    im_list = os.listdir(im_dir)
    im_list.sort(key=lambda x: int(x.split('.')[0]))
    img = Image.open(os.path.join(im_dir, im_list[0]))
    size = img.size

    fourcc = cv2.VideoWriter_fourcc('m', 'p', '4', 'v')
    videoWriter = cv2.VideoWriter(video_dir, fourcc, fps, size)
    for i in im_list:
        im_name = os.path.join(im_dir + i)
        frame = cv2.imdecode(np.fromfile(im_name, dtype=np.uint8), -1)
        videoWriter.write(frame)
    videoWriter.release()


if __name__ == '__main__':
    video_storedir = 'G:/dataset/video_new.mp4'
    if not os.path.exists(video_storedir):
        os.mkdir(video_storedir)
    path = 'G:/dataset' + '/' + 'example_Trim' + '_new/'
    frame2video(path, video_storedir, 30)

but it doesn't work, and run is still work, and the corresponding folder doesn't have the processed video....

the screenshot is: