中文资料找半天没找到，最后google 英文到stackoverflow 才找到，记录下
先安装好ffmpeg，网上教程可查
然后opencv等库

import os
import cv2
import subprocess 

filename = r'视频文件路径' 


def get_frame_types(video_fn):
    command = 'ffprobe -v error -show_entries frame=pict_type -of default=noprint_wrappers=1'.split()
    out = subprocess.check_output(command + [video_fn]).decode()
    frame_types = out.replace('pict_type=', '').split()
    return zip(range(len(frame_types)), frame_types)


from PIL import Image


def save_i_keyframes(video_fn):
    frame_types = get_frame_types(video_fn)
    i_frames = [x[0] for x in frame_types if x[1] == 'I']
    if i_frames:
        basename = os.path.splitext(os.path.basename(video_fn))[0]
        res_dir = os.path.join(os.path.dirname(video_fn), 'frame')
        os.mkdir(res_dir)
        cap = cv2.VideoCapture(video_fn)
        for frame_no in i_frames:
            cap.set(cv2.CAP_PROP_POS_FRAMES, frame_no)
            ret, frame = cap.read()
            outname = basename + '_i_frame_' + str(frame_no) + '.jpg'
            Image.fromarray(frame).save(os.path.join(res_dir, outname))
            print('Saved: ' + outname)
        cap.release()
    else:
        print('No I-frames in ' + video_fn)


if __name__ == '__main__':
    save_i_keyframes(filename)