code: def _is_videofile(self, f):
          
          if os.path.isfile(f):
              types = mimetypes.guess_type(f)
              mtype = types[0]
              if (mtype and mtype.split('/')[0] == 'video') or (os.path.splitext(f)[1] in self.VIDEO_EXTS):
                  return True
          return False
docs: 判断 f 是否是视频文件