It is not an infringement to post a video on Douyin using a video from Taobao. As long as the video you post is not suitable for the intellectual property, it will not be considered an infringement. If the person who uses Taobao also posts a video on Douyin, and you post it later, then your post will also be considered an infringement, because the other person posted it first, and if you post it later, it will be considered as copying.