No, a doctor would not be required to follow a video or a written post. To be effective, a "living will" (as it's commonly called; it's better called, however, an "advance health care directive") must be correctly written (using the right language & terminology), executed, witnessed, and notarized as required by your state. The technicalities are critical--getting the details wrong can invalidate the document. Someone wanting to provide such directions should let an attorney draw it up for him/her.