Video and audio should not autoplay on your site. While I am not one for absolutes but along with never using Comic Sans, I would say autoplay does not have a place in a website. People may visit your site in a situation where they need to be discreet. Or maybe they have a sleeping child and are finally sitting down to look some things up and they get greeted by a loud sound.
Your website content should be able to stand on its own without sound or video, remember that people will be visiting your site who may not be able to hear or see and you need to account for this.
Please just don't use autoplay.