Autoplay videos are not a perfect science.
Many browsers block the autoplaying of videos, mostly for privacy and user experience reasons.
We actually don't recommend using autoplay videos unless the recipient is expecting for the video to autoplay.
By default sound is always off in autoplay videos.
That said, we do have an option to allow a video (in a video landing page or as an embedded video) to autoplay.
To make a video autoplay, go to the video edit page in the Player tab select autoplay.
Here's how to do that.
Here's what an autoplay looks like.