Autoplay videos are not a perfect science.
Many browsers block the automatic play of videos, mostly for privacy and user experience reasons.
We actually don't recommend using autoplay videos unless the recipient is expecting the video to autoplay.
By default, the 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 video autoplay, go to the video edit page in the Player tab select autoplay. Here's how to do that:
Here's what autoplay looks like: