To enable or disable Audio (mute video) please go to Players page
On the Player page, you will have a list of players in your account.
To enable or disable mute click the Edit icon on the right of the player.
In the Muted section select On or Off.
Videos that have Autoplay On must be muted in order to play them on all modern browsers.
After you finished editing it make sure to Preview player behavior to make sure you got the desired outcome.