Hmm, looks like Safari (desktop version, mobile version does not support auto play) is having some issues with the auto play attribute. Another way to approach the issue would be to star the video with js using the start action on the scene.
He means that you put custom code in the start action of the current scene.
So you open the scene where you work in.
Click outside of the Scene "stage"
on the right you will have the "actions" bar in the sidebar.
The Actions bar has a "start", "end", Mouse move actions.