Videos won't autoplay

Can anyone help?

I've created a presentation with animated text, lots of photos and videos.

But when I create view-only link and check it, nothing plays automatically. Not the animations or the videos. I have to press the arrow keys to move from slide to slide (which is fine) and then press play manually to get anything to play.

Is there a setting I need to change to get everything to play automatically, so the viewing only has to press the arrow key to get from page to page?

Also, the first page of the presentation is loading as a different size to the rest of the presentation. Can't figure out why...

I'm new to Express so maybe I should have chosen a different format other than presentation?

Help greatly appreciated!