Both are needed to keep both the width and the height of the image responsive.
This css gives the image its natural dimensions. So I would think that you don't need both max-width and max-height. Either max-width: 100% or max-height: 100% (together with the other css) would also do the job (?).
The developer who wrote that tutorial may have overlooked something, but don't worry - the official documentation has other demos and they work fine.
And they're very easy to manipulate. For example this is a combination of the "Silky Smooth" scroll demo and the official scroll demo: http://codepen.io/anon/pen/mPZZoo
Thanks Beverleyh. I didn't know until now what velocity.js was.
There's one problem with this script on my (recent) iPad Air. On the Silky Smooth page, Scroll and Reverse don't work.
Ddadmin, thanks for the comment. Much appreciated.
My 'icons' are in fact HTML-entities.
There's an overlay, but I made it invisible.
Maybe I should use 'real icons' and a visible overlay. I'll give it a thought.
Nice! The interface probably could be refined- the icons, maybe add an overlay to the page that dismisses the player when clicked on etc- but overall it looks like a solid script!