Parallax 'background-image/position/attachment' jQuery animation is jittery
===

Here's the breakdown...

- wrapper (position:relative; overflow:hidden; )
    - section-container (position:absolute)
        - multiple child sections

I attach a mousewheel event listener and animate (with easing) the 'top' position of 'section-container'. As this position changes, the 'background-position' of each section moves vertically based on the position of 'section-container's 'top' property (continually updated through a setTimeout()).

All of that works as it should, except as the 'background-position' changes, the image has a bit of a jitter. This doesn't happen if the 'background-attachment' is set to 'fixed'... but I don't want that.

Can anyone explain this, with a possible fix? I continually refer to the https://victoriabeckham.landrover.com/ site and can't figure out what they're doing differently to get theirs operating so efficiently.