Hi Jack,
Thanks for responding!
You're right, the scrollbar's not acting as a scrubber, it's just the trigger for the replay and to advance the content.
Re scrolling 'even 1px' and what to do if the user scrolls immediately - there's definitely some logic to be worked out! Ideally I want to play the full video on load and then scrub to the halfway point, while also scrubbing the 2nd content/timeline. This would let me address the logic (onLeave, onEnterBack, etc) and look good whichever direction is being scrolled.
...I just spent the whole day replying to this and trawling the forums for umpteen different solutions that 'might' fit my purposes. Finally as the sun is about to set, I stumbled across this thread, which is actually an old answer from you Jack (thanks again)! No canvas, no blobs, just sprites... Thank goodness, because my head is spinning with everything I've read today!
I should be able to work with that, assuming 390 images isn't too heavy. Failing that, I might have to delve into canvas - what do you think? ['blobs' probably best left alone...although they are mentioned in this thread, which is also potentially useful]
Crazy thing is, I remember finding the original tutorial for this ages ago, wish I'd stumbled across this link sooner...doh! ?♀️