Some of you might remember when a 3mb flash animation could pack in some 5 minutes of animation, with the more advanced ones even having chapter/scene selectors, which could also include clickable easter eggs and other kinds of interactions during the scenes.
I try to avoid recommending proprietary software but FYI the multimedia authoring tool formerly known as FutureSplash Animator which you presumably knew as Adobe Flash Professional (or perhaps Macromedia Flash before that) in fact lives on today as Adobe Animate and it can now target HTML5/SVG/WebGL/etc.
There are also many free/libre open source alternatives to it.