Here is an example of what I was talking about in my post above. This link is to a Hype Demo that I did today as part of an answer to someone's questions on this Forum. Hype Project here: Scene_ReturntoTime.hype.zip (27.7 KB)
This animation is just about as simple as it gets: a small Hype generated graphic going back & forth on a timeline. (I am referencing just "Scene 1" here, not "Scene 2" with the rotating square).
All of four major browsers do not render this animation in a smooth fashion, though each displays a slightly different result. The "Position with CSS left/top" is off. "Use Webkit graphics acceleration" is on (turning it off made no difference for the non-webkit browsers, as would be expected - but for Chrome & Safari - WebKit "off" was really bad animation).
I have had much larger JPGs & PNGs do just fine, and others not as well. I have yet to discover exactly why there is this variance - and why there is any issue at all for small basic graphics.