Hey that's cool. How'd they do it? I guess some sort of logic to look for movement in the image and put the stars around it?

Flash (and other) video compression uses a similar algorithm to look for parts of a video that are more static. (To avoid re-sending information about a static background, for example.) I'd guess it's a modification from compression technology.

to avoid re-sending information about a static background for example. I wonder if they built theirs from scratch or just modified

They're just overlaying sprites (stars in this case) in areas of high deltas (changes). That's all.

it would be cool if the sprites had some ballistic motion after they were spawned... with velocity based on the initial direction of the delta that spawned the sprite + some gravity, maybe some turbulence and random lifespans and size changes.

I've had too many years making particle effects....

Very cool. So this is what Justin was flipping out over at the YC mixer, I take it?

Hey, that's one way to flirt with the ladies...casting your spell.

That is pretty gosh darn impressive. Good work guys!