Apple uses their HTTP Live Streaming system for this. It is essentially a refreshing m3u playlist of 10 second MP4 video chunks that are served as normal files via HTTP, over their standard CDN.

It works well as long as the playlist refreshes properly, and the data gets deployed to the CDN fast enough.

Pretty big, they're using the massive Akamai network handling 15-20% of all internet traffic.

https://en.wikipedia.org/wiki/Akamai_Technologies#Customers

30-40% if you include PRISM.

Edit: Ok, fair enough with the down mod, I made a witty remark, but seriously, how do you measure internet traffic? In photons going to designated recipients, as if they were sealed love letters?

If the NSA required a copy of every bit flying around the Internet, wouldn’t the amount of traffic caused by Akamai remain the same, percentage wise?

(15 out of 100 is 15%. 30 out of 200 is also 15%.)

Yeah, but they only need one copy of what's on akamai, plus the metadata.

They may not be great at 2-way cloud sync, but they know how to use a CDN (iTunes, App Store, etc)

So true. Steve Jobs saw the potential of Akamai back in 1999, when it was a small company and when most people hadn’t heard of them. Back then, Apple invested US$12.5 million in Akamai, for 5 percent of the shares of the company. (Akamai’s valuation has gone up to 36x since then)

In those first years, Jobs also promoted Akamai on stage at keynotes and Apple wrote glowing press releases about how well the Akamai network held up streaming Apple’s keynote addresses. http://www.apple.com/pr/library/2000/07/24Apple-and-Akamai-D...

Apple + Akamai + Star Wars is what really made it all come together, according to this former Apple engineer: https://www.quora.com/Movie-Trailers/How-did-Apple-com-becom...

It'll hold up fine.

It currently stops for 10 seconds every 30 seconds. Hardly "hold up fine" by me.

It's running great! Nice job, Apple!