How can I prepare for Apple WWDC 2018 event live broadcast and rebroadcast?
To prepare for 2018 WWDC I would recommend three things:


AppleTV and updating it now for the Live Stream and Rebroadcast of the main presentation in the morning and afternoon of the first day. These keynote events are highly viewed and usually available for on-demand viewing and professionally produced.
WWDC app on the App Store is also very good if you are a registered developer as you can watch many of the sessions live and should expect to be able to rebroadcast.
Safari web browser is the third best option - in past years -there were not any sort of YouTube or third party browsers.


As to why these three avenues were selected last year is that the sessions under developer NDA require authentication with an AppleID. Also, on a technical level - the streaming used the latest QuickTime codecs for presumable efficiency, quality. Also, there would be marketing synergies of potential value to Apple by using their own technology for a high stakes  / high pressure / high expectations and in demand public event. 

Hopefully this helps people prepare for the 2018 remote viewing of the sessions at this year's developer conference.

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As a postscript - the WWDC app is showing the live stream on rebroadcast within hours of the main event completing.