For the record, Apple has never announced or said that the A8 is capable of playing 4K video, but it actually is capable of running 4K video flawlessly
http://m.tuaw.com/2014/11/21/exclusive-the-iphone-6s-a8-chip-can-play-4k-video/?post=1&icid=tuaw_home_latest_art
http://m.tuaw.com/2014/11/21/exclusive-the-iphone-6s-a8-chip-can-play-4k-video/?post=1&icid=tuaw_home_latest_art