Most current Android flagships can record 4K Ultra HD video footage with their rear cameras, but Apple eschewed the option on its new iPhone 6 and iPhone 6 Plus, deeming it unfit for prime time. Given the overheating warnings and storage problems that 4K bring on, Apple might have a point, and yet its fresh phones are perfectly capable of playing back 4K videos.
There are plenty of apps out there in iTunes that bring the much desired 4K recording ability to the two new iPhones, recording it in 30fps. If you wondered what one such app can do, check out the results from ProCam 2 below. The app itself costs $1.99, and then if you want the 4K recording option unlocked, you'd have to shell out five bucks more. The video is actually captured with 3264×1836 resolution, and upscaled to the 4K's 3840×2160 standard, panning slowly around to avoid hiccups.
source: ProCam 2 via RedmondPie