Technically put, the iPhone 6 camera is capable of 24-30fps 4K video. It could technically record enough frames per second at the 4K resolution for smooth video. However, Apple didn't decide to add this functionality to the camera app. This is likely due to the size of the video files as well as how 4K TVs are not mainstream. Outlook looks good for the 6S with a similar sensor to take 4K video natively though... Samsung's Galaxy S5 and Note 4 already do but they're just trying to be ahead of .