Xperia 1 display resolution
The Xperia 1 conforms to the Sony 4K definition of 3,840 horizontal pixels (in landscape orientation). With a 21:9 aspect ratio, this results in 3,840 x 1,644 pixel resolution.
Watching 4K video in 21:9 aspect ratio
The Xperia 1 lets you enjoy 21:9 aspect ratio content, edge to edge and without letterboxing. This aspect ratio is optimal for movies created in 21:9 format and available in 4K resolution.
Playing back recorded 4K video in 21:9 aspect ratio
You can record 21:9 4K video using Cinema Pro, and play it in true 4K quality on the Xperia 1.
Watching non-4K content
Xperia 1 uses advanced upscaling technology to display non-4K content, enhancing contrast, colour and clarity.
Watching content in 16:9 aspect ratio
On the Xperia 1, content with 16:9 aspect ratio is by default displayed with pillar boxing. You can also zoom in to fill the screen, with top- and bottom cropping as a result.
I'm having trouble playing 4K content, why is that?
The 4K standard refers to the horizontal display resolution of approximately 4000 pixels. The vertical number of pixels is not standardised.
The Xperia 1's pioneering screen design allows the phone to display 4K in a cinematic 21:9 aspect ratio, which translates into a 3840 x 1644 resolution.
Anything recorded or streamed in that resolution will be played in full 4K on this display.
Currently, the most commonly used resolution in various 4K streaming apps is 3840 x 2160. That means it uses a slightly higher vertical resolution than the resolution associated with the 21:9 aspect ratio.
Because the X1 screen design allows only for 1644 and not 2160 vertical lines, whatever is streamed or played will revert to an HD resolution to avoid not showing a part of the picture.