To output 4K movies on a blu-ray disc to play, you have a uhd player. Sony brings a new version out, the UBP-X700. That has support for the latest imaging techniques, such as HDR10 and Dolby Vision.
UHD movies are still quite expensive, you have to pay soon to be three tens for a single movie. It is just as well that this player also has wi-fi onboard, so you make your own movie files it can stream.
Or play them via usb. The device can o.a. handle .mp4 – and .mkv-files. Only music playback is also an option, with support for .mp3’s and .flac-files. The player costs 270 euros.