A 4K source video gets convert down to 2K (1080) by the cpu if you only have 1080 HDTV or monitor/computer.
Good to know one can still play the video (albeit at 2K) until one upgrades the computer and monitor to 4K.
But if your video card in the computer can handle 4K and have a 4K monitor attached you should be able to watch it in 4K, same for the the UHDTV.