4K videos are not playing smoothly?

I always use mpv video player to play all types of video formats
In my laptop ( dell inspiron 5559 core i3 ), 4k videos of dimension 3840 x 2160 (of 30fps) were playing very smoothly with mpv video player yet . But today I reinstall Ubuntu 18.04, after installation complete, I again install mpv using the command sudo apt install mpv

and 'mpv' installed successfuly but now I found that 4k videos (of 30fps) are not playing smoothly.

• I always use mpv video player to play all types of video formats.
• I never ever use 'vlc' to play 4k videos or hd videos because every time mpv done that job very smoothly.
• may be i missed some packages for videos.
• I tried to play 4K videos with other players like (mplayer, gnome-mpv, and ubuntu default player) but no one play 4K videos smoothly.
• 4K videos were playing properly before i did reinstall .

What is the problem ?, i am very upset to face such kind of problems ?