Go to Settings -> Video and disable hardware acceleration for video decoding. Thank you, It solved my problem. However I think this is not the actual solution, because without gpu acceleration, cpu is in under a lot of usage like above the 80%. I think developer team need to update gpu acceleration...

4K is working well on KMP but Splash can't run it properly. Splash shows the movie like there is a gray filter on it, but movie's preview tumbnail thing shows movie's colours well. Also while movie is playing, I can see some pixels when movements happen in the movie like when you forward the movie i...