Held on Khadas EDGE (RK3399) advanced tests on 4K TV (resolution of the XFCE desktop environment full 4K). MPV and Gstreamer plays all files all formats (including 4K) without problems in full screen. Separately describe browser. I installed system components, MPV Gstreamer and KODI. The system part is the default armsoc. I use a regular browser (not accelerated versions of 32 bits). Once again, the desktop Resolution = 4K (XFCE). YouTube through the browser to full screen easily pulls all versions 1080p videos. When you select 4K video, the video is played in "chunks" - 2-3 seconds of smooth playback, then freezes and turns the white circle on the screen, then again 2-3 seconds smoothly and so constantly. I think this is a limitation of my Internet channel (or YouTube itself). Because the video itself (in YouTube 4K mode) shows smoothly and without friezes in the intervals when it works. So if you do "window" display mode, playable - "pieces". Maybe not enough of some buffer settings or anything, I'm not an expert. The conclusion I made for myself. RK3399-perfectly copes with any task of playing full-screen video. For local video (USB SD eMMC) or from a local network with a NAS where there is no bandwidth limit, any video goes without brakes to full screen with 4K scaling. For video from the Internet-no problem running any video for which enough channel. By the way, even the 1080p video on the 4K screen looks very good, I'm impressed.
By the way, the window from the applications, after installing the script are dragged quickly , almost as it was before the installation of the script, there are no protracted movements.
I agree with the opinion of @JMCC, for a component to work properly, it is important to have a properly configured system with the right kernel.
p.s.
By the way, when the desktop 4K resolution and full - screen video playback in YouTube, there was another problem-it is very difficult to see the mouse cursor, it is very small and have to look for a long time on the screen where it is.
But i'm can see much more information (video options or comments) immediately on the screen ....