I've tried CoreELEC as suggested and it plays videos smoothly even at 4k
Now the question is that now I have Ubuntu 16 and Kodi 17 on my ODROID-C2 (and I use also the OS, so I'd like not to use CoreELEC installation directly)
maybe I must upgrade to hardkernel's Ubuntu 18? (and the Kodi 18 that I think it has available)
I'm not sure anyway as to what is exactly failing here...
does somebody know if the new kernel or libs for Ubuntu 18 have video corrections?
PS: as a side note, I also tested a RPi2 and it couldn't show but vga garbage on Samsung TV, even though the Kodi GUI is clean
that's the reason I was almost convinced this was a TV/HDMI issue