This is limited to some users of specific Intel video chipsets, but: if you get odd screen artifacts in X, the ‘vesa’ driver may work just fine for you. Or turn acceleration off. Or set ‘drm.i915.enable_execlists=0’ according to zrj on #dragonflybsd.
(Updated to reflect all the answers in the thread and elsewhere.)
From what I read, the OP did not use VESA.
“Thank you! With Intel video-driver and Option “NoAccel” “true” the artifacts – bad screen are not observed in DragonFly BSD and 480 pix YouTube video is good.”
Am I missing something? Where does a user say “VESA is better” ? Maybe you are confusing the driver with x11-drivers/xf86-video-vesa ?
I didn’t link to the right part of the thread. I’ll update it now.