Michael thank you for your reply
These are linked and native DNxHD files, both have the same problem.
I’ve tried the following things: new user settings; installing last QT 7.7.9; updating video card driver; installing GPU Driver ; switching monitors; and re-installing AMC8.4.4
but still having the problem.
I noticed that when I change the Display Color Space in Composer window it flashes a frame of video.
Any idea?
Thanks in advance!