Problem with 4K Samsung TV

depending on your model, your macbook pro's hdmi may be only 1.4, ie supporting only 1080. see here:

https://support.apple.com/en-us/HT204388

to feed a 4k monitor, you may need an active adapter display port to hdmi 2.0. for my mac pro, i use one from club 3d which works fine.

make sure you are using a hdmi 2.0 cable, too.

I think you have a problem with HDCP (Hi Def Content Protection), and that is why you might be seeing this problem. Both the Mac and the Samsung TV have to do a handshake for the picture to come through. No handshake, no picture. This might not have been a problem with HDMI 1.4 but with HDMI 2.0 and up, yes, it sure is a problem. All components must support the new standard (and new HDCP) or you get nothing, at least in terms of 4k picture. It'll support 1080, maybe, but 4k ? Not a chance. So, how to fix this, right? check the cable you're using to connect your Mac Pro to your Samsung TV. It must support HDMI 2.0 and HDCP 2.2 as well. also see if setting screen mirroring either on or off makes a difference (I think it's under system preferences, then monitors/display) . I don't know what model of Mac pro you have, so I can't say for sure if it'll output 4k or not, probably it'll do 1080... maybe 2k??? . I think also it sets the video out as HDMI when the cable is plugged in, at least I hope so.

Hope this helps a bit....

John B