This is very annoying, and undocumented. Basically, you do not have to change anything on the linux side. It is just the TV that needs to know you are connecting a laptop/pc. To do this on samsung:

1. Connect your laptop/pc to the HDMI port labeled DVI. For me, that is HDMI 4
2. Go to the source list on the tv
3. Scroll to the port (HDMI4). Press and hold options.
4. Rename the port. It should have the name “PC”
5. Stuff should work now

To select the HDMI out for audio, install pavucontrol and open that. It will let you choose the output.