4K Video mATX suggestions

[Tatti]

Hello all,
I'm looking at building a new micro PC for use in the front room to play UHD 4K video on my TV in the front room, but don't want a monster box sitting around looking out of place.
A mATX build is what I was looking at, to build from scratch, but wanted advice on what specs I might need CPU, GPU and motherboard to help me run 4K video smoothly. As with all new builds, you want the components as inexpensive as possible but don't want to compromise too much either.
All help with suggestions is gratefully recieved before I start ordering components.

With thanks,
Tatti

 

[Tatti]

Thanks Bluntwrapped, very useful.
To update, I had been looking at my options but wasn't sure if iGPU was capable, but have come up with this as a starter; probably a bit overkill, perhaps some alternatives could be suggested. I haven't added a case yet, but have a couple in mind and will update later.

In my basket

Option #1
M/board - ASRock Z390M ITX DDR4 mITX
Processor - Intel CORE i5 9400 2.94GHz
RAM - Corsair Vengence LTX DDR4 8GB (2x4GB) BLACK
Power - be quiet! SFX Power 2 300W '80 Plus Bronze'
Total = £423 before shipping

Option #2
As above, but with added GPU MSI GeForce GTX 1650 Super AERO ITX 4GB DDR6
And upgraded Power be quiet! SFX-L 500W '80 plus Gold modular'
Total = £616 before shipping

 

[Tatti]

Thank you for all the advice folks, I have lots of options to consider now. The NUC and shield look good options.