That depends. Assuming you are using the Plex app on the Samsung, video may be fine. There are different ways to encode files so just saying 4K doesn’t guarantee anything. The audio may be a bigger issue. In some cases, if the audio isn’t supported, it may need to transcode the video too. The TV would need to support passing through the audio. Supporting it locally and being able to passthrough are different and typically not specified in the device’s specs. Also depends on if you use ARC, optical, or eARC. Plex doesn’t support eARC yet. ARC and optical have limitations on what it can passthrough even if the TV/receiver support it.
A better setup is to use a dedicated streaming box like an Apple TV, NVidia Shield, Roku, etc. Then connect the box to the receiver and from the receiver to the TV. This way all the passthrough is done via HDMI which is better. Of course, each box has it’s own limitations too. Currently, the NVidia Shield has the best range of supported audio and video codecs.
There is an entire write up done by a user with lots of details for using 4K. It’s a good read, [INFO] Plex, 4k, transcoding, and you - aka the rules of 4k.
