I thought this video was rather interesting, because at 12:27, the presenter crunches the numbers to find out how many years it would take for a new computer purchase to be more environmentally friendly (in regards to total CO2 expended) compared to using a less efficient used model.
Depending on the specific use case, it could take as little as 3 years to breakeven in terms of CO2 if both systems were at max power draw forever, and as long as 30 if the systems are mostly at idle.
You don’t really want to live transcode 4K. That’s a tremendous amount of horsepower required to go real time. When you rip your movies you want to make sure they’re in some format that whatever player you’re using can handle. If that means that you use a streaming stick in your TV instead of the app on your TV that’s what you do. I think you could technically do it with a 10th+ gen Intel with embedded video. I know that a Nvidia 2070 super on a 7th gen Intel will not get the job done for an upper and Roku. So all of my 4K video is either h264 or HEVC so it all direct plays on my flavor of Roku.