How does converting a video to 4K actually work?

Upscaling software is getting better all the time, but there are still some caveats to be aware of.

Upscaling software is getting better all the time, but there are still some caveats to be aware of.<p><img src="https://www.engadget.com/img/gallery/how-does-converting-a-video-to-4k-actually-work/intro-1786115696.jpg" /></p>