A native 4K Blu-ray player and a 4K upscaling Blu-ray player differ in the way they handle video content. A native 4K Blu-ray player is capable of playing 4K Ultra HD content directly from a disc, providing a resolution of 3840x2160. This results in a higher quality image compared to upscaling, as the player receives the full 4K resolution directly from the disc. Additionally, native 4K Blu-ray players can also play High Dynamic Range (HDR) content and support 3D playback.
On the other hand, a 4K upscaling Blu-ray player is able to convert standard Blu-ray discs (which have a resolution of 1080p) into a 4K Ultra HD picture. While this can improve the overall video quality, it is not the same as playing native 4K content, as the player is essentially guessing at what the additional pixels should look like. This can sometimes result in a less sharp or detailed image compared to native 4K playback. However, upscaling can still provide a noticeable improvement in picture quality, especially on larger TVs.
In summary, a native 4K Blu-ray player offers the best picture quality as it can play 4K Ultra HD content directly from a disc, while a 4K upscaling Blu-ray player can improve the quality of standard Blu-ray discs, but it is not the same as playing native 4K content.