UltraHD Blu-Rays are Good for 8K

In an article in What Hi-fi, the author explains why he really likes the higher quality that he can get from UltraHD Blu-Rays. If you have an 8K TV with upscaling or an upscaling processor, it has long been the case that the best source for upscaling content to 8K is an UltraHD Blu-Ray. While streaming platforms often restrict the bandwidth of content because of the cost of distribution, the UltraHD Blu-Ray specification allows up to 144 Mbps of bandwidth, so allowing creators to get as close as possible to the original content quality.
