The 4K Blu-ray player found in the Xbox Series X console was put to test by none other than Vincent Teoh from HDTVTest, one of the most respectable YouTube channels for expert, scientific TV reviews, and the results are a bit disappointing.
A lot of people use their gaming consoles as a media player, be it for streaming music, YouTube, Netflix, or watching 4K movies. The gaming console equipped with a 4K Blu-ray player makes a perfect combo for any entertainment room. We've seen folks upgrading to OLED TVs even before the Next-gen consoles have launched, and you expect that system to perform flawlessly when you hook it up, at least when outputting UHD content to your shiny new television.
Well, having an OLED TV is just half the job. A good 4K player needs to output all colors correctly for that TV to perform as intended. Everything starts with the black color.
As shown in the HDTVTest video, Xbox Series X is struggling with outputting the true black, with 0,0,0 RGB pixel value and 0 cd/m2. Instead, by using the reference monitor (Canon DP-V2411 4K) the results show that "the Blu-ray app on the Xbox Series X would always display a black video signal as a very very dark shade of grey with RGB subpixel values of 11, 11, 11, resulting in a minimum luminance level (MLL) of 0.00243 cd/m2 instead of 0 cd/m2. "
So, your TV will be getting the signal of a very dark shade of grey, instead of true black color, which could lead to outputting all colors incorrectly.
The good news is that this problem is only present when watching 4K Blu-ray content, there's no issue while playing games.
Due to this issue, not to mention the lack of support for Dolby Vision, HDR10+, and 3D Blu-rays, HDTVTest currently does not recommend using the Xbox Series X for high-quality 4K Ultra HD Blu-ray playback.
It's strange that the last-gen console, Xbox One X, doesn't have this type of issue. We'll just have to wait to see are Microsoft's engineers going to acknowledge this issue and act accordingly, by releasing an update to the Media player, that will hopefully fix the problem.