Here is how I know it's a UHD Blu Ray issues, everything streaming, HDR 10 and Dolby Vision from the Fire Cube looks extraordinary, I mean jaw dropping but from Sony X800 its not as satisfying. I just redeemed the 4k HDR Resident Evil Afterlife on Movies anywhere and it's freaking stunning. Last night I watched free from Amazon video "The Da Vinci Code" 4k HDR 10 and it was also stunning. Something is just missing from UHD Blu Ray.
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Now don't forget 2 things.
First, the Bluray should be choosing it's own HDR. And this goes back to my comment about the Video information. You need to find that I think. So we know absolutely that it's choosing the correct HDR Format. But this is almost certain to be correct.
The second is the bigger issue. What is THE TV MODE. Like I was writing in my last comment. My Bluray chooses HDR, and my TV instantly switches to HDR Effect Mode.
But. - When I stream my TV is set to "Standard" mode. Now on my TV "Standard" really pops..! And "HDR Effect" seems a bit muted in direct comparison. But I can just change the TV Video mode to "Standard" if I want that same pop.!
I don't think it's the player. Because with a 4K disc you can't change these settings if you TV is set properly. The 4K sets the proper HDR, and the proper TV mode.
And remember no matter what your viewing on MoviesAnywhere, that HDX isn't any better than a regular Bluray at Best.
I think you're seeing different TV Mode setting. So change it. Your TV probably remembers what you choose last and is repeating it..!