I tried the Jazz video posted here and my S8 play the video but it doesnt play it with HDR no matter if i play it with MX player or samsung player. So far the only video that has played with HDR on my S8 but only using the samsung player is the video found on below link. MX player, plays the video but without HDR.
In this video you really can see the difference in colors and details. The only way I see you can see that you can be sure that you are playing with HDR active is because the samsung player show the legend HDR, please see the screenshot, from here and the differences in colors and details i can assure that MX player is not playing it with HDR active because colors are all wash when you compare both.
So if you want to try if a video plays with HDR or not just use the samsung player and if you see the "HDR" in the screen like in my screenshot that means that the video is playing correctly with HDR otherwise is not even if you see nice colors and the video looks good. It will look much better with the HDR active.
Is there anyway we could activate HDR on MX player or will this be a feature to be added on future releases?
http://demo-uhd3d.com/fiche.php?cat=uhd&id=144