Same problem - commenting again for visibility!
The last driver that doesn't have this issue is 18.104.22.168. So this problem has been introduced with the 2019 Edition drivers, with the new Relive features.
Players I have tested include MPC-HC, MPC-BE, WMP, Films & TV player in W10. The machine is dual booted with Windows 8.1 where the problem also occurs using the Windows 7 driver, so I can only assume this also affects Windows 7.
I run an RX 480 with the LG 29" Ultrawide 29UM67 over Displayport.
Please can you check if you have Enhanced Sync enabled under Radeon Settings > Gaming > Global Settings? Enhanced Sync can cause some corruption or flickering in 2D applications. You may be required to add the media player to Radeon Settings as an application profile and set Enhanced Sync to disable.
Enhanced sync is disabled globally. The last known working driver version is 22.214.171.124. Short of reverting to that, you either have to disable Freesync entirely or use a D3D exclusive fullscreen mode if the video player supports that. These are only workarounds though. There's another thread about the issue here:
I have been unable to reproduce this issue. Below is the system i tested and the steps i followed.
Win 10 1903
Samsung CF791 3440x1440P @100HZ FreeSync enabled
Samsung U32E850R 3840x2160 @ 60HZ FreeSync enabled
I downloaded the K-Lite Standard codec pack which includes Media Player Classic. Ran it using default install options.
Downloaded the The Simpsons Movie – 1080p Trailer from here https://www.h264info.com/clips.html
Watched the clip on both displays, firstly in windowed mode, then in full screen mode, saw no tearing or stuttering.
I then recorded some game footage using ReLive, 2160P, 30Mbps AVC 60FPS and saw no tearing or stuttering.
I would appreciate it if you could provide some suggestions on how to reproduce this behavior.