Game is using dx12 when started with "-dx12" command line option. Find attached the corresponding proton log with dx12 enabled (gfx didn't get better)
steam-597820.log
The missing videos are more than just the into. It affects the preview when unlocking abilities and some ingame videos where the plot is told.... Hoping we can get a GE build where this is working (Last release is not)
Has issues with mfplat even with GE build, but mfplay=d allows it to run and get in game WINEDLLOVERRIDES=mfplay=d %command%

You can simply "Esc" the black screen away with regular proton and without dll overrides and play the game though.
BIOMUTANT (597820)
Issue transferred from https://github.com/ValveSoftware/Proton/issues/4865.
@hollowsaibot posted on 2021-05-27T20:34:09:
The game doesn't show properly the sceen. There is a problem with the light.
The 6.1-GE-1 it was the only one that shown me the intro video (where is black on the YT recorded video)
Just runing the game as a first time
https://youtu.be/V-izv69nlVA
<System information omitted, please see [#4865](/issue/ValveSoftware/Proton/4865)>
After check the Brightness configuration i realized that the first step to adjust the darkness affected in that way. But there is a sense of over-saturation when it's to much dark.
On Brightness at 50% it looks normal by now (just tested a few minutes)
*Using Proton-6.1-GE-1
Do the videos work with 6.1-GE-2?
With 6.1-ge-2 they work for me at least @fidelix
@fidelix They do but I occasionally had weird crashes where the game would freeze and stay open, and Steam would think it's still open, but Steam's screenshot window would appear indicating the process was dead somehow
(Nvidia card)
The newest Proton experimental gives this error.

Tracking note: Marking the last comment as resolved because it should be fixed in Proton Experimental. If you're still seeing an issue with winegstreamer in Proton Experimental, then please add a new note for the Proton devs to ponder.
@kisak-valve Very nice, the error got fixed.
But now every time you achieve something big (like solving a puzzle or clear an area) the HUD shows the colourful media foundation replacement.



proton experimentalx2 2021-06proton 6.1-ge-1x1 2021-05WINEDLLOVERRIDES=mfplay=dx1 2021-05WINEDLLOVERRIDES=mfplay=d %command%x1 2021-05
Compatibility Report
System Information
I confirm:
Symptoms
Find attached the proton log
steam-597820.log