The Bard's Tale IV: MP4 Blank screen issue (566090)

Compatibility Report

• The Bard's Tale IV
• Steam AppID of the game: 566090

System Information

• GPU: 1080Ti
• Driver/LLVM version: nvidia 396.54.06
• Kernel version: 4.18
• Link to full system information report as Gist: tba
• Proton version: 3.7.6

I confirm:

• that I haven't found an existing compatibility report for this game.
• that I have checked whether there are updates for my system available.

Symptoms

The MP4 video files don't play in-game

Reproduction

Just load the game, splash screens and menu use MP4, they show as black.

Games current state

Game seems to work otherwise but be sure to not install VCDIST2013/15 because that causes a Unreal4 cooked pc bug. There may also be some audio clicking issues which I am working around resolving.

Other

If you know howto get MP4 working (installing codec into proton or dxvk prefix) then let us know, I have tried a few codecs and such already without luck.

Reproduce The Bard's Tale IV with Proton 3.7.6 and inspect the MP4 playback failure described for the splash screens and menu. Generate the mentioned steam-566090.log with PROTON_LOG=1 and compare the result against the reported system information; done means the MP4 videos display in-game.