How to install video codecs? Game says Unknown MIME type for 'matroska, webm'

I'm getting a crash to desktop for "The Last Caretaker" regardless of which proton compatibility I choose, and after enabling PROTON_LOG I see a likely cause:
606794.500:0184:02b0:fixme:dmo:demuxer_create Unknown MIME type for format "matroska,webm", url "../../../Voyage/Content/Movies/CompanySplash_4k_60fps.mp4" -- this leads me to believe I need some sort of codec pack in bazzite but not sure if that's something that would be provided by a flatpak extension or if I should install them some other way?

PeteOP•12/13/25, 4:03 PM

I can play the video in VLC so I assume this codec needs to be installed somehow inside the scope of the steam flatpak's ability to see it

Ally The Protogen•12/13/25, 4:15 PM

Go into ProtonPlus, download the latest version of ProtonGE, restart Steam, and switch The Last Caretaker to use it in the games Steam properties

PeteOP•12/13/25, 4:17 PM

Thanks, I will try that.

PeteOP•12/13/25, 4:21 PM

So I have a weird setup because I started on a different fedora atomic distro (Aurora) but swapped to bazzite when they dropped support for the nvidia proprietary drivers. I had steam already installed when I rebased, so I wound up with two steams -- the one bazzite comes preinstalled with, and my preexisting flatpak install.

The game does not work in the flatpak install from aurora, but it seems to work in the bazzite steam, so maybe I'll take the opportunity to move over to using the bazzite steam instead.

Thanks for your help!

How to install video codecs? Game says Unknown MIME type for 'matroska, webm'

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