Solved it! Though I don’t know what caused it in the first place
First I found this
Then this
And then this
Which shows multiple people with the exact same issue, though it still seems pretty rare. The DLL files mentioned in those threads (DolbyDecMFT.dll in both System32 and SysWow64) were already in place on my PC, so I could not register them as described in those threads and also unregistering didn’t work, both actions gave me an error. I could also not remove or replace them because they are system files and are protected against tampering through file ownership by the TrustedInstaller system user, with very limited permissions for anyone else. I also noted then that those DLL files had a “date modified” property of just a few days ago, right around the time this issue started happening. So suspecting that I had likely found the cause, I decided to take a risk.
For anyone else reading, beware: tinkering with system DLL’s can be VERY RISKY. Do not proceed if you don’t have backups and/or aren’t really familiar with tinkering in windows to repair a damaged system and/or aren’t comfortable in the command line. Messing with the wrong DLL’s can and will brick your system or cause data loss or cause corruption, or… Downloading DLL files from the internet can also be risky and can lead to malware, incompatibility or damage
- I first took a full image backup of my device.
- Then I took ownership of both those DLL files and gave myself Full Control permissions on them
- The previous step enabled me to delete them, which I did
- Then I downloaded the DLL files found for instance in the comments of the second link above. You could also take them from another system where plex desktop doesn’t have this issue, which would be much better and safer. I didn’t have a second system though
- I put those DLL files in the System32 and SysWow64 folders. See download link below
- Then I registered those DLL files like so (in an elevated, administrator command prompt)
regsvr32.exe “C:\Windows\SysWOW64\DolbyDecMFT.dll”
and
regsvr32.exe “C:\Windows\System32\DolbyDecMFT.dll”
Then rebooted my device. Et voilà, direct play of HEVC EAC3 produces sound again, It’s fixed!
So either something damaged those DLL files or something else happened to them or their registration in windows. This could very well be a coincidence but I did update my plex desktop client around the time those DLL’s were modified. Does doing so change anything with those DLL files? Are those DLL’s some of the licensed codecs you were talking about? Is it possible a plex desktop update caused this, or perhaps I changed settings in the plex desktop app? Any other suggestions as to what could have caused this?
[edit]
Here is a link to those same DLL files but a much newer version than the ones linked in the threads above. Above are from 2017 (v10.0.10586.0) and these are from 2022 (v10.0.19041.1466). These newer ones also work, just tested them. I took them from this (archived) reddit thread. Also, this newer version has separate DLL’s for the sytem32 (32-bit) and SysWow64 (64-bit) folders, which the DLL’s linked in the above threads to not, those are just a single DLL file. Ignore the registry file in the zip, it is not needed.
