As I mentioned before the transcoder error is a generic error which can be returned for lots of different underlying issues.
The common issue that is known about and affected many users and giving rise to this generic error message was windows 10 update KB4338819 which Microsoft superseded with a second update 6 days later: KB4345421.
If you have a problem please provide logs of the issue and if you are running on Windows, please state the Windows Build number (Start / Settings / System / About :and then Windows Specifications / OS Build
for logs see
https://support.plex.tv/articles/201643703-reporting-issues-with-plex-media-server/
https://support.plex.tv/articles/200250417-plex-media-server-log-files/
See
