Transcoding fails with FFmpeg exit code 187

[TheDreadPirate]

When you install Jellyfin via apt, which is what the script you used does, it also creates the service. And it includes a boot load of other options that yours isn't using. Remove the service file you created and use the one that is already present.

/etc/systemd/system/multi-user.target.wants/jellyfin.service

Code:

[Unit]
Description = Jellyfin Media Server
After = network-online.target

[Service]
Type = simple
EnvironmentFile = /etc/default/jellyfin
User = jellyfin
Group = jellyfin
WorkingDirectory = /var/lib/jellyfin
ExecStart = /usr/bin/jellyfin $JELLYFIN_WEB_OPT $JELLYFIN_FFMPEG_OPT $JELLYFIN_SERVICE_OPT $JELLYFIN_NOWEBAPP_OPT $JELLYFIN_ADDITIONAL_OPTS
Restart = on-failure
TimeoutSec = 15
SuccessExitStatus=0 143

[Install]
WantedBy = multi-user.target