Database Issue Detected: The Jellyfin database (library.db) is having problems.

'Database is locked': This usually means another process is using the database, or Jellyfin shut down improperly. Stop the Jellyfin server completely, wait a few seconds, and restart it. Ensure no backup scripts are running.
'Disk image is malformed': This indicates database corruption. You may need to restore from a backup or, as a last resort, delete the database files (this will erase metadata and watch history).
'Disk I/O Error': Jellyfin was unable to read or write to the database file. This points to a deeper issue like failing hardware (dying HDD/SSD), a network storage problem, or incorrect file system permissions on the database folder itself.

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Corrupt File: The media file is likely corrupted or incomplete. Try playing it in another application like VLC to confirm.
Unsupported Format: While rare, this could be an exotic or unusual file format that your version of FFmpeg does not support.
Permissions: In some edge cases, this can be a permission issue where Jellyfin can see the file exists but cannot read its contents.