Moving "live" thumbnails?

[theguymadmax]

Yes, that's the Trickplay feature in Jellyfin.
To enable it:

1. Go to your library settings and turn on Trickplay image extraction.
   
2. Choose where to save the Trickplay images:
   • Next to your media (recommended for easier migration), or
     
   • In the Jellyfin metadata folder.
     You can change this setting later if needed.
     
3. Decide if you want Trickplay images to generate automatically when new media is added, or leave it disabled and generate them manually later using the Generate Trickplay Images scheduled task.
   (Note: I don’t have automatic generation enabled.)
   
4. Navigate to Dashboard → Playback → Trickplay and enable "Only generate images from key frames".
   This speeds up the process, which can otherwise take days or even weeks depending on the size of your library.
   
5. Go to Dashboard → Scheduled Tasks and run Generate Trickplay Images.
   

Once the images are generated, you'll see a preview image appear when scrubbing the timeline in your media.