I've let this loose on a large directory with lots of video files, and if I'm not mistaken thumbnails are being both

• generated on the main thread, blocking user interactions with the app
• not cached, thus requiring the same process again when e.g. having performed a search and clearing the query

Edit: I'm not sure whether instead of building a proprietary thumbnail store, windows' integrated one might be possible to tap into? I remember recently having required to clear that one and IIRC it's just another folder on the hard drive