The I/O Bottleneck
In Ubuntu, the default file manager (Nautilus) attempts to be as helpful as possible by providing visual previews of your files. If you open a folder containing a massive collection of video files (.mp4, .mkv, .avi), Ubuntu doesn’t just show a generic movie icon; it actually utilizes a background tool (often `ffmpegthumbnailer` or `totem-video-thumbnailer`) to automatically read the first few seconds of every single video file and generate a custom thumbnail image. While this looks nice, if you have a slow mechanical hard drive or are accessing a network-attached storage (NAS) drive, this automatic thumbnail generation can completely max out your disk I/O, causing the file manager to freeze for minutes at a time.
Disabling Media Previews
To speed up folder navigation and stop Ubuntu from automatically creating thumbnails for massive video files, you must restrict the file manager’s preview generation capabilities.
Open the Files (Nautilus) application. Click the hamburger menu (three horizontal lines) in the top-right corner of the window and select Preferences. A new dialogue box will appear. Click on the Search & Preview tab (or just the “Preview” tab depending on your specific Ubuntu version). Locate the section labeled Thumbnails. You will see an option for “Show thumbnails” with a dropdown menu. If you want maximum performance, change this dropdown from “All files” to Never. If you still want image thumbnails but only want to stop video previews from crashing network drives, change the dropdown to Local files only, and ensure you lower the “Only for files smaller than” limit to something very small, like 10 MB. Since most videos are larger than 10MB, the thumbnailer will ignore them, instantly speeding up your system.