This is because Auto Movie Thumbnailer works using MPlayer; it also gets help from ImageMagic Suite and a MediaInfo plugin.
The interface is not very attractive, but you can access features easily, especially if you are a power user.
What you can actually do in Auto Movie Thumbnailer is searching your hard drive for movies, taking screenshots of them and obtaining thumbnail index pictures. You can create presets for these operations and predefine the output directory and the output file name, enable log display and write logs to a document of your choice.
During the process of taking screencaps, you receive information from a progress bar displaying the run time on the current file and the number of items that are processed. Additionally, you can preview output items.
After getting your screencap, you have a large number of possibilities to customize its layout and design: changing background, frame color, padding, adding an info header, inserting timestamps, and saving items in the JPG or PNG file format.
Although nor perfect or extremely attractive, Auto Movie Thumbnailer does its job well and once you get used to it, you will be able to generate screen caps like an expert.
The application is being constantly updated and many fixes are added for each new version. Even so, Auto Movie Thumbnailer works very well and uses a small amount of system resources.
First of all, Auto Movie Thumbnailer offers support for a variety of formats (AVI, MPG, QuickTime, Real Media, Windows Media etc.); if a format is supported by MPlayer, it will be supported by Auto Movie Thumbnailer, too.