Icaros is a clever tool which allows Explorer to display thumbnails for videos, as well as the cover art embedded in various audio files.
The program works by using FFmpeg to extract the thumbnails, and so it can work with almost any FFmpeg-supported video type (which is just about everything ever created). Launching Icaros displays the current list of "thumbnail filetypes registered", which looked like ".mkv;.mk3d;.ogm;.ogv;.flv;.flac;.ape;.mpc;.mka;.avi" for us. But if you'd like to support something else, click "Deactivate Icaros", add a semicolon and its extension to the end of the list, click "Activate Icaros", and thumbnails should now be available.
You don't have to worry about this kind of low-level detail, as for the most part Icaros just works. But if you do need to make some tweaks, there are a few other options available.
Setting a "thumbnail offset" tells the program where within the file to extract its thumbnail (25% means after 15 minutes of one hour video).
Enabling black/ white frame detection tells Icaros to check for almost all black or white thumbnails, and if there's a problem, to look for something better.
As we've mentioned, the program can use embedded cover art for thumbnails, but this isn't enabled by default. Launch Icaros, click Advanced and check "Use embedded Cover Art for thumbnails" to turn it on.