In order to do this, we are doing to install a very popular codec pack. K-Lite Codec Pack is a collection of codecs and tools. Codecs are required to play audio and video. With the K-Lite Codec Pack you should be able to play 99% of all the movies that you download from the internet.
This codec pack also allows you to make thumbnails for FLV and other file types. While going through the installation, on the “Select Additional Tasks” screen, scroll down and choose to file types for which you require thumbnails.
If you know another way to get this done, do let us know by leaving a comment.