I thought this question might get a better response in AskUbuntu, as it seems to have more to do with Ubuntu than Windows at a glance.
Let's say I have a foo.mkv file. Thumbnail previews work in both Windows 7 and Ubuntu.
When I change the filename to anything random like foo.bar or when I remove the extension itself (making it just foo), Nautilus shows thumbnails normally like if it can recognize what type of files they are – without looking at file extension.
This however, doesn't happen in Windows 7. Windows starts asking me things like which application I want to use to open that file as soon as I remove file extension (forget thumbnails…) etc.
So, How does this thumbnail preview work in Windows 7 and Ubuntu? What makes Ubuntu recognize files "out of the box" unlike Windows 7?
Best Answer
I think Ubuntu uses the file header to identify file type and generate the thumbnail on that basis , but in windows a file containing meta data named Thumbnail.db would be updated when windows explorer scan file types (based on the file extension).
This document supports my answer . http://specifications.freedesktop.org/thumbnail-spec/thumbnail-spec-latest.html#CREATION
Ubuntu uses Nautilus that complies with Freedesktop implementation, that uses file MIMEtype . Visit above link for more specifications.