Extra Files showing on Windows?

[supanatral]

When I copy a file, lets say video.mp4 to a windows computer and then look at the file using windows, there would be an extra file called "._video.mp4" and its 4kb in size. What is this file for and why can't I see it in OSX?

 

[symphonix]

Your Mac will write this tiny, hidden file for any file it accesses on a Windows formatted drive or share. It contains the thumbnail preview or icon for the file, along with any metadata associated with the file (comments, spotlight indexing info, etc). You can delete these files if you want, and no harm will come of it, but they are so small they can be safely ignored.