I believe there is a (minor) bug in the script which searches for matching thumbnails for video files .
Finding the generic thumnail works fine, but not when ive uploaded a specific thumbnail for that file.
The _filetypes table lists the possible files etc, but they are all lowercase and it appears the functions to find thumbnail dont work when extension is uppercase.
If I have 4 vidoes: film1.mpg, film2.MPG, film3.avi, film4.AVI.
They all have a matching thumbnail, thumb_filmx.png.
So the main part of the names are all lowercase, only some extensions is uppercase.
In my coppermine release (1.4.2, ill check 1.4.3 soon), only film1 and film3 dislays their thumnail.
I can run a db update to change all capital extensions to lowercase, and then rename all the files as well. but better if the function just lowercased the match when looking for specific thumbnails.....