Hi!
I have solved this issue!
The solution is pretty much simple:
- Empty your "~/.cache/thumbnails" folder.
- Install totem (sudo apt-get install totem).
- Update (CTRL+R) any folder with ogv files and that's it!!
It's kinda funny that ffmpegthumbnailer is not able to create thumbnails for an open media standard like ogv or, maybe, the issue is that some MATE-related thumbnailer facility is not being able to find the appropriate codecs to create thumbnails.
I'm marking this as "[SOLVED]".
See you!
Marcelo