I think I've finally figured out how to get video thumbnails to show up in Nautilus, the Gnome file manager. I'm running FC4.
If you have the default totem installed, remove it,
Install totem-xine from the Livna repository,
yum install totem-xine
Under your regular user account (not root), delete everything in the ~/.thumbnails/fail directory,
rm -r *
Close any open Nautilus windows
Open Nautilus (View as Icons) and go to a directory with video files.
After a few seconds new video thumbnails should be automatically generated and appear!
The "Totem Movie Player" that comes with a default install of FC4 is practically useless. When you remove the totem package and install the totem-xine package, you now have an excellent video player that actually works since totem-xine uses the Xine library as its backend video engine.
The totem-xine package contains a utility program called “totem-video-thumbnailer” which hooks into the gnome system and is automatically called by nautilus to generate video thumbnails. You can see the hooks in the Configuration Editor (/desktop/gnome/thumbnailers).
Now nautilus should be happy to generate preview images of your video files and show you nice thumbnails, right? Almost. There currently does not seem to be any mechanism for gnome to realize that you have added video thumbnailing capability. So how can we make gnome understand this?
That's where the ~/.thumbnails directory comes in. Your ~/.thumbnails directory is where Gnome applications store preview images (thumbnails) for file types they recognize such as PDFs or PNGs or JPEGs. This thumbnail cache is used to speed up subsequent thumbnail display in Gnome applications like Nautilus and gthumb by avoiding generating thumbnails again.
There can be three subdirectories of your ~/.thumbnails directory: normal, large, and fail. They may not all exist depending on how much file browsing you have done.
Before you installed totem-xine, gnome was unable to create video thumbnails for your video files, so it put entries in the “fail” subdirectory so it would know it need not try again next time you browsed those video files.
After you install the totem-xine package, video thumbnails can be generated, but gnome still sees entries in the "fail" directory so it doesn't even try. To force gnome to realize that you can now generate valid video thumbnails, you need to delete everything in the “fail” subdirectory.
Once you clear out the "fail" subdirectory, new thumbnails can be created and they will be placed in the "normal" subdirectory. Video thumbnailing should now work.
Gnome thumbnailing seems to be a work in progress. For more information about Gnome thumbnailing, see the Thumbnail Managing Standard, http://jens.triq.net/thumbnail-spec/directory.html
FYI, the video thumbnail is a snapshot taken 1/3 of the way through the video.