Before I upgraded to Ubuntu 12.04, thumbnails on video files worked nicely, after the upgrade, thumbnails aren't generating on video files and only on video files, most of them are .mkv files. I have some .pdf files and they all have thumbnails. I have tried to clear the thumb cache, but no luck.
Please ensure that the necessary packages are installed by running the following command in the terminal:
sudo apt-get install gstreamer0.10-plugins-bad gstreamer0.10-plugins-base gstreamer0.10-plugins-good gstreamer0.10-plugins-ugly totem libxine1-ffmpeg
Also, please delete the thumbnails that failed to load by running the following command:
In Ubuntu 13.10, the folder changes to: .cache/thumbnails, so you should delete those failed files instead:
I followed the instructions in this forum and it worked perfectly.
sudo apt-get install libxine1-ffmpeg
Then to force nautilus to generate new thumbnails execute
rm -r ~/.thumbnails/fail
rm -r ~/.thumbnails/normal
killall -9 nautilus
These commands will remove (delete) thumbnails from these folders.
Open nautilus again and you should be able to see thumbnails for all your videos.