Some videos have no thumbnail?

Question

I just downloaded a video series and opened the videos folder to find that some of the videos have thumbnails and some do not. How can I force the others to generate thumbnails? I have tried playing the videos with out thumbnails but they did not generate; I also tried renaming them, but no luck.

All videos are mp4 and play fine.
I did tell Ubuntu when installing to install 3rd party codecs etc.

Answer 1

Try clearing the thumbnail cache by typing this in the terminal:

sudo rm -r $HOME/.thumbnails/fail
sudo rm -r $HOME/.thumbnails/normal

Close any Nautilus window and now check your video series.