Can't see video (mp4 / mpeg) thumbnail on gThumb

Can't see video (mp4 / mpeg) thumbnail on gThumb ?

Install thumbmailer:

sudo apt-get install libxine1-ffmpeg

sudo apt-get install ffmpegthumbnailer

Convert to mpeg:

ffmpeg -i video-2014-02-28-16-57-10.mp4 video-2014-02-28-16-57-10.mp4.mpg

 for f in *.mp4; do ffmpeg -i "$f" "${f%.wav}.mpg"; done