As well as we can see thumbnails for videos it would be nice to see album arts of music files (flac, mp3) in Thunar (like in Nautilus or Caja) and thumbnails for djvu files (for pdf file it works well).
That sounds like bug 12041. Which tumbler version do you have installed? I do not know if djvu files can be handled without implementing a new tumbler plugin. However, one can install MATE's document viewer Atril which provides this functionality (/usr/share/thumbnailers/atril.thumbnailer).
Tumbler 0.2.5-1 Ok, I'll try Atril, thanks.
Thumbnails emerged after installing other than VLC player (Totem, xplayer etc. with its additional libs).