In multiple versions of lubuntu (since a couple of years ago, up to and including lubuntu 13.04) I have noticed that gthumb does not play videos.
The problem is fixed by installing package gstreamer0.10-x
A little more detail: The videos that are not working are from a Canon camera. I am not sure if other videos work or not in gthumb.
gthumb uses gstreamer to play videos. The abovementioned package is described as "GStreamer plugins for X11 and Pango". So the lack of video in gthumb in my system is either:
- due to my hardware (and thus the additional plugin solves my problem)
- hardware independent (and then all lubuntu installations should have this problem).