Comment 6 for bug 453863

I also had this bug - when I open a video file (like an avi or flv or mp4). However I found a solution on the ubuntu forums - I ran the following commands:

rm ~/.gstreamer-0.10/*
This removed the Gstreamer settings for the current user.

I then installed Gstreamer-Tools (check in synaptic to see if you already have it, if not install it - or run "sudo apt-get install gstreamer-tools" without quote marks).

and then ran the gstreamer-tools command:
gst-inspect
to rebuild the gstreamer settings.

This fixed playing the video layer for all these formats!

I hope you find this useful.

Matt