Transitions with GStreamer Editing Services freezes, but works OK without transitions

Question

I'm trying to use gstreamer's GStreamer Editing Services to concatenate 2 videos, and to have a transition between the two.

This command, which just joins 2 segments of the videos together without a transition, works fine:

ges-launch-0.10 vshort01.mov 0 5 vshort02.mov 5 5 -r -o file:///tmp/foo.mov

Here is the output from it:

$ ges-launch-0.10 vshort01.mov 0 5 vshort02.mov 5 5 -r -o file:///tmp/foo.mov
save_path: (null)
load_path: (null)
Adding file:///home/rory/vshort01.mov inpoint:0:00:00.000000000 duration:0:00:05.000000000
Adding file:///home/rory/vshort02.mov inpoint:0:00:05.000000000 duration:0:00:05.000000000
Done

If I try to have a short transition between the 2 videos with this command, it just hangs.

ges-launch-0.10 vshort01.mov 0 5 +transition crossfade 2 vshort02.mov 5 5 -r -o file:///tmp/foo.mov

The output, I get is this:

save_path: (null)
load_path: (null)
Adding file:///home/rory/vshort01.mov inpoint:0:00:00.000000000 duration:0:00:05.000000000
Adding <transition:crossfade> duration 0:00:02.000000000
Adding file:///home/rory/vshort02.mov inpoint:0:00:05.000000000 duration:0:00:05.000000000

And there it hangs. The file /tmp/foo.mov stays at 0 bytes, and there is no CPU activity.

I am using package ges0.10-tools version 0.10.1-1 on ubuntu 11.04 natty. I have tried a freshly built version of gst-editing-services from a git clone today c2668d058501513b734c8a8013a5e78c817712bb

I tried without the -r -o … options (i.e. telling ges-launch to display the video, not render it to a file), and the same problems occur. With the +transitition, then the window opens (to show the video) showing the first frame of the first video. But the video doesn't play and there is no CPU usage etc.

How do I get it to make a file and to put a transition between them?