No thumbnailer available

[John Frankish <j-frankish slb com>]

Using:

rygel-0.14.1
gupnp-0.18.3
gupnp-av-0.10.1
gupnp-dlna-0.6.6	
gupnp-tools-0.8.1
tumbler-0.1.25

I get:

(rygel:1907): Rygel-WARNING **: No thumbnailer available: Failed to find thumbnails folder.

If I understand correctly, rygel should trigger tumbler to start via dbus, but this doesn't seem to be happening. How is the interaction meant to work and where is it looking for the thumbnails folder?