Juan Pablo Bouza has a nice short writeup on how to use Blender, the pre-eminent open source 3d rendering and animation tool, with Ardour, so that they share a common timeline.
wow, nice 
Thank you, you answered the question I have been searching for: am I a moron for placing SEO spam on a website that doesn’t permit links in forum posts? The answer seems to be a resounding “yes”.
I tested the Ardour/Blender combo as described by Senor Bouza. Worked perfectly. Blender is an awesome program, it’s quite impressive to watch the two apps play nice together.
Btw, Blender is becoming a capable video editor.
Best,
dp