How can I overlay a BluffTitler animation onto a video background?
You can export an animation with transparency info (32 bits RGBA) by choosing File > Export as Movie and selecting the Uncompressed AVI with Transparency radio button. Alternatively you can do the mixing inside BluffTitler by using the video layer. Also some NLEs offer chroma key transparency. You can set the background colour in BluffTitler with the menu item File > Set Background Colour….