Xara3D generates an alpha channel, since it can save one to a PNG file as a still image. I know I can't save a video/animation with an attached alpha channel (not sure what file format would do that), but is there any way to save JUST the alpha channel of an animation? That's the approach taken by another animation program called Particle Illusion.

When you export an AVI file, you can choose to export either the animation itself, or a gray-scale version of the animation's alpha channel. You can then easily recombine these in things like Adobe After Effects for nice looking results. Is there any chance of doing this in Xara3D? Since it's already generating the alpha channel, maybe it's as simple as a checkbox that says whether the alpha channel or the main animation is saved when the AVI file is exported?