How to Create geometric shape masks in Blender 2.4 or 2.5

Using a geometric shape to mask out a portion of one video, so that you can substitute in a different video on top of it. Whether you're new to the Blender Foundation's popular 3D modeling program or a seasoned graphic artist just interested in better acquainting yourself with the application, you're sure to be well served by this free video tutorial. For more information, including detailed instructions, take a look!