I tracked some footage for a client using Boujou, and rendered it out into an AVI format. The camera solve works fine in Max. I added an bitmap parameter for the environment so it would render out the AVI with the object in it. The problem I am having is that it seems that whenever I add an object to a scene and render it out that the object's opacity has significantly decreased. I am using the default mental ray parameters and haven't changed a thing.
Im not clear to what is happening or why... but I would suggest moving away from AVI's and instead render out image sequences with alpha channels(TIF, TGA, PNG) and then compositing the layers in post production software(After effects!) that way you have a lot more control and its a lot easier to fix any problems like the above. (you simply duplicate the 3D render and tweak the opacity of the lower layer to control opacity levels of all transparent areas)