Do I have to use the La Maison plugin and render using mental ray? Is it possible to extract motion vectors using the Software Renderer? I noticed that the Motion Blur section in the Render Globals for the Software Renderer has a checkbox for "Keep Motion Vectors". Is it possible to extract motion vectors using this? Thanks!
Yes you have to use the Mental Ray shader http://www.revisionfx.com/generalfaqsMVFrom3D.htm
I am noticing though reading the sub Maya FAQ that it still says "# a value of 1 for Normalize transltes to a value of 32 for our 'MaxDisplace' value. 2 --> 64, 3 --> 128, 4 -->256, 5 --> 512, 6 --> 1024, 7 --> 2048, 8 --> 4096". That's to be ignored with the latest lm_2dMv version.
Unfortunately Maya puts the Motion Vectors when you press Keep Motion Vectors into auxiliary channels of an IFF which no app supports so there is nothing we can do with it.