I've nearly completed a Blender composite which has taken much longer than it should have. A lot of the problems have stemmed from the motion tracking not matching when the 3D work was done in Maya, then brought back into Blender for compositing, pre rendered image sequences seem to jitter/move in a skittish manner. I have managed to get around it somewhat by having to scale/translate in x/y to try to make the pre rendered geometry to match to the background plate.
My question is this, I have certain elements which are more problematic than the rest, I've created motion tracks for the background plate which track good. How do I setup the composite nodes to attach a pre rendered image sequence to anchor to a motion track marker, I also need to be able to offset the x and y and possibly scale the image sequence so that they fit and match the background plate. Each element will have a mask or two to mix into the factor of an alpha over node too.