Level four

So now we're going to open up after effects. First thing you're going to do is import your clip, so go file>import>file and find your clip. Now drag that clip form the project window onto the new composition icon lower down.

This will make a new composition for you with settings that match your video. Handy!

Now we go file>import>file again, but this time find the first image in the tiff sequence you just rendered, then making sure you check the "TIFF sequence" box you click open and you should now have your rendered shot.

These are the settings you'll be importing in.
Note: If you want to have a smoother model you can do another render of just your subject matter with mental ray and put that on top. these are the settings I would use

Firstly uncheck the "use depth map shadows" on whichever lights you have creating them

Then under render settings switch to Mental Ray and switch quality to production

I would recommend doing this because it allows you independent control of your shadows and your model.

So with both sequences in there your composition should look something like this

So now we click the arrow next to the shadow layer, which should be the lower one

And then down to Opacity, which we can mess around with until the scene looks right

I put mine down to 37%

Now, depending on the footage you're using you may one to use one or two effects to make it look more like the shot you are using. If you are doing an action shot you may want to use motion blur, or if you are using particularly low quality footage you can try and add some noise to your render. The effects list is on the right

Now we're going to add the composition to the render queue. So go composition>add to render queue

Make sure you go into the "output module" menu (it will say "lossless" to begin with) and check Audio Output on.

Then click format options and change the compression type to something high quality, like Apple ProRes 422.

Then we can click "render" and take a look at what we get.

And if it all turned out OK, then mission accomplished! I'll post up what I came to.