As I was unhappy with the introductory Nuke courses provided by FXPHD, I decided to give their competitor Digital Tutors a try. They take a different tack, showing more of the fundamentals behind everything than any practical applications. So while I know a lot of what goes behind what I already know, I didn't learn any useful skills a Nuke professional will need to know. I should probably just blame this on it being an introductory course more than anything.
One section they do go over is the Corner Pin technique. If you've ever seen a computer screen on TV or in the Movies there's about a 99% chance that they were looking at a blank screen. Its much easier and more flexible to add the screen in post rather than to have it designed, created, and played back in sync for every take live on set where time is money.
After reading in your footage you start by tracking each of the four corners you want to track. In the footage provided by Digital Tutors they show a wall mounted TV. You want to pick four high contrast areas in the corners to get the best track. You also want to place the trackers in a clockwise order, otherwise you'll have a issue lining up the corner pins.
You'll then need to read in your insert footage and attach the corner pin node remembering to link the trackers to the four corner pins by control clicking and dragging in the same clockwise order. Then Merge the insert over the original footage.
Then comes the finessing. I changed the blend mode to "Screen" to preserve the reflections over the inserted footage. To help the reflections, a grade was put on the display before the inserted footage to make the black screen closer to true black and not a washed out grey. I then added a edge blur to blend the sharp edges into the black edges of the display. I added a blur node to the insert footage mainly because the inserted footage was 1080p and the Digital Tutors stock footage it is going into was 480p. Finally a grade was put on the inserted footage so to match the brightness and contrast of what a screen would look playing on a TV outside.
I'm not happy with the final results. Partly because of the poor footage resolution provided by the tutorial, but mainly because the workflow they suggest does not leave room for much flexibility. You do not have much control of the reflection or the size and placement of the inserted footage. If you place a transform node after the corner pin the center point is scales from is not relative to the center of the corner pin. You could approximate the corner pin center but it was just easier for me to adjust the Corner Pin node's "from" settings to offset the footage. Also the final grade of matching the inserted footage to the background footage is fixed and can't change to if the background gets brighter, darker, etc. Any change to one would require hand animating the grading of the other. I feel there must be a better workflow to give more flexibility and results with greater accuracy. Back to the tutorial drawing board.