Anders, this is a terrific video tutorial. Your presentation is great and your explanations are very clear. Thank you very much.
I would like to comment on two portions of the technique.
Near the beginning, you create a selection on the TV screen and save the selection. Later on, you load the TV screen selection back in and then create the layer mask. You could skip saving the selection. Instead, once you have the view image re-sized on top of the TV screen, make the top layer invisible, create the selection and feather it, make the top layer visible again and then create the mask.
Secondly, you mention that the shift key should be held down while doing the free transform so as to not change the aspect ratio. This is really not necessary since in the end, the image is being distorted to fit the TV screen despite its aspect ratio. All that is really necessary is to get the four corners of the image positioned at the four corners of the TV screen. You can use Distort right from the start if you want.
Please, don't take this as criticism. I have also dealt with this problem numerous times but nowhere near as nicely as you have.
I love the use of screen mode to display the window reflection and the use of the shadow. Really nice touches.
I really enjoyed your tutorial. I can sure use the info.
Have you ever used this to insert a fire into a fireplace. I would think if you had some fireplace shots that it should work?
Thanks for the sharing your information. Conrad