How do I do screen composition in Blender. Cinema 4d has buffers you can render out and replace the screen with images or videos in after effects. How do I go about placing moving pictures on the screen of a blender 3d iPhone model or an iMac.
You can use the compositor for this.
Normally I add 2 materials to the object. One for the case and one for the screen. The faces for the screen I assign to the screen material.
When the screen material is selected under settings you can set the pass index to 1 (default is 0). With this pass index you can extract the visible parts in the compositor
for the screen make sure that the UV coordinates are correct. make sure you select "material index" and "UV" in the render passes
Normally in these cases you can render out to OpenEXR Multilayer, and load the prerendered images directly in the compositor.
In Cycles, you can create a plane, UV unwrap it, create a new material with an emission shader set to 1.0 of strenght, assign an image texture and select a movie as image. You can control start frame, lenght and offset between the timeline and the movie's frame numbers.
In Blender Internal is similar: instead of an emission shader, tick the "shadeless" option of your screen material.