I've scanned through the entire Premiere PDF and there is nothing obvious and simple about how to "window" an image. I've visited several websites; again nothing obvious and simple. So, I'll have to ask the experts here.
What I want to do is to create a rectangular area – my window – within my 1920 x 1080 frame, within which all clips in my sequence appear. Any part of any clip which is outside that window, is black.
I don't need instructions how to do it, but I would like to know the name of the function in Premiere that will allow me to create a "window", so I can look it up.
I have tried what to me was an obvious, but inverted, method. Basically a mask:
1. Create a new item that is Black Video (p255 of the PDF).
2. For test purposes, set the size of the Black Video to, say, 800 x 1080, so the mask is full height but only 800 wide.
3. Drag that Black Video to a layer above my clips.
My theory was that parts of a clip that lay under the Black Video would not appear. And it worked – sort of. The problem was, there was an unexplainable (to me) offset. The boundaries of my Black Video (as shown when I clicked on Effect Controls > Motion) were different from how the clip underneath was being "windowed". The offset was not constant, vertically or horizontally, and seemed to be acting like a Drop Shadow in Indesign, with the light source set at a certain angle.
Any suggestions how to "window" clips?
Aside: within InDesign, these "windows" that I am thinking of are created automatically every time you set up a new Text Frame. Done it thousands of times over the years. Dump an image in the frame, and the frame forms a window for the image. No part of the image inside can appear outside the window.