Re: Applied video to a material and now want to have that material scale properly onto an object

The easiest way to do it, IMO, is to set the width/height proportions appropriately in your editing or compositing application. In this case you would pad the top and bottom to make the footage square. You might also want to scale it down if you don't need the full resolution in Cinema. Output to a frame sequence instead of a compiled movie format to speed up playback in Cinema.

Then load your footage in a material and apply it to the polygon. Click on the newly-created texture tag and set the projection to flat. You may have to use the texture axis tool to rotate the mapping so that the Z axis is pointing the right way. Then, right click on the texture tag and select "fit to object". That will assign the exact scale and position you need.

If you don't want to make the texture/footage square first you can follow a similar procedure, but you'll have to to do some manual positioning and scaling. You can get the aspect ratio right by adjusting the scaling in the texture tag (e.g. set it to x: 128%, y: 78%). Then scale uniformly in the texture axis tool and move into position.