I am new to video editing so if my terminology is wrong, I apologize. I am making a video with output settings : 720p and dimensions 640 x 480. I am inserting a series of video clips but their dimensions are smaller than 640 x 480. Instead of the video clip slide expanding up to 640 x 480, I want it to remain the same size but have a black cinema box or border box around the video clip. How can this be accomplished with a video editor?