How to Add a Background in Premiere Pro
Add a background in Premiere Pro by placing it on a lower track, then keying or masking your subject. Covers Ultra Key, color mattes, blurred fills and audio.
To add a background in Premiere Pro, put the background (an image, a video clip or a solid color matte) on a video track below your subject, then make the unwanted parts of the subject clip transparent so the lower track shows through. Premiere Pro composites from the top track down, so anything transparent on an upper track reveals what sits beneath it.