A selection of green screen footage, transitions and reveals. The relevant areas of these clips are perfectly solid and can easily be removed using the chroma key effect in your editing software. By making the green areas of a clip transparent you're enable to either place, now isolated, moving objects over your footage or 'reveal' secondary footage inside the transparent areas.
Chroma key compositing, or chroma keying, is a visual effects (VFX) post-production technique for compositing (layering) two images or video streams together based on color hues. The technique is used extensively to remove a background from the subject of a video, revealing a secondary video clip in the transparent areas – particularly in the news broadcasting, motion picture and video game industries.
For more information about "keying" read our blog post "How to use green screen footage in your video".