Techniques (methods and devices) that permit a user to define multimedia transitions in terms of user-supplied assets are described. The user supplies the assets necessary to generate the transition such as, for example, an asset movie, an asset matte movie and a background matte movie. (The specific assets required may vary depending upon the transition to be generated.) These assets are then automatically combined (e.g., through compositing) to render a completed multimedia object in which the defined transition is used to visually transition a first image or frame to a second image or frame. The same techniques used in some generic transformation of images or movies are also disclosed.