Abstract: A computer based system (101) combines clips of image frames in which elements from selected input frames are combined to produce an output sequence derived from a plurality of clips. A display unit (105) displays spatially overlaid clips as layers (501,502,503) in a three-dimensional space; User commands specify how elements from a plurality of displayed clips are to be composited spatially to produce compositing data. In addition, temporally displaced clips are displayed as a time-line having clip segments (801, 802, 803) joined by transitions. Attributes of said transitions are modified in response to user generated edit data and a rendering engine (901) renders selected input frame data in combination with said compositing data and said editing data to produce viewable output data.