Provided are, among other things, systems, methods and techniques for introducing variation into a video clip, e.g., by (a) accessing an input video clip that includes a sequence of input video frames; and (b) providing a user interface through which a user is able to design an output video clip by specifying attributes for a set of output video frames, with such attributes: (i) being specified in reference to the input video frames, and (ii) including identification of which of the input video frames is to be used for individual ones of the output video frames.