1. Apparatus, comprising a memory storing computer-readable instructions, and a data processing unit coupled to the memory, operable to execute the instructions, and based at least in part on the execution of the instructions operable to perform operations comprising: in response to user input, selecting a reference in a video comprising a sequence of frames; determining a sequence of values of a similarity measure from respective comparisons between the reference and a respective ones of the frames of the video; identifying in the video one or more candidate regions of ones of the frames of the video based on identification of one or more respective valleys in the sequence of similarity measure values, wherein each of the one or more identified candidate regions comprises a frame of the video that corresponds to a respective one of the one or more valleys in the sequence of similarity measure values; and in response to user selection of at least one of the candidate regions, presenting one or more of the frames of the selected candidate region on a display; and in response to user input, designating at least one of the presented frames as a boundary of a segment of the video.