Video Transition detection is an early step towards its high level segmentation and indexing. The visual rhythm is a technique used for reducing the amount of data in a video: it transforms a 3d data set (a time sequence of 2d frames) into a single 2d image. Then, we can search for patterns in the 2d image coresponding to transitions in the initial video, the concept of longest common subsequence of a string is used in this work to transform the 2d image into a 1d signal. Further, transition detection is performed using this 1d signal whose simpler and reduced representation leads to the definition of fast algorithms identifying the different transitions