A method of modifying a digital data stream composed of a sequence of frames, where each frame represents an image and includes a data field specifying a presentation time stamp value for the frame. If there is a discontinuity in presentation time stamp value between a next frame and a first frame, a value representing a stream time stamp of interest is assigned to a variable for representing the value of the stream time stamp of interest at a point of discontinuity in presentation time stamp, and a value of the presentation time stamp is assigned to a variable for representing the first frame's clock time based on presentation time stamp, and the next frame is stored in a database using as an index the value representing a stream time stamp of interest.