52. The improvement recited in claim 49 wherein the signal to be identified includes a video signal, and wherein said feature string extracting means includes means for detecting predetermined events in the video signal and determining the time intervals between detected predetermined events to generate the feature string.
52. The improvement recited in claim 49 wherein the signal to be identified includes a video signal, and wherein said feature string extracting means includes means for detecting predetermined events in the video signal and determining the time intervals between detected predetermined events to generate the feature string. 56. The improvement recited in claim 52 wherein the predetermined event detecting means includes means for comparing the video envelopes of two frames.