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. 61. The improvement recited in claim 52 wherein said predetermined event detecting means includes means for monitoring the video envelopes of two frames, means for obtaining a predetermined number of samples from each envelope, means for comparing the magnitudes of counterpart samples to obtain a difference in counterpart samples, and means for taking the average of the differences and for indicating a detected predetermined event whenever the average exceeds a predetermined level.