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.
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. 63. The improvement recited in claim 61 wherein said predetermined number of samples is eighty.