Video time base corrector

Abstract

In a time base corrector which converts incoming video signals to digital form and writes the digitized signals in sequentially enabled units of a main memory at a clocking rate varying generally in accordance with time base errors in the incoming signals, whereupon the signals temporarily stored in the memory are read out or fetched from the successive main memory units at a standard clocking rate and reconverted to analog form for eliminating the time base errors: a drop-out memory stores drop-out information in respect to drop-outs detected in the incoming video signals written in each of the main memory units; drop-outs are eliminated in the output from the time base corrector by rewriting, in each memory unit storing video signals having drop-out as indicated by the drop-out memory, video signals from another memory unit shown by the drop-out memory to be free of drop-out, with such rewriting being effected simultaneously with the read out of the video signals from such other memory unit; and upon the rewriting of video signals in a memory unit, the stored drop-out indicating information in respect to that memory unit is erased from the drop-out memory. Further, the clocking rate for reading out the video signals from each of the main memory units is modulated in accordance with velocity error information stored in a velocity error memory during writing of such video signals in the respective main memory unit, and the velocity error memory is operative, upon rewriting in a main memory unit for eliminating drop-out, to replace the velocity error information stored in respect to such main memory unit with the velocity error information associated with the main memory unit from which the rewritten video signals are drawn.