Patent GB-1443105-A (GB)
Title: Video tape recording control apparatus and method
IPC: G11B27/024
Filed: 1974-05-24
Abstract: 1443105 Video tape recording CANADA SECRETARY OF STATE OF 24 May 1974 [6 June 1973] 23333/74 Heading G5R To record a selected number of video frames a video tape is located so that video recording means is adjacent a first video position on the tape, from which position it is desired to record the selected number of frames, and audio recording means is adjacent a first audio position on the tape, the tape is then rewound until the audio recording means is at a second audio position a predetermined length behind the first audio position in the rewind direction, the audio recording means impressing a continuous audio signal along said predetermined length during the rewind, such recorded audio signal is then detected while the tape is moved forwards; the video recording means and a frame counter are turned on when the detected audio signal ceases, and the video recording means is then turned when the frame counter reaches a count corresponding to said selected number of frames. When a forward button (70), Fig. 4 (not shown) is pressed control relays, Fig. 4, engage forward tape transport and playback by audio head 13 of an audio control signal recorded during rewind and lasting for 8 sees., a detector 15 sensing the end of this audio signal to enable, via RS flip-flop 39 and inverter 41, a counter 27 and a gate 43. The next vertical sync. pulse therefore passes from separator 55 and shaper 57 through gate 43 to set RS flip-flop 45 thereby turning on the video recording circuitry, a divide-by-two flip-flop 63 passing vertical sync. pulses at the frame rate to counter 27 which on reaching a preset frame count acts via a delay 65 on a flip-flop 53 which opens a gate 51 to the next vertical sync. pulse whereby this pulse resets flip-flop 45 to turn off the video record circuits. Circuit 53 also acts via the control relays to stop tape transport two seconds after the lost frame was recorded, the tape then being rewound and after a blank two seconds rewind period detector 31 detects the last recorded video signal and gives an output via a half-field delay 33 to turn on audio oscillator 29 whereby audio head 13 records a continuous 8 second control signal for controlling the start of the reset video recording cycle, this audio record period ending when a relay (K4), Fig. 4, having a 10 sec. operating delay, operates 10 sees. after the stat of rewind. The control relay then puts the apparatus into the stop state ready for a further video recording cycle on operating button (70). An audio track erase head 67 and bias oscillator 69 may be provided. The delay 65, or alternatively a delay at location 65<SP>1</SP> or 65<SP>11</SP>, allows time for all of the last vertical sync. pulse to be recorded before the video record circuits are turned off, and delay 33 is provided to allow for the slower response of the audio circuits relative to the video circuits. The audio control signal may alternatively be recorded during rewind at the start rather than the end of a video recording cycle. A switch 83 may be operated during video recording to temporarily disable counter 27 and extend the video recording period by for however long switch 83 is operated. A switch unit (S1 to (S6), Fig. 4, enables changeover from the above mode of operation to manual contol, a switch (81) then allowing manual control of rewind. A safety switch (S7) allows playback operation without the recording circuits being activated, as above, due to the absence of an audio control signal.