Method and Apparatus for Tape Recording Time-Spaced Segments of Video Information From a Video Camera

The present invention relates generally to video tape recording systems, and, more particularly, to such systems in which multiple segments of video information are to be recorded on a tape sequentially, but at time-spaced intervals.

When a video tape recorder is employed to record television programs, it is typically run in a recording mode for relatively long, uninterrupted periods of time. Moreover, a recorder used to record television programs will only rarely be operated in playback mode in such a manner that two or more recorded program segments are played back without stopping the tape. However, when a recorder is utilized in conjunction with a video camera, in what might be referred to as a "home movie" mode of operation, the recorder will be started and stopped very frequently, and the recorded scene length will typically be only several seconds long.

Tape transport apparatus used in video recording systems require a significant time interval to accelerate the tape to recording speed, and to decelerate the tape when recording is to be stopped. If the tape is merely decelerated at the end of the recording of one scene, and accelerated again at the beginning of the recording of the next scene, line and field synchronizing signals recorded on the tape with the video information would be unevenly spaced along the tape. Even if recording was suppressed during the tape acceleration and deceleration times, there would be a significant discontinuity in the sequence of synchronization signals. Consequently, if the tape was to be played back at full speed, there would be a temporary loss of synchronization in the reproduced video image, and an accompanying roll of the picture image at each scene change. Since the scenes may be only several seconds long, these frequent losses of synchronization would be a continual source of inconvenience and annoyance to viewers of the system.

In recorders of the helical scan type, the aforedescribed problem has been solved by back-spacing the recorder on completion of one scene; then, on starting recording of the next scene, synchronizing the camera with the video material recorded at the end of the previous scene before switching to the recording mode. However, in helical scan recorders, it may take as long as five or six seconds to bring the tape transport apparatus up to recording speed and to lock onto the synchronization signals obtained from the tape. Clearly, this delay period is unacceptable, since the scene itself may not be much longer than the delay period. Accordingly, there has been a real need for a video tape recording system in which synchronization is preserved between sequentially recorded scenes, without the penalty of a large delay time prior to the recording of each scene. The present invention fulfills this need.

The present invention resides in a method and corresponding apparatus for recording sequential, time-spaced scenes in a video tape recorder of the longitudinal type. In longitudinal video tape recorders, the tape is moved at a relatively high speed with respect to a stationary record/playback head, rather than at a slower speed with respect to a rapidly rotating head. Basically, and in its most fundamental method terms, the invention comprises the steps of decelerating the tape to a stop after recording a first scene, accelerating the tape in the opposite direction until recording speed is reached, moving the tape at a relatively high speed in the opposite direction for a preselected period of time, and decelerating the tape to a stop again. On recording a second scene, the tape is accelerated to recording speed in the original direction, and synchronization pulses are read from the tape and utilized to synchronize the operation of a video camera before the recorder is again switched to the recording mode. The steps of accelerating the tape to recording speed, and locking onto the synchronization signals reproduced from the tape, take only a few hundred milliseconds to perform, and this delay is scarcely noticeable to the user of the system.

In terms of novel apparatus, the invention comprises means for stopping and back-spacing the tape upon deactuation of the camera at the end of a particular scene, means for accelerating the tape to recording speed upon actuation of the camera at the start of the next scene, and means for synchronizing the recording system and the camera with synchronization signals read from the tape, prior to switching the recorder to the recording mode and recording the next scene.

More specifically, the method of the invention comprises the steps of determining whether the camera has just been switched off at the end of a scene, and, if it has, waiting for the next vertical synchronization pulse on the tape, switching to playback mode, and decelerating the tape to a stop. Then follow the backspacing steps of accelerating the tape in a direction opposite to the original recording direction, waiting for a preselected time to elapse, and again decelerating the tape to a stop. The method also includes the steps of determining whether the camera has just been switched on to record a new scene, and, if it has, accelerating the tape to recording speed, synchronizing the tape transport apparatus with horizontal synchronization pulses read from the tape, waiting for at least one vertical synchronization pulse and, on detection of the vertical synchronization pulse, resetting the camera synchronization and switching to the recording mode.

It will be appreciated from the foregoing that the present invention provides a video recording system in which synchronization is preserved between sequentially recorded scenes, without the penalty of a large delay time prior to the recording of each scene. Other aspects and advantages of the invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings.

FIG. 1 is a simplified schematic diagram showing portions of a longitudinal video tape recording system in which the present invention may be employed;

FIG. 2 is a velocity-versus-location diagram relating to movement of the recording tape in accordance with the invention; and

FIG. 3 is a flow chart defining the sequence of functions performed by the apparatus of the invention, and particularly by the controller of FIG. 1.

As shown in the drawings for purposes of illustration, the present invention is concerned with a technique for recording multiple sequential scenes in a video tape recording system, in such a manner that the scenes may be played back without loss of synchronization. In accordance with the invention, this is accomplished in a longitudinal video recording system by back-spacing the recording tape at the end of each recorded scene and then, before starting recording of the next scene, very rapidly synchronizing operation of the recording system with synchronization signals obtained from the tape.

In longitudinal video tape recording systems, the recording tape is moved relatively rapidly with respect to a record/playback transducer head, rather than being moved at a slower speed with respect to one or more rapidly rotating transducers. To obtain substantial recording time on a tape, there are usually multiple longitudinal recording tracks positioned across the width of the tape. The tape direction is reversed when the end of the tape is reached, and the recording head is appropriately stepped to a new track position.

As shown in FIG. 1, such a longitudinal tape recording system includes a capstan, indicated by reference numeral 10, which drives a recording tape 12 past a record/playback transducer 14. The capstan 10 is mechanically coupled to a drive motor 16 which has associated with it a tachometer 18 for obtaining an accurate determination of the motor speed.

It will be appreciated that the speed of the tape 12 relative to the transducer 14 has to be accurately regulated both during recording and during reproduction of video information. Any of a number of different techniques might be used for controlling the speed of the motor 16, but for purposes of illustration, the motor is shown as being controlled primarily by means of a servo control loop comprising the tachometer 18, a phase comparator 20 and a motor drive amplifier 22. The tachometer 18 generates pulses at a line frequency rate when the tape is moving at the desired speed, and these pulses are transmitted over line 24 to one input of the phase comparator 20, the other input of which, on line 26, is a signal at a reference frequency. The output of the phase comparator 22 is connected by line 32 to the motor drive amplifier 22, the output of which is connected by line 34 to the motor 16. It will be appreciated that, when the phase comparator 20 detects any phase difference between pulses generated by the tachometer 18 and pulses supplied over line 26 at the reference frequency, a difference signal is generated in the phase comparator and is used in the motor drive amplifier 22 to drive the motor either faster or slower until the detected phase difference is driven to zero. The effect of the tachometer servo control loop, then, is to lock the motor speed to the rate of reference-frequency signal supplied on line 26.

As shown in FIG. 1, line 26 is connected to the movable contact terminal of a three-position switch 36 having a "record" position, a "playback" position and an accelerate/decelerate position. In the "record" position, the switch 36 connects line 26 to a line 37 on which is provided a reference signal, at the desired line-frequency rate, derived from a crystal-controlled pulse generator 38. Thus, in the recording mode, the tape speed is locked to the reference frequency by means of the aforedescribed servo control loop.

In the playback mode, an additional servo control loop is brought into operation, to synchronize operation of the motor 16 with synchronization signals read from the tape 12. More specifically, signals from the tape 12 are detected by the record/playback transducer 14, which is connected to the movable contact terminal of single-pole-double-throw switch 40 having a record and a playback position. In the playback position, the signal from the transducer 14 is transmitted over line 42 to a demodulator 44, where it is demodulated to obtain a composite baseband video signal, on line 46 from the demodulator. Line 46 transmits the baseband signal to a conventional synchronization separator 48 which derives from the baseband signal horizontal synchronization signals, for output on line 50, and vertical synchronization signals, for output on line 52. The horizontal synchronization signals on line 50 are transmitted to another phase comparator 54, the other input of which is a reference signal supplied on line 37 from the pulse generator 38. The phase comparator 54 generates an error signal on line 55, which is employed to control the frequency of a voltage-controlled oscillator 56, and the output of the oscillator is connected by line 57 to the playback position terminal of the three-position switch 36. Thus, in playback mode, synchronization signals derived from the tape are compared with the reference-frequency signals in the phase comparator 54, and the voltage controlled oscillator 56 generates pulses at an appropriate frequency to drive the tape in synchronism with the reference frequency on line 37.

For purposes of speed control during acceleration and deceleration, the reference signal on line 26 is supplied over line 58 from a controller 60. This signal can be varied in frequency by the controller, as indicated diagrammatically by a variable-frequency oscillator 62 controlled by signals from the controller over line 64.

It will be appreciated that the variable-frequency reference signals on line 58 needed for controlled acceleration and deceleration of the tape 12 can be generated in any of a variety of ways. For example, an acceleration ramp of increasing frequency can be synthesized within the controller 60 itself, rather than by means of the external oscillator 62. In addition, it should be noted that the simplified schematic of FIG. 1 does not include time base error correction circuitry, which would normally be needed to correct for fluctuations in tape speed caused by variations in tape tension, or by other factors, such as irregularities in the tape transport apparatus. While such circuitry is essential to the proper reproduction of recorded video information, it forms no part of the present invention, and has therefore been omitted for clarity.

In addition to generating what are essentially speed control signals on line 62, the controller 60 also generates a motor direction control signal on line 66 to the motor drive amplifier 22, and receives vertical synchronization signals from the sync separator 48 over line 52. In the recording mode, a video camera 70 generates both video and, optionally, audio signals on line 72, and these are suitable modulated and processed, as indicated at 74, before transmission over line 76 to the switch 40, and thence to the record/playback transducer 14. When the camera 70 is activated or deactivated, an appropriate signal is transmitted over a camera switch signal line 78 to the controller 60, which controls the motor 16 in response to these signals. As will be further described, the controller 60 also provides a synchronization reset signal on line 80 to the video camera 70. The controller 60 also generates a record/playback control signal, as indicated at 82, to control the switches 36 and 40, and for other purposes in the recording system.

It will be appreciated that the controller 60 may utilize hard-wired logic to perform the necessary motor control functions, as determined in part by the camera switch signal on line 78 and in part by the vertical synchronization signal on line 52. More conveniently, however, the controller 60 can take the form of a microcomputer or microprocessor, and it may then be used to perform other control functions associated with the recording system. Whether the controller 60 is implemented in hard-wired form or in microprocessor form, the functions it performs are identical, and these are defined by the flow chart of FIG. 3, taken in conjunction with the velocity-location diagram of FIG. 2.

In FIG. 2, the direction of recording on the longitudinal recording tape is from left to right, i.e., the tape is translated from right to left with respect to the stationary record/playback transducer 14. When a scene, indicated as scene n, is being recorded, the camera switch signal on line 78 (FIG. 1) indicates that the camera switch is actuated, and the controller 60 generates a record signal on line 82, which maintains the switches 28 and 40 in the record position. Accordingly, a reference frequency at the line scanning rate will be supplied to the phase comparator 20, and the motor 16 will be driven at recording speed in the forward direction.

When the camera switch is released, the signal on line 78 conveys this information to the controller 60, and, on detection of the next vertical synchronization pulse from the tape, as indicated at 90 in FIG. 2, the controller will decelerate the tape until it has stopped. The controller 60 effects the deceleration by generating on line 58 a series of pulses at a continually reducing frequency. The controller 60 also controls the switch 36 so that, during acceleration or deceleration, the controller-generated, variable-frequency signals on line 58 are connected to the input of the phase comparator 20 over line 26. Since the motor 16 is constrained by the feedback loop comprising the tachometer 18, phase comparator 20 and motor drive amplifier 22, to conform with the pulse rate of the signals supplied on line 26 to the phase comparator 20, the motor will slow down at an approximately linear rate, as shown by the ramp 92 in FIG. 2. However, due to varying frictional effects related to the motor 16 and tape transport system, the motor and the tape may slow down at a more rapid rate, as indicated by the steeper ramp 94. In any event, the tape will be decelerated to a zero velocity at some location between the points indicated at 96 and 98, depending upon the frictional effects involved.

As soon as it has stopped, the tape will be accelerated in an opposite direction, as indicated by the acceleration ramps 100 and 102, respectively, again depending on the frictional effects which were present during deceleration. On reaching recording speed in the reverse direction, as indicated by points 104 and 106, respectively, the tape is transported at recording speed in the opposite direction for a predetermined period of time, i.e., to points 108 or 110. Then the tape is decelerated to zero velocity again, as indicated by the alternate deceleration ramps 112 and 114. If the frictional effects in the reverse direction of tape movement are exactly equivalent to the frictional effects during deceleration in the forward direction, the tape will reach a rest position, indicated at 116, which will be the same regardless of which of the two alternate paths is followed. As a practical matter, the frictional effects as measured in the two tape directions will probably be approximately equal, and the tape will therefore reach approximately the same rest position in all cases.

After reaching the rest position indicated at 116 (FIG. 2), the tape will remain in this position until the camera switch is once again actuated to begin recording the next scene. When this occurs, the tape is accelerated, as indicated by the acceleration ramp 118. On reaching recording speed again in the forward direction, the tape provides the controller 60 with recorded vertical synchronization information over line 52. On detection of the first or a subsequent vertical synchronization signal obtained from the tape, synchronization of the camera 70 is reset by transmitting an appropriate signal over line 80. At the same time, the system is switched to the recording mode, and the video information from the camera 70 is then recorded in synchronism with the recorded information in the previous scene. One or more fields of the previous scene will be necessarily erased as the new scene is recorded, but the amount lost information is relatively insignificant, and not noticeable during playback.

The foregoing functional sequence of operations of the controller is illustrated in flow chart form in FIG. 3. On entry to this functional sequence, a check is first made, as indicated at block 130, to determine whether the camera 70 has just been switched on. It is has not, a question is asked to determine whether the camera 70 has just been as indicated at block 132. If it has not, there has been no change since the last time these questions were posed, and exit is made as shown at 134. It will be appreciated that, if the controller 60 is in microprocessor form, the microprocessor will, on exit from the described functional sequence, be performing other functions unrelated to the present invention, as indicated by the broken line 136. If it is determined in block 132 that the camera 70 has just been switched off, this indicates that the scene presently being recorded is to be ended. On detection of the next vertical synchronization pulse, as indicated in block 138, the system is switched to playback mode, as indicated in block 140, and the recorder is decelerated to a stop, as indicated in block 142. Then, the tape is accelerated in the reverse direction, as indicated in block 144, is moved at recording speed in the reverse direction for a preselected time, as indicated in block 145, and is again decelerated to a stop, as indicated in block 146. At this point, the tape rests in the position shown at 116 in FIG. 2, and nothing further remains to be done until the camera is again activated.

When this occurs, it will be detected in block 130, after which a check is made for the direction in which the tape is being transported, and for an end-of-tape condition, as indicated in block 148. It will be appreciated that, in longitudinal-type recorders, the recording tape may be moved in either direction, so it is necessary to determine the current direction of travel before initiating recording of a new scene. Similarly, when the tape approaches the end of a reel, appropriate action must be taken to avoid starting a new scene too close to the time at which the tape will be reversed. The statistical probability of this occurring is relatively low, but it is necessary to make allowance for such an occurrence. The tape is accelerated to recording speed, as indicated at block 150, and the tape transport system is synchronized with horizontal synchronization signals from the tape, as indicated at block 152. In fact, this latter function is not performed by the controller, but by the servo-control loop described in conjunction with FIG. 1. Synchronizing with the horizontal synchronization signals from the tape takes only a few milliseconds. Then, the first or a subsequent vertical synchronization pulse is detected from the tape, as indicated at block 154, and, at this point, a reset pulse is supplied to the camera 70 over the synchronization reset line 80, as indicated at block 156. Finally, and essentially simultaneously with the generation of the reset pulse on line 80, the system is switched to the recording mode, as indicated at block 158, and exit is made from this functional sequence. Acceleration and synchronization at the start of recording a new scene can be accomplished in only a few hundred milliseconds, as compared with several seconds for a helical scan recorder.

Although the controller 60 is believed to be more than adequately disclosed by the accompanying drawings and the foregoing description, an even more detailed disclosure switched off, is provided by Appendixes A and B to this specification. Appendix A sets forth the input/output port allocations for an F-8 microprocessor, part no. 3870, manufactured by Mostek Corporation, of Carrollton, Texas, Fairchild Camera and Instrument Corporation, of Mountain View, California, and others. The microprocessor is used to perform the functions of the controller 60, and the port allocations are needed to completely define the hardware interface between the microprocessor and other components shown in FIG. 1. Appendix B is a complete listing, in both source language and hexadecimal code, of the programs stored and executed in the microprocessor, including the programs which perform the functions of the controller 60.

It will be appreciated from the foregoing that the present invention represents a significant advance in the field of video tape recording. In particular, it provides a convenient technique for recording successive scenes on a video tape with loss of synchronization between the scenes when they are played back. Although the invention is best suited for application in the recording of multiple scenes from a video camera source, the same technique can also be easily adapted for recording successive program segments from other sources, such as television program segments recorded off the air. It might be advantageous, for example, to edit television program material by stopping the recorder during portions of a program that a user did not wish to record. The edited portions of the program could then be played back without loss of synchronization between the scenes. if the video source from which a recording is being made is a television broadcast, it is necessary to synchronize that tape movement with both horizontal and vertical synchronization signals contained in the video source, before switching to the recording mode.

It will also be appreciated that, although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.