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Description  |
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FIELD OF THE INVENTION
The present invention relates to an apparatus which permits the
simultaneous recording and playback of video material with a variable
delay between the recording of a given segment of a video program and the
subsequent playback of that segment.
BACKGROUND OF THE INVENTION
In the broadcast industry, audio and video recording and playback machines
have been used to delay live broadcasts by several seconds to permit
deletion of inappropriate language or gestures. These machines provide a
fixed delay between the recording and playback of a given section of audio
and/or video.
Many commercially available video cassette recorder (VCR) machines, i.e.,
videotape recorders with multiple heads, permit the user to play back
recorded material immediately after it has been recorded, by positioning
the play-back head after the record head. This enables the user to monitor
the quality of the recording and watch the broadcast essentially live.
These machines do not allow the user to vary the delay between the
recording and playback of segments of video.
More particularly, such conventional machines do not allow one to view
material as it is being recorded, other than simultaneously or immediately
after it has been recorded, as above. This imposes many inconveniences.
For example, often one will anticipate arriving home at a particular hour,
sometime after the commencement of a particular broadcast program one
desires to watch. One must therefore set one's VCR to commence recording
at the beginning of the program. If one then arrives a few minutes after
the beginning of the program, one can watch the end of the program in real
time, but cannot see its beginning until after the entire program has been
recorded.
Similarly, often one will be watching a particular program when one must
temporarily cease watching it, for example, to take a telephone call or
the like. It would obviously be convenient to be able to record the
program from that point forward, complete the telephone call, and simply
watch the remainder delayed by the length of time of the interruption.
However, no devices are now available which permit this facility. It also
is not possible to employ two separate video cassette recorders to
overcome these inconveniences.
OBJECTS OF THE INVENTION
A principal object of the present invention is to provide an improved video
recorder and playback device that can be used to record and playback video
material independently, for example, so as to allow the viewer to pause
the playback for a variable period of time without interrupting the
recording.
A further object of the present invention is to provide an apparatus that
can be used to record and playback video material while allowing the user
to effectively reposition the stored material with respect to the playback
device to allow "fast forward" or "rewind" of the material being played
back, without interruption of the recording.
SUMMARY OF THE INVENTION
These objects are achieved, according to the present invention, by
recording video on a recording medium while simultaneously playing back
previously recorded video from the medium, while allowing control of a
variable time delay between recording and playback.
The video recorder of the invention is described in three embodiments. In
the first "sequential" and second "random access" embodiments, the
functional attributes of the device are identical. In the third "multiple
tape" embodiment, the functional attributes are somewhat different.
In the first "sequential" embodiment, the video program material is
recorded on a sequential medium, typically videotape. In a second "random
access" embodiment, the video signal is converted to digital form and
recorded in a random access memory, which can be any of several known
types. For example, this random access memory could employ magnetic or
optical media or a solid state memory.
More particularly, the term "random access memory" is commonly used to
refer to a particular type of solid state memory. The term as used herein
includes such solid state devices, but as a consequence of the particular
nature of the invention, such devices as magnetic or optical discs, which
permit rapid access to essentially any portion of the stored records, are
also included. Not included within the term "random access memory" as used
herein is tape storage media, which is sequential in character. That is,
use of tape media requires that a quantity of tape be physically moved in
order to access a particular record (except when sequentially stored
records are accessed). This is not true of "random access" memory devices
as used herein.
In the first "sequential" embodiment of the invention, the video signal is
recorded continuously on tape as in the prior art. The signal can be
recorded in analog form as conventional, or could be converted to digital
form and stored as a sequence of digital samples. In either case, in this
embodiment of the invention, the signal is stored in its original sequence
on tape. However, instead of providing a fixed physical spacing between
recording and playback heads as in the prior art, the device of the
invention comprises an accumulator for physically storing a variable
quantity of tape between the recording and playback heads, and comprises
separate tape transport mechanisms for driving the tape past the recording
and playback heads so that these can be independently controlled.
For example, suppose one has programmed a machine according to the
invention to commence recording at a particular time, say 10:00 p.m. One
then arrives home at, say, 10:30 p.m. In the interim, the tape recorded by
the record head has been physically stored in the accumulator located
between the record head and the playback head. Therefore, if one then
wants to commence watching the stored program, one can activate the
playback drive, driving the tape from the accumulator past the playback
head, while the tape continues to be fed into the accumulator, completing
the recording of the program. One can readily "fast forward" through
unwanted program material such as commercials, while recording the entire
program without interruption.
Similarly, if one is watching a program and receives an interruption such
as a telephone call or the like, one can cause the program to be recorded
while storing the tape in the accumulator. One can subsequently return to
the program and watch the portion of the program which has been stored in
the interim. If the interruption is comparable in length to the combined
length of all unwanted program material, ultimately one may catch up to
the program before its end.
In the random access embodiment, the video signal is stored on random
access media such as a magnetic or optical disk or in solid state memory.
A control device maintains the addresses of the segment(s) of the recorded
material in the memory device, so that they can be reassembled in the
proper sequence for playback. Typically the video signal will be converted
to digital form prior to storage.
In both "sequential" and "random access" embodiments of the invention the
video program material is effectively stored in a so-called FIFO (first
in-first out) buffer of variable length so that the user can view the
video material in the sequence in which it is broadcast, while varying the
delay between recording and playback of given material.
In the third "multiple tape" embodiment of the invention, three essentially
conventional video tape cassettes (or other tape supply devices) and three
separately controllable tape transport mechanisms, with three
corresponding record and playback heads, are employed. A microprocessor
controls the individual motion of the three tapes past their respective
recording and playback heads, responsive to user controls. In this
embodiment of the invention, the user can still view a program while a
subsequent portion of the program is being recorded. However, the user may
experience delays during certain operations of the device. In essence, one
of the tapes records while a second can be playing back previously
recorded material. The microprocessor maintains a list of the sequence in
which the various segments of the program are recorded and can readily
play them back in their proper sequence responsive to user instructions.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood if reference is made to the
accompanying drawings, in which:
FIG. 1 is a schematic diagram of a video recorder in the first "sequential"
embodiment of the invention;
FIG. 2(a), 2(b) and 2(c) show schematically the steps in operation of a
particular accumulator for tape which may be useful in implementation of
the "sequential" embodiment of the invention of FIG. 1;
FIG. 3 is a schematic diagram of a "random access" embodiment of the
invention;
FIG. 4 is a flow chart for a computer algorithm which can be used to
implement the features of the invention in the "random access" embodiment
of FIG. 3;
FIG. 5 shows a block diagram of the "multiple tape" embodiment of the
invention; and
FIG. 6 shows a diagram illustrating the operation of the "multiple tape"
embodiment of the invention over time.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As described above, this invention includes three preferred embodiments: a
first "sequential" embodiment in which the video program material is
recorded on conventional videotape or the like, in its original sequence,
a second "random access" embodiment in which the information is stored as
addressable blocks of information on a medium other than tape per se, and
a third "multiple-tape" embodiment of the invention. In each, the manner
of storage of the video signal on the medium is not itself particularly
significant. For example, in the first embodiment of the invention, the
video signal could be digitized prior to storage rather than stored in
analog form as broadcast, and as stored in video recorders as currently
used. Due to the sequential nature of tape, comparable facilities for
physical handling of the tape are needed to provide variable delay between
recording and playback according to the invention, regardless of the
actual method of recording employed.
FIG. 1 shows an embodiment of the invention in which tape stored in a
conventional video cassette is employed according to the invention to
allow variable delay between recording and playback. A supply of video
tape 1 is provided wound on the supply spindle 2 of a conventional
videotape cassette 3. The tape is threaded past rollers 4 and 5 and the
combination of record head 6 and a generally conventional drive mechanism,
shown schematically as a capstan 6a. Capstan 6a is controlled by a control
circuit 32 which also controls a comparable capstan 18a (or equivalent
conventional drive element) driving the tape past the playback head 18.
The motion of the tape 1 past the record head 6 and the playback head 18
is thus independently controllable, in contrast to conventional video tape
recorders, wherein the tape is driven past the two heads by a single drive
mechanism, so that a variable delay between record and playback can not be
provided.
The tape leaving the combination of the record head 6 and the capstan 6a
passes by roller 7 and is driven by a pair of rollers 8, 9 onto an
accumulator tray 10. Pairs of rollers 11, 12 and 13, 14, the operation of
which is detailed below, control the disposition of the tape on the tray.
Tape is pulled from the tray by rollers 15, 16 before passing by roller
17, the combination of playback head 18 and capstan 18a, and rollers 19
and 20 and is finally wound upon the takeup spindle 21 of the tape
cassette 3. At least roller pairs 8, 9; 11, 12; 13, 14; and 15, 16, in
addition to spindles 2 and 21 and capstans 6a and 18a, are powered for
positive tape motion control, responsive to control signals from
controller 32.
When the unit is in record mode, the rollers of pairs 8, 9, and 11, 12 are
caused to rotate in opposite directions to pull the tape off the rotating
supply spindle 2 past the combination of record head 6 and capstan 6a, and
push the tape into the accumulator portion 27 of the tray 10, that is
between roller pairs 11, 12 and 13, 14. When the unit is in playback mode,
the rollers of pairs 13, 14 and 15, 16 are rotated in opposite directions
to pull the tape from the tray 10 and past the combination of playback
head 18 and capstan 18a, after which it is wound upon the rotating takeup
spindle 21.
If the playback operation is paused during a recording operation, takeup
spindle 21, capstan 18a and roller pairs 13, 14 and 15, 16 stop rotating,
responsive to control signals from controller 32, while the supply spindle
2, capstan 6a, and roller pairs 8, 9, and 11, 12 continue rotating, so
that the tape begins to accumulate in the tray 10 between roller pairs 11,
12, and 13, 14. In order to ensure uniform storage of the tape on the
accumulator tray, rollers 11 and 12 are moved back and forth across the
tray 10 in a direction perpendicular to the line between the pairs of
rollers 8, 9 and 15, 16. This is accomplished by a reciprocation mechanism
shown, for example, as including rotating eccentric 22. One end of a rod
24 is affixed to the eccentric at a pivot point 23. The opposite end of
rod 24 drives the assembly of rollers 11 and 12 transversely across the
tray, as indicated by arrows 11a, 12a. The rollers 11 and 12 and the
reciprocating drive rod assembly move linearly along the tray as the tray
fills over time, as indicated by arrow 33. This causes the accumulated
tape to be deposited in the accumulator portion 27 of the tray 10 in a
uniform zig-zag pattern, as shown. In some cases, additional devices to
control the disposition of the tape on the tray may be desirable; for
example a wall preventing the stacked end portions of the loops of tape
from extending behind the rollers 11 and 12 may be desirable.
When the playback mode is restarted, capstan 18a, roller pairs 13, 14 and
15, 16 and spindle 21 are set rotating again, responsive to control
signals from controller 32, to pull the tape accumulated at 27 past the
playback head 18 and onto the takeup spindle 21. In this case the amount
of tape in the tray 10 will remain constant as one section of tape moves
out of the tray and past the playback head 18 while another section of
tape moves past the recording head 6 and into the tray 10.
If the unit is put into fast forward mode, capstan 18a, and roller pairs
13, 14 and 15, 16 pull tape out of the accumulator portion 27 of the tray
faster than the rollers 8, 9 and 11, 12 deposit new tape in the tray, so
that the amount of tape in the tray decreases.
It will be apparent that independent control of the speed of the capstans
6a and 18a, as well as the associated rollers, under control of the
control circuitry 32, is important so that according to the invention a
variable delay between recording and playback can be provided. This allows
playback to be paused or reversed, or the speed of the tape past the
playback head to be increased (in the "speed search" or "fast forward" or
"rewind" modes) without affecting the speed of the tape past the recording
head.
In order to preserve the normal rewind function, for example, to allow one
to see the same scene repeatedly, without impeding the record function, it
is important that the recorder also permit tape in the FIG. 1 embodiment
to be returned to the tray 10 from the takeup spindle 21. Tape on the
takeup spindle 21 can be returned to the tray 10 by reversing the
direction of the capstan 18a and roller pairs 13, 14 and 15, 16. Eccentric
28 and rod 29 are provided to drive rollers 13 and 14 back and forth. This
ensures the tape is stacked in the regular zig-zag pattern. Moreover, this
stacking can be accomplished while tape is entering the accumulator
portion of the tray 10 from the recording side via rollers 8, 9 and 11,
12. Hence any section of the recorded portion of the tape can be brought
to the playback head 18, and the conventional pause, speed search, reverse
search, fast forward, and rewind functions can all be accomplished with
respect to the portion of the tape that has already been recorded on,
without disturbing recording of new material on the portion of the tape
withdrawn from the supply spindle 2.
FIGS. 2(a)-2(c) show an alternative embodiment 10a of the accumulator of
FIG. 1. In this embodiment, the rollers 8 and 9 drive the tape 1 between
sets of opposed idler rollers 34 and 35. The sets of idler rollers are
mounted on frames 36 and 37 which are movable with respect to one another
as shown by arrows 39 and 40. Relative movement of the sets of rollers
allows more or less tape to be stored in the accumulator 10a, depending on
the direction of the relative movement. For example, when the record and
playback capstans 6a and 18a are operating at the same speed, that is so
that no net tape is to be stored in or withdrawn from the accumulator, the
sets of idler rollers 34 and 35 are stationary. If it is desired to store
tape in the accumulator 10a, for example, so as to enable the viewer to
take a telephone call during the recording of a program, the first set of
rollers 35 begins gradually to move in one direction away from the line
connecting the input rollers 8 and 9 and the output rollers 15 and 16,
while the other set of rollers 34 moves in the opposite direction. As
shown in FIGS. 2(b) and (c), as these sets of rollers 34 and 35 move
further apart, a gradually increasing amount of tape 1 is stored in the
accumulator 10a. When it is desired to withdraw tape from the accumulator
10a faster than it is being fed into the accumulator, for example during
fast forward playback of a program being recorded, the sets of rollers 34
and 35 are gradually brought closer to one another. The accumulator 10a is
simply controlled by controlling the movement of the frames 36 and 37 in
accordance with the control signals provided to the capstan 6a and 18a by
the controller 32.
FIG. 3 shows schematically a "random access" embodiment of the invention,
in which the video signal is stored on a non-sequential medium in digital
format.
In this embodiment, the recording device (FIG. 3) includes a signal
sampling circuit 51 and an analog-to-digital converter 52 which together
create digital samples of the video signal being recorded, which are
stored in a random access memory 53. Playback is accomplished by
retrieving these stored samples from memory 53 and converting them back
via a digital-to-analog converter 54 to an analog video signal. The
reconstituted analog video signal is supplied to a video signal generator
55 which outputs a conventional video signal which can be displayed on a
standard TV display 56. Recording and playback may be done essentially
simultaneously by multiplexing writing to and reading from the memory 53.
In this embodiment playback can clearly take place from any portion of the
memory and at any speed without affecting the recording. Control of such a
random access memory to implement the various desired functions mentioned
above is well within the skill of the art.
The locations at which the digitized video samples are stored in the random
access memory 53 are controlled by an address controller 58, which in turn
is responsive to commands received from a user control panel 50. Operation
of the address controller 58 is generally described in connection with
FIG. 4.
To conserve the amount of storage space required to store a given quantity
of the digitized video signal, the digitized signal can be compressed in a
data compressor 57, removing redundant information prior to storage, and
decompressed in a decompressor 59 prior to reconstitution by the
digital-to-analog converter 54. Such data compressors and decompressors
are known per se and the details of their operation are not critical to
the present invention.
FIG. 4 shows a flow chart for an algorithm which can be used to control
storage and retrieval of such digitized video samples from the memory 53
(FIG. 3). The algorithm is entered at block 100, at which a byte of the
digitized video signal is received from the analog to digital converter
52. At step 102, this byte is stored in the memory 53 at an address
designated by a write pointer. The write pointer is then incremented by
one at block 104. The subsequent byte will thus be stored at the next
address in memory 53. This process allows data representing the video
signal to be continuously stored. During simultaneous playback, in block
106 a byte stored at a location pointed to by a read pointer is fetched
from the memory 53 and sent at block 108 to the digital-to-analog
converter 54, which as noted above converts it back to an analog signal
which is sent to the display 56. At block 110 the interrupt mask of the
computer is checked briefly to allow an interrupt from the user control
panel 50. At block 112 any interrupt from the control panel is detected;
such an interrupt might indicate, for example, that the orderly playback
process implemented by blocks 106 and 108 is to be varied. If so, at block
114 the read pointer is changed to implement the command received via the
interrupt. Block 100 is then reentered. If no interrupt is detected, the
read pointer is incremented at block 116 and block 100 is reentered, so
that both recording and playback continue.
As discussed above, the "sequential" embodiment of FIGS. 1 and 2(a)-2(c)
relate to physical storage of tape media in a manner which permits a
variable amount of tape to be stored between the recording and playback
heads, so as to provide a variable delay between recording and playback
times. As discussed in connection with FIGS. 3 and 4, it is also possible
to store the video signal as a series of digital samples and to read the
data out of the memory as needed for playback purposes. This eliminates
the mechanical necessity of storing varying amounts of tape addressed in
connection with FIGS. 1 and 2(a)-(c). Thus in the "random-access"
embodiment of the invention, the digitized video signal is stored in
individually addressable portions, which are accessed in the sequence in
which they were stored, to reconstitute the original video signal.
The flowchart of FIG. 4 contemplates that each byte of the digital data
representative of the video signal will be stored separately and accessed
individually. It will be recognized by those of skill in the art that
digitizing a typical video signal results in generation of a large number
of data bytes per second, yet that the user does not require access to
each data byte separately; in most circumstances, allowing the user to
access the signal at one second intervals will be more than adequate.
Therefore, the processing steps could be simplified in a manner well
understood by those of skill in the art, by storing the digitized data in
blocks of length equivalent to one second and allowing the user simply to
access these in sequence, through the interrupt routine as described above
or the like. Maintaining control of the sequence of blocks of data
representing the stored signal is simply a matter of maintaining a list in
sequence of the addresses at which the blocks were stored in the memory.
The system's response to user commands would be much faster than
experienced with conventional video recorders. "Fast forwarding", for
example, would be accomplished simply by jumping ahead in the list of
addresses.
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