U.S. patent application number 11/246327 was filed with the patent office on 2006-02-09 for method and apparatus for selectively playing segments of a video recording.
Invention is credited to Kyle Fields, Jerry Iggulden, Alan McFarland.
Application Number | 20060029363 11/246327 |
Document ID | / |
Family ID | 36974579 |
Filed Date | 2006-02-09 |
United States Patent
Application |
20060029363 |
Kind Code |
A1 |
Iggulden; Jerry ; et
al. |
February 9, 2006 |
Method and apparatus for selectively playing segments of a video
recording
Abstract
A video recording and playback device (10) incorporates a
processor (114) for processing the video signal to detect the
presence of commercial messages. Video and audio event detectors
(102, 104) detect the presence of events in the signal as it is
recorded. The timing relationship of the detected events is
analyzed to classify the video segments between events as program
material or as commercial messages. After a program is recorded,
control marks are generated (132) to indicate the beginning and end
of commercial groups so that they will be skipped during subsequent
replay of the recorded program.
Inventors: |
Iggulden; Jerry; (Santa
Clarita, CA) ; Fields; Kyle; (Sacramento, CA)
; McFarland; Alan; (North Hollywood, CA) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD
SEVENTH FLOOR
LOS ANGELES
CA
90025-1030
US
|
Family ID: |
36974579 |
Appl. No.: |
11/246327 |
Filed: |
October 6, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09384468 |
Aug 27, 1999 |
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11246327 |
Oct 6, 2005 |
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08573433 |
Dec 15, 1995 |
5987210 |
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09384468 |
Aug 27, 1999 |
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08304781 |
Sep 12, 1994 |
5696866 |
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08573433 |
Dec 15, 1995 |
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08177813 |
Jan 4, 1994 |
5692093 |
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08304781 |
Sep 12, 1994 |
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08002782 |
Jan 8, 1993 |
5333091 |
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08177813 |
Jan 4, 1994 |
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08103067 |
Aug 6, 1993 |
5455630 |
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08177813 |
Jan 4, 1994 |
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Current U.S.
Class: |
386/250 ;
348/E7.091; 375/E7.183; 375/E7.192; 386/326; 386/E5.02; 386/E5.07;
G9B/15.003; G9B/15.011; G9B/15.023; G9B/15.03; G9B/27.001;
G9B/27.008; G9B/27.02; G9B/27.021; G9B/27.027; G9B/27.029;
G9B/27.034; G9B/27.036; G9B/27.044; G9B/27.045; G9B/27.049 |
Current CPC
Class: |
G11B 27/323 20130101;
G11B 27/28 20130101; H04N 19/142 20141101; G11B 27/107 20130101;
G11B 15/1875 20130101; H04N 5/76 20130101; G11B 15/1816 20130101;
H04N 5/9201 20130101; G11B 15/023 20130101; H04N 5/7755 20130101;
H04N 5/775 20130101; G11B 27/028 20130101; H04N 19/179 20141101;
G11B 27/3054 20130101; G11B 27/3036 20130101; G11B 2220/65
20130101; G11B 2220/90 20130101; G11B 27/024 20130101; H04N 19/87
20141101; H04N 5/765 20130101; G11B 15/026 20130101; G11B 27/324
20130101; G11B 15/087 20130101; H04N 7/002 20130101; G11B 27/24
20130101; G11B 27/328 20130101; G11B 2220/20 20130101; G11B 27/11
20130101; G11B 27/002 20130101; H04N 5/78263 20130101; G11B
2220/455 20130101; G11B 2220/91 20130101; G11B 2220/41
20130101 |
Class at
Publication: |
386/046 ;
386/125 |
International
Class: |
H04N 5/76 20060101
H04N005/76; H04N 5/781 20060101 H04N005/781 |
Claims
1. A video processing method comprising: (a) detecting events
within video information comprising a plurality of video segments;
(b) analyzing respective times of occurrence of a plurality of said
detected events within the video information to classify video
segments between events as being one of a first type and a second
type; and (c) playing only the video segments of the first
type.
2. The method of claim 1 wherein the video information is recorded
on a recording medium.
3. The method of claim 1 wherein the recording medium is a magnetic
disk.
4. The method of claim 1 wherein the recording medium is an optical
disk.
5. The method of claim 1 wherein the second type of video segments
comprise commercial messages.
6. A video processing system comprising: (a) a video player having
a play mode for presenting video information comprising a plurality
of video segments; (b) means for detecting events within the video
information; (c) means for analyzing respective times of occurrence
of a plurality of said detected events within the video information
to classify video segments between events as being one of a first
type for retention during play and a second type for elimination
during play; and (d) means for playing only the first type of video
segments.
7. The video processing system of claim 6 wherein the video
information is recorded on a recording medium.
8. The video processing system of claim 6 wherein the recording
medium is a magnetic disk.
9. The video processing system of claim 6 wherein the recording
medium is an optical disk.
10. The video processing system of claim 6 wherein the second type
of video segments comprise commercial messages.
11. In a video device having at least a play mode, a method of
cueing a recording medium having video information recorded thereon
to a beginning of a recorded video segment comprising: (a)
detecting events within the video information; (b) analyzing
detected events to identify an event which has no following event
within a predetermined period of time; and (c) entering the play
mode at said event which has no following event within a
predetermined period of time.
12. The method of claim 11 wherein the recording medium is a
magnetic disk.
13. The method of claim 11 wherein the recording medium is an
optical disk.
14. A method of cueing a video recording medium having video
information recorded thereon to a beginning of a recorded video
segment comprising: (a) detecting events within the video
information; (b) analyzing detected events to identify an event
corresponding to a beginning of a video segment; and (c) commencing
play of the video information at said event corresponding to the
beginning of the video segment.
15. The method of claim 14 wherein the recording medium is a
magnetic disk.
16. The method of claim 14 wherein the recording medium is an
optical disk.
Description
RELATED APPLICATIONS
[0001] This is a continuation of co-pending U.S. patent application
Ser. No. 09/384,468 filed Aug. 27, 1999, which is a continuation of
U.S. patent application Ser. No. 08/573,433 filed Dec. 15, 1995,
now U.S. Pat. No. 5,987,210, which is a continuation-in-part of
U.S. patent application Ser. No. 08/304,781 filed Sep. 12, 1994,
now U.S. Pat. No. 5,696,866, which is a continuation-in-part of
U.S. patent application Ser. No. 08/177,813 filed Jan. 4, 1994, now
U.S. Pat. No. 5,692,093, which is a continuation-in-part of U.S.
patent application Ser. No. 08/002,782 filed Jan. 8, 1993, now U.S.
Pat. No. 5,333,091, and of U.S. patent application Ser. No.
08/103,067 filed Aug. 6, 1993, now U.S. Pat. No. 5,455,630.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to the field of video recording and
playback systems, and particularly to a method and apparatus for
selectively omitting certain program content during playback of a
recorded video signal.
[0004] 2. Background Art
[0005] It is commonplace to record a commercially broadcast
television program on a video tape recorder (VTR, also referred to
as a video cassette recorder or VCR) for viewing at a later time.
When later viewing the recorded program, many, if not most, viewers
prefer to watch only the program material without also viewing
commercials, promotional messages and the like that are typically
broadcast at intervals during the program.
[0006] Even before the advent of popularly priced video tape
recorders, there have been many attempts to provide home television
viewers with a system to suppress commercial messages. Early
efforts included systems that would mute the audio signal for a
predetermined period of time when a commercial message was sensed.
As VCRs became more popular and "time-shifting" became a convenient
way to view television programs, more sophisticated methods for
eliminating commercial messages have been proposed.
[0007] One prior art approach to commercial elimination has been to
pause the VCR in the record mode when a commercial message is
sensed. A system of this type is disclosed in U.S. Pat. No.
4,319,286, which issued on Mar. 9, 1982 to Hanpachern. In this
system, the absence of video modulation during a video frame (i.e.,
a blank frame) is detected and used to trigger a timing circuit.
When triggered, the timing circuit causes a pause command to be
sent to a video tape recorder. The pause command remains asserted
for a predetermined period of time, or longer if the timing circuit
is retriggered. For example, the timing circuit may be set for 32
seconds so that if blank frames are detected at 30 second intervals
(a typical length for a commercial message) the VCR will remain in
the pause mode until 32 seconds after the last such blank frame.
Quite a few prior art references disclose variations on this type
of system, wherein the VCR is paused for a fixed period of time
following detection of a blank frame in the video signal. For
example, PCT Application No. WO81/00945 by Johnston and Koombes
discloses a system of this type. Such systems are claimed to be
relatively effective for eliminating commercial messages, but
suffer certain drawbacks. In this regard, program material
immediately following a commercial break is irretrievably lost
since the VCR is held in the "pause" mode for a predetermined
period of time (30 to 60 seconds or more) following each break in
the television signal. Furthermore, additional program material may
be irretrievably lost if the timing circuit is falsely triggered,
such as by a fade between scenes in the program.
[0008] Other prior art systems have sought to overcome these
drawbacks. For example, U.S. Pat. No. 5,151,788 to Blum discloses a
system for eliminating commercials from a video signal that
performs real time analysis of the video signal immediately
following a blank frame. If there is a high level of "activity" in
the signal immediately following a blank frame, a commercial
message is presumed and the VCR is commanded to pause. On the other
hand, if a low level of activity is detected, the preceding blank
frame is presumed to be a fade and the VCR is commanded to resume
recording. This approach solves the problem of losing a fixed
amount of program material if a VCR pause if falsely triggered, but
it is still susceptible to misclassification. If a program fade is
immediately followed by an "active" scene, this will be
misclassified as a commercial. On the other hand, a commercial with
a low level of "activity" will be misclassified as program
material.
[0009] A different approach to eliminating commercial messages is
to automatically rewind a VCR to the beginning of a commercial
message each time one is detected while recording a television
program. One such system is disclosed in U.S. Pat. No. 4,750,052,
which issued on Jun. 7, 1988 to Poppy and Samelson. A virtually
identical system is disclosed in U.S. Pat. No. 4,752,834, which
issued on Jun. 21, 1988 to Koombes. In both of these systems, fades
(i.e., blank frames) in the video signal are detected and the time
interval between successive fades is determined in a timing
circuit. If the timing criteria for a commercial message are met,
the VCR is rewound to the position of the fade associated with the
beginning of the commercial message and the VCR is returned to the
record mode. This process repeats for each commercial message that
is detected. These systems permit an editing decision to be made
after an entire commercial has been aired; however, as with the
other systems previously described, program material is still
irretrievably lost if there is a false detection of a commercial.
Furthermore, the frequent rewinding of the tape during long
commercial breaks accelerates the wear of the VCR tape transport
mechanism as well as the tape itself.
[0010] Yet a different approach is disclosed by Mizuki in Japanese
patent document 58-146072, which was published on Aug. 31, 1983. A
similar system is disclosed in U.S. Pat. No. 4,570,192, which
issued on Feb. 11, 1986 to Hori. In both of these systems, a video
program is viewed by an operator as the program is recorded or is
replayed. The operator places an electronic mark on the tape at the
beginning and end of each commercial message or any other undesired
recorded material. When the tape is subsequently replayed, either
for viewing or transcription to another tape, the VCR is commanded
to fast-forward through the portions of tape bounded by the applied
marks. These systems rely entirely on human intelligence to
classify the different portions of the video signal.
[0011] Still other systems are known that discriminate commercial
messages based on characteristics of the transmitted video signal.
A system of this type has been marketed in Japan by Mitsubishi
under the name "Auto-Cut". In this system, the audio channel is
monitored for the presence of a second audio program (SAP) and/or
stereo modulation. Many of the programs that viewers wish to tape
are broadcast in dual languages (e.g., Japanese and English) and/or
with monaural sound. However, commercial messages in Japan are
generally broadcast in stereo and in the Japanese language only.
Thus, a VCR with the Auto-Cut system is able to record a monaural
program or one with SAP and suspend recording during commercials.
Other systems marketed in Japan operate on a similar principle, but
record the entire program and then place the VCR in a fast scan
mode during playback when stereo sound or the absence of SAP is
detected.
[0012] All known prior art automatic commercial elimination systems
rely on real-time signal analysis to classify the broadcast signal
as program material or as a commercial message. This is true
whether the classification is being performed during the recording
or playback process. Prior art automatic systems do not examine
detected events in the full context of surrounding events. Thus,
misclassification is relatively common. When done during the
recording process, such misclassification will cause portions of
program material to be irretrievably lost.
SUMMARY OF THE INVENTION
[0013] The present invention provides a method and apparatus for
controlling the operation of a video recording and playback device
so as to automatically eliminate commercial messages during
playback of a recorded television signal.
[0014] The apparatus of the present invention comprises a video
recorder/player having at least a record mode, a play mode and a
fast scan mode; a recording medium for insertion into the video
recorder/player so as to record a video signal thereon in the
record mode and play the video signal recorded thereon in the play
mode; event detection means for detecting events within the video
signal (such as black frames in combination with silent frames);
means for marking the recording medium with a first type of mark in
proximity to a respective event recorded on the recording medium; a
data memory for storing the times of occurrence of events detected
in the record mode; means for analyzing the events to classify
segments of the video signal as being of a first category (e.g.,
program material) or of a second category (e.g., commercial
messages); means for positioning the recording medium to beginning
and ending positions of each segment classified as being of the
second category; means for marking the recording medium with a
second type of mark in a predetermined relationship to a
corresponding first mark at the beginning positions and with a
third type of mark in predetermined relationship to a corresponding
first mark at the ending positions.
[0015] The present invention also provides a video recording method
comprising the steps of recording a video signal on a recording
medium; monitoring the video signal as it is recorded to detect
events therein; marking the recording medium with a first type of
mark in proximity to a respective event recorded on the recording
medium; storing data representative of a time of occurrence of each
event; analyzing the data to classify segments of the video signal
between events as being of a first or second category; positioning
the recording medium to beginning and ending positions of each
segment of the video signal classified as being of the second
category; marking the recording medium with a second type of mark
in predetermined relationship to a corresponding first mark at each
of the beginning positions; and marking the recording medium with a
third type of mark in predetermined relationship to a corresponding
first mark at each of the ending positions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a functional block diagram of a commercial
elimination system according to the present invention.
[0017] FIG. 2 is a functional schematic of the video event detector
circuitry.
[0018] FIG. 3 is a functional schematic of the audio event detector
circuitry.
[0019] FIG. 4 is a functional block diagram of an alternative
embodiment of a commercial elimination system according to the
present invention.
[0020] FIG. 5 is a schematic diagram of the video line integrator
of FIG. 4.
[0021] FIG. 6 is a schematic diagram of the audio signal integrator
of FIG. 4.
[0022] FIG. 7 is a functional flow diagram of the recording
phase.
[0023] FIG. 8 is a functional flow diagram of the recording phase
in an alternative embodiment of the invention.
[0024] FIG. 9 illustrates the operations performed in the tape
marking phase.
[0025] FIG. 10 is a functional flow diagram of the playback and
over-ride phases.
[0026] FIG. 11 illustrates over-writing the control track signal to
place commercial elimination marks on the video tape.
[0027] FIG. 12 illustrates the format of the sync mark.
[0028] FIG. 13 illustrates the format of the "A" mark.
[0029] FIG. 14 illustrates the format of the "B" mark.
[0030] FIG. 15 is a functional flow diagram of the movie cueing
feature of the present invention.
[0031] FIG. 16 is a schematic diagram of the video field integrator
of FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
[0032] In the following description, for purposes of explanation
and not limitation, specific details are set forth in order to
provide a thorough understanding of the present invention. However,
it will be apparent to one skilled in the art that the present
invention may be practiced in other embodiments that depart from
these specific details. In other instances, detailed descriptions
of well-known methods, devices and circuits are omitted so as to
not obscure the description of the present invention with
unnecessary detail.
[0033] U.S. Pat. No. 5,333,091 discloses a control unit that is
coupled between a conventional VCR and a conventional television
receiver/monitor. This "stand alone" control unit processes the
video signal prior to being recorded to detect events within the
signal and to modulate the recorded signal with a time code. The
spacing and duration of the detected events is analyzed to classify
the video signal between events as either program material or
commercial message material. A map of the video signal is stored in
the control unit. Upon playback of the recorded program, the map is
retrieved and control signals are sent to the VCR to rapidly scan
through the commercial messages as the program is replayed.
[0034] The subject of this disclosure is a system functionally
similar to that disclosed in U.S. Pat. No. 5,333,091, but which is
preferably incorporated within a video recording device such as a
VCR. Although a VCR is the preferred recording mechanism, the
invention is not limited in this regard and may be practiced with
other video recording media such as magnetic discs or writable
optical discs. FIG. 1 is a partial block diagram of a video
recording device 10 according to the present invention. For
clarity, only those functions related to commercial elimination are
shown. Of course, it will be recognized that certain functions may
be housed in a unit that is physically separate from the VCR, if
desired. For example, the event detection circuitry comprising
functional blocks 102, 104, 106 and 108 and the commercial
elimination microprocessor 114 with its associated memories 116,
118 could all be housed in a unit that is attached to the VCR by an
interface cable or umbilical, or that is attached directly to a
plug-in socket on the VCR. Such a configuration could be utilized
to adapt a basic VCR chassis for use in different markets where
differing broadcast protocols require specialized commercial
detection processing.
[0035] Referring still to FIG. 1, the "VIDEO IN" and "AUDIO IN"
signals originate from the VCR tuner in a recording mode of
operation or from the VCR playback heads in a playback mode of
operation. These signals are applied at video and audio event
detectors 102 and 104, respectively, which are more fully described
below. The outputs of event detectors 102 and 104 are interrogated
by commercial elimination microprocessor 114 to build an event list
that will be processed by a commercial detection algorithm.
[0036] All commercial detection and elimination functions are
controlled by microprocessor 114. Associated with microprocessor
114 is random access memory (RAM) 116 for scratch pad storage and
read only memory (ROM) 118, which stores the operating instructions
for processor 114. In a typical embodiment, processor 114, RAM 116
and ROM 118 should have the following characteristics:
TABLE-US-00001 Processor type 8 bits ROM space 8K bytes RAM space
700 bytes Instruction execution time 1 to 2 .mu.sec A/D converter
inputs 2 (multiplexed) A/D conversion time 50 .mu.sec or less
External interrupts 1 Communications port I.sup.2C or
equivalent
[0037] If event detection is implemented external to the processor,
such as in analog circuitry, processor 114 need not have
analog-to-digital (A/D) conversion capability.
[0038] Microprocessor 114 communicates extensively with VCR control
microprocessor 120. With respect to commercial elimination
functions, VCR control microprocessor 120 monitors the real time
tape counter 122 and controls the operation of tape transport 124.
In some embodiments, it may be advantageous to combine the
functions of processors 114 and 120 into a single processor.
[0039] Nearly all of the functions of commercial elimination
microprocessor 114 are automatically controlled. However, two user
controls are provided. A MODE switch 126 allows the user to select
a fully automatic commercial elimination mode, a manual mode or to
disable all commercial elimination functions. A SKIP button 128
provides user control of the commercial skipping function when
operating in the manual mode. Controls 126 and 128 may be placed on
the front panel of device 10; however, they are preferably included
on a remote control transmitter that provides user controls for all
of the conventional VCR functions. Alternatively, the choice of
operating mode may be effected through an on-screen menu rather
than a dedicated control 126.
[0040] The commercial detection algorithm executed by
microprocessor 114 identifies the location of commercial groups on
a video tape. To implement the commercial elimination feature, the
video tape is marked at the beginning and end of each commercial
group. These markings are preferably written onto the control track
of the video tape with control head 130. During the marking
operation, the commercial identification markings are provided by
control signal generator 132. When the video tape is replayed, the
commercial identification markings are read by control signal
decoder 134. Although marking of the control track is preferred,
the present invention may also be practiced by applying the tape
markings elsewhere, such as in the vertical blanking interval of
the video signal, in which case the read/write functions can
utilize the video play and record heads of the VCR.
[0041] As mentioned above, the "VIDEO IN" and "AUDIO IN" signals
originate from the VCR playback heads in the playback mode of
operation. During commercial skipping, it is desirable to mute both
of these signals. For this purpose, the video signal is routed
through video switch 136, which also receives the output of video
generator 138. The latter circuit provides a constant video signal,
such as a solid blue screen. Other types of video screens may be
developed by video generator 138. An operator control may be
provided to over-ride video switch 136 if it is desired to view the
video signal as commercials are scanned past. Muting switch 140
mutes the audio output signal during fast scan, although this is a
feature that is already implemented in most VCRs.
Video Event Detection
[0042] In one embodiment of the invention that is described in
detail herein, video event detector 102 detects "black" frames in
the video signal. A "black" frame is one in which there is
essentially no video signal at all, such as is characteristic of
frames immediately preceding and following commercial messages in
television broadcasts of the major U.S. networks.
[0043] One embodiment of detector 102 is shown in greater detail in
FIG. 2. Detector 102 monitors the incoming video signal and
provides a signal to the commercial elimination processor 114
whenever the video falls within black detect limits. Black frame
detection includes the following elements: [0044] Signal clamping,
for automatic level control [0045] Filtering to reduce effects of
video noise [0046] Comparison to a threshold level [0047] An active
area detection window [0048] Latched detection output
[0049] The detection of black video level is accomplished by
comparing the video level to a precise threshold level in
comparator 208. To be effective, this threshold is very near the
black video level. Accurate control of the video signal is required
to allow for correct detection with changing video signal levels.
The input video signal is first amplified by amplifier 202 and then
the video level is normalized through the use of a DC clamp circuit
204. This circuit is activated in the back porch area of each
horizontal video line. A control pulse signal is generated in sync
separator/timing circuit 106 that occurs from the trailing edge of
the horizontal sync to the end of the video back porch. This signal
drives clamping circuit 204 that sets a DC level in the video
signal prior to detection.
[0050] There are many types of noise commonly present in video
signals. The black detector preferably includes a low-pass filter
206 to provide filtering of fast, spurious luminance signals,
characteristic of video "snow". This type of noise is very common
and originates from poor video reception and other interference. By
providing a high frequency bypass to ground, the effects of such
noise are greatly reduced.
[0051] Once the video signal has been properly conditioned and
filtered, it is compared against the fixed DC threshold level in
comparator 208. The threshold is preferably set at about 25 IRE.
Any video luminance excursion that exceeds this threshold will
change the output state of the comparator. This function requires a
relatively high speed signal comparator capable of responding to
signal changes in the microsecond range.
[0052] Detector 102 is sensitive to video level excursions that
exceed the preset threshold level. To prevent false detection, the
event detection window generator 108 provides a detection window
that gates the detector within a rectangular portion of the
viewable screen at window gate 210. Timing for generation of the
detection window is provided from sync separator and timing circuit
106, which detects the horizontal and vertical synchronization
pulses within the video signal and provides logic level timing
signals for the video processing circuitry. Sync separator 106 may
be constructed with discrete components using well known video
circuits or may utilize a commercially available integrated circuit
such as a Motorola MC 44145 device or equivalent.
[0053] The rectangular detection window excludes the start and end
of the video frame, thereby eliminating video occurring during
vertical blanking. The window also excludes the left and right
edges of the picture to eliminate false detection due to video
effects occurring in the horizontal sync areas of the picture. Some
television scrambling systems will produce a video signal at the
extreme edges of the picture, and this will be disregarded.
[0054] The output of the detection comparator 208 can be a fast
pulse, necessitating that it be latched for sampling by the
commercial elimination processor. A simple latch device 212 is
provided that will capture any detection event occurring during the
video frame. Once the state of the latch has been sampled by the
commercial elimination processor it is cleared for the next video
frame.
Audio Event Detection
[0055] Pauses in television audio are also important indicators for
commercial detection, especially when they occur simultaneously
with the occurrence of video events such as black frames. The
silent frame detector 104, shown in greater detail in FIG. 3,
monitors the incoming audio signal and provides an output when
periods of silence are detected in the audio. The audio detection
circuitry contains the following elements: [0056] Summing of left
and right audio channels (if stereo audio) [0057] Amplification of
signal prior to detection [0058] Filtering [0059] Comparison to a
threshold level [0060] Latching of detection output
[0061] The input audio signals from both stereo channels are
buffered by circuits 302. For best response, both left and right
audio signals are summed together prior to detection. This is
easily accomplished using a summing node 304 and simple amplifier
306. The audio level is amplified so that detection of very low
level audio is enhanced. An amplification factor of approximately 2
to 4 will provide adequate signal to the audio comparator 310. This
amplification also provides AC coupling of the signal to present an
audio level that can be easily referenced to ground. Filter 308
removes static and other high frequency noise.
[0062] The audio detection is accomplished by comparing the audio
level to a fixed threshold level which is set so that any
noticeable audio level will exceed this threshold and change the
output level of the comparator 310. The output of the level
comparator 310 is held by latch 312 so that any fast audio
excursion is captured for subsequent sampling by the commercial
elimination processor. This sampling is typically accomplished
every video frame, at the same time the black detector is
sampled.
Digital Event Detection
[0063] While event detection with analog circuitry as described
above provides satisfactory performance, a digital event detection
approach is preferred since a variety of detection schemes can be
implemented through software.
[0064] Although it is conventional for television broadcasts within
the United States to have black frames preceding and following
commercial messages, such is not necessarily the case. Broadcasters
could insert virtually any video signal during program breaks. For
example, a blue screen could be used (as is the case in France). A
constant video signal of this sort, which need not be black, is
referred to herein as "flat", i.e., the video signal is essentially
constant throughout the frame. To detect "flat frame" events, the
video event detection may be implemented to declare an event if the
video signal within a field or frame varies from an average value
by a predetermined amount. Since black frames are a subset of flat
frames, such a flat frame detector is equally capable of detecting
black frames.
[0065] Frames immediately preceding and following commercial
messages may not even be flat. For example, a broadcaster could
insert a patterned screen or a solid screen superimposed with the
broadcaster's logo. To handle these situations, video event
detection may employ a scene change (or cut) detector which
compares the video signal within a plurality of screen windows from
frame to frame. When the average video signal within any one or
more of the windows changes by a predetermined amount, a scene
change is declared. If there are two scene changes within a
predetermined period of time (e.g., a change from program to a
broadcaster logo screen followed by a change to a commercial
message) an event is declared. The time interval for declaring an
event of this type should be relatively short (on the order of five
seconds or less) to minimize the number of false events detected.
In some markets, such as Japan, the transition from program to
commercial is an instantaneous cut. Detecting commercials in this
environment also requires the ability to detect scene changes.
[0066] With reference to FIG. 4, an alternative embodiment
designated generally as device 10' is shown, in which any of the
above-described event detection strategies can be selectively
implemented. In this embodiment, the actual event detection is
performed by software in microprocessor 114' based on digitized
samples of the video signal from video line integrator 152.
Processor 114' preferably includes a multiplexed analog-to-digital
(A/D) converter as previously indicated. One such processor
suitable for this application is the ST9296 from SGS, which has
four analog inputs multiplexed to an 8-bit A/D converter.
Alternatively, A/D conversion could be performed in a separate
device that provides digital inputs to the microprocessor.
[0067] FIG. 5 illustrates the analog circuitry of video line
integrator 152 for processing the video signal prior to digital
sampling. The VIDEO IN signal is preferably integrated across each
complete video line between successive back porch regions of the
horizontal blanking interval, although less frequent integration
may be used as subsequently described. The output voltage of the
integrator is asserted at one of the multiplexed A/D inputs of
processor 114' where it is captured for conversion to an 8-bit
binary value.
[0068] Processor 114' stores each of the binary values which
represents the integrated luminance level of the respective video
line. It should be noted that it may not be necessary to sample and
store the luminance level of every video line. For example,
sampling approximately 60 out of the 240 active lines in a video
field may be sufficient to characterize the field.
[0069] With representative samples of the luminance levels of
individual video lines, processor 114' detects the presence of
video events. For flat field detection, samples within an entire
video field are examined. The maximum and minimum luminance values
are located and the difference is computed. This difference is then
compared to a predetermined threshold. The field is declared to be
"flat" if the difference is below the threshold.
[0070] As already mentioned, black fields (or black frames) are a
subset of flat fields. To detect a purely black frame, the absolute
luminance level of a flat field detected with video line integrator
152 may be tested to determine if it is below a predetermined
threshold level. However, black frame detection may be enhanced by
use of a positive slope analog integrator 153 that amplifies the
video signal and integrates only positive slopes. Integrator 153
operates in parallel with video line integrator 152 and is sampled
and reset every video field. The digitized sample is then compared
in software to a fixed threshold to determine if the field is
black. This approach allows for accurate detection of black fields
without falsely detecting low luminance scenes within a regular
television program.
[0071] A schematic diagram of a circuit suitable for use as video
field integrator 153 is presented in FIG. 16. It should be observed
that the output signal is inverted, i.e., the reset level is +5V
and the signal integrates down to ground. However, it is convenient
to consider the circuit a positive integrator with reference to a
"pure black" video signal (7.5 IRE). The black level offset
adjustment should be set so that a field of pure black video
generates a negligible integration voltage at the end of the field
(i.e., a +5V output).
[0072] Scene change or "cut" detection is also made possible with
device 10'. Luminance levels of a video frame are compared to
corresponding luminance levels of the following video frame. If a
sufficient number of lines exhibit a change in luminance exceeding
a predetermined threshold, then a scene change is declared. While
it is possible to compare each video line for which a luminance
value is determined with the corresponding line of the next frame,
efficiency is increased if comparisons are made between
corresponding horizontal bands of multiple lines. For example, the
screen may be divided into 15 horizontal bands and the luminance
levels of lines within each band averaged. The average luminance of
each band is then compared to the corresponding value of the
following frame.
[0073] Referring now also to FIG. 6, an audio signal integrator 154
is illustrated. In the case of a stereo VCR, the AUDIO IN signal in
FIG. 6 is the sum of the left and right channels for the previously
described embodiment. The integrated audio signal voltage is
asserted at one of the multiplexed A/D inputs of processor 114'.
The integrator is reset on command from processor 114'. It should
be noted that the audio signal may be sampled at a much slower rate
than the video signal, perhaps only once per video frame, in which
case silent frame detection involves a simple threshold
comparison.
[0074] In order to ensure accurate commercial detection, "events"
are preferably declared on the basis of information obtained from
both the video and audio detectors. For example, in the North
American market, an event is declared only if there is coincidence
of a black frame and a silent frame. Testing has shown, however,
that the audio and video events are not always in phase with each
other. If there is only a single black frame between commercials,
audio silence may not occur in the exact same frame. To accommodate
this, the event detection software should allow audio and video
events to be skewed from each other by up to several frames.
[0075] Coincidence of video and audio events is also problematic
when detecting cuts. The event detection software should look for
audio silence that is simultaneous with the video cut, that
precedes the video cut, and/or that follows the video cut. An
alternative approach could implement an audio cut detector,
somewhat similar to the video cut detector, that looks for
discontinuities in the audio levels between successive video
frames.
[0076] It will be observed that there is no functional unit in
device 10' corresponding to the event detection window generator
108 of device 10. As should be apparent, the window function can be
readily performed by software in processor 114' which receives the
video sync signals as interrupts. This gives greater flexibility in
sizing the detection window. This is particularly helpful for
dealing with superimposed identification logos that are now
included in many broadcasts. These logos, which can be transparent
or solid, monochrome or color, are most frequently inserted in a
corner of the picture. Broadcast sources may leave a logo inserted
all of the time, may remove the logo during paid commercial time,
or may insert the logo only periodically. To ensure accurate event
detection in the presence of logos, the video lines where logos may
be present are simply ignored. In NTSC format, there are 21
non-picture lines in the vertical blanking interval, or about 1.3
milliseconds. Ignoring 4 milliseconds of video from the vertical
blanking interval causes sampling to begin on about line 63. In PAL
or SECAM formats, about 5.2 milliseconds should be ignored from the
vertical blanking interval. An equal amount of time should be
ignored at the end of the field, before the vertical blanking
interval.
[0077] Another approach for excluding graphic logos is to sample
alternate video fields with different active window areas. For
example, the first field of each frame could sample only the top
two-thirds of the field, thereby excluding all lines in the bottom
one-third of the field. The second field of the frame could then
sample the lines in the bottom two-thirds of the field. If either
field is determined to be flat or black, this can be declared an
event.
Operational Description
[0078] The operating modes of devices 10 and 10' are basically
similar to a conventional VCR. Recording and playback of video is
accomplished in the same manner as on any other VCR. However, when
the commercial elimination feature is enabled, device 10/10'
performs additional functions during the various VCR operating
modes. Most of these additional functions do not require
interaction with the user.
[0079] By use of the MODE switch, the user may select between two
basic operating modes--manual and automatic. This selection affects
the handling of the video tape during the playback phase of device
10/10' as described below. All of the other operating phases of
device 10/10' are identical in both manual and automatic modes.
[0080] The commercial elimination functions of device 10/10' can
best be understood in terms of the various operating phases, each
of which is described below.
Recording Phase
[0081] FIG. 7 shows the operations that are performed in the
recording phase. This phase is active whenever the VCR is in record
mode (either from key entry, or from timer operation), and the
commercial elimination feature is enabled. From the user's
perspective, video programs are recorded as on any standard VCR.
However, as indicated in FIG. 7, the device is transparently
performing other functions while recording is in progress.
[0082] During the recording phase, the event detectors are sampled
and the tape location of each event, obtained from the real-time
tape counter, is stored in an event list in temporary memory. For
purposes of commercial detection processing, an "event" is
determined in accordance with the particular broadcast protocol of
the program being recorded. As previously discussed, black video
frames are events of interest in many TV markets, particularly
North America. In other markets, such as Japan, video cuts are
events of interest. In this description, North American
broadcasting conventions are presumed. However, it will be
recognized that device 10/10' is operable in other markets with
suitable modifications.
[0083] As events are detected, the video tape is marked in real
time with a "sync" mark at the location of each detected event. The
sync mark, the format of which is more fully described below,
starts at the beginning of the event and has a duration of four
video fields. The purpose of the sync marks is to precisely
indicate the possible start and end points of a commercial group.
Since the sync marks are written onto the tape prior to the event
analysis which classifies the program segments between events as
program or commercial, the sync marks by themselves do not indicate
the presence of a commercial group. During the subsequent
processing and marking phases, the positions of the commercial
groups will be determined and indicated by writing different marks
on the tape.
[0084] The sync marks facilitate precise switching between the
normal play and fast scan modes which provides the best viewing
experience in the playback phase. However, the use of sync marks is
not essential to the operation of device 10/10'. Without sync
marks, the marks identifying the beginning and ending of a
commercial group may be written on the tape with reference to the
real-time tape counter.
[0085] The recording phase is normally terminated whenever the VCR
stops recording (whether by manual action, end of tape, timer or
other function). After recording, the commercial elimination
processor enters the processing phase (described below). If the
recording session is less than a predetermined minimum length, say
15 minutes, the stored events may be erased, and the processing
phase may be bypassed. At any time during the recording phase the
user can disable the commercial elimination feature by setting the
MODE switch to OFF. This has the effect of canceling all data
stored for the current session and prevents operation of the
commercial elimination processing phase.
[0086] Application of the sync marks to the control track is
ordinarily done at the time a video program is recorded. However,
it may be desired to mark a tape that has been previously recorded
on a different VCR which lacks the commercial elimination functions
of the present invention. In such case, a modified recording phase
is implemented in which the previously recorded video tape is
"played" while event detection and sync marking proceeds in the
manner described above. Subsequent processing and marking is then
accomplished in the same manner as for a newly recorded tape so
that the tape may thereafter be played with commercial elimination
enabled.
Processing Phase
[0087] This phase is active for a short time following the
recording phase. Its purpose is to analyze the event list and
determine when commercial groups occurred. This process involves
applying a commercial elimination algorithm (described below) that
analyzes the event list and identifies the occurrence of television
commercial groups. The algorithm produces a commercial group list
that includes the start and stop point of each commercial group
identified within the recording session. This list of commercial
groups is used during the tape marking phase to indicate the
commercial groups on the video tape. Since the location of
individual events is no longer needed, the event data in memory may
be erased or overwritten after completion of the processing
phase.
[0088] FIG. 8 illustrates an alternative embodiment, one that is
particularly useful if the size of RAM 116 is limited. In this
embodiment, the processing phase is integrated with the recording
phase so that processing is performed "on-the-fly". The event list
is processed continuously with a sliding window having a width of
approximately two minutes or as necessary to accommodate the
decision rules discussed below. The event list can thus be
organized as a first-in-first-out file requiring only a modest
amount of RAM since relatively few events occur within a two minute
period. Such "on-the-fly" processing is particularly advantageous
when cut detection is utilized to identify events. In this case,
there is a relatively large number of events which would require a
sizable memory to store the event list for an entire recording
session.
Tape Marking Phase
[0089] FIG. 9 diagrammatically illustrates the tape marking phase
operations. After the processing phase is complete, the commercial
group list in memory indicates the start and end points of the
commercial groups that were identified within the recording
session. In the marking phase, the VCR is rewound to the
approximate beginning of the first commercial group. The tape is
then marked by writing signals on the control track to identify the
start and end of each commercial group. Each start and end mark is
associated with a corresponding sync mark as more fully explained
below. The real-time tape counter is used throughout the marking
phase to indicate the current tape position to the commercial
elimination processor. This is compared to the values stored in the
commercial group list to control the tape transport and marking
operations. Since the sync marks are written on the control track
during the recording phase, their position is always accurate with
respect to the recorded video signal. In performing the marking
operation, the VCR can use the position of the sync marks to
correct the real-time tape counter for any accumulated error. After
the entire recording session has been marked (which may take a few
minutes), the tape is left positioned at the end of the recording.
The VCR returns to standby mode of either Stop or Off (if in
Program Timer mode). Upon successful completion of the tape marking
phase, the commercial group list in memory may be deleted.
[0090] During the marking phase, the VCR operation can be stopped
by the user selecting OFF with the MODE switch, or by pressing STOP
on the VCR. This will have the effect of canceling all commercial
elimination operational phases, and returns the VCR to Stop mode at
its current position. Subsequent selection of MANUAL or AUTO with
the MODE switch will not restart commercial elimination operations
until the next recording or playback session.
[0091] Each commercial group is marked with unique marks at the
start (called the "A" mark) and end (called the "B" mark) of the
group. This allows device 10/10' to differentiate the marks, and
determine if the tape is entering or leaving a commercial group.
The location of each B mark is advanced ahead of the actual event,
to allow time for the VCR to brake and enter the normal Play mode
when quickly skipping through a commercial group.
[0092] Whether or not commercials are detected in a recording
session, a B mark is written approximately 54 seconds before the
end of the session. This B mark is written so that any program
material of a subsequent adjacent recording session will not be
missed if the manual skip feature is used. This end of recording B
mark is omitted only if the recording session was less than 15
minutes in length or if commercial elimination has been
disabled.
[0093] In performing the marking operation, it is important to
consider the effect of transport mode changes. Depending on the
configuration of the tape transport, errors may occur in the
real-time counter when the transport is changed between play, stop,
rewind and fast forward modes. Such errors are most likely to occur
when changing from an "on-head" mode to an "off-head" mode or vice
versa. If the magnitude of these errors is significant, marking
should be accomplished using only "on-head" transport modes (e.g.,
forward and reverse scan) to reduce the cumulative effect of
real-time counter errors.
Playback Phase
[0094] FIG. 10 illustrates the operations performed during the
playback phase. When the VCR is placed into Play mode, and the
commercial elimination feature is enabled, the commercial
elimination processor samples signals from the tape control track,
looking for the marks that indicate the start and end of each
commercial group. In the automatic operating mode, the VCR performs
the following actions upon detection of an "A" mark at the start of
each commercial group: [0095] the VCR outputs a blue screen (unless
blue screen feature is disabled); [0096] the audio outputs are
muted; and [0097] the tape is advanced at fast forward or forward
scan speed.
[0098] When the VCR is skipping and a "B" mark is detected at the
end of a commercial group, the VCR performs the following actions:
[0099] the tape is returned to normal Play mode; [0100] the video
signal is monitored for the sync mark at the end of the commercial
group; [0101] when the sync mark is detected (or after a 2-second
time-out if the sync mark is not detected), the blue screen video
is disabled and the audio outputs are enabled.
[0102] In manual operating mode, no automatic action is taken at
the start of a commercial group. During playback in the manual mode
of operation, device 10/10' functions like a conventional VCR,
except that the user has the option to view or skip commercials.
The recorded video signal, including commercials, is played back at
normal speed. However, at any time the user can press the SKIP
button, which causes device 10/10' to immediately generate a blue
video screen, mute the audio, and forward scan to the start of the
next program segment, thereby skipping over the current or next
commercial group. Note that the VCR will start skipping to the end
of the next commercial group as soon as the SKIP button is pressed
(regardless of whether the VCR is currently in a commercial or
television program segment). The skipping process will
automatically stop at the end of the next commercial group.
[0103] In order to improve the effectiveness of commercial
elimination, it may be desirable to bypass automatic fast scanning
of certain commercial groups. In particular, commercial groups at
the beginning and ending of a recorded program often contain
promotional messages, teasers, program lead-ins/lead-outs and other
material that many viewers wish to see. Such materials are often
interspersed with commercials and may be classified as such by the
commercial detection algorithm. Accordingly, it may be desirable to
refrain from automatically fast scanning through commercial groups
at the beginning and ending of a recording session. Such groups
would nevertheless be marked in the manner previously described and
could therefore be scanned through upon actuation of the SKIP
button. To obtain the full benefit of this feature, it is
preferable that each program which the user desires to record be
made the subject of a separate recording session. Thus, even if two
programs which the user desires to record are aired back to back,
VCR timer commands should be separately entered for each program.
Otherwise, lead-ins and lead-outs between the two programs may be
automatically scanned through.
Over-Ride Operation
[0104] During the playback phase, the user may wish to stop the
commercial skipping process. This can be accomplished in two ways.
The user can disable commercial elimination entirely by selecting
OFF with the MODE switch. This will cause the VCR to play the tape
as would a conventional VCR. No further commercial elimination
actions are taken until reenabled by the MODE switch.
[0105] Alternatively, the user can temporarily over-ride commercial
elimination while the VCR is skipping a commercial group as shown
at block 520 in FIG. 10. This may be conveniently accomplished by
pressing Play on the remote control or front panel of the VCR. If
the VCR is currently skipping a commercial group, the reception of
the Play command will cause the VCR to immediately resume normal
play mode and cancel blue screen and audio muting. This feature
allows the user to temporarily stop the commercial elimination
operation if the user wishes to view the commercial. This feature
can also be used in the event that a commercial group is falsely
detected during program material. Alternatively, the user can
simply press the stop button to stop the VCR.
[0106] Over-ride operation does not change the current operating
mode and does not disable commercial elimination functions except
within the commercial group being skipped at the time of the
over-ride. After an over-ride, the VCR will again skip the next
commercial group if the automatic mode is selected. Commercial
elimination can only be permanently disabled by setting the MODE
switch to OFF.
[0107] Once a commercial group is over-ridden, device 10/10' will
no longer attempt to skip that commercial group while in the
automatic mode unless the tape is positioned at least three minutes
ahead of the start of the group. This allows the user to back up
and view a skipped video segment (which may have been falsely
marked as commercial) without the playback phase attempting to skip
that video segment again. This will occur when the tape is rewound
to any position less than three minutes before the start of the
group. However, for playback that occurs more than three minutes
from the start of the over-ridden commercial group, device 10/10'
will perform the normal commercial skipping process.
Commercial Detection Algorithm
[0108] The commercial detection algorithm detects the presence and
location of commercial groups within a television program. The
algorithm processes data obtained during a recording session in the
form of an "event list". The event list is stored temporarily in
RAM memory until it is processed, either during or at the end of
the recording session. The list contains entries for each
occurrence of an event. In the described embodiment designed for
the North American television market, the detectors respond to
"black" and silent video frames, and an event is declared if both
conditions occur simultaneously.
[0109] By analyzing these events, and the timing relationships
between them, the detection algorithm is able to determine the
probable locations of commercial groups within the recorded
session. The result of this analysis is a commercial group list,
which indicates where the commercial groups start and end on the
video tape.
[0110] Each event in the event list contains the value of the
real-time tape counter at the beginning of the event. The detection
algorithm determines the interval between events, measured in video
frames. By applying a set of logical rules, the algorithm
determines if the segment defined between two events is a
commercial or a program segment. The algorithm takes each event and
processes all subsequent events that occur within a time window
established by the decision rules. For each of these subsequent
events, the time differential dt is calculated and the following
decision rules are implemented:
[0111] 1. Is dt less than or equal to 34.99 seconds?
[0112] 2. Is dt less than 49.99 seconds and greater than 43.0
seconds?
[0113] 3. Is dt less than 64.99 seconds and greater than 58.0
seconds?
[0114] If there is an affirmative response to any one of the
decision rules, the corresponding segment following the event being
examined is considered to be a commercial. The foregoing decision
rules have been optimized for maximizing the commercial detection
rate and minimizing the program (i.e., false commercial detection)
error rate for North American television broadcasting. Different
decision rules may be required in other television markets. For
example, as mentioned above, there are no black frames to identify
commercials in Japanese television broadcasts. Here, the decision
rules take advantage of the high degree of accuracy (within a few
frames) in the length of commercial messages. In other markets,
such as Europe, there is little consistency in broadcast standards
so that a combination of rule sets is required.
[0115] It will be recognized that the above-stated decision rules
may be supplemented with additional rules to enhance the accuracy
of commercial detection. Efforts are ongoing to determine an
optimum rule set. At the cost of greater complexity, the rules may
be adaptively changed for the particular recording environment. For
example, different rules may be invoked as functions of the time of
day, broadcast channel, etc.
[0116] After analyzing the event list data, the algorithm has
determined the suspected locations of individual commercials within
the recorded session. The next step is to combine these individual
commercials into groups of commercials. Commercial groups consist
of two or more individual commercials--it is presumed that a single
commercial will not be broadcast in isolation. By calculating the
start and end times of each commercial group, the algorithm
generates a commercial group list, which is also stored in RAM
memory. A group is saved only if the total duration of the group is
greater than 55.99 seconds.
[0117] Once the commercial group list is completed, or more
frequently if on-the-fly processing is used, the event list can be
erased from RAM memory since it is no longer needed. As described
above, the commercial group list is used during the marking phase
to control the placement of the start and end commercial group tape
marks. Upon completion of the marking phase, the commercial groups
can also be erased from RAM memory since the video tape is now
permanently marked with the locations of each commercial group.
Control Track Marking
[0118] The device of the present invention applies the commercial
elimination "A" and "B" marks to the control (CTL) track of the
video tape. The hardware required to support this marking feature
already exists in most VCRs. The "A" and "B" marks modify the duty
cycle of the synchronization signal written onto the control track
at the time the program was recorded. Many VCRs currently implement
a similar feature for placing index marks on the tape. The
preferred technique utilized with the present invention for
applying marks to the video tape is similar to the one described by
Hori in U.S. Pat. No. 4,570,192.
[0119] Referring to FIG. 11, the video tape control track signal,
as defined in the published standards for the VHS format, consists
of a periodic signal in synchronization with the video frame
timing. The signal is recorded with a rectangular wave format, and
read back from the tape as a differentiated pulse train. The pulses
indicate the rising and falling edges of the control track pulse
signal. For video tape synchronization (tracking), the rising edge
of the signal (positive playback pulse) is used to control the tape
motor servos; the falling edge (negative playback pulse) is
ignored. Therefore, as long as the rising edges of the control
track signal are not disturbed, the duty cycle of the control track
signal can be altered without affecting the operation of the video
servo system.
[0120] When overwriting the control track with "A" and "B" marks,
the VCR detects the control track signal and waits until just after
the rising edge is detected before enabling control track record
current. After the rising edge is detected, the write current is
enabled and the timing of the duty cycle measured to control the
polarity of the applied signal. The head write current is disabled
before the actual end of the pulse in order to prevent overwriting
the next rising edge of the control track pulse.
[0121] In order to improve compatibility with various VCR models,
and to reduce noise associated with fast rise time signals, the
leading edge of the overwrite wave form is preferably ramped. This
improves readability when transferring a video tape between
machines, that may have different head alignments or track
widths.
[0122] Three types of marks are applied to the video tape: sync
marks, A marks and B marks. These are designed to be compatible
with VHS standard indexing marks. Each of the three types of marks
is unique so that the VCR can readily distinguish between the
beginning and ending of a commercial group. The marks comprise a
sequence of video fields in which the control track signal is
altered to have a duty cycle of either 27.5% or 60%.
[0123] The formats of the control track marks are illustrated in
FIGS. 12-14. FIG. 12 shows the sync mark, which is generated by
device 10/10' during the recording phase of operation to mark the
locations of detected events. For operation in North America where
one or more black frames is a reliable indicator of a program
transition, a sync mark is written upon simultaneous detection of a
black frame event and a silent frame event. The sync mark consists
of 4 cycles of the control track signal with a 27.5% duty cycle.
The time between the beginning of the detected event and the
beginning of the sync mark preferable does not exceed 500 msec.
[0124] The A mark, which denotes the beginning of a commercial
group, is shown in FIG. 13. This mark is written over a
corresponding sync mark that was generated during the recording
phase. During the marking phase, when the sync mark associated with
the calculated start of a commercial group is detected, the control
track is overwritten with the A mark. At the same time, the VCR
tape counter is corrected for any error. If a sync mark is not
detected within .+-.2 seconds of its expected position, the A mark
is nevertheless written, but the VCR tape counter is not
updated.
[0125] The length of the A mark is preferably related to the length
of the commercial group that follows. This allows the option, in
the playback phase, of placing the VCR in its off-head fast forward
mode to scan past a long commercial group. In most VCR transports,
the off-head fast forward speed is significantly faster than the
on-head forward scan speed. In an exemplary embodiment, the A mark
has 8 cycles at a 27.5% duty cycle if the commercial group has a
playing time of three minutes or less and has 12 cycles at 27.5%
duty if the commercial group is longer than three minutes. Of
course, these numbers are somewhat arbitrary and other values can
be used if desired. The decision of whether or not to go off-head
depends on the characteristics of the tape transport mechanism and
involves a trade-off between the time required to unload the head
and the time saved by moving the tape at the higher fast forward
speed. With some transport mechanisms, it may be more efficient to
always remain on-head.
[0126] FIG. 14 illustrates the format of the B mark, which is
written near the end of each commercial group. This mark is written
substantially before the sync pulse corresponding to the actual end
of the commercial group so that the tape transport will have
sufficient time to return to the normal play speed at the end of a
commercial skipping operation and reestablish tracking, if
necessary. The B mark preferably consists of 24 cycles at 27.5%
duty cycle and ends at a fixed period of time before the ending
point of the commercial group. In an exemplary embodiment, the B
mark ends 50 seconds of playtime before the sync mark to
accommodate a relatively high fast scan speed. It is preferred that
the formats of the tape markings be consistent in all devices built
according to the invention so that video tapes recorded on any one
such device can be replayed on another with identical commercial
elimination functionality.
[0127] It is possible that A and B marks may be written over
previously written sync marks. To insure that the marks do not
appear to be extended as a result of such overwriting, each of the
marks preferably includes at least two cycles of 60% duty factor at
the leading and trailing edges of the mark so that the mark is
clearly delineated.
[0128] In accordance with VHS standards, indexing marks may also be
encoded on the control track using a variable duty cycle. Index
marks are typically recorded on the video tape at the start of a
recording, or they can be manually written or erased in some VCR
models. The VHS index mark consists of a solid pattern, e.g., 61-64
cycles, of 27.5% duty cycle pulses. In order to insure reliable
detection of an index mark without interference by commercial
elimination marks, the VCR control software should require at least
25 successive control track cycles at the 27.5% duty cycle for
identification of an index mark. Requiring 25 cycles for index mark
detection allows the VCR to differentiate between the commercial
elimination marks (which are all shorter than 25 cycles) and index
marks.
[0129] Each time a new recording is made, an index mark should be
recorded at the start of the recording session. This will ensure
that the recorded program will not be skipped over as a result of
an A mark recorded earlier on the tape. This can occur if a user
partially rewinds a tape and starts a new recording that erases a
previously recorded B mark. If the tape is subsequently rewound to
a position preceding the last A mark of the old recording, there is
no B mark to cause the VCR to return to the play mode. However,
since an index mark can also be detected as a B mark, recording the
index mark will ensure that the new recording is not skipped.
[0130] The following table indicates the number of sequential
cycles required for reading and writing commercial elimination
marks and index marks: TABLE-US-00002 Type of Mark Write Read Sync
mark 4 cycles 2 to 4 cycles A Mark (short commercial group) 8
cycles 7 or 8 cycles A mark (long commercial group) 12 cycles 11 or
12 cycles B mark 24 cycles .gtoreq.16 cycles Index mark .gtoreq.61
cycles .gtoreq.25 cycles
[0131] When reading 1, 5, 6, 9 or 10 cycles, no valid mark is
detected.
[0132] The marking operation, briefly described above in connection
with FIG. 10, is accomplished with the following steps:
[0133] 1. Rewind to a position before the start of the first
commercial group in the recording session.
[0134] 2(a). Play until 2 seconds prior to start of the commercial
group.
[0135] 2(b). Detect sync mark (or time-out after 2 seconds if sync
mark not found).
[0136] 2(c). Correct for error in real-time tape counter.
[0137] 2(d). Overwrite control track with "A" mark.
[0138] 2(e). Begin fast forward or scan toward the end of the
group.
[0139] 2(f). Enter play mode 55 seconds (or as far in advance as
required) prior to the end of the group.
[0140] 2(g). Overwrite control track with "B" mark.
[0141] 2(h). Advance to the start of next commercial group.
[0142] 3. Repeat 2(a)-(h) above for all commercial groups.
[0143] 4. Fast forward to end of recording session and stop.
Movie Cueing
[0144] In pre-recorded videos of motion pictures, it is common
practice to include a number of "trailers", commercials and other
advertising messages before the feature. These can have an
aggregate playtime of 10 minutes or more, which is often an
unwelcome distraction to the viewer. A VCR constructed in
accordance with the present invention can be readily adapted to cue
a pre-recorded motion picture to the beginning of the feature
presentation.
[0145] FIG. 15 is a flow diagram of the software routine that
implements the movie cueing feature of the present invention. This
routine is preferably implemented in processor 114' of apparatus
10', although it could also be implemented in a stand alone device.
In this description, it is presumed that the motion picture is
recorded on a video cassette. However, it will be understood that
the invention is not limited in this regard and the movie cueing
feature may be implemented to operate with any recording medium.
When a pre-recorded movie is placed in device 10', the tape is
first rewound to the beginning. This may be accomplished by
actuating a "MOVIE" control on the front panel of the device or on
a remote control transmitter. Alternatively, the device may
automatically sense that a pre-recorded movie has been inserted.
This may be accomplished by examining the video signal. In this
regard, most pre-recorded movies have a copy protection feature,
wherein a pattern of white bars is cyclically modulated in a
portion of the vertical blanking interval. The presence of such
copy protection is easily detected with the video event detection
circuitry of apparatus 10'. Other video characteristics of
pre-recorded movies include the absence of commercial elimination
markings and recording at standard play (SP) speed. These
characteristics can be used to exclude recordings that are clearly
not pre-recorded movies.
[0146] Once the tape has been rewound, it is advanced while the
video signal is monitored for flat frame events. As in broadcast
television, the trailers and commercials on a pre-recorded movie
are typically separated by blank frames. As flat frames are
detected, the value of the real time tape counter is stored. If the
tape has advanced for more than 3 minutes of playing time without
detection of a flat frame event, it is presumed that the feature
presentation has been located. The tape is then rewound to the
location of the last detected event, and the VCR is stopped or
paused. This may be accompanied by an on-screen display that
prompts the viewer to press PLAY in order to begin the movie.
[0147] While flat frame events are being logged, the tape is
preferably being advanced at a fast scan speed, provided that the
video noise bars characteristic of fast scanning do not interfere
with detection of flat frame events. Filtering of the video
detector output may be required to eliminate the effects of such
noise bars. Alternatively, the detector may have a direct hardware
interface to the servo electronics and head switching signals to
provide a gating signal. This gating signal will allow the detector
to ignore video within the noise bars. The audio detector should
receive the audio signal even in fast scanning mode so that
detected video events can be matched with audio silence.
Information Decoding
[0148] It will be recognized that the video event detection
capability of device 10/10' has the inherent capability for
decoding information modulated on the video signal. Individual
video frames can be modulated as black or non-black to provide a
simple binary coding scheme. Although this affords a relatively low
data rate, it can be an effective way to transmit data to device
10/10' if only black frame detection is provided. One application
for such data communication is the transmission of time-of-day
information so that the built-in clock of device 10/10' will always
have the correct time. Inexpensive television broadcast time is
often available in early morning hours. Such time can be
advantageously utilized to transmit information to all receiving
devices. The devices can be preprogrammed to scan for information
at certain times of the day when normal use of the device is
unlikely. Thus, for example, the device may enter a scan mode at 3
a.m. to search for a data header encoded with black frames. When
the header is located, the data which follows is decoded and stored
in processor 114. Aside from time-of-day, the coded information may
include, for example, new operating instructions for processor 114.
In this way, the commercial elimination algorithm can be
periodically and automatically updated.
[0149] It should be apparent that the data communication bandwidth
can be substantially higher in device 10' since up to each video
line can be sampled. If all video lines are utilized to encode
individual data bits, the communication bandwidth increases to 15.7
kHz.
[0150] It will be recognized that the above described invention may
be embodied in other specific forms without departing from the
spirit or essential characteristics of the disclosure. Thus, it is
understood that the invention is not to be limited by the foregoing
illustrative details, but rather is to be defined by the appended
claims.
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