Note: Descriptions are shown in the official language in which they were submitted.
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COMPRESSED DIGITAL-DATA SEAMLESS VIDEO SWITCHING SYSTEM
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of application Serial Number
08/887,314, filed July 7, 1997, which is a continuation of application Serial
Number
08/443,607, filed May 18, 1995, now U.S. Pat. No. 5,724,091, which is a
continuation-in-part of application Serial Number 08/166,608, filed December
13,
1993, abandoned, which is a continuation of application Serial Number
07/797,298,
filed November 25, 1991, abandoned.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to interactive response systems, and
more particularly to an interactive television system which provides
interactive
programming using compressed, digital data having more than one video signal
on a
broadcast channel, or a multiplexed signal within a digital format, or both.
The invention also relates to seamlessly switching between video signals while
viewing a first video signal, even though the video signal switched to may be
on a
different broadcast channel, or on the same channel multiplexed with, the
currently
viewed video signal.
2. Description of the Prior Art
2o Interactive systems are well known in the art. By synchronizing parallel
tracks
of an information storage media, and relating the content of the various
tracks, it was
found that interactive activity could be simulated. For example, commonly
owned
Freeman, U.S. Patent No. 3,947,972 discloses the use of a time synchronized
multi-
track audio tape to store educational conversations. One track is employed to
relay
educational interrogatories to a user, and the remainder of the tracks,
selectable by a
switching mechanism, are used to convey responsive messages.
These systems progressed to interactive television, wherein multiple broadcast
or cable channels were switched in response to user selections to provide
interactive
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operation. Commonly owned Freeman, U.S. Patent No. 4,847,700 discloses an
interactive television system wherein a common video signal is synched to a
plurality
of audio channels to provide content related to user selectable responses.
Commonly owned Freeman, U.S. Patent No. 4,264,925 discloses the use of a
conventional cable television system to develop an interactive system.
Standard
television channels with time synchronized content are broadcast to a
plurality of
users. Each user switches between channels responsive to interrogatories to
provide
interactivity.
These systems have been tailored to include memory functions so that the
system can be more interactive, individually responsive, and so that
customized
messages may be given to the various categories of users responsive to
informational
queries. Freeman, U.S. Patent No. 4,602,279 discloses the use of a memory to
store
demographic profiles of television viewers. This information is stored to be
recalled
later for providing target specific advertising, for example. Prior art
interactive
television systems were generally concerned with providing one signal (i.e.
one video
signal) per channel, whether the channel is on cable television, broadcast
television, or
a VCR. Because cable and broadcast television channel capacity is becoming
limited
as more and more cable channels are being utilized for conventional
programming,
and interactive systems of the type described require multiple channels, it is
desirable
to reduce the channel capacity required for such systems while still providing
at least
the same level of interactivity.
U.S. Patent No. 5;724,091 disclosed and claimed seamlessly switching
between video signals while viewing a first video signal, even though the
video signal
switched to may be on a different broadcast channel, or on the same channel
multiplexed with, the currently viewed video signal. What is needed, however,
is a
less complex method and system for seamlessly switching between compressed
digital
video signals in a low cost digital set top environment.
SUMMARY OF THE INVENTION
The present invention is a digital cable television system which utilizes
digital
3o video signals to provide customized viewing responsive to user selections.
A
standard cable or direct broadcast satellite television distribution network
is utilized
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for transmitting interactive and other programming to users. The present
invention
allows a plurality of viewers to be simultaneously provided with a plurality
of
different digitally compressed program signals. Further, interactive programs
comprises a plurality of video signals.
The video signals are converted into digital format for transmission. In a
digital format, it is possible to transmit more than one video signal per
cable
television channel. Further, it is possible to transmit video signals via
conventional
telephone lines. If desired, the various digital video signals may be
compressed
before transmission. Compression allows an even larger number of video signals
to
be transmitted over a channel of the transmission media. Preferably, the
compression
scheme used is one of the MPEG standard compression schemes, including MPEG2,
MPEG4 and MPEG7. The video signals are fed into a digital data and video
format,
preferably in the MPEG format.
As part of the digital signal transmission, some of the signals are
interactive
and individualized programming. Such enhanced content is created by utilizing
conventional video production techniques and by providing a multiplicity of
video,
audio, graphics and data in any combination thereof. The multiple video and
audio
information is time synchronized and, in most instances, preferably related in
content.
The subsequent interactions at the remote sites are controlled by the end use
and
producer, via the insertion of data codes representing a scripting language.
These
codes are preferably integrated and sent with the interactive video and audio
signals
and may be inserted either at a program control center or cable headend.
An multiplexes combines the various digital signals into a reduced number of
transmission data streams for transmission. The various NTSC television
channels
may be allocated in a predetermined fashion to maximize the number of
simultaneously transmittable signals. The multiplexes in conjunction with the
television transmission system multiplexes the desired data streams onto the
desired
channels, and transmits these signals over the NTSC channels. The number of
video
signals which may be multiplexed onto a data stream on a single transmission
channel
will vary depending on the video signals to be transmitted. The television
channels
containing a data stream of multiplexed video signals may be transmitted over
a
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standard cable television distribution network, or direct broadcast satellite
transmission system.
After encoding, compression, multiplexing and modulation, the program
signals and interactive program signals are distributed by a transmission
means
including, but not limited to, satellite, cable television, fiber optics,
public switched
telephone network, terrestrial broadcast, closed circuit, etc., where the
modulation
technique is defined by the means of transport. Additionally, the distributed
content
may include a signal conversion or retransmission prior to receipt by the end
users.
The programs are received at an end user's location and connected to the
to appropriate reception device. Receptions devices, for example, may include,
but are
not limited to, cable television receivers/converters, satellite receivers,
terrestrial
broadcast receivers, personal computers, etc.. The receiver receives one or
more
television channels, some or all containing a multiplexed data stream of video
signals
or non-multiplexed digital video signals, and in conjunction with a signal
selector,
15 selects a particular data channel/ data stream for playback, then selects a
particular
video signal from the data stream's multiplexed signal, and finally expands
the video
signal, if necessary, for playback to a television monitor.
The signal selector may comprise a controller and software, for example, in a
digital set top box. The controller and software in a digital set top box
operate to
20 control the receiver and signal selector to select a particular digital
video signal.
A user inputs responses preferably via a standard remote device. The user may
be simply changing from one digital channel to another or providing responses
to an
interactive program. In the interactive program embodiment, the user
selectably
responds to information displays or interrogatory messages and the signal
selector
25 selects a particular multiplexed video signal and de-multiplexes, expands
and displays
the selected video signal. Alternatively, the signal selector may select a
video signal
based on personal profile information stored in memory.
If more signals are needed for an interactive program than were mappable to a
data stream on a single channel, the signal selector in conjunction with the
receiver is
3o programmed to switch between the various video signals within a multiplexed
data
stream as well as between data streams among the various broadcast channels to
provide the necessary level of interactivity.
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The various information segments in the various video signals preferably
relate in real-time and content so that an interactive conversation can occur
as the
video signal is played back and the user responds to the various
interrogatories on the
video signals. The use of multiple signals per channel may be used for many
types of
interactive programs, including those disclosed in the previously mentioned
U.S.
Patents, for example, field synchronized multiple camera angles from a
sporting
event, or an interactive game show. However, the present invention also covers
the
use of various video signals not related in real-time and content.
In a two-way embodiment, the various signals which comprise the interactive
program may be switched at the head end rather than at the receiver. This
embodiment may be used in a cable television system, a direct broadcast
satellite
system, a conventional telephone system modified to receive digital video
signals, or
any other appropriate transmission system capable of sending digital video
signals.
The multiple choice control unit, rather than the hand-held multiple choice
controller,
selects a desired video signal by relaying the multiple choice selections of
the user
through a relay box back to a remotely located switching station, preferably
the cable
television source. The multiple choice selections may be relayed to the
switching
station in any conventional means, such as two-way cable television,
telephone, or FM
transmission. If the interactive programming is being transmitted over a
telephone
line, the multiple choice selections may be relayed back over the same
telephone line.
The switching station receives the multiple choice selection of the user and
routes the
correct signal down the appropriate cable channel, telephone line, or other
transmission media for the particular user. In such an arrangement, only a
single link
is required between the subscriber or receiver and the head end so that the
one channel
link can be used to receive a plurality of different channel selections
dependent on the
interactive choice relayed from the receiver to the video switch at the head
end.
If desired, the two-way link may be used for other purposes, such as to
transmit user demographic data back to the programming source for commercial
reasons, or to allow an interactive game show player to win prizes, for
example.
3o Once a signal is demodulated, the digital data stream is demultiplexed into
its
constituent elements such as video, audio graphics and data. The demultiplexed
digital data stream is directed to the appropriate decode devices, i.e., video
to video
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decoder, audio to audio decoder, graphics to display driver and control data
to
applications software. .
In the interactive program embodiments, the application software reads the
data and processes the scripting language. Further, the interactive
application
software processes input from the end user. Based upon a combination of
inputs, it
then decides upon the appropriate action. The viewing experience is then
enhanced,
based upon the individualization of the content by switching among the video,
audio,
graphical and data elements.
The system of the present invention allows improved performance during
l0 switching, making the channel switches transparent. Virtual channel
applications for
enhanced programming and addressable advertising will need to enable frequent
switching among multiple MPEG video streams. When a channel change is required
by a user response to an interactive interlude, a slight imperceptible delay
is
programmed to allow the expansion algorithm an opportunity to adjust to the
rapid
15 change from one video signal to another.
During the delay, previously obtained video information is displayed while the
interactive system locates, receives, demultiplexes, decompresses, decodes,
and
processes the new video signal. This allows the interactive system to switch
to the
new video signal without flicker or distortion appearing on the TV screen,
i.e., a
2p seamless switch.
Disclosed are different methods to achieve this seamless switching. One
involves an analog video frame buffer. Another uses two tuners. Other
alternatives
include: (a) using two digital video buffers; (b) using a large memory; (c)
using a
large buffer in an embodiment similar to that of (b); and (d) switching at the
cable
25 headend.
The present invention includes a preferred improved method and system for
seamless switching between MPEG compressed digital signals in a digital set
top,
HDTV or personal computer environment. While the MPEG standard discusses the
use of splice points, such points are difficult to insert in video streams
that come from
30 different sources, which is the typical cable television environment. This
is because
streams that have been compressed at separate times may have different clocks
and
therefore different timing information. By making some modifications on the
encode
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process for the virtual channel applications, novel enhancements can be made
to
splicing. Such enhancement s of the present invention include locking the time
bases
of the multiple channel encoders, genlocking the video sources, time
synchronizing
the start of the encode process, and inserting splice points at the
appropriate locations
in the GOP. The present invention utilizing these constraints and others for
various
virtual channel applications has the significant advantage of requiring
virtually no w
hardware changes to most conventional digital set top converters.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a block diagram of the Interactive Television System of the
1o present invention.
FIGURE 2 is a block diagram of the system of the present invention in a two-
way transmission configuration.
FIGURE 3 is a block diagram of one embodiment to achieve seamless
switching between video signals.
FIGURE 4 is a block diagram showing an alternative embodiment to achieve
seamless switching between video signals.
FIGURE 5 is a block diagram of an embodiment of a central programming
location.
FIGURE 6 is a block diagram showing video splice points and time gaps in
the video programming streams.
FIGURE 7 is block diagram of an alternative embodiment of a reception box.
FIGURE 8 is a block diagram of alternative audio frames.
FIGURE 9 is a block diagram of a TV broadcast station switcher.
FIGURE 10 is a block diagram of an embodiment for Non-related Program
Switching.
FIGURE 11 is a block diagram of an embodiment for Switching within
Multiple Event Programming.
FIGURE 12 is a block diagram of an embodiment for Seamless Picture-in-
Picture Program Switching.
FIGURE 13 is a block diagram of an embodiment for Switching within
Multiple Commerce/Shopping Programming.
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FIGURE 14 is a block diagram of an embodiment for Digital Program
- Insertion - Addressable Advertising.
FIGURE 15 is a block diagram of an embodiment for Seamless Switching
from a Group of Signals to Other Signals at a Server.
FIGURES 16A and 16B are block diagrams of an alternative Two-Tuner
Embodiment.
FIGURE 17 is a block diagram of an alternative Two-Tuner Embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
to The present invention is an interactive television system in which a
plurality of
viewers are simultaneously provided with a plurality of different program
information
message signals. A plurality of video signals 1 are provided. Video signals 1
may be,
for example, various field and/or audio synchronized camera angles of a
sporting
event, or a game show having a content and host acting responsively to user
15 selections. Alternatively, video signals 1 may be any video signals
suitable for
interactive conversation, such as those described in U.S. Patent Nos.
4,847,700,
3,947,972, 4,602,279, 4,264,925, or 4,264,924, the contents of which are
incorporated
specifically herein by reference. Various types of time and content related
video
signals exist which are suitable for interactive operation.
2o In previous systems, these various signals would be transmitted to a
receiver
on separate broadcast or cable channels, each requiring a separate 6 MHZ NTSC
channel. According to the present invention, video signals 1 are directed to
analog-to-
digital ("A/D") convertors 2 which convert the various video signals into
digital
format for transmission. AID convertors 2 may be of any conventional type for
25 converting analog signals to digital format. An A/D convertor may not be
needed for
each video signal 1, but rather fewer convertors, or even a single convertor
are
capable of digitizing various video signals 1. Interactive video programs may
also be
delivered to a cable or other distribution network in pre-digitized and/or
precompressed format.
30 Digital conversion results in very large amounts of data. It may therefore
be
desirable to reduce the amount of data to be sent, allowing more signals to be
sent
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over a single transmission channel. For example, a single frame of digitized
NTSC
video represents over 350 Kbytes of data. Therefore, two hours of standard
video is
about 80 Gbytes. Since there are 30 frames/sec in such video, the data
transfer rate is
22 Mbytes/sec. This large amount of data is preferably reduced by digital
compression.
In order to reduce the data transfer requirements, the various digital video
signals are preferably compressed before transmission. The video may be
compressed
by any conventional compression algorithm, the two most common types being
"processor intensive" and "memory intensive."
The processor intensive approach performs compression by eliminating non-
changing aspects of a picture from the processing in the frame-to-frame
transfer of
information, and through other manipulations of picture information involving
mathematical computations that determine the degree to which a given motion in
a
picture is perceptible to the human eye. This approach depends on high-speed
processing power at the transmission point.
The memory approach involves division of a picture frame into hundreds of
minuscule blocks of pixels, where each block is given a code representing its
set of
colors and variations in luminance. The code, which is a much smaller
increment of
information than all the information that would describe a given block of the
picture,
is transmitted to the receiver. There, it calls up the identically coded block
from a
library of blocks stored in the memory of the receiver.
Thus, the bit stream represents a much smaller portion of the picture
information in this approach. This system is generally limited by the variety
of
picture blocks which may be stored in the receiver, which relates directly to
memory
size and microprocessor power.
Examples of commonly known compression techniques which may be used
with the invention are JPEG, MPEGl and MPEG2.
Data Compressors 3 are provided to reduce the data for each video signal
which must be transmitted. Data compressors 3 may be of any conventional type
commonly known in the art for compressing video images, such as those
previously
described. Compression of the various video signals might be done with fewer
data
compressors 3 than one compressor per video signal. In a conventional analog
NTSC
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system, by way of example, it is customary to transmit one video signal per 6
MHZ
channel. By digitizing the video signal. it is possible to. send a data stream
containing
more than one video signal in one channel. Compressing the digitized signals,
allows
even more video signals to be transmitted over a single transmission channel.
The
number of signals which may be sent over a single channel is generally related
to, for
example, a) the type of video being sent; b) the video compression scheme in
use; c)
the processor used and memory power; and d) the bandwidth of the transmission
channel.
Compression techniques exploit the fact that in moving images there is very
to little change from frame-to-frame. Editing out the redundancies between
frames and
coding just the changes allows much higher compression rates. The type of
video
which normally contains a great deal of high-speed movement, such as occurs at
live
sporting events, will, therefore, have the lowest compression rates. Movies,
on the
other hand, which normally have a lower frame rate and less frame-to-frame
change
15 than a live sporting event will achieve higher compression rates.
Currently,
commonly known compression schemes have compression rates that vary from 2:1
to
10:1 for satellites, and 2:1 to 5:1 for cable television systems, depending on
the degree
of motion.
Once the various video signals 1 have been digitized and compressed,
20 multiplexer 4 combines the various digital signals into a reduced number of
transmission data streams for transmission. For example, if 68 NTSC channels
are
available, and each channel is capable of transmitting either 4 digitized,
compressed
slow moving video signals (e.g. movies) or 2 digitized, compressed, high-speed
video
signals (e.g. sports), then the various NTSC channels should be allocated in a
25 predetermined fashion to maximize the number of simultaneously
transmittable
signals.
As an example, the broadcast frequency corresponding to a first NTSC
channel may contain a data stream of separate digitally compressed non-
interactive
movies. On this frequency, the data stream would contain video signals
representing
30 a number of movies. However, the video signals, unlike those of an
interactive
program, are not related in time and content. The frequency corresponding to a
second channel might contain a digital data stream of an interactive sports
program,
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consisting of two multiplexed compressed high-speed video signals that are
preferably
related in time and content. The frequency corresponding to a third channel
might
contain a digital data stream of an interactive movie consisting of four
multiplexed
compressed video signals which are related in time and content. The frequency
corresponding to a fourth channel might contain an analog NTSC signal relating
to
local programming. Therefore, using the invention, four NTSC channels could
contain a channel of multiplexed movies, an interactive sports program, an
interactive
movie, and local programming.
Multiplexer 4 receives the incoming compressed, digitized video signals and
in a predetermined conventional fashion, in conjunction with transmitter 5,
multiplexes the desired video signal onto the desired channels, and transmits
these
signals over the NTSC channels. Certain NTSC channels may contain only one
video
or other signal, in analog or digital form.
As indicated earlier, the number of video signals which may be multiplexed
onto a data stream on a single transmission channel will vary. Also, the
number of
channels which use data streams may vary. The transmission data streams are
transmitted by transmitter 4 via transmission media 6 to a receiving station
7. The
transmitter 4, media 6, and receiver 7 may be any conventional means for
transmitting
digital video signals including broadcast television, cable television, direct
broadcast
satellite, fiber optic, or any other transmission means. Alternatively, the
invention
may be self-contained in a stand-alone system, as explained below.
The transmission means may also be a telephone system transmitting a digital
video data stream. Thus, a multiplexed data stream containing several
broadcast
channels or an interactive program with related video signals may be sent
directly to a
user over a single telephone line. The aforementioned digital transmission
devices
may include means for transmitting analog signals as well.
In one of the preferred embodiments, the digital transmission signal is
transmitted using a cable television system. Receiver 7 receives various NTSC
channels, some or all containing multiplexed or non-multiplexed digital video
signals.
Ordinarily, more than one channel will be transmitted by transmitter 5 and
received by
receiver 7 as in an ordinary cable television system. However, each of the
different
channels may have a data stream containing several digitized video signals
thereon.
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Therefore, receiver 7 preferably operates in conjunction with signal selector
8 to select
a particular NTSC channel for playback, then to select a particular video
signal from
the data stream's multiplexed signal, and finally to uncompress or expand the
compressed video signal, if necessary for playback to monitor 10.
Multiple choice controller 9 operates to control receiver 7 and signal
selector 8
to select a particular video signal for playback. In practice, a user need not
know that
multiple signals per channel are in use. If, for example, 68 channels with 4
signals-
per-channel were in use, controller 9, in conjunction with receiver 7 and
signal
selector 8 might be programmed to represent these channels to the user as
channels 1-
2-72. Monitor 10 may be, for example, a conventional television. Signal
selector 8
preferably includes a conventional de-multiplexer for selecting a particular
video
signal from the data stream on the channel currently being received by
receiver 7.
Signal selector 8 further includes the necessary un-compression or expansion
apparatus corresponding with the compression scheme in use by compressors 3.
In practice, an interactive sporting event program might be transmitted on a 6
MHZ cable television signal using a compression-multiplexing scheme which
allows
two sports video signals (A and B, for example) to be transmitted over a
single NTSC
channel (channel 34, for example). It might be desired to have four video
signals (A-
D, for example) for the particular interactive sporting event. A first video
signal
(signal A) may contain the standard broadcast signal of the game; the second
video
signal (signal B) may contain a close-up view of the game action; a third
video signal
(signal C) may contain a continuously updated replay of game highlights; the
fourth
video signal (signal D) may contain statistical information. These four video
signals
(A-D) may, for example, be multiplexed as follows: video signals A and B
multiplexed onto a data stream transmitted on cable channel 34; video signals
C and
D multiplexed onto data stream transmitted on cable channel 35. Alternatively,
all
four video signals (A-D) could be multiplexed into one data stream carried on
one
frequency channel. These four signals may, however, be mapped by controller 9,
or
signal selector 8, to play as separate channel displays for the user which,
when the
3o viewer makes choices on the multiple choice controller, a seamless switch
occurs
therebetween. Each video signal of this interactive program may include a
label
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which reads, for example, "Full-Screen Action -- Press A: Close-up Action --
Press
B: Replay -- Press C: Statistics -- Press D."
As shown, if more signals were needed for an interactive program than were
mappable to a data stream on a single channel, signal selector 8 in
conjunction with
receiver 7 may be programmed to switch between the various video signals 1 as
well
as the various broadcast channels to provide the necessary level of
interactivity.
However, preferably all the various video signals associated with a particular
interactive program are multiplexed onto a single channel.
Additionally, the signal selector 8 may store information relating to current
and previous user responses. For example, the personal profile of the viewer
or
previous response patterns of the viewer could be stored in memory. This
information
may be used in conjunction with commands transmitted within the video signals,
as
discussed in patent No. 4,602,279, incorporated herein by reference. The
stored
personal profile information and received commands may be used to switch
interactively between data streams and video signals without any additional
response
from the user.
The multiplexed interactive program may be transmitted over a single
telephone line, if desired. In this embodiment, multiple choice controller 9
is
programmed to switch between the various video signals on the single telephone
line.
If additional channels were desired, a two-way configuration is used as
described
below.
The system of the present invention may be utilized in an educational
embodiment. In this embodiment, information is stored on each data stream in a
plurality of reproducible information segments, each of which comprises a
complete
message reproducible by the receiver directly in response to the selection of
the video
signal by signal selector 8 responsive to a user selection on multiple choice
controller
9. Each of the information segments in the various data streams contain
interrogatory
messages with associated multiple choice responses, responsive messages,
informational messages, or combinations thereof.
The various information segments in the various data streams preferably relate
in real-time and content so that an interactive conversation may occur as the
video
signals are displayed and the user responds to the various interrogatories
contained in
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the video signals. As a user answers a particular interrogatory with a
multiple choice
response, the information in the video signal associated with the particular
selection is
displayed by the signal selector 7. The various interrogatories, responsive
messages,
and informational messages may generally be contained in any one, more than
one or
all of the various video signals.
The use of a data stream containing multiple video signals per broadcast ..
channel may be used for many types of interactive programs, such as those
disclosed
in the previously mentioned U.S. patents. Other interactive programs may be
developed which are within the scope of the present invention.
The present invention may also be utilized as a stand-alone system with no
transmission means necessary. In this embodiment, the digitized video signals
that
make up an interactive program are stored in local storage means such as video
tape,
video disk, memory (e.g., RAM, ROM, EPROM, etc.) or in a computer. Preferably,
the digital video signals are multiplexed onto a standard NTSC signal. The
particular
storage means may be connected to any of the interactive boxes disclosed in
Figures
3-5, and described below. The interactive boxes would then be connected to a
television set. Alternatively, the circuitry in Figures 3-5 below could be
implemented
on a board and inserted into a standard personal computer (PC). A separate
microprocessor on the interactive board is not necessary for this
configuration since
the standard PC processor performs the functions of the processor 108 shown in
Figures 3-5.
As shown in FIG. 2, the system of the present invention may be operated in a
two-way configuration. In this mode, the various video signals 1 are processed
as
previously described, being digitized by A/D convertor 2 and compressed by
video
compressors 3. The signals are then routed to a central switching station 14.
In this
embodiment, the switching between the various video signals is accomplished at
the
head end rather than at the receiver. Multiple choice control unit 9 relays
the multiple
choice selections of the user through a relay box I7 back to the remotely
located
switching station 14. The multiple choice selections may be relayed by relay
box I7
to the switching station by any conventional means, such as two-way cable
television,
telephone, or FM transmission. Switching station 14 receives the multiple
choice
selection of the user and routes the desired signal to transmitter 5 which
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conventionally transmits the desired video signal down the appropriate cable
channel
for the particular user. If desired, transmitter S may also transfer
conventional
programming on the cable television channels not being used for interactive
programming. Alternatively, switching station 4 may include multiplexing
equipment
as previously described, and thus operate multiple interactive or
noninteractive
programs over a single television channel.
For example, if it were desired to implement the interactive football game
program as previously described, a single NTSC cable channel may be allocated
for
the program. However, in this instance, the video signals would be present at
the
transmitting end. In response to a signal from wireless controller 9, a signal
is sent by
relay box 7 to the cable TV switching station which routes the desired video
signal to
the requesting viewer. Such a system requires very fast switching equipment,
but can
be implemented using digital imagery.
Alternatively, it may be desirable to transmit the interactive sporting event
over a single telephone line. When the user enters a selection on controller
9, a signal
is sent via the telephone line to the central switching station which routes
the desired
signal of the interactive program over the user's telephone line so that a
single link
handles both the interactive choice being made at the receiver and the
transmission of
that choice, out of a plurality of choices, from the head end where the actual
switching
takes place in response to the interactive selection made at the receiver.
The two-way link between the user and the switching station may be used for
other purposes. For example, demographic data may be transferred from the user
to
the broadcast network for commercial purposes, such as targeted advertising,
billing,
sending a game show winner a winning number for pickup of a prize, or other
commercial or non-commercial purposes.
As previously described, compression systems generally perform less
efficiently when frame-to-frame content includes many changes in pixel content
(e.g.,
during fast motion or scenery changes). The system of the present invention
may be
advantageously programmed to ease the processing burden on the uncompression
program. When a key on the controller is depressed to select a desired signal,
a slight
imperceptible delay may be effectuated if desired. This delay allows the un-
compression or expansion algorithm a short period of time to adjust to the
rapid
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change from one video signal to another which ordinarily causes a degradation
in the
efficiency of the algorithm causing video glitches to appear on the screen
display.
As shown in Figure 7, a two way link (similar to Figure 2) may also be used,
employing virtual channels back to the user. In this embodiment, multiple
video
signals, preferably related in time and synchronous to each other, are present
at a
cable headend 300 on multiple channels A, B, C, . . . N of a video signal bus
250. The
signals may be locally generated or received from a remote location (such as a
sporting arena) by receivers 200, 202, 204, and 206. Alternatively, if the
remotely
received signals are digitally multiplexed onto one channel, a digital
demultiplexer
would replace receivers 200-206 and would demultiplex the signals and place
each
signal on a separate bus channel. The local or remote signals are synchronized
by
sync circuit 208. A number of remote control interactive switches 210, 212,
214, 216,
and 218 are connected to video signal bus 250. The multiple channels on bus
250 are
provided synchronously and simultaneously to the series of remote control
interactive
switches 210, 212, 214, 216, 218. These remote control interactive switches
are
dynamically allocated to users who request access to an interactive program.
Each
switch is connected to a frequency agile modulator 220, 222, 224, 226, 228 to
assign
the switch a virtual channel in order to connect a signal from bus 250 to a
specific
user at a remote site. Each switch is assigned to a single user so the number
of
switches present at the headend is the limiting factor to the number of users
who can
interact simultaneously. If it is assumed that only a portion of the users
will interact
simultaneously, an algorithm is used to determine the optimum number of remote
switches necessary to assure an acceptable percentage of access.
After passing through the frequency agile modulators 220, 222, 224, 226, 228,
the signals from video signal bus 250 progress through the cable (or broadcast
TV)
system 260. The signals may pass through RF feed 262 and amplifier 230. The
user's
set top box 232, 234, 236, containing a frequency agile demodulator, is tuned
to the
frequency of the associated frequency agile modulator 220, 222, 224, 226, 228.
The
decoded signal from the set top box 232, 234, 236 is displayed on television
monitor
10.
When a user desires to interact, the user issues a command on the controller
9.
The command is received by the set top box 232, 234, 236. A user request is
sent
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back down the cable or other transmission system 260 to one of the remote
switches
210, 212, 214, 216, 218. At the appropriate time, based on the user request
and the
algorithm for interactivity which accompanies the program, the remote switch
makes
a cut during a vertical blanking interval from one signal on bus 250 to
another signal
on bus 250. The result of this switch is modulated by one of the frequency
agile
modulators 220, 222, 224, 226, 228 and sent down the virtual channel to the
user, who
sees a seamless cut from one image to the other as a result of the
interaction. The
signal delivered to the user may be full bandwidth or compressed video.
Likewise the
video signal on the bus 250 delivering the simultaneous signal to the multiple
remote
switches 210, 212, 214, 216, 218 may be compressed video. This embodiment
allows
for a relatively low cost remote user box because the most costly switching
equipment
is located at the headend and each remote switch may be allocated to any user.
Therefore, the cost is spread over the larger population of users.
As an example, it is assumed that the signal received by receiver 206 is
placed
on bus line 270 of the video signal bus 250 and is forwarded to set top box
236 and
displayed on monitor 10. At some point the set top box 236 causes a user
request to
be generated. The user request is based on a current or past entry on
controller 9
and/or information stored in set top box 236 (e.g., information stored could
be
previous user response information or personal profile information). The cable
TV
system 260 may amplify the user request at amplifier 230 while carrying the
user
request back to frequency agile modulator 226, which communicates the request
to
remote switch 216. During the vertical blanking interval, the remote switch
216
disconnects from old bus line 270 and switches to the appropriate line on the
video
signal bus 250, in this example line 280, based on the user request. This is
shown by
the dotted-line connection at 290. The signal from the new connection
(received by
receiver 204) is sent through the frequency agile modulator 226 on channel 47
and the
cable TV system 260 to the user's set top box 236. The new signal is
seamlessly
displayed on television monitor 10, without any switching occurring at set top
box
236.
As alternatives to the cable headend 300 and cable TV 260 of Figure 7, a
telephone central office and/or telephone lines may be used. This alternative
would
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allow the set tops 232, 234, 236 to receive interactive programming from a
telephone
company or cable headend via telephonic communication.
Figures 3, 4, 7, 16 and 17 show preferred embodiments of the receiver 7 and
signal selector 8 of the present invention to enable seamless flicker-free
transparent
switching between the digital video signals on the same channel or different
channels.
These embodiments may be connected to any transmission media or simply
connected ...
to the output of any stand-alone storage means for the digitized multiplexed
interactive program. Preferably, the receiver 7 and signal selector 8 are both
components of an interactive program box 11, which connects to a television or
other
display monitor. Alternatively, the required functionality of the RF receiver
7, signal
selector 8 and monitor could all be combined in a standard personal computer
by the
addition of a few components to the personal computer. To provide this
capability,
only an RF demodulator board, digital demultiplexer, decompressor(s), frame
buffer(s), and sync components need to be added to the personal computer.
These
items, and any other components, may be connected to the PC processor and
storage
elements as disclosed in Figures 3, 4, 7, 16 and 17. In this embodiment, the
user
makes selections via the computer keyboard.
Figure 3 shows an embodiment with a single analog frame buffer. Figure 4
includes pairs of RF demodulators, error correctors, and demultiplexers and/or
a pair
of digital video buffers, as described below.
Figure 3 shows an embodiment which allows for a seamless video switch
between two or more separate digital video signals. As shown in Figure 3, a
microprocessor 108 is connected to RF demodulator 102 and digital
demultiplexer
106. The microprocessor 108 directs demodulation and demultiplexing of the
proper
channel and data stream to obtain the correct video signal. The proper channel
is
determined either by examination of the user's input from user interface 130
and/or
any other information or criteria (such as personal profile information)
stored in
RAM/ROM 120. For example, the RAM/ROM 120 could store commands provided
within the video signals as discussed in patent No. 4,602,279, and
incorporated herein
3o by reference. The user interface 130 may be an infrared, wireless, or wired
receiver
that receives information from multiple choice control unit 9.
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The RF demodulator 102 is part of the receiver 7, and demodulates data from
the broadcast channel directed by the microprocessor 108. After the data
stream is
demodulated, it passes through a forward error correction circuit 104 into a
digital
demultiplexer 106. The demultiplexer 106 is controlled by microprocessor 108
to
provide specific video, audio and data signal out of a number of video; audio
and data
signals located within the data stream and steer them to the appropriate
device for use ..
within the system. In order to seamless splice from one video stream to the
other it is
preferred to perform the switch in the digitally compressed domain thereby
eliminating the need to decode two video audio and data streams at the same
time.
When the compressed digital video is sent to the video decode function it is
first stored in memory 160 until there is enough information buffered to
ensure
continuous playback of the video stream. Because of the compressed nature of
the
video information, a relatively small buffer 160 can hold a significant amount
of video
information (on the average of five to six frames). This means that there is a
significant delay from the time the compressed video is received to the time
it is
decompressed and played out. Therefore, the preferred method for switching in
the
set top would be to select the new video on the way into the video buffer 160
while
continuing to play out the old video to the monitor. Because the incoming
stream has
been created by producing syntactically correct MPEG segments that are
sliceable,
2o this can be achieved easily. By this method there is no need for additional
hardware
in the receiver. A video always appears to the viewer to be a single video
stream with
no repeated or dropped frames.
MPEG allows for the reconstruction of the video clock at the receiver 11
through use of a data field called the PCR (Program Clock Reference). This is
necessary to ensure that the decoder can play out the decoded video at the
same rate as
it was input to avoid dropping or repeating frames. Additional embedded
information
in the MPEG stream includes the PTS (presentation time stamp) and DTS Display
Time Stamp. These signals are used to maintain lip synchronization with the
audio
and also to inform the receiver when to present the video and audio to the
display.
Figure 4 shows an alternate, dual tuner embodiment for seamless switching
between separate video signals. In this embodiment, the microprocessor 108
controls
the selection of the RF channel that is demodulated by RF demodulators 102A,
102B.
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The demodulated data streams enter the forward error correctors 104A, 1048. At
the
output of the forward error correctors, the data streams are transmitted to
the input of
the digital demultiplexers 106A, 1068.
As with the RF demodulators 102A, 1028, the digital demultiplexers 106A,
1068 are controlled by the microprocessor 108. This configuration allows the
microprocessor 108 to independently select two different individual time-
multiplexed
video signals on different channels and data streams. If all the video signals
of an
interactive program were contained on a single channel or data stream, it
would only
be necessary to have a single RF demodulator, forward error corrector, and
digital
demultiplexer serially connected and feeding into the two digital video
buffers.
Two data streams are provided from the digital demultiplexers 106A and
1068. The output of the demultiplexers contain a multiplicity of video, audio
and
data that can now be directed to the appropriate device under microprocessor
108
control. In this way it is no longer necessary to have all of the information
contained
in one RF channel. Instead the information can be found at different
frequencies in
the RF spectrum and we will still be able to splice among the streams. By
placing a
simply digital switch at the output of the two demultiplexers we can avoid
duplicating
the entire decode chain. It should be noted that this is only a cost saving
approach and
duplication of the rest of the chain would work as well.
A standard MPEG stream contains different types of encoded frames. There
are I frames {Intracoded), P frames (Predicated) and B frames (Bi-
directionally
predicted). A standard MPEG structure is known as a GOP (group of pictures).
GOP's usually start with I frames and can end with P or B frames. There is
generally
only one I frame per GOP, but many P and B frames. While it is not necessary
to
have any I frames, they are useful for many reasons.
GOP's that end with B frames are considered open. GOP's that end with P
frames are considered closed. For the present invention, preferable code is
closed
GOP's to ensure that there are no motion vectors pointing to frames that are
outside of
the current GOP.
MPEG also reorders the video frames from their original display order during
the encode process in order to code the video more efficiently. This reorder
must be
undone in the decoder in order for the video to present properly.
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Frame Order I 2 3 4 5 6 7 8 9 10 I1 12 13 14 15 16 17 18 19 20
Frame Type I B B P B B P B B P I B B P B B P B B P
Typical
Frame Reorder 1 4 2 3 7 5 6 10 8 9 11 14 I 2 I 3 17 15 16 20 18 19
Transmission
Order
Frame Type I P B B P B B P B B I P B B P B B P B B
GOP1 GOP2
Splices occur at the end of the B frame at the end of GOP1 prior to the I
frame
of GOP2. It is important to point out that with appropriate controls the
encoder can
code with variable GOP length and place splice frames accurately to achieve
the
desire interactive effect. If the content is unrelated then the encoder can
splice at the
end of every GOP allowing for a multiplicity of switching opportunities.
Because the
GOP ends on a P frame, a closed GOP is yielded.
Improved Seamless Switching in a Digital System
Any of the above-described reception unit embodiments can be used to handle
the seamless switching of the present invention. In the preferred embodiment,
however, seamless video switching at the reception units is enhanced through
certain
novel modifications to the encoding process.
As set forth above, seamless switching between digital video signals; whether
representing independent television programs or different related signals
within one
interactive program, is critical to the viewing experience. Seamless switching
is
defined as video stream switching that does not produce visible artifacts. The
effect
of the encoding process is to simplify and enhance the seamless switching
process.
The encoding process is performed at a central location, the elements of which
are shown in Figure 5. As seen in Figure 5, a plurality of video signals 300
are shown
which could comprise live or prerecorded video streams. The origin of the
video
signals could be from cameras for live video, video servers, video tape decks,
DVD,
satellite feed, etc. The video signals can be in MPEG format, HDTV, PAL, etc..
A
plurality of audio signals 308 may originate from CD, tape, microphones, etc..
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The data codes, shown emanating from the data code computer 316 in Figure
5, are the interactive commands for interactive processing used by the set top
converter, as discussed above. Preferably, the data codes are part of an
interactive
scripting language, such as the ACTV scripting language, originating in a
coding
computer 316. The data codes are also forwarded to the encoder 312. These data
codes facilitate the multiple interactive programming options at the reception
units.
This embodiment requires a data channel for enabling a synchronous switch
between
a first video stream and a second video stream. This data channel comprises
the codes
which link together the different program elements and information segments on
the
different video signals.
Referring again to the video signals 300, the plurality of video signals 300
are
genlocked in the video genlock device 304 and thus, time synchronized. The
time
synchronized video signals are directed into the video and audio encoder 312.
In the.
preferred embodiment, compatible encoders 312 are required at the cable
headend to
work with the digital reception units at the remote sites. The interactive
applications
of the current invention are preferably facilitated by synchronizing the
commands at
the headend to a specific video frame and a specific audio frame. This level
of
synchronization is achievable within the syntax of the MPEG-2, 4 or 7
specifications.
In order to facilitate the seamless switch at the reception sites, the video
encoders 312 are preferably time synchronized. This synchronized start is
necessary
to ensure that the splice points that have been placed in the video content
occur at the
correct frame number. While it is not necessary to obtain this level of
accuracy for all
program types, it is achievable in this manner. This provides content
producers with
the ability to plan video switch occurrences on a frame boundary within the
resolution
of the Group of Pictures (GOP). SMPTE time code or Vertical Time Code (VTC)
information can be used to synchronize the encoders 312. Additionally, a
splice can
be placed accurately at any frame by utilizing the variable length GOP. Upon
command from an external controlling device such as the ACTV command code
computer 316, the encoder 312 can be directed to insert a splice at an frame
number.
3o Making encoder modifications at the headend ensures more effective seamless
switching at the set top converters.
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As shown in Figure 5, multiple video signals 300, data codes 316 and audio
signals 308 are input into the encoder 312. In the preferred embodiment, four
video
channels are input into the encoder 312. However, more or less video streams
may be
input based on the content that is to be delivered. In the current
environment,
practical limitations for the number of videos are based on picture quality.
Ultimately, however, there will he no limit to the number of videos and audios
that
can be contained within a single channel. Further, all current limitations can
be
removed through the use of the alternate embodiment that describes a two tuner
implementation.
1o Preferably, the encoder 312 uses a standard MPEG-2 compression format.
However, MPEG-4 and MPEG-7 as well as other compression formats, such as
wavletts and fractles could be utilized for compression. These techniques are
compatible with the existing ATSC and DVB standards for digital video systems.
Certain modifications, however, are made to the MPEG stream in order to
facilitate
the preferred seamless switching at the set top box. These modifications to
the
encoding scheme are described below with reference to the video frame
structure 332
shown in Figure 6.
Switches at the remote reception sites will occur at the video splice point
336.
Program switching is facilitated through the provision of splice points. The
splice
points are identified within the program stream via the adaptation field data.
Program
switching occurs at these points based on user inputs, personal profile
information
stored in memory at either the set top converter or the headend, and commands
from
the program source.
With respect to creation of the video splice point 336, the video encoder
inserts splice points at every Group of Pictures (GOP), as shown in Figure 6.
A GOP
consists of generally one I frame and a series of P and B frames, based on
parameters
set within the MPEG scheme. Preferably, the GOP is encoded as a "closed" GOP
structure, which means that the GOP concludes on a P frame. Therefore, no
motion
vectors to the next GOP are present. If motion vectors cross from one GOP to
the
next GOP, artifacts are created and visible when the screen is switched. Thus,
a
closed GOP structure is necessary for compliance with MPEG syntax and to
ensure
the absence of visible artifacts after execution of the splice.
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The GOP length is programmable and can be within 1 to infinite frames of
video. It is preferred, however, that the GOP comprise 10-15 video frames.
Referring
to Figure 6, four video signals are shown. It is desired that a seamless
switch be made
from any video signal to any other video signal.
As shown in Figure 6, seamless video switching occurs on a GOP video-frame
boundary. For pre-recorded material, splice points need to be identified for
switch ...
points. For programming where "free" channel selection is required (e.g.,
sports), all
GOP boundaries are encoded as splice points. While the switch must appear
seamless, it need not occur immediately. For example, a command or key input
1o requires a finite time for processing. Therefore, a video switch may be
delayed by up
to 1.5 GOP's.
As shown in Figure 6, splices take advantage of the non real time nature of
MPEG data during transmission through the digital channel to create a time gap
340
in which the decoder can be switched from decoding one stream to decoding the
other
during the gap 340. Thus, the gaps 340 shown in Figure 6 represent the switch
times.
The key is that the most complex video is completed and through the channel
before
the first packet of the next GOP is through the channel. By encoding at a
lower bit
rate than the channel capacity, some extra time is created at the end of the
GOP in
order to switch. In this way, two MPEG streams are merged to create a single
2o syntactical correct MPEG data stream. These gaps can be created at the
encoder 312,
shown in Figure 5, using any compression scheme.
The audio signals, preferably, are encoded using the AC3 format. The present
invention, however, covers any conventional audio encoding scheme.
All of the various video, audio and data signals are digitized and combined in
the encoder 312, in Figure 5. Preferably, the compressed and encoded signal is
output
in DS3, Digital High Speed Expansion Interface (DHEI) or any other
conventional
format. The data type is not important, it is just data. The encode process
then
outputs a digital data stream at the appropriate bit rate for the target
channel.
The modulator 320 may utilize one of several different possible modulation
schemes. Preferably, 64-QAM is chosen as the modulation scheme. If so, the
data
rate at the output of the modulator 320 is around 29.26 Mbps. However, any of
the
following modulation schemes, with respective approximate data rates, or any
other
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conventional modulation scheme (such as FSK, n-PSK, etc.) can be used with the
present invention.
Modulation Scheme Rate
64-QAM 29.96 Mbps
256-QAM 40 Mbps
8 VSB 19.3 Mbps
64 QAM PAL 42 Mbps ...
256 QAM PAL 56 Mbps
Separate NTSC channels are then combined in a conventional combiner,
preferably using frequency modulation. Thus, seamless switching at the set top
converters can occur from one signal to another within one NTSC channel or
from
one NTSC channel to another NTSC channel, as discussed below.
In summary, seamless switching at the decoder is facilitated at the encoder
312
by time synchronizing the signals, time locking the encoders and creating a
time
gap 340 to each of the digital video streams (which represents the difference
between
the encode rate and the channel capacity) to GOPs, defined below.
After encoding, modulation and multiplexing, the signals can be transmitted to
reception sites via satellite, wireless, land line, broadcast, or any other
conventional
transmission system. In the preferred embodiment, the signals are distributed
to
remote sites via cable or other transmission media.
Reception Sites
At the reception sites, preferably consisting of the elements shown in Figure
7,
the signal is received via a tuner mechanism 344. The tuner 344 may be a wide
band
tuner, in the case of satellite distribution, a narrow band tuner for standard
MPEG
signals, or two or more tuners for seamlessly switching between different
signals
located in different frequency channels, as explained below. In the case of
MPEG
signals, the tuner 344 tunes to the particular NTSC channel indicated from
command
by the host processor 360. The host processor 360 is preferably a Motorola
68331
processor, but may be any conventional processor including PowerPC, Intel
Pentium,
etc.
The signal is then forwarded to the demodulator 364. The demodulor 364
demodulates the combined signal, strips off the FEC and forwards the digital
signals
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to the video and audio decoder 372. At the digital decoder 372, the signals
are
separated and decompressed. The decoder 372 strips off the program
identification
number (P1D), and routes these PlDs to the appropriate decoder, whether video,
data,
audio or graphics. The audio is preferably forwarded to the Dolby digital
processing
IC 380. The selected video and audio is then decoded, as explained below, and
the
video is sent to the video digital-to-analog (D/A) converter 388 which
prepares the ...
selected video for display.
A phase lock loop (PLL) recovers the encode clock, which was encoded in the
PCR portion of the MPEG adaptation field. Preferably, a ROM holds the
operating
t0 system for the reception unit 342 and is backed up with Flash-ROM to allow
for
downloadable code. Further, there are memory devices connected to the
decoders 372, 380 and graphic chip 376, which are used to store graphics
overlays, for
example. Furthermore, profile data for various users in the home can be stored
in
nonvolatile RAM or ROM 352.
A backchannel encoder and modulator 368 are present for sending data back to
the headend. Such data may comprise personal profile information, interactive
selections, demographic data for targeted advertising purposes, game show
scores, etc.
Further, the reception unit 342 permits new software applications to be
downloaded to the unit. These applications can control the unit and redefine
the
functionality of the units within the constraints of the hardware. Such
control can be
quite extensive, including control of the front-panel display, the on-screen
display, all
input and output ports, the MPEG Decoder, the RF tuner, graphics chip and the
mapping of the IR remote functions.
Preferably, the interactive programming technology, including providing for
multiple camera angles, individualized advertising, etc., of the present
invention is
implemented as a software application within the reception unit 342. Such
technology
is preferably located within ROM or Flash-ROM 352 of the reception unit, shown
in
Figure 7. The interactive technology, however, could alternatively be located
in any
type of memory device including RAM, EPROM, EEPROM, PROM, etc.. As such,
3o the software shall have access and control over the hardware elements of
the device.
In the preferred embodiment, no additional hardware is required for full use
of the
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interactive programming technology within the reception unit 342 to achieve
the
performance described above.
Any type of conventional remote control device 348 can be used with the
present invention. It is preferred, however, that the remote control device
348 be an
infrared (IR) device and include four or more option buttons and their
associated IR
codes. ..
Seamless video switching at the reception unit 342 is explained in the
paragraphs below. The reception unit 342 shown in Figure 7 preferably is
capable of
real-time MPEG-2, MPEG-4 or MPEG-7 decoding. The reception unit 342 monitors
user interactions and information transmitted from the program source and
seamlessly
switches video and audio streams as appropriate.
Based upon the viewer's responses and requests, the unit automatically and
seamlessly switches between video, graphics and audio programming sequences
reflecting the viewer's earlier responses. The interactive technology of the
present
invention permits a high level of interactivity while not requiring the set
top unit 342
to transmit any information back to the programming source.
In the video decoder 372, shown in Figure 7, the header data is stripped off
the
MPEG stream. The particular video is then selected based on a command from the
host processor 360. The associated audio is sent to the audio decoder portion
380.
The selected video is buffered in a standard video buffer and then output for
decoding.
The physical buffer size is defined by the MPEG standard, herein incorporated
by
reference. Enough time must be allowed at the initial onset of decoding to
fill up the
buffer with I-frame and other data.
After buffering, the selected video goes through various steps of an MPEG
decode process, which utilizes a variable length decode (VLD) preferably.
Generally,
the variable length decode converts the run-length encoded datastream and
converts it
into its longer bitstream format. The bitstrearn is decoded into its
constituent parts i.e.
motion vectors, dct coefficents and the like so that the video can be
reconstructed.
Subsequently, the datastream is converted into frequency domain information
using an
3o inverse Discrete Code Transform DCT filter. If the frames are intercoded,
the pixel
data is generated and stored in a buffer.
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Referring to Figure 7, the seamless switch from one to another MPEG video
stream is explained. Switches will occur on video splice points, as shown in
Figure 6.
When the demux/decoder 372 in Figure 7 sees the splice point, it switches to
the
selected video signal which is sent to the buffer. Thus, prior to the switch,
the first
video signal frames are still being buffered. The next signal PID is loaded
into the
decoder 372 from the host processor 360. In order to accomplish a switch to
one of ...
the four video streams, the video decoder 372, shown in Figure 7, must
identify the
PID number of the new video stream. Further, it is preferred that each
incoming
video and audio stream shall have its own PID, known to the interactive
application
stored in memory at the set top converter 342, in order to facilitate seamless
switching
among the independent video and audio streams. It must then call the routine
that
performs the switch. This next PID, identifying the next selected video
signal, can be
based on either user selection or by way of the interactive control codes or
both. Once
the next PID is loaded, the decoder 372 begins to look for the selected video
stream
and, because of the gap 340 created in the video datastream, the decoder 372
will
always find the header information of the next video. Once the splice point
indicator
of the first video is seen by the decoder 372 and the second video signal is
identified
by the decoder 372, the second compressed video signal begins to load into the
buffer
as the first video signal continues to plays out. The new video signal is
selected based
on either user selection or based on an interactive control code.
One of the items necessary for a seamless switch is the splice point counter
and a splice point flag. Both of these indicators are placed in the adaptation
field of
the MPEG video streams. The splice point counter indicates the number of video
packets prior to the splice point. The splice point flag indicates that the
splice count is
present in the stream. Once the decoder 372 determines the splice point, it
can begin
buffering the next video stream and continue decompressing the signal as if it
were
one MPEG stream.
Audio Switching
As with the video streams, preferably four AC-3 audio streams, each of which
is identified by a unique PID, exist per service. P117 numbers are obtained
from the
MPEG-2 transport table such as SI, PG, and PM at the invocation of the
interactive
service. One of these PIDs is selected as the default audio channel and is
selected
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upon acquisition of a service. The remaining three channels are optional and
shall be
selected by the Control Program based on Control Messages and/or User Input.
While
audio channels normally switch with the associated video channel, they may
also be
switched independently.
In the preferred embodiment, switching occurs on frame boundaries, as shown
in the digital frame representation 392 of four audio streams of Figure 8.
When .,.
switching from one channel to another, one frame may be dropped (in this case,
frame
5), and the audio resumes with frame 6 of the new channel. The audio decoder
380 is
capable of audio switching by provision of the insert of audio splice points
at the
l0 encoder 312, shown in Figure 5. Preferably, the encoder 312 inserts an
appropriate
value in the splice countdown slot of the adaptation field of the current
audio frame.
When the audio decoder 380 detects this splice point the decoder 380 may
switch audio channels. Although the audio splice is not seamless, the switch
will be
nearly imperceptible to the user.
Data Commands
Because the data commands are time sensitive in the digital embodiments,
they are sent from the headend via a command data PID (Packet Identification).
The
commands must be synchronized with video GOP's at the encoder end. In order to
accomplish this, the data codes computer 316, shown in Figure 5, must send
individual commands as a whole packet. Each command can consist of as few as
two
bytes. Therefore, the generator must pad the rest of the packet with code FF
(hex)
bytes. When this whole packet is sent to the encoder 312, the encoder 312 will
transmit it at its earliest convenience. If a partial packet is sent to the
encoder 312, the
encoder 312 does not send the command until subsequent commands filled the
remainder of the packet.
The commands, as identified in ( 1 ) ACTV Coding Language, Educational
Command Set, Version 1.1, and (2) ACTV Coding Language, Entertainment
Command Extensions, Version 2.0, both of which are herein incorporated by
reference, are formed by stringing together two to six byte long commands. The
command data is presented to the encoder's ISO interface and packet stuffed to
ensure
timely transmittal of the command data.
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The Control Program is preferably stored in RAM 352. The processor 360
receives instructions from the Control Program. Further, key inputs such as
user
responses, personal profile information as well as control messages are used
by the
processor 360 in making switching decisions.
Preferably, the Control Program operates in five modes as determined by the
received interactive command messages. The five modes are as follows: ...
~ Switch Audio and/or Video Based on User Input
~ Switch Audio based on User Input and stored data
~ Switch Audio and/or Video based on User Input and stored data
to ~ Switch Audio and/or Video based on Control Messages
~ Switch Audio and/or Video based on Control Messages and stored
previous input.
Multiple modes may be used by the Program simultaneously.
The first mode above, switch audio and video channels, is the simplest mode
of operation. The Control Program is commanded by the microprocessor 360 to
accept one of the four Remote input key codes and to switch to the
corresponding
audio/video channel. The Program performs this switch on the video frame
boundary
at the end of the current GOP. Once the new channel is displayed, the Program
has
the capability to update the On-screen display with new text and/or graphics
messages
either received in the datastream from the headend or stored locally.
The second mode above, Display One Video Channel and Switch Audio
Channels, continuously displays a single video channel. When a remote input
key
code is received, the video continues but the audio channel is switched on the
appropriate audio frame boundary. As mentioned above, the appropriate audio
frame
2S boundary is determined by examining the splice point counter value in the
adaptation
field. The choice made by the user is stored in a RAM register. Any time a
choice is
made by the user, the key code and the previously stored choices are reviewed
by the
Program to determine the next audio channel.
The third mode identified above, Switch Audio/Video Channels Based on
User and Previous Choices, displays an initial audio/video channel. When
commanded by the Command Message stream, text is displayed on the On-Screen
display. The Program then waits for a user input. When the user input is
received, it
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is stored in a RAM register along with previous user choices. The register is
examined by the Program and then, based on stored logic, determines the next
audio/video channel to be displayed.
The fourth mode identified above, Switch Audio/Video Channels Based on
Control Messages, also displays an initial audio/video channel. The Program
then
waits for a control input from the Control Message stream. Based on this
input, the ...
Program switches channels on the video frame boundary at the end of the
current
GOP.
The fifth mode above, Switch Based on Control Messages and Previous
Choices, displays an initial audio/video channel. The Program then waits for a
control
input from the Control Message stream. When the Control Message input is
received,
it is stored in a RAM register along with the previous user and control
message
choices. This register is then examined by the Program to determine the next
audio/video channel to be displayed.
Di ital Video Systems and Applications
The following paragraphs disclose several applications using the digital
embodiments disclosed above in Figures 1-8 and the two tuner embodiments,
described below, of Figures 16 and 17.
TV Broadcast Station Switching
In this embodiment 412, the seamless switch from one signal to another signal
is done at a TV broadcast control center and forwarded to the users' digital
reception
sets 408, as shown in Figure 9. At the headend 396, several digital programs
are
combined according to any of the methods explained above.
Upon receipt of the programs by the broadcast station, the signals are fed
into
a digital stream selector 400. This selector comprises the elements discussed
above in
any of the alternative embodiments for performing a seamless switch (Figure 1-
4, 7,
15-17), except for the fact that this unit is not located at the remote sites.
The unit
works in the same manner as discussed above. Regardless of whether the digital
stream selector 400 selects amongst multiplexed signals in one datastream on
one
channel, centered on a certain frequency, or between signals in different
datastreams,
or from a received signal to a locally inserted ad, all such switches are
seamless in the
embodiment shown in Figure 9. As discussed above, selections can be made as a
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function of station prerogative, remote user selections and/or personal
profile
information (transmitted to the TV station via a backchannel), or targeted
advertising.
Once a selection is made the program signal is transmitted by any
conventional means 404 to the remote sites 408 for presentation.
Non-related Program Switching
Figure 10 discloses an embodiment 430 for switching between non-related ...
programs. In other, words, this is simply switching from one TV channel to the
next
TV channel. Presently, switching from one signal to another cannot be
accomplished
without flicker in the digital environment.
In the present invention, a viewer may switch from one program to another
program, whether related or unrelated, and the transition will be seamless. In
other
words, there will be no visible artifacts present in switching from one
program to
another program.
If the programs are compressed and multiplexed within one MPEG stream,
any of the embodiments disclosed herein are capable of performing the seamless
switch. If the programs are in separate NTSC channels, one of the digital "two
tuner"
embodiments (Figures 4, 16 and 17) must be used to allow for the frequency
shift.
The high level elements of the system 430 for non-related program switching
are shown in Figure 10. Preferably, the non-related programming is compressed
and
multiplexed using an MPEG stream into one datastream using one NTSC channel at
a
video encoder chassis 416. Non-related programming can be combined into one
MPEG stream or can be in directed into different NTSC channels. For example,
programming may consists of sports, news, sitcom or children's programming.
These
programs are modulated at a modulator/upconverter 420 and transmitted across
any
suitable transmission means 429 as discussed above.
End users are capable of viewing digital programming on either a digital
monitor/tuner, a personal computer or through an external converter 428,
connected to
an analog television set, in which case the seamless switch is performed in
the
converter. Either of these various components allows a user to "surf' channels
based
on a viewer's preferences. Again, the reception unit can be selected from any
of the
alternatives explained in Figures 1-4, 7, 15-17.
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Seamless Switchin;~ within Multiple Event Pro rg amming
In this application, shown in Figure 11, a system 450 is provided for allowing
a user to switch between separate events within a single program. For example,
an
Olympics broadcast may simultaneously comprise several programs corresponding
to
different events, e.g. skiing, speed skating, figure skating, ski jumping etc.
Preferably,
these separate event programs are compressed and multiplexed into one MPEG
digital ..
stream at the video encoder chassis 434, passes through the
modulator/upconverter 438 and transmitted as a single NTSC signal via the
transmission means 442. These event programs, however, may also be encoded at
the
broadcast center onto separate NTSC channels.
After modulation and subsequent transmission, these programs are received at
the remote sites 446. The remote sites 446 include a reception unit, which
contains
either a digital monitor/tuner, a personal computer, or a external digital
converter
connected to a monitor. The user may select between the different programming
events via his or her remote control device. When the user desires to switch
to
another event program, the switch will be performed seamlessly according to
any of
the methods and systems discussed above (Figures 1-4, 7, 15-17).
Seamless Picture-in-Picture Pro,g_ram Switching
Figure 12 discloses an embodiment 470 for switching between preferably non-
related programs using "picture-in-picture". Regardless of whether the user is
switching between programs in the small framed display or the large framed
display,
all such switches are seamless with the present invention.
In the present invention, a viewer may switch from one program to another
program in either of the two displayed windows. In other words, there will be
no
visible artifacts present in switching from one program to another program.
The high level elements of the system for picture-in-picture program
switching 470 are shown in Figure 12. Preferably, four to seven programs are
compressed and multiplexed into an MPEG stream into one datastream on one NTSC
channel at the video encoder chassis 454. Other programs are combined into
other
3o MPEG datastreams at the video encoder chassis 454. For example, programming
may
consists of sports, news, sitcom or children's programming. These programs are
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modulated and transmitted across any suitable transmission means 462, as
discussed
above.
End users are capable of viewing digital prograrriming on either a digital
monitor/tuner, a personal computer or through an external converter 466,
connected to
an analog television set, in which case the seamless switch is performed in
the
converter. The embodiment and flow disclosed in Figure 12 allows a user to
invoke ,..
the picture-in-picture feature and seamlessly switch between different
programs
within a single MPEG stream. If switching from one MPEG multiplexed stream to
another is desired, the converter, PC or digital monitor/tuner 466 will
require the
employment of a multiple tuner/decoder, examples of which is shown in Figures
4, 16
and 17.
Switching within Multiple Commerce/Shoppin Pro ramming
One application of the current invention involves a transaction based system
with return paths, as shown in Figure 13. As with the other embodiments
discussed
above, the video encoder 474 compresses and multiplexes several different
programs
onto one or more NTSC channels for transmission to the remote sites.
Preferably, several different types of shopping programs are compressed and
multiplexed onto a single NTSC channel. For example, separate programs may be
directed at clothes, jewelry, housewares, etc. If more programs are necessary
than
2o allowable on a single NTSC channel, more than one NTSC channel may be
utilized
by the present invention.
The programs are transmitted to the end user reception units 486, as shown in
Figure I3, over any suitable transmission means 482. At the reception units
486, the
user can seamlessly switch between different product genres. Alternatively,
the
reception unit 486 can switch to certain product programming based on personal
profile or demographic information. In this manner, only those products which
most
closely match or suit a particular individual's interests and desires will be
presented to
the user. Such data can be stored in either storage in the reception unit 486
or at the
headend.
If the user determines that he or she would like to purchase or receive
additional information regarding a product, the backchannel 490, such as that
shown
in Figure I0, can be used to transmit such requests back to the central
location.
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Digital Program Insertion - Addressable Advertising
Figure 14 discloses an embodiment 526 for providing digital program
insertion. At certain predetermined times during the programming, certain
advertisements are displayed to the viewer. In the preferred embodiment,
advertisements are individualized to the particular viewer based on personal
profile
information or demographic information. Such targeted advertising is described
in
the following paragraphs.
At the central location, a plurality of advertisements is inserted into the
programming stream. Preferably, the central location uses a hybrid digital
insertion
system for insertion of the advertisements into the programming. Hybrid
digital
equipment replaces the tape decks of the analog system with computers, disk
drives
and decoder cards, as set forth in the CableLabs Cable Advertising White
Paper,
herein incorporated by reference. The advertising content 506 may originate
from any
one of a number of possible sources, including, but not limited to, server,
tape decks,
satellite feed. For storage, preferably the spots are digitally encoded and
compressed
in an off line process, using MPEG1, MPEG1.5, MPEG2, or a proprietary method.
Distribution from the encoder to the server and to the playback systems can be
done
through a network or by disk or tape.
After encoding, the spots are distributed to a server for storage until
required
2o for playback. Preferably, a spot can be played directly from the server to
a decoder
card, for conversion back to analog. The spot is converted to analog, then
sent
through the insertion switcher in the conventional manner. The output video
and
audio would then be forwarded to the audio and video encoder shown in the
central
site configuration in Figure 5, after which the spots are digitally encoded
and
compressed as described in the paragraphs above, with reference to Figure 5.
Although not as efficient as digital advertising insertion, the actual
switching
of the advertising into the programming can also be accomplished with
conventional
advertising insertion systems, using analog or tape based systems.
The placement and display of advertisements into the programming stream are
controlled through the use of signaling and addressability command insertion
498.
Personalized advertising can be effectuated by addressing certain
advertisements for
certain viewers. For example, a certain car company wants to individualize its
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commercial to best meet the needs and desires of the viewer. If it is known
that a
particular user is male and enjoys outdoor activities, the programmer may want
to
show the advertisement corresponding to the Car Company's Sports Utility
Vehicle as
opposed to a small economy car. The advertisements can be pushed to the end
user
based on data stored at the remote end user unit or in the stream addressed to
the end
users device via the set-top controller in the provider's headend.
Preferably, several advertising options are encoded according to the manner
described above with reference to Figure 5. Because the advertising spot
videos are
genlocked and time synched at the encoder 510, switching from the main
1o programming to one of the advertisements will appear seamless to the
viewer.
Seamless Switching from a Group of Signals to another Group of Signals at a
Server
In another embodiment of the present invention. the process of switching
among live and served video content is described. As opposed to switching from
a
single digital signal to another single digital signal at the remote reception
units, this
embodiment allows for a seamless transition from one group of signals to
another
group of signals. It is necessary that the transition take place in a manner
such that the
output bitstream is continuous and correct to the MPEG syntax. Proper
switching
ensures that any standard MPEG decoder plays the resulting bitstream as if it
were a
stream with no errors.
The preferred embodiment 530 for performing this switch is shown in Figure
15. The elements of Figure 15 are located at a cable headend or alternatively,
at a
centralized op center for a satellite distribution network. For purposes of
explanation,
a group of live signals are denoted as the Group A signals and the Group B
signals are
presumed to be stored prerecorded signals, preferably stored at the server
550. For
example, the Group A signals may comprise several videos representing
different
camera angles at a sporting event. The Group B signals may represent a series
of
commercials. It is understood, however, that both the Group A and/or Group B
signals could represent either prerecorded or live signals.
In this embodiment, it is desired to switch from the Group A signals to the
Group B signals. The Group A signals are received at the server 550 from a
real time
encoder 546, located either locally or at a remote site. A specialized MPEG
digital
packet is inserted into the Group A content stream on a specific channel. The
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Command and Control terminal 534 provides an analog tone in the video signals
prior
to analog-to-digital conversion. Once the signals reach the Real Time Encoder
546
from the Command and Control terminal 534, the Real 'Time Encoder 546 inserts
a
digital tone at the appropriate point in the Group A digital stream upon
detection of
the analog tone. Once the tone is inserted, the Group A digital stream is
output from
the Real Time Encoder 546 and forwarded to the Server 550 at the headend. Once
received at the server, the Group A stream is forwarded to an MPEG transport
switch
device in the server 550. The Control Terminal 538 sends a command to the MPEG
transport server switch device to cause the switch to begin looking for the
inserted
l0 digital tone.
In order to play back the Group B content, the server switch device must
decode timing information from the Group A digital stream and subsequently,
restamp
the Group B content with the appropriate timing signals from Group A.
Preferably,
this is accomplished by genlocking to the PCR's videostream, preferably the
same
stream with the digital tone embedded therein, and stripping out the program
clock
reference (PCR) out of the videostream to recreate the encode clock of the
original
Group A content. At this point, the switch device has the ability to re-insert
the
timing information into the Group B content to prepare it for playout.
Upon detection of the digital tone, the server switch device initiates a
transition to the Group B digital stream, comprised of the Group B prerecorded
signals. Preferably, the server switch device has prior knowledge of the
length of the
Group B content and, therefore, when the server switch device senses the end
of the
Group B content, it switches back to the Group A content. The resulting
digital
stream output from the server to the transmitter comprises both Group A and
Group B
content. The transmitter 554 forwards the digital data stream to the remote
reception
sites, as previously described.
In this manner, at certain times during the presentation of a sporting event,
represented via the plurality of live digital video signals (i.e., the Group A
content),
for example, the received videostream at the receive converter units will
automatically
3o transition to the Group B prerecorded content based on the action by the
server switch
device, for example. The decoder at the reception sites then selects one of
the
advertisements in the Group B content, as previously described. At the end of
the
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advertisements, the decoder automatically begins receiving the Group A content
again
and selects one of the live signals, as previously described. In this manner,
a seamless
switch from live encoded video content to prerecorded content is effectuated
at the
server.
Two Tuner Embodiments for Seamless Switching
Digital Stream to Digital Stream Switch .,.
A two tuner embodiment 558 for providing seamless switching from a digital
signal located in one frequency channel (hereinafter, "Channel A") to another
digital
signal located in another frequency channel (hereinafter, "Channel B") is
shown in
Figures 16A and 16B.
As shown in Figures 16A and 16B, this embodiment comprises two
tuners 560A, 560B (for tuning to separate frequency channels), a
microprocessor 564
(for selecting the frequency channels and digital signals embedded therein),
digital
demodulators 568A, 568B (for demodulating the signals from the carrier), a
digital
demux/decoder 572 (for stripping out the selected audio, video and data of the
selected content from the composite digital stream) and a display processor
576 (for
formatting the video signal for display).
This embodiment operates to switch from one digital data stream in Channel A
to another digital data stream in channel B as follows. A first tuner 560A is
tuned to
Channel A and is receiving a composite digital stream, preferably comprising a
plurality of digital video, audio and/or data signals, in the associated
frequency
channel. The composite digital stream is passed from the first tuner 560A to a
digital
demodulator 568A. The type of demodulation can be any of those conventionally
known in the art, such as those described above.
The composite digital stream is then directed to the input of the digital
demux/decoder 572, wherein the selected audio and video signals are stripped
from
the composite digital stream in a demux 573 and forwarded to the audio and
video
decoders 575, 574, respectively. Those signals are then decompressed and
decoded
based on the signal encoding scheme, preferably one of the MPEG schemes. Once
decoded, the audio and video (and/or data, if appropriate) are forwarded to
the display
processor 576 and subsequently to the monitor.
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Once a decision is made to switch to another digital signal in frequency
Channel B, the microprocessor 564 sends a command to the second tuner 560B to
pretune to the Channel B frequency. The composite digital stream in Channel B
is
passed through the digital demodulator 5688 and forwarded to the digital
demux/decoder 572. At this time, the digital demultiplexer 572 receives both
the
digital streams located on Channel A and Channel B. Thus, if both Channel A
and .--
Channel B carried four digital signals, the demultiplexer 572 receives eight
digital
signals. The digital demultiplexer 572 receives a command from the
microprocessor 564 indicating which of the digital signals to strip out from
the
composite digital stream from Channel B. Separately, the digital demultiplexer
572
strips out the selected video and audio (and/or data) signals from the
composite digital
streams from Channel's A and B. The selected signals are forwarded to the
video and
audio decoders 574, 575. The video decoder 574 switches from the currently
displayed video signal to the newly selected video signal as described above
with
reference to Figures 6 and 7. Therefore, the decoder 574 identifies the splice
point in
the present stream. Once the decoder 574 detects the splice point, it
determines that it
is the appropriate time to switch to the second stream. The decoder 574 begins
loading the second stream into the buffer and a seamless switch is effectuated
because
of the time gap in the first stream. Once the second stream is output from the
decoder,
it is forwarded to the display processor 576, where the video signal is
formatted for
display.
The audio decoder 575 performs the switch from the present audio stream to
the second audio stream, in the same manner as described above with reference
to
Figure 11. Once the switch is completed, the second audio stream is forwarded
to the
display processor 576.
Switch from Analog Signals to Digital Si;~nals or Di i~tal Si nals to Analog-
SJ~nals
A two tuner embodiment 590 for switching from an analog signal located in a
first RF channel to a digitally compressed signal in a second RF channel or
vis versa
is shown in Figure 17. In this embodiment, a viewer is watching a particular
channel,
whether it be an analog or digital signal, in one specific RF frequency and
there is a
decision made to switch to another channel, whether it be analog or digital,
in a
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different RF frequency. Two tuners 560A, 560B are used to transition from one
RF
frequency to a different RF frequency.
Assuming by way of example that the viewer is currently watching a channel
(Channel A) with an analog signal and the decision is made to switch to a
digitally
compressed signal in a different channel (Channel B), the embodiment of Figure
17
operates as follows. With respect to the analog signal, one of the tuners 560A
tunes to ...
the RF frequency associated with Channel A. Because the channel carries an
analog
signal, the tuner 560A directs the signal to the analog demodulator 569A and
VBI
decoder 570A. The analog demodulator 569A demodulates the analog signal using
any conventional analog demodulation scheme known in the art. The VBI
decoder 570A strips out any information (e.g., interactive commands, close
captioning) embedded in the vertical blanking interval {VBI). The demodulated
analog signal is then forwarded to the analog display processor 580, which
formats the
analog signal, and then outputs it to the VBI switch 588 and then display
device.
If a decision is made to switch to a channel containing muxed and compressed
digital signals, the microprocessor 564 determines the RF frequency location
of this
channel and forwards the information in a command to the second tuner 560B.
Upon
receipt of the command, the second tuner 560B pre-tunes to the indicated
second RF
frequency (Channel B). The output of the Channel B is forwarded to the input
of the
digital demodulator 568B, which demodulates the signal using any of the
digital
demodulation schemes known in the ari. The digital data stream is output from
the
demodulator 568B and received at the digital demux/decoder 572. The
microprocessor 564 sends a command to the digital demux/decoder S72 indicating
the
selected digital signal. The digital demux/decoder 572 demultiplexes the
plurality of
digital signals and decompresses such signals. The resulting selected
constituent parts
{audio, video and data) are then forwarded to the appropriate decoders 574,
575 (see
Fig. 16B), as described above with reference to Figure 16, whereby the video
decoder 574 begins to decode the video information and sends a signal to the
microprocessor 564 signaling that the stream was properly decoded and that the
audio
3o was in lip synchronization.
The video and audio signals are then forwarded to the digital display
processor 584, wherein the signals are converted from digital to analog. The
resultant
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analog signals corresponding to Channel B are then input into the VBI switch
588.
Upon command from the microprocessor 564 to switch the two videos, the VBI
switch 588 switches during the appropriate time during the vertical blanking
interval,
resulting in a switch from the analog to the digital channel.
If it is desired to switch from a digital channel to an analog channel, the
process identified above is simply reversed and the second tuner 560B pre-
tunes to the ._
analog channel. Further, the embodiment shown in Figure 17 can switch from
analog
to analog channels.
Although the present invention has been described in detail with respect to
to certain embodiments and examples, variations and modifications exist which
are
within the scope of the present invention as defined in the following claims.
41
