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Description  |
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TECHNICAL FIELD
The invention relates to the transmission and distribution of video
programming and more particularly to a method and apparatus for rapid
channel selection and for providing fast forward, reverse and channel
pause functions when receiving digital video programming.
BACKGROUND ART
In recent years considerable attention has been focused on systems for
providing wide arrays of video programming to subscribers. A number of
commentaries have suggested that future systems will provide 500 channels
of video information into each subscriber's home. The trend in development
of video distribution, as in many communications industries, is toward all
digital transmissions. In particular, a number of systems have recently
been proposed for distributing video information in compressed, digital
data form.
U.S. Pat. No. 5,247,347 to Litteral et al., the disclosure of which is
herein incorporated in its entirety by reference, discloses an enhanced
public switched telephone network which also provides a video on demand
service using compressed digital data transmissions.
One network has been proposed for the distribution of compressed, digitized
broadband information, including video information, to subscribers. That
network utilizes optical fiber to connect information sources and
subscribers to a broadband ATM switch. The fiber carries a standardized
transport stream such as a SONET OC-12 transport stream. The techniques
disclosed herein apply to other networks as well, such as ones in which
QAM, ADSL, digital cross connect and multiple carrier transport mechanisms
are used. An adaptive digital multiplexer/demultiplexer permits unused
digital capacity on an optical fiber to be allotted to other video
sources. A gateway, called a level 1 gateway, manages the establishment of
connections between subscribers and the information sources. A digital
entertainment terminal at the subscriber's location provides all necessary
user functions for the use of the network.
The transmission of programming, in particular, video programming where
wide bandwidth is required, has been known to include a variety of
compression techniques. Modern decoders of compressed video information
will adapt their operating modes in dependence upon the properties of the
incoming signal. It is also often the case that video programming is
distributed in multiplexed format which requires that either the decoder
or an associated demultiplexer be aware of where in the multiplexed stream
particular programs are located.
One of the widely accepted standards for the distribution of video
programming is that promulgated by the Organisation Internationale de
Normalisation (International Organization for Standardization) under
Standard ISO/IEC JTC1/SC29/WG11 entitled "Coding of Moving Pictures and
Associated Audio". The particular working group responsible for that
standardization effort is also known as the Motion Picture Experts Group
(MPEG).
MPEG compression and decompression standards have been evolving. The
current advanced version is generally known as MPEG-2. The MPEG-2 standard
is hereby incorporated by reference in its entirety. In the language of
the MPEG-2 standard, a "program" comprises video source material and audio
source material which share a common time base. One or more elementary
digital streams representing the source material (e.g. video or audio), as
well as other data, are combined into single or multiple streams suitable
for storage or transmission. System coding follows the syntactical and
semantic rules imposed by the MPEG-2 specification and provides
information to enable synchronized decoding without either overflow or
underflow of decoder buffers over a wide range of retrieval or receipt
conditions.
Under the MPEG-2 standard, an incoming individual video signal and related
audio signal are encoded and packetized into video packetized elementary
stream (PES) and audio packetized elementary stream, respectively. The
video and audio PES from one or more programs are combined into a
transport stream for transmission or storage.
The transport stream is designed for use in environments where errors are
likely, such as storage or transmission in lossy or noisy media. Transport
stream packets are 188 bytes in length. Transport stream packets are
generally divided into two sections. The first section constitutes header
information and the second constitutes payload. Header information
includes, among other information, a synchronization byte, transport
scrambling control and a thirteen bit program identification (PID)
indication. PID value 0 is reserved as an indication that the packet
includes program association table data. PID value 1 is reserved for
conditional access such as encryption. PID value 0x1FFF is reserved for
administrative (no-op) packets utilized for synchronizing the link. Other
program identification numbers are utilized to identify transport packets
with the program source from which they originate.
FIG. 1 depicts a transport stream utilizing the MPEG-2 standard. As
indicated above, each transport packet in the transport stream carries a
program identification number (PID). Packets identified by PID 0 carry
program association table information. As illustrated in FIG. 1, a program
association table maps a particular program source with PID values
assigned to packets associated with that source. Thus, the program
association table defines PID identification of program maps for each
source of programming in the transport stream. As illustrated, the program
map for CBS is found in packets labeled PID 132; the program map for NBC
is found in packets labeled PID 87 and so forth.
The program map for CBS illustrated in FIG. 1 as that associated with PID
132 identifies the PID numbers for the packetized elementary streams (PES)
for the video and audio channels associated with the particular program.
One should note at this time that more than two PID's may be associated
with a program. For example, there could be a data channel associated with
the program which would include data for closed captioning for the hearing
impaired. There could be a number of audio elementary streams for, for
example, carrying respective different languages. Thus the programming map
provides some flexibility beyond that required for merely associating a
single video and audio elementary streams.
Once the program map is known, the program decoder can be set to extract
the desired elementary streams (e.g. PID 56 in FIG. 1 and PID 74 shown in
FIG. 1) for decoding and presentation. Transport packets of PID=56
represents the video elementary stream associated with CBS' MPEG video
system. Within CBS' video elementary stream are video sequence headers
which define things like frame rate and resolution. After the video header
sequence, the normal video syntax occurs which, in the case of MPEG,
includes the normal frames associated with video compression such as I
frames, B frames and P frames used in MPEG.
The elementary stream with, for example, PID=74 is the audio stream
associated with the video shown in transport packets, such as those, for
example, with PID=56 as defined in program map at PID=132.
A typical MPEG-2 transport demultiplexer and decoder is shown in FIG. 2.
The data link specific interface 210 converts the incoming data link
format (e.g. optical fiber encoded data) to a form (e.g. electrical) for
demultiplexing and decoding. Transport stream demultiplexer 220 monitors
the PID's of the incoming transport stream packets to identify those
selected for decoding and routes those to respective video (230) and audio
(240) decoders. Since the video and audio associated with the same program
are derived from a common clock, clock control 250 drives both decoders.
Note that the transport stream demultiplexer includes functionality, such
as that described in connection with the description of the transport
stream of FIG. 1, necessary to identify the particular PID's needed to
extract information from the transport stream to present the desired
program to the user.
In the distribution of video programming, and particularly in the context
of video on demand, which can allow subscribers access to a large number
of channels of video information, it may be desirable to provide a number
of channels, each carrying the same program but with delayed start times.
This is illustrated functionally in FIG. 3 in which a program source would
presumably play one video repeatedly which could be transmitted over one
channel undelayed and over subsequent channels delayed by incremental
amounts from the start time of the first channel so that, at any one time,
a number of channels carries the same program delayed by differing
amounts. The transport stream will additionally include a plurality of
broadcast channels. The subscriber will select from those channels
available.
Referring again to FIG. 1, when a subscriber tunes, for example, to CBS for
the first time, before decoding can take place, a program association
table and the program map for the selected channel must be received in the
stated order from the transport stream. Thereafter, a packet from the
video elementary stream must arrive with header information about the
frame rate, and resolution for display of the image and the like before
the decoder can be set up to actually decode the payload data associated
with the video elementary stream. This process takes a relatively great
deal of time even in the high-speed world of digital video transmission.
The process must be repeated each time a new channel is selected. As a
result, if a subscriber switches channels quickly (channel surfing), in an
attempt to glimpse what is on each channel, the set-up time for each
channel can be significant and the process of moving from channel to
channel likely becomes much slower than a user would find acceptable. One
way around this problem is to repeat header information often, but this
results in a loss of bandwidth which would reduce the quality of the
resultant image.
This delay problem existing in modern video compression systems also exists
with respect to encryption. When a particular video program is encrypted,
the encryption key is sent only infrequently. When first tuning to an
encrypted program source, the subscriber would necessarily need to wait
for the encryption key to be downloaded, assuming he is authorized, before
decoding of the picture could begin. As a result, the speed at which
channels can be changed is further inhibited.
In the distribution of video programming, it is desirable to provide the
user with VCR-like functionality, including fast forward, fast reverse and
channel pause features. Provision of these features is difficult if one
program source is being provided to a number of users in a broadcast-like
function, when using a digital transport stream like the ones previously
described. An individual subscriber cannot affect the playback, for
example, without affecting the playback for all subscribers currently
tuned to that program.
DISCLOSURE OF THE INVENTION
Accordingly, an object of the invention is to provide fast user channel
change capability for a compressed digital data input stream.
Another object of the invention is to receive encrypted programming from a
multichannel digital stream without delay.
Yet another object of the invention is to obtain VCR-like functionality
with a received compressed digital data input stream.
The above objects and other objects of the invention are satisfied, at
least in part, by providing a channel decoder for selecting and decoding
one of a plurality of programs, such as video programs, from a transport
stream of digital data, such as an MPEG-2 transport stream. Programs have
properties which may vary from program source to program source such as
resolution and frame rate. For example, movies typically are shown at 24
frames per second whereas live video is shown at 30 frames per second.
Although frame rate and resolution are expressly mentioned, the invention
encompasses any encoded variable parameter(s) of the MPEG syntax or of
other syntax necessary to recover the encoded video.
The objects recited above and other objects of the invention are achieved
by providing a channel decoder for decoding one of a plurality of programs
which have properties such as resolution and frame rate which may vary
from program to program and from time to time. A user activates a
selection mechanism such as a remote unit for selecting a program. Once
selected, at least one elementary stream of the program is provided for
decoding. A parameter monitor and store identifies and stores at least one
property of each program selected. An elementary steam decoder decodes an
elementary stream into output data in accordance with the properties
stored by the parameter monitor and store for the particular program
associated with the elementary stream. Thus, when a program is selected,
the elementary stream decoder is initialized with stored information about
the program.
User activated program selection can occur by using a transport stream
demultiplexer which selects one program from a transport stream containing
a plurality of programs or it can occur by using circuit switching for
selecting one program from a plurality of programs available over a
switched network.
The types of properties which can be the object of detection and storage
include but are not limited to: (1) the location of one or more program
elementary streams within the transport stream and (2) control parameters
for the decoder such as frame rate, resolution or encryption key.
The invention is also directed to a method of permitting rapid channel
change in a system having a channel decoder for selecting and decoding one
of a plurality of programs. The representation of each program has
properties which may vary from program to program and from time to time,
and that information is detected and stored and the channel decoder is
initialized with the stored information about one particular program when
that program is selected.
The invention is also directed to apparatus for providing special functions
such as fast forward, fast reverse and program pause for a user receiving
a particular program in a system providing a plurality of programs. At
least one group of programs of said plurality of programs contains
different versions of the same program source material, the versions
having staggered starting times (i.e. one offset by a respective number of
time delay increments from a first program of said group). A memory
contains a data structure having information identifying how to access
each program of said group and contains a pointer to the program of said
group which should be decoded for presentation to said user. A user
indicates desired program selection activates special functions using
conventional apparatus such as a remote control or panel switches. When a
user indicates that the user requires a special function the pointer is
changed to point to a program with a different starting time.
When the special function indicated is that of fast forward, the pointer is
changed to point to a program starting earlier than the program pointed to
when said indication was received.
When the special function indicated is that of fast reverse, the pointer is
changed to point to a program starting later than the program pointed to
when said indication was received.
When the special function indicated is that of program pause, when a first
pause indication is received, a pause time stamp of the last block of data
received prior to receipt of said pause indication is stored. When a
second pause indication is received, the pointer is changed to point to
the first later starting program of the group which has a block time stamp
earlier than that stored in response to the first pause indication.
Resumption of display is deferred until the time stamp of the data block
being received equals that of the pause time stamp.
The invention is also directed to a method of providing rapid channel
selection in a digital program distribution system having a channel
decoder in which information about the properties or location of programs
or both is downloaded to the decoder during initialization, and the
operational state of said decoder is set based on that information when a
program is selected.
The invention is also directed to a method of providing fast forward, fast
reverse and channel pause functions in a program distribution system in
which at least one program is distributed in a plurality of versions
having staggered start times in which, at the user location, one of said
versions is selected in dependence on a selected one of said functions;
and the version of the program selected is decoded for presentation to the
user.
Additional objects, advantages and novel features of the invention will be
set forth in part in the description which follows, and in part will
become apparent to those skilled in the art upon examination of the
following or may be learned by practice of the invention. The objects and
advantages of the invention may be realized and attained by means of the
instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 depicts the use of an MPEG-2 transport stream in delivering video
programming.
FIG. 2 depicts a generic MPEG-2 decoder.
FIG. 3 depicts functionally the use of staggered start times for a single
program delivered as separate programs within a program group.
FIG. 4 depicts one embodiment of the invention utilizing monitoring and
storage at a subscriber's location.
FIG. 5 depicts exemplary components of information contained within storage
such as utilized in FIG. 4.
FIG. 6 is a block diagram of a digital entertainment terminal (DET) used in
FIG. 4.
FIG. 7 represents a channel change logic used by the embodiment of FIG. 4.
FIG. 8 depicts an additional embodiment of the invention which utilizes a
program map to distinguish programs of a program group having staggered
start times.
FIG. 9 represents a flow chart of the logic of the fast forward, fast
reverse and channel pause functions.
BEST MODE FOR PRACTICING THE INVENTION
The principles of the invention are applicable to a large number of
implementations. For simplicity of presentation, a CATV distribution model
will be utilized. Such a model is shown in FIG. 4. In a CATV distribution
system, a CATV head end 400 supplies a number of channels of video
programming in an MPEG-2 multiple program transport stream over a
distribution medium 410 such as, for example, coaxial cable, copper line,
fiber optical cable, or wireless transmission. Programming can be derived
from a number of sources. Typical sources illustrated in FIG. 4 include a
satellite down-link 401, a switched video circuit 402 from a video
switching network, a live feed 403 or a video on demand (VOD) server 404.
Individual digital entertainment terminals (DET) are located at each
subscriber's premises. A DET is essentially an intelligent set top box.
The DET may be subject to user infrared remote control in a conventional
manner. The functionality of a DET could, of course, be incorporated into
a TV set instead of being a stand-alone component.
The digital entertainment terminal exemplified in FIG. 4 includes a link
specific interface 421, a transport stream demultiplexer 422, a video
decoder 423, an audio decoder 424 and clock control 425, for
implementation of the generic MPEG-2 decoder shown in FIG. 2. The
transport stream demultiplexer and the video and audio decoders are
constructed to respond and feed information to monitor and storage unit
426.
The monitor and storage unit 426 is illustrated as a part of transport
stream demultiplexer but the functionality could be implemented as part of
other components of the DET or as a stand alone component. Specifically,
the functionality of monitoring and storage could be implemented with
software running on DET microprocessor 660 of FIG. 6.
The monitor and storage unit 426 monitors the incoming transport stream on
an ongoing basis, examining every packet. The latest version of the
program association table (PID=0 of FIG. 1) is extracted and stored for
later use. A data structure suitable for such use is shown in FIG. 5. Also
extracted from the data stream, are the program map information (e.g. PID
131 of FIG. 1), information from video sequence headers of video
elementary streams defining, for example, frame rate, resolution and
information to facilitate set up of the audio decoder. Alternatively, data
entries for a particular program can be updated only when that program is
selected for reception. This approach imposes fewer demands on the CPU
used for implementing the DET.
The monitor and storage unit 426 is capable of being preloaded with
information during an initialization sequence such as might occur during
DET turn on. In one scenario, the DET, upon turn-on (either power-up or
warm start) would send a message to the head end 400 via the signalling
channel (FIG. 6) of the data link specific interface. The head end would
then send a data packet using, for example, a transport packet with the
adaptation field set to 11, for example, and the transport private data
flag set to 1 which would be received by the monitor and storage unit to
store the pre loaded data sent from the head end 400.
The monitoring and storage unit permits rapid channel changing without a
need to wait for the particular transport packets that contain the
information required to set up the transport stream demultiplexer and the
elementary stream decoders.
FIG. 5 depicts one organization of information (i.e., a table) which could
be utilized in conjunction with FIG. 4. Stored table 500 includes program
field 510, program map location field 520, elementary stream location
(PID's) field 530, frame rate field 540, resolution field 550, crypto key
field 560 and locations for additional information. It is only necessary
that one or more of the fields be included to facilitate acceleration of
the switching time between channels by eliminating waiting states while
information is being downloaded. Typically these are fields that affect
the operation of either the transport stream demultiplexer or the
elementary stream decoders.
FIG. 6 depicts an implementation of a digital entertainment terminal at a
functional level. Data link specific interface 610, transport system
demultiplexer 620, MPEG video decoder 630 and MPEG audio decoder 640
correspond generally to the generic MPEG decoder described in conjunction
with FIG. 4. Video RAM 651, graphics overlay controller 652, NTSC encoder
653, mixer 654 and RF modulator 655 perform the usual functions associated
with such devices in a video processing environment. The graphics overlay
controller permits text to be overlaid on top of images and permits the
display of menus required for information about available programming and
selection information. Video RAM 651 is a standard video buffer. NTSC
encoder 653 translates bit mapped video from the video RAM into base band
video using the NTSC raster scan format. RF modulator 655 combines audio
and video signals from the NTSC encoder 653 and the mixer 654 and
translates them to different position in the frequency spectrum, typically
to the frequency of an incoming channel on a standard television set.
Microprocessor 660 controls the DET. System memory 665 shares a bus 690
with the microprocessor 660. System memory is partitioned into
non-volatile random access memory (NVRAM) 666 and random access memory
667. The information discussed in conjunction with FIGS. 4 and 5 is stored
in system memory.
IR receiver and IR transmitter 670A and 670B, respectively, provide an
infrared interface to a standard infrared remote control. The remote
control will send channel selection and channel change signals to the
microprocessor over the IR receiver and optinally receive commands and
display information back from the microprocessor over IR transmitter link
670B. The information transmitted over the infrared link to the DET
includes fast forward, fast reverse and channel pause information. The
microprocessor responds to the information received from the remote
control and implements channel selection and channel change utilizing the
information from the table in system memory to set up the transport system
demultiplexer and the MPEG video and audio decoders in accordance with the
stored parameters, such as those illustrated in FIG. 5. As described more
hereinafter, activation of fast forward, fast reverse or channel pause is
also implemented using information stored in system memory.
RS232 transceiver 681 and PCMCIA port 683 represent traditional data IO
ports. Magnetic card reader 682 permits the use of credit card, debit card
or other types of authorization cards for payment of billing generated
through the digital entertainment terminals linked to the central office.
FIG. 7 illustrates the flow of the logic required to implement the
information storage of FIGS. 4 and 5. The storage can essentially can be
thought of as a type of cache memory which stores the last value sent for
a particular data item if it represents a change from the pervious value.
Cache memory permits values to be retrieved from a convenient storage (in
this case at the DET) without the necessity of going to the source of the
original information (the transport stream).
FIG. 7 depicts channel change logic for effecting programming selection.
Operationally, a channel change indication is detected in block 700. The
channel selected is translated to a specific network channel in block 701.
A decision is made whether the channel selected has been previously
selected at block 702. If it has not, the signal Decode-go is set to false
(703) and the high speed channel is monitored for the headers and sections
needed to decode the program. When these are received, the information is
used to decode the MPEG stream (705). If the channel has been previously
selected, the MPEG decode section is initialized to the last known values
(704) and decoding begins (705). If decoding cannot occur successfully,
the application terminates decoding (706). If decoding is successful, the
incoming MPEG transport stream is examined and classified into one of
three categories (710). The first is a video sequence header which refers
to a PID with program information. The "video sequence header" branch
(711-713) examines the header (711) of video packets containing video data
payload. If the settings contained in the header differ from the last time
a video sequence header was received for that program, the new settings
would be stored in cache (713) and applied to the decoder. Once past the
header, the "video data" payload is decoded (722) if the signal decode-go
is true (721). If there is no disparity between the header information and
the cache settings for the program, decode-go will be true and the payload
video data will be immediately decoded.
The third branch of the MPEG syntax is the "PSI" branch (730-734). PSI
stands for p | | |
