U.S. patent application number 12/342582 was filed with the patent office on 2009-05-14 for providing video streams of a program with different stream type values coded according to the same video coding specification.
Invention is credited to Benjamin Cook, Jeffrey C. Hopper, Arturo Rodriguez.
Application Number | 20090122185 12/342582 |
Document ID | / |
Family ID | 37062182 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090122185 |
Kind Code |
A1 |
Rodriguez; Arturo ; et
al. |
May 14, 2009 |
PROVIDING VIDEO STREAMS OF A PROGRAM WITH DIFFERENT STREAM TYPE
VALUES CODED ACCORDING TO THE SAME VIDEO CODING SPECIFICATION
Abstract
Methods and systems for the efficient and non-redundant
transmission of a single video program in multiple frame rates,
optionally employing a combination of video coding standards, in a
way that is backwards-compatible with legacy receivers only
supportive of some subsection of frame rates or of some subsection
of video coding standards.
Inventors: |
Rodriguez; Arturo;
(Norcross, GA) ; Cook; Benjamin; (Flowery Branch,
GA) ; Hopper; Jeffrey C.; (Decatur, GA) |
Correspondence
Address: |
THOMAS, KAYDEN, HORSTEMEYER & RISLEY;SCIENTIFIC ATLANTA, A CISCO COMPANY
600 GALLERIA PKWY SE, SUITE 1500
ATLANTA
GA
30339-5994
US
|
Family ID: |
37062182 |
Appl. No.: |
12/342582 |
Filed: |
December 23, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11132060 |
May 18, 2005 |
|
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12342582 |
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Current U.S.
Class: |
348/446 ;
348/E7.003 |
Current CPC
Class: |
H04N 21/85406 20130101;
H04N 21/4402 20130101; H04N 21/2365 20130101; H04N 21/235 20130101;
H04N 7/012 20130101; H04N 21/435 20130101; H04N 21/2662 20130101;
H04N 21/234309 20130101; H04N 21/440263 20130101; H04N 21/234363
20130101; H04N 21/25808 20130101; H04N 21/440218 20130101 |
Class at
Publication: |
348/446 ;
348/E07.003 |
International
Class: |
H04N 7/01 20060101
H04N007/01 |
Claims
1. A method, comprising: providing a multiplexed plurality of
streams (MPOS) corresponding to a program, the MPOS comprising a
first video stream and a second video stream each coded according
to a first video specification, wherein the first video stream
comprises a first representation of the program and a combination
of the first and second video streams comprises a second
representation of the program; and providing association
information corresponding to the program, the association
information comprising a plurality of stream associations, wherein
each respective stream association comprises a stream type, wherein
the first video stream corresponds to a first stream type value and
the second video stream corresponds to a second stream type value
different than the first stream type value, wherein the first
stream type value identifies the first video specification as the
coding specification used to encode the first video stream.
2. The method of claim 1, wherein the second stream type value
identifies which video stream of the first video stream and the
second video stream corresponds to the second video stream.
3. The method of claim 2, wherein the second stream type value
further identifies the picture format used to code the second video
stream.
4. The method of claim 2, wherein the second stream type value
further identifies the first video specification as the coding
specification used to encode the second video stream.
5. The method of claim 1, wherein each respective stream
association further comprises a respectively corresponding
identifier for packets of the stream in the MPOS.
6. The method of claim 5, wherein the first video stream is
identified as a video stream via a first packet identifier
association to a first video type and the second video stream is
identified as a video stream via a second packet identifier
association to a stream type not corresponding to a video
stream.
7. The method of claim 5, wherein the first video stream is
identified as a video stream from a first packet identifier
association to the first stream type, and the second video stream
is identified as a video stream via a second packet identifier
association to the second stream type corresponding to a stream
other than a video stream.
8. The method of claim 1, wherein all audio streams of the MPOS are
common to a receiver that processes the first video stream
exclusively and a second receiver that processes the first and
second video stream.
9. The method of claim 1, wherein providing further comprises
providing presentation time stamps corresponding to compressed
pictures in the first and second video streams in reference to a
common clock.
10. An apparatus, comprising: a memory; and one or more processors
configured to: provide a multiplexed plurality of streams (MPOS)
corresponding to a program, the MPOS comprising a first video
stream and a second video stream each coded according to a first
video specification, wherein the first video stream comprises a
first representation of the program and a combination of the first
and second video streams comprises a second representation of the
program; and provide association information corresponding to the
program, the association information comprising a plurality of
stream associations, wherein each respective stream association
comprises a stream type, wherein the first video stream corresponds
to a first stream type value and the second video stream
corresponds to a second stream type value different than the first
stream type value, wherein the first stream type value identifies
the first video specification as the coding specification used to
encode the first video stream.
11. The apparatus of claim 10, wherein the second stream type value
identifies which video stream of the first video stream and the
second video stream corresponds to the second video stream.
12. The apparatus of claim 11, wherein the second stream type value
further identifies the picture format used to code the second video
stream.
13. The apparatus of claim 11, wherein the second stream type value
further identifies the first video specification as the coding
specification used to encode the second video stream.
14. The apparatus of claim 10, wherein each respective stream
association further comprises a respectively corresponding
identifier for packets of the stream in the MPOS.
15. The apparatus of claim 14, wherein the first video stream is
identified as a video stream via a first packet identifier
association to a first video type and the second video stream is
identified as a video stream via a second packet identifier
association to a stream type not corresponding to a video
stream.
16. The apparatus of claim 14, wherein the first video stream is
identified as a video stream from a first packet identifier
association to the first stream type, and the second video stream
is identified as a video stream via a second packet identifier
association to the second stream type corresponding to a stream
other than a video stream.
17. The apparatus of claim 10, wherein the one or more processors
are further configured to provide audio streams of the MPOS,
wherein all of the audio streams are common to a receiver that
processes the first video stream exclusively and a second receiver
that processes the first and second video stream.
18. The apparatus of claim 10, wherein the one or more processors
are further configured to provide presentation time stamps
corresponding to compressed pictures in the first and second video
streams in reference to a common clock.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of copending U.S. utility
application entitled, "Higher Picture Rate HD Encoding and
Transmission with Legacy HD Backward Compatibility," having Ser.
No. 11/132,060, filed May 18, 2005, which is entirely incorporated
herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to digital television and,
more specifically to receivers with different capabilities for
receiving, processing and displaying the same emission of a
compressed video signal, each receiver providing one in a plurality
of picture formats according to its respective capability.
BACKGROUND OF THE INVENTION
[0003] There are many different digital television compressed video
picture formats, some of which are HD. HDTV currently has the
highest digital television spatial resolution available. The
picture formats currently used in HDTV are 1280.times.720 pixels
progressive, 1920.times.1080 pixels interlaced, and 1920.times.1080
pixels progressive. These picture formats are more commonly
referred to as 720P, 1080i and 1080P, respectively. The 1080i
format, which comprises of interlaced pictures, each picture or
frame being two fields, shows 30 frames per second and it is deemed
as the MPEG-2 video format requiring the most severe consumption of
processing resources. The 1080P format shows 60 frames per second,
each frame being a progressive picture, and results in a doubling
of the most severe consumption of processing resources. A receiver
capable of processing a maximum of 1080i-60 is also capable of
processing a maximum 1080P-30. However, broadcasters intend to
introduce 1080P-60 emissions and CE manufacturers intend to provide
HDTVs and HDTV monitors capable of rendering 1080P-60, in the near
future. 1080P-60 includes twice as much picture data as either
1080i-60 or 1080P-30. Dual carrying channels or programs as
1080P-60 and 1080i-60 would not be an acceptable solution because
it triples the channel consumption of a single 1080i-60
transmission.
[0004] Therefore, there is a need for encoding 1080P-60 video for
transmission in a way that facilitates the superior picture quality
benefits of a 1080P-60 signal to 1080P-60 capable receivers while
simultaneously enabling legacy 1080i-60 capable receivers to
fulfill the equivalent of a 1080P-30 signal from the transmitted
1080P-60 signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a high-level block diagram depicting a
non-limiting example of a subscriber television system.
[0006] FIG. 2 is a block diagram of a DHCT in accordance with one
embodiment of the present invention.
[0007] FIG. 3 illustrates program specific information (PSI) of a
program having elementary streams including encoded video streams
which may be combined to form a single video stream encoded as
1080P-60.
[0008] FIG. 4A illustrates first and second video streams in
display order.
[0009] FIG. 4B illustrates pictures according to picture types in
display order.
[0010] FIG. 4C illustrates transmission order of the pictures in
display order of FIG. 2B.
DETAILED DESCRIPTION
[0011] The present invention will be described more fully
hereinafter with reference to the accompanying drawings in which
like numerals represent like elements throughout the several
figures, and in which an exemplary embodiment of the invention is
shown. This invention may, however, be embodied in many different
forms and should not be construed as being limited to the
embodiments set forth herein; rather, the embodiments are provided
so that this disclosure will be thorough and complete, and will
fully convey the scope of the invention to those skilled in the
art. The present invention is described more fully hereinbelow.
[0012] It is noted that "picture" is used throughout this
specification as one from a sequence of pictures that constitutes
video, or digital video, in one of any of a plurality of forms.
Furthermore, in this specification a "frame" means a picture,
either as a full progressive picture or in reference to a whole
instance of a full frame comprising both fields of an interlaced
picture.
[0013] Video Decoder in Receiver
[0014] FIG. 1 is a block diagram depicting a non-limiting example
of a subscriber television system (STS) 100. In this example, the
STS 100 includes a headend 110 and a DHCT 200 that are coupled via
a network 130. The DHCT 200 is typically situated at a User's
residence or place of business and may be a stand-alone unit or
integrated into another device such as, for example, the display
device 140 or a personal computer (not shown). The DHCT 200
receives signals (video, audio and/or other data) including, for
example, MPEG-2 streams, among others, from the headend 110 through
the network 130 and provides any reverse information to the headend
110 through the network 130. The network 130 may be any suitable
means for communicating television services data including, for
example, a cable television network or a satellite television
network, among others. The headend 110 may include one or more
server devices (not shown) for providing video, audio, and textual
data to client devices such as DHCT 200. Television services are
provided via the display device 140 which is typically a television
set. However, the display device 140 may also be any other device
capable of displaying video images including, for example, a
computer monitor.
[0015] FIG. 2 is a block diagram illustrating selected components
of a DHCT 200 in accordance with one embodiment of the present
invention. It will be understood that the DHCT 200 shown in FIG. 2
is merely illustrative and should not be construed as implying any
limitations upon the scope of the preferred embodiments of the
invention. For example, in another embodiment, the DHCT 200 may
have fewer, additional, and/or different components than
illustrated in FIG. 2. A DHCT 200 is typically situated at a user's
residence or place of business and may be a stand alone unit or
integrated into another device such as, for example, a television
set or a personal computer. The DHCT 200 preferably includes a
communications interface 242 for receiving signals (video, audio
and/or other data) from the headend 110 through the network 130
(FIG. 1) and for providing any reverse information to the headend
110.
[0016] DHCT 200 is referred to as a receiver such as receiver 200
throughout this specification. The DHCT 200 further preferably
includes at least one processor 244 for controlling operations of
the DHCT 200, an output system 248 for driving the television
display 140, and a tuner system 245 for tuning to a particular
television channel or frequency and for sending and receiving
various types of data to/from the headend 110. The DHCT 200 may, in
another embodiment, include multiple tuners for receiving
downloaded (or transmitted) data. Tuner system 245 can select from
a plurality of transmission signals provided by the subscriber
television system 100, including a 1080P-60 program. Tuner system
245 enables the DHCT 200 to tune to downstream media and data
transmissions, thereby allowing a user to receive digital media
content such as a 1080P-60 program via the subscriber television
system. The tuner system 245 includes, in one implementation, an
out-of-band tuner for bi-directional quadrature phase shift keying
(QPSK) data communication and a quadrature amplitude modulation
(QAM) tuner (in band) for receiving television signals.
Additionally, a user command interface 246 receives
externally-generated user inputs or commands from an input device
such as, for example, a remote control. User inputs could be
alternatively received via communication port 274.
[0017] The DHCT 200 may include one or more wireless or wired
interfaces, also called communication ports 274, for receiving
and/or transmitting data to other devices. For instance, the DHCT
200 may feature USB (Universal Serial Bus), Ethernet, IEEE-1394,
serial, and/or parallel ports, etc. DHCT 200 may also include an
analog video input port for receiving analog video signals. User
input may be provided via an input device such as, for example, a
hand-held remote control device or a keyboard.
[0018] The DHCT 200 includes signal processing system 214, which
comprises a demodulating system 213 and a transport demultiplexing
and parsing system 215 (herein demultiplexing system) for
processing broadcast media content and/or data. One or more of the
components of the signal processing system 214 can be implemented
with software, a combination of software and hardware, or
preferably in hardware. Demodulating system 213 comprises
functionality for demodulating analog or digital transmission
signals. For instance, demodulating system 213 can demodulate a
digital transmission signal in a carrier frequency that was
modulated, among others, as a QAM-modulated signal. When tuned to a
carrier frequency corresponding to an analog TV signal,
demultiplexing system 215 is bypassed and the demodulated analog TV
signal that is output by demodulating system 213 is instead routed
to analog video decoder 216. Analog video decoder 216 converts the
analog TV signal into a sequence of digitized pictures and their
respective digitized audio. The analog TV decoder 216 and other
analog video signal components may not exist in receivers or DHCTs
that do not process analog video or TV channels.
[0019] A compression engine in the headend processes a sequence of
1080P-60 pictures and associated digitized audio and converts them
into compressed video and audio streams, respectively. The
compressed video and audio streams are produced in accordance with
the syntax and semantics of a designated audio and video coding
method, such as, for example, MPEG-2, so that they can be
interpreted by video decoder 223 and audio decoder 225 for
decompression and reconstruction after transmission of the two
video streams corresponding to the 1080P-60 compressed signal. Each
compressed stream consists of a sequence of data packets containing
a header and a payload. Each header contains a unique packet
identification code, or packet_identifier (PID) as is the casein
MPEG-2 Transport specification, associated with the respective
compressed stream. The compression engine or a multiplexer at the
headend multiplexes the first and second video streams into a
transport stream, such as an MPEG-2 transport stream.
[0020] Video decoder 223 may be capable of decoding a first
compressed video stream encoded according to a first video
specification and a second compressed video stream encoded
according to a second video specification that is different than
the first video specification. Video decoder 223 may comprise of
two different video decoders, each respectively designated to
decode a compressed video stream according to the respective video
specification.
[0021] Parsing capabilities 215 within signal processing 214 allow
for interpretation of sequence and picture headers. The packetized
compressed streams can be output by signal processing 214 and
presented as input to media engine 222 for decompression by video
decoder 223 and audio decoder 225 for subsequent output to the
display device 140 (FIG. 1).
[0022] Demultiplexing system 215 can include MPEG-2 transport
demultiplexing. When tuned to carrier frequencies carrying a
digital transmission signal, demultiplexing system 215 enables the
separation of packets of data, corresponding to the desired video
streams, for further processing. Concurrently, demultiplexing
system 215 precludes further processing of packets in the
multiplexed transport stream that are irrelevant or not desired
such as, for example in a 1080i-60 capable receiver, packets of
data corresponding to the second video stream of the 1080P-60
program.
[0023] The components of signal processing system 214 are
preferably capable of QAM demodulation, forward error correction,
demultiplexing MPEG-2 transport streams, and parsing packetized
elementary streams and elementary streams. The signal processing
system 214 further communicates with processor 244 via interrupt
and messaging capabilities of DHCT 200.
[0024] The components of signal processing system 214 are further
capable of performing PID filtering to reject packetized data
associated with programs or services that are not requested by a
user or unauthorized to DHCT 200, such rejection being performed
according to the PID value of the packetized streams. PID filtering
is performed according to values for the filters under the control
of processor 244. PID filtering allows for one or more desired and
authorized programs and/or services to penetrate into DHCT 200 for
processing and presentation. PID filtering is further effected to
allow one or more desired packetized streams corresponding to a
program (e.g., a 1080P.sub.--60 program) to penetrate DHCT 200 for
processing, while simultaneously rejecting one or more different
packetized stream also corresponding to the same program. Processor
244 determines values for one or more PIDS to allow to penetrate,
or to reject, from received information such as tables carrying PID
values as described later in this specification. In an alternate
embodiment, undesirable video streams of a program are allowed to
penetrate into DHCT 200 but disregarded by video decoder 223.
[0025] A compressed video stream corresponding to a tuned carrier
frequency carrying a digital transmission signal can be output as a
transport stream by signal processing 214 and presented as input
for storage in storage device 273 via interface 275. The packetized
compressed streams can be also output by signal processing system
214 and presented as input to media engine 222 for decompression by
the video decoder 223 and audio decoder 225.
[0026] One having ordinary skill in the art will appreciate that
signal processing system 214 may include other components not
shown, including memory, decryptors, samplers, digitizers (e.g.
analog-to-digital converters), and multiplexers, among others.
Further, other embodiments will be understood, by those having
ordinary skill in the art, to be within the scope of the preferred
embodiments of the present invention. For example, analog signals
(e.g., NTSC) may bypass one or more elements of the signal
processing system 214 and may be forwarded directly to the output
system 248. Outputs presented at corresponding next-stage inputs
for the aforementioned signal processing flow may be connected via
accessible memory 252 in which an outputting device stores the
output data and from which an inputting device retrieves it.
Outputting and inputting devices may include analog video decoder
216, media engine 222, signal processing system 214, and components
or sub-components thereof. It will be understood by those having
ordinary skill in the art that components of signal processing
system 214 can be spatially located in different areas of the DHCT
200.
[0027] In one embodiment of the invention, a first and second
tuners and respective first and second demodulating systems 213,
demultiplexing systems 215, and signal processing systems 214 may
simultaneously receive and process the first and second video
streams of a 1080P-60 program, respectively. Alternatively, a
single demodulating system 213, a single demultiplexing system 215,
and a single signal processing system 214, each with sufficient
processing capabilities may be used to process the first and second
video streams in a 1080P-60 capable receiver.
[0028] The DHCT 200 may include at least one storage device 273 for
storing video streams received by the DHCT 200. A PVR application
277, in cooperation with the operating system 253 and the device
driver 211, effects, among other functions, read and/or write
operations to the storage device 273. The device driver 211 is a
software module preferably resident in the operating system 253.
The device driver 211, under management of the operating system
253, communicates with the storage device controller 279 to provide
the operating instructions for the storage device 273. Storage
device 273 could be internal to DHCT 200, coupled to a common bus
205 through a communication interface 275.
[0029] Received first and second video streams are deposited
transferred to DRAM 252, and then processed for playback according
to mechanisms that would be understood by those having ordinary
skill in the art. In some embodiments, the video streams are
retrieved and routed from the hard disk 201 to the digital video
decoder 223 and digital audio decoder 225 simultaneously, and then
further processed for subsequent presentation via the display
device 140.
[0030] Compressed pictures in the second video stream may be
compressed independent of reconstructed pictures in the first video
stream. On the other hand, an aspect of the invention is that
pictures in the second video stream, although compressed according
to a second video specification that is different to the first
video specification, can depend on decompressed and reconstructed
pictures in the first video stream for their own decompression and
reconstruction.
[0031] Examples of dependent pictures are predicted pictures that
reference at most one picture (from a set of at least one
reconstructed picture) for each of its sub-blocks or macroblocks to
effect its own reconstruction. That is, predicted pictures in the
second video stream, can possibly depend one or more referenced
pictures in the first video stream.
[0032] Bi-predicted pictures (B-pictures) can reference at most two
pictures from a set of reconstructed pictures for reconstruction of
each of its sub-blocks or macroblocks to effect their own
reconstruction.
[0033] In one embodiment, pictures in the second video stream
reference decompressed and reconstructed pictures (i.e., reference
pictures) from the first video stream. In another embodiment,
pictures in the second video stream employ reference pictures from
both the first and second video streams. In yet another embodiment,
a first type of picture in the second video stream references
decompressed pictures from the second video stream and a second
type of picture references decompressed pictures from the first
video stream.
Enabling Receivers with Different Capabilities
[0034] The present invention includes several methods based on two
separate video streams assigned to a program rather than a single
stream with inherent built-in temporal scalability. Existing
receivers capable of processing 1080i-60 video streams today would
be deemed "legacy HD receivers" at the time that broadcasters start
emissions of 1080P-60 programs. If a 1080P-60 program was
transmitted without the advantage of this invention the "then"
legacy HD receivers would not know how to process a 1080P-60 video
stream, nor be capable of parsing the video stream to extract a
1080P-30 signal from the received 1080P-60. The legacy HD receivers
were not designed to identify and discard pictures from a single
1080P-60 video stream. Furthermore, 1080P-60 in the standard bodies
is specified for a 1080P-60 receiver without backward compatibility
to 1080i-60 receivers.
[0035] This invention enables 1080i-60 receivers to process the
portion of the 1080P-60 program corresponding to a first video
stream and reject a complementary second video stream based on PID
filtering. Thus, by processing the first video stream, a 1080i-60
receiver provides a portion of the 1080P-60 program that is
equivalent to 1080P-30. The invention is equally applicable, for
example, to 1080P-50, assigning two separate video streams to a
program. Future 1080P50-capable receivers process the 1080P-50
video from the two separate video streams according to the
invention, while legacy 1080i-50-capable receivers process a
1080P-25 portion of the 1080P-50 video program.
[0036] Hereinafter, 1080P-60 is used for simplicity to refer to a
picture sequence with twice the picture rate of a progressive
1080P-30 picture sequence, or to a picture sequence with twice the
amount of picture elements as an interlaced picture sequence
displayed as fields rather than full frames. However, it should be
understood that the invention is applicable to any pair of video
formats with the same picture spatial resolution, in which a first
video format has twice the "picture rate" of the second. The
invention is also applicable to any pair of video formats with the
same picture spatial resolution, in which a first video format has
"progressive picture rate" and the second has an "interlaced" or
field picture rate, the first video format resulting in twice the
number of processed or displayed pixels per second. The invention
is further applicable to any two video formats in which the first
video format's picture rate is an integer number times that of the
second video format or in which the number of pixels of a first
video format divided by the number of pixels of a second video
format is an integer number.
[0037] Stream Types and Unique PIDs
[0038] The MPEG-2 Transport specification referred to in this
invention is described in the two documents: ISO/IEC 13818-1:2000
(E), International Standard, Information technology--Generic coding
of moving pictures and associated audio information: Systems, and
ISO/IEC 13818-1/Amd. 3: 2003 Amendment 3: Transport of AVC video
data over ITU-T Rec. H.222.0 |ISO/IEC 13818-1 streams.
[0039] In accordance with MPEG-2 Transport syntax, a multiplexed
transport carries Program Specific Information (PSI) that includes
the Program Association Table (PAT) and the Program Map Table
(PMT). Information required to identify and extract a PMT from the
multiplexed transport stream is transmitted in the PAT. The PAT
carries the program number and packet identifier (PID)
corresponding to each of a plurality of programs, at least one such
program's video being transmitted as encoded 1080P-60 video
according to the invention.
[0040] As shown in the FIG. 3, the PMT corresponding to a 1080P-60
program carries two video streams, each uniquely identified by a
corresponding PID. The first video stream in the PMT has a unique
corresponding PID 341 and the second video stream has its unique
corresponding PID 342, for example. Likewise, the first and second
video streams of the 1080P-60 program have corresponding stream
type values. A stream type is typically a byte. The stream type
value for the first and second video streams are video_type1 and
video_type2, respectively.
[0041] In one embodiment, the stream type value, video_type1 equals
video_type2, therefore, both video streams are encoded according to
the syntax and semantics of the same video specification (e.g.,
both as MPEG-2 video or as MPEG-4 AVC). A receiver is then able to
identify and differentiate between the first video stream and the
second video stream by their PID values and the relationship of the
two PID values. For example, the lower PID value of video_type1
would be associated with the first video stream. However, legacy HD
receivers would not be able to incorporate such a processing step
as a feature. However, there may be two types of legacy receivers.
During a first era, legacy receivers may be HD receivers that are
capable of processing a first video stream encoded according to the
MPEG-2 video specification described in ISO/IEC 13818-2:2000 (E),
International Standard, Information technology--Generic coding of
moving pictures and associated audio information: Video. The second
video stream would likely be encoded with a video specification
that provides superior compression performance, for example, MPEG-4
AVC as described by the three documents: ISO/IEC 14496-10 (ITU-T
H.264), International Standard (2003), Advanced video coding for
generic audiovisual services; ISO/IEC 14496-10/Cor. 1: 2004
Technical Corrigendum 1; and ISO/IEC 14496-10/Amd. 1, 2004,
Advanced Video Coding AMENDMENT 1: AVC fidelity range extensions. A
second era, on the other hand, may comprise legacy HD receivers
that are capable of processing 1080i-60 video encoded according to
the MPEG-4 AVC specification. Because the latter legacy receivers
have yet to be deployed, these receivers could be designed to
support identification of the first video stream in a multiple
video stream program from the lowest PID value corresponding to
video_type1 in the PMT. Alternatively, the first video entry in the
PMT table, regardless of its PID value, would be considered the
first video stream.
[0042] In another alternate embodiment, the streams are encoded
according to different video specifications and the values of
video_type1 and video_type2 in the PMT differ. For example, the
first video stream would be encoded and identified as MPEG-2 video
in the PMT by a video_type1 value that corresponds to MPEG-2 video.
The second video stream would be encoded with MPEG-4 AVC and
identified by a video_type2 value corresponding to MPEG-4 AVC.
[0043] In yet another alternate embodiment, video_type2 corresponds
to a stream type specifically designated to specify the
complementary video stream (i.e, the second video stream of a
1080P-60 program). Both video streams could be encoded according to
the syntax and semantics of the same video specification (e.g, with
MPEG-4 AVC) or with different video specifications. Thus, while the
values of video_type1 and video_type2 are different in the PMT
table for a 1080P-60 program, both video streams composing the
1080P-60 program could adhere to the same video specification.
Thus, video_type1's value identifies the video specification used
to encode the first video stream, but video_type2's value
identifies both:
[0044] (1) the video stream that corresponds to the second video
stream of the 1080P-60 program, and
[0045] (2) the video specification (or video coding format) used to
encode the second video stream.
[0046] A first video_type2 value then corresponds to a stream type
associated with the second stream of a 1080P-60 program that is
encoded according to the MPEG-2 video specification. A second
video_type2 value corresponds to a stream type associated with the
second stream of a 1080P-60 program that is encoded according to
the MPEG-4 AVC specification. Likewise, other video_type2 values
can correspond to respective stream types, each associated with the
second stream of a 1080P-60 program and encoded according to a
respective video coding specification.
[0047] In yet another novel aspect of the invention, when
video_type2 does not equal video_type1 and their values signify
different video specifications, pictures in the second stream can
still use reconstructed pictures from the first video stream as
reference pictures.
Transmission Order of Pictures
[0048] Encoded pictures in the first and second video streams are
multiplexed in the transport multiplex according to a defined
sequence that allows a single video decoder in a 1080P-60 receiver
to receive and decode the pictures sequentially as if the pictures
were transmitted in a single video stream. However, because they
are two separate video streams, a 1080i-60 receiver can reject
transport packets belonging to the second video stream and allow
video packets corresponding to the first video stream to penetrate
into its memory to process a portion equal to 1080P-30 video.
Encoded pictures in the first video stream are transmitted in
transmission order, adhering to the timing requirement and
bit-buffer management policies required for a decoder to process
the first video stream as a 1080P-30 encoded video signal.
[0049] In one embodiment of the invention, FIG. 4A depicts the
first and second video streams in display order. P represents a
picture and not a type of picture. Pi is the ith picture in display
order. In a 1080P-60 receiver, the blank squares represent gaps of
when the picture being displayed is from the complementary video
stream. The width of a blank square is one "picture display" time.
Non-blank squares represent the time interval in which the
corresponding picture is being displayed.
[0050] Still referring to FIG. 4A, in a 1080i-60 receiver, a
1080P-30 picture corresponding to the first video stream is
displayed and the width of two squares represents the picture
display time. Video stream 1 is specified as 30 Hertz in
alternating 60 Hertz intervals that correspond to even integers.
Video stream 2 is specified as 30 Hertz in alternating 60 Hertz
intervals that correspond to odd integers.
[0051] FIG. 4B depicts pictures according to picture types in
display order. Ni signifies the ith Picture in display order, where
N is the type of picture designated by the letter I, P or B. In one
embodiment, all the pictures in video stream 2 are B pictures and
the 1080P-60 receiver uses decoded pictures from video stream 1 as
reference pictures to reconstruct the B pictures.
[0052] FIG. 4C corresponds to the transmission order of the
pictures in display order in FIG. 4B. Each picture is transmitted
(and thus received by the receiver) at least one 60 Hz interval
prior to its designated display time. I pictures are displayed six
60 Hz interval after being received and decoded. I pictures are
thus transmitted at least seven 60 Hz intervals prior to its
corresponding display time. The arrows from FIG. 4C to FIG. 4B
reflect the relationship of the pictures' transmission order to
their display order.
[0053] Blank squares in FIG. 4C represent gaps when no picture data
is transmitted for the respective video stream. The width of a
blank square can be approximately one "picture display" time.
Non-blank squares represent the time interval in which the
corresponding picture is transmitted. One or more smaller
transmission gaps of no data transmission may exist within the time
interval in which a picture is transmitted. In essence, video
stream 1 and video stream 2 are multiplexed at the emission point
in a way to effect the transmission order reflected in FIG. 4C and
transmission time relationship depicted in FIG. 4C.
Bit-buffer Management
[0054] A sequence of video pictures is presented at an encoder for
compression and production of a compressed 1080P-60 program. Every
other picture is referred as an N picture and every subsequent
picture as an N+1 picture. The sequence of all the N pictures is
the first video stream of the 1080P-60 program and the sequence all
the N+1 pictures is the second video stream.
[0055] A video encoder produces the first video stream according to
a first video specification (e.g., MPEG-2 video) and the second
video stream according to a second video specification (e.g.,
MPEG-4 AVC). In one embodiment the second video specification is
different than the first video specification. In an alternate
embodiment, the first and second video specifications are the same
(e.g., MPEG-4 AVC).
[0056] The video encoder produces compressed pictures for the first
video stream by depositing the compressed pictures into a first
bit-buffer in memory, such memory being coupled to the encoder.
Depositing of compressed pictures into the first bit-buffer is
according to the buffer management policy (or policies) of the
first video specification. The first bit-buffer is read for
transmission by the video encoder in one embodiment. In an
alternate embodiment, a multiplexer or transmitter reads the
compressed pictures out of the first bit-buffer. The read potions
of the first bit buffer are packetized and transmitted according to
a transport stream specifications such as MPEG-2 transport.
[0057] Furthermore, the video encoder, the multiplexer, or the
transmitter, or the entity performing the first bit-buffer reading
and packetization of the compressed pictures, prepends a first PID
to packets belonging to the first video stream. The packetized
first video stream is then transmitted via a first transmission
channel.
[0058] Similarly, the second video stream is produced by the video
encoder and deposited into the first bit buffer. The second video
stream is read from the first bit-buffer by the entity performing
the packetization, and the entity prepends a second PID to packets
belonging to the second video stream, and the transport packets are
transmitted via a first transmission channel.
[0059] In an alternate embodiment, the second video stream is
produced by the video encoder and deposited into a second bit
buffer. The entity performing the packetization reads the second
video stream from the second bit buffer and prepends the second PID
to packets belonging to the second video stream. The packetized
second video stream is then transmitted via a first transmission
channel.
[0060] Both first and second video streams are packetized according
to a transport stream specification, such as MPEG-2 Transport.
Packets belonging to the second video stream are thus identifiable
by a 1080P-60 capable receiver and become capable of being rejected
by a receiver that is not capable of processing 1080P-60
programs.
[0061] The bit buffer management policies of depositing compressed
picture data into the first and/or second bit-buffers and reading
(or drawing) compressed-picture data from the first and/or second
bit-buffers, are according to the first video specification. These
operations may be further in accordance with bit-buffer management
policies of the transport stream specification. Furthermore, the
bit-buffer management policies implemented on the one or two
bit-buffers may be according to the second video specification
rather than the first video specification. In one embodiment, the
first video stream's compressed data in the bit-buffer is managed
according to both: the bit buffer management policies of the first
video specification and the transport stream specification, while
the second video stream's compressed data in the applicable
bit-buffer is managed according to the bit buffer management
policies of the second video specification as well as the transport
stream specification.
[0062] The bit-buffer management policies described above are
applicable at the emission or transmission point in the network,
such as by the encoder and the entity producing the multiplexing
and/or transmission. Bit-buffer management policies, consistent
with the actual implementation at the emission or transmission
point, are applicable at the receiver to process the one or more
received video streams of a 1080P-60 program. The bit-buffer
management policy implemented at the emission or transmission point
may be provided to the receiver a priori for each program (e.g.,
with metadata) or according to an agreed one of the alternatives
described above that is employed indefinitely.
Enabling More Than Two Receivers with Different Respective
Processing Capabilities
[0063] In an alternate embodiment, the video encoder constitutes
two video encoders, a first video encoder producing the first video
stream according to the first video specification, and a second
video encoder producing the second video stream, which is
interspersed for transmission in the transmission channel according
to the pockets of "no data" transmission of video stream 1 (as
shown in FIG. 4C). The second video encoder further producing the
second video stream according to the second video
specification.
[0064] In yet another embodiment, the process of alternating
transmission of compressed pictures corresponding to the first
video stream and compressed pictures corresponding to the second
video stream, results in transmission of a first set of consecutive
compressed pictures from different the first video stream when it
is the turn to transmit the first video stream, or a second set of
consecutive compressed pictures from different the second video
stream when it is the turn to transmit the second video stream. For
instance, instead of alternating between one compressed picture
from the first video stream and one from the second video stream,
two consecutive compressed pictures from the second video stream
may be transmitted after each transmission of a single compressed
picture of the first video stream. Thus, a 1080P-90 Hertz program
can be facilitated to 1080P-90 receivers and a 1080P-30 portion of
the 1080P-90 program to 1080P-30 receivers. Furthermore, by
packetizing every second compressed picture in the second video
stream with a third PID value that is different than the first and
second PIDs, three corresponding versions of the compressed
1080P-90 program are facilitated respectively to a
1080P-30receiver, a 1080P-60 receiver, and a 1080P-90 receiver, the
latter being able to receive and fulfill the full benefits of the
1080P-90 program.
[0065] In yet another embodiment, the number of consecutive
compressed pictures that is transmitted from the first video stream
may be grater than one. For instance, if two consecutive compressed
pictures from the first video stream are transmitted and three
compressed pictures from the second video stream are transmitted
after transmission the two from the first video stream, a number of
receivers with different processing capabilities may be enabled. If
two different PID values are employed, a 1080P-50 receiver will
receive a 1080P-50 Program and a 1080P-20 receiver will receive a
1080P-20 corresponding portion. However, if five different PID
values are used for the 1080P-50 program, five receivers, each with
different processing capability will be capable of receiving a
portion of the 1080P-50 program.
Third Video Specification
[0066] Headend 110 may receive from an interface to a different
environment, such as from a satellite or a storage device, an
already compressed 1080P-60 program--a single video stream encoded
according to a third video specification and according to a first
stream specification. The first stream specification may be a type
of transport stream specification suitable for transmission or a
type of program stream specification suitable for storage. The
third video specification may comprise of the first video
specification, the second video specification, or both the first
and second video specifications respectively applied, for example,
to every other compressed picture. However, the already compressed
1080P-60 program is received at headend 110 encoded in such a way
that it does not facilitate reception some of its portions by
receivers with processing capability that are less than those of a
1080P-60 receiver. In other words, it is received without
information to inherent signal its different portions to receivers
with different processing capabilities.
[0067] Another novel aspect of this invention is that at least one
from one or more encoders, one or more multiplexers, or one or more
processing entities at the point of transmission at headend 110,
effect packetization of the compressed pictures of the received
1080P-60 program with a plurality of different PIDS, then
transmitting the 1080P-60 program as a plurality of identifiable
video streams via the first transmission channel. Thus, headend 110
effects proper packetization and prepending of PID values to enable
reception of at least a portion of the 1080P-program to receivers
with different processing capabilities that are coupled to network
130.
[0068] The present invention includes methods and systems capable
of transmitting compressed video signals according to one or more
compression video formats, where compressed video signals
correspond to television channels or television programs in any of
a plurality of picture formats (i.e., picture spatial resolution
and picture rate), including 1080i-60 and 1080P-60 formats. The
compressed video signals which correspond to television channels or
television programs in any of a plurality of picture formats are
received by a plurality of receivers, where each receiver may have
a different maximum processing capability. Therefore, the present
invention contemplates at least the following combinations for
encoding, transmission and reception of video signals. In the
following combinations of trio "input/receiver/display," the input,
such as 1080P-60 input in the first combination instance, refers to
a compressed video stream that is received at receiver 200 from
network 130 via communication interface 242. The display, such as
the 1080P-60 Display in the first combination instance is a
television, a display, or a monitor coupled to DHCT 200 via output
system 248. The DHCT 200 provides the compressed video stream
corresponding to the "input" in "decoded and reconstructed" form
(visible pictures) via output system 248. The receiver, such as
1080P-60 Receiver in the first combination instance, refers to a
receiver, such as DHCT 200, that has the processing capability
specified in the trio.
1080P-60 Input/1080P-60 Receiver/1080P-60 Display
[0069] In order to process a 1080P-60 compressed video signal, a
1080P-60 capable receiver receives a compressed 1080P-60 video
stream via a network interface (or a communication interface). The
1080P-60 compressed video signal is input by storing it in its
memory and the receiver decodes with a video decoder (or
decompression engine) all the pictures corresponding to the
1080P-60 video signal (or compressed video stream). A 1080P-60
capable display is driven by all the decoded 1080P-60 pictures.
1080i-60 Input/1080P-60 Receiver/1080P-60 Display
[0070] In order to process a 1080i-60 compressed video signal, the
1080P-60 capable receiver receives a compressed 1080i-60 video
stream via a network interface (or a communication interface). The
1080P-60 compressed video signal is input by storing it in its
memory and the receiver decodes with a video decoder (or
decompression engine) all the pictures corresponding to the
compressed 1080i-60 video signal stored in memory. The 1080P-60
receiver then deinterlaces the decoded 1080i-60 signal with a
de-interlacing algorithm based on information in two or more 1080i
fields, including a current 1080i field. The deinterlacing
algorithm makes decisions based on spatial picture information as
well as temporal information. The deinterlacing algorithm can
further base decisions on motion estimation or motion detection. A
1080P-60 capable display is driven by all the decoded 1080P-60
pictures.
1080P-60 Input/1080P-60 Receiver/Non-1080P-60 Display
[0071] In order to process a 1080P-60 compressed video signal, the
1080P-60 capable receiver receives a compressed 1080P-60 video
stream via a network interface (or a communication interface). When
driving a non-1080P-60 display, the receiver outputs a portion of
all the decoded 1080P-60 pictures or processes and scales the
pictures of the decoded 1080P-60 signal for display. When driving a
non-1080P-60 display such as a 1080i-60 display, the 1080P-60
capable receiver could process a 1080P-60 compressed video signal
in full (as explained above) and output (or display) a portion of
each of the decoded 1080P-60 pictures. The portion may be a
temporally-subsampled portion, a spatially-subsampled portion, or a
portion resulting from a combination of a temporal-subsampling and
spatially-subsampling. Alternatively, when driving a non-1080P-60
capable display, the 1080P60-capable receiver is informed by the
user or through a discovery mechanism that the display is not
1080P-60. Consequently, the 1080P-60-capable receiver can behave as
if it was a 1080P-30 receiver by not processing the second video
stream.
1080i-60 Input/1080P-60 Receiver/Non-1080P-60 Display
[0072] When driving a non-1080P-60 display, a 1080P-60 receiver
processes a 1080i-60 compressed video signal and outputs the
decoded 1080i-60 pictures according to the picture format required
to drive the non-1080 display, processing and scaling the pictures
of the decoded 1080i-60 signal as required to drive the
non-1080P-60 display.
1080P-60 Input/1080i-60 Receiver/Non-1080P-60 Display
[0073] In order to process a 1080P-60 compressed video signal, a
1080i-60 capable receiver receives a compressed 1080P-60 video
stream via a network interface (or a communication interface). The
receiver inputs a first portion of the 1080P-60 compressed video
signal by storing it in memory of receiver 200 and the receiver
rejects a second and complementary portion of the 1080P compressed
video signal by prohibiting it from penetrating any section,
portion or buffer of its memory. The receiver 200 decodes with a
video decoder (or decompression engine) all the pictures
corresponding to the first portion of the 1080P-60 video signal;
processing it as if it were a 1080i-60 compressed video signal. A
1080i-60 capable display is driven by the decoded first portion of
the 1080P-60 pictures.
1080P-60 Input/1080i-60 Receiver/1080P-60 Display--A
[0074] In order to process a 1080P-60 compressed video signal, a
1080i-60 capable receiver receives a compressed 1080P-60 video
stream via a network interface (or a communication interface). The
receiver inputs a first portion of the 1080P-60 compressed video
signal corresponding to a 1080i-60 compressed video signal by
storing it in its memory and rejects a second and complementary
portion of the 1080P compressed video signal by prohibiting it from
penetrating any section, portion or buffer of its memory. The
receiver decodes with a video decoder (or decompression engine) all
the pictures corresponding to the first portion of the 1080P-60
video signal, processing it as if it were a 1080i-60 compressed
video signal. The receiver deinterlaces a decoded 1080i-60 signal
with a deinterlacing algorithm based on information in two or more
1080i fields, including a current 1080i field. The deinterlacing
algorithm makes decisions based on spatial picture information as
well as temporal information. The deinterlacing algorithm can
further base decisions on motion estimation or motion detection. A
1080P-60 capable display is driven by all the decoded and
deinterlaced 1080i-60 pictures as a 1080P-60 signal.
1080P-60 Input/1080i-60 Receiver/1080P-60 Display--B
[0075] In order to process a 1080P-60 compressed video signal, a
1080i-60 capable receiver receives a compressed 1080P-60 video
stream via a network interface (or a communication interface). The
receiver inputs a first portion of the 1080P-60 compressed video
signal corresponding to a 1080i-60 compressed video signal by
storing it in its memory and rejects a second and complementary
portion of the 1080P-60 compressed video signal by prohibiting it
from penetrating any section, portion or buffer of its memory. The
receiver decodes with a video decoder (or decompression engine) all
the pictures corresponding to the first portion of the 1080P-60
video signal, processing it as if it were a 1080i-60 compressed
video signal. In order to drive a 1080P-60 capable display that is
capable of receiving a 1080i-60 signal and internal deinterlacing,
the display is driven by all the pictures of the decoded 1080i-60
compressed video signal as a 1080i-60 signal. The 1080P-60 display
deinterlaces the received 1080i-60 signals according to its
deinterlacing capabilities.
Encoding and Transmission
[0076] The encoder produces a 1080P-60 encoded video stream
according to a video specification (i.e., MPEG-2 video or MPEG-4
AVC), and assigns a first PID value to packets of every other
encoded picture corresponding to the 1080P-60, and assigns a second
PID value to every packet of the subsequent picture to the "every
other" picture just mentioned, where the second PID value is
different from the first PID value. Denoting "every other picture"
by N, every subsequent picture is then N+1; and the first PID_value
is used for N, while the second PID_value is used for N+1.
[0077] The encoder in one embodiment encodes all pictures according
to a single video format, e.g., MPEG-4 AVC, and adheres to the
buffer model of the video specification. The encoder in a second
embodiment encodes the pictures that correspond to N according to a
first video specification and in compliance with the video
specification's buffering model, and according to a variable-bit
rate model. The encoder further encodes the alternate pictures,
every "N+1" picture, according to a second video specification, the
second video specification being different from the first video
specification. These alternate pictures are encoded according to
the syntax of the second video specification, but managed and
transferred into a transmission buffer according to the first video
specification's buffering model. The encoder further employs in its
"encoding loop" a model, or parts thereof, of a receiver's video
decoder, including reference pictures, in it's memory.
[0078] Encode 1080P at 60 frames per second, into a single output,
ensuring that every other picture (in both decode order and
presentation order) is a non-reference picture.
[0079] Every picture encoded is a progressive frame representing
1/60.sup.th seconds. Now, every other picture can be separated into
a new PID. This new PID may be called "PID B", and the other PID
may be called "PID A". PID B contains only non-reference pictures
that can optionally be included in the decoding of PID A. In this
separation process, the original picture ordering must be
maintained within the multiplex. For example, a picture in one PID
must end before the next picture begins in the other PID.
[0080] For backwards-compatibility, the frame rate value in PID A
should be set at 30 frames per second; and the temporal references
in PID A should be corrected for the separated pictures; and as a
convenience, the temporal references in PID B should be set to
match those in PID A, such that each picture pair shares a temporal
reference number. The 1080P-60 capable decoder will be aware that
the frame rate is actually 60 frames per second, and will support
the pairs of duplicate temporal references. When decoding both PID
A and PID B in combination, the decoder should expect two of every
temporal reference number, adjacent in presentation order.
Therefore, for example, it can use the temporal reference numbers
to detect a missing picture. Picture re-ordering within the decoder
may be based on the sequence of picture types received, as
normal.
[0081] The following are examples of this scheme demonstrating how
a decoder could receive PID A alone, or receive the combination of
PID A and PID B. In these examples, the "B"-type pictures represent
non-reference frames. Also, these examples are given in decode
order, and the numbers represent temporal references (indicating
presentation order).
Example 1, IBBBP . . . :
[0082] Before temporal reference number (TRN) correction:
PID A: I3_B1_P7_B5_P11_B9_P15_B13.sub.--
PID B: _B0_B2_B4_B6_B8_B10_B12_B14
[0083] After TRN correction:
PID A: I1_B0_P3_B2_P5_B4_P7_B6.sub.--
PID B: _B0_B1_B2_B3_B4_B5_B6_B7
Example 2, IBP . . . :
[0084] Before TRN correction:
PID A: I1_P3_P5_P7_P9_P11_P13_P15.sub.--
PID B: _B0_B2_B4_B6_B8_B10_B12 _B14
[0085] After TRN correction:
PID A: I0_P1_P2_P3_P4_P5 _P6_P7.sub.--
PID B: _B0_B1_B2_B3_B4_B5_B6_B7
[0086] In the PMT, PID B can be designated by a new stream_type. A
common set of audio streams may serve each case: 1) using only PID
A 2) using both PID A and PID B.
[0087] In the above described method of encoding and transmission,
the separation of every other frame occurred after encoding. In an
alternative embodiment, separation occurs prior to encoding. At one
encoder's input, supply every other frame of a 1080P-60 hz signal.
Encode this as 1080P-30 hz. Simultaneously, supply another encoding
process with the alternate frames, also at 1080P-30 hz.
Presentation time stamps (PTSs) shall be generated for every
picture, referencing a common clock. The result is two video
streams, each being legitimate 1080P-30 hz. A 1080P-60 capable
decoder may decode both simultaneously, as a dual-decode operation,
to be recombined in the display process. There need be no further
correlation between the two PIDs than the commonly referenced PTSs.
For example, the group of pictures (GOP) structures, as defined by
the video specification (e.g., MPEG-2 video GOP) may be
independent, and the buffering may be independent. To recombine the
dual 1080P-30 streams into a single 1080P-60 output, the
dual-decoder's display process will choose decoded pictures to put
on display in order of PTS. If the picture for a particular time
interval has not yet been decoded, possibly due to some data
corruption or loss, then the previous picture will simply be
repeated through that time interval. If any picture is decoded
later than its PTS elapses, it is to be discarded. Even though both
PIDs may be completely independent, because they reference the same
clock, there is no risk that a picture from one PID is sent later
than the presentation time of a following picture from the other
PID, as long as each PID's buffer is maintained compliantly within
the multiplex.
[0088] PID B in the PMT may be designated by a new stream_type,
which may be allocated by MPEG, or which may be a user-private
stream_type that indicates a privately managed stream. The new
stream_type would not be recognized by legacy receivers, so the
associated PID B would be ignored. As an additional method of
unambiguous identification of the special second PID, the
registration_descriptor may be used in the ES_descriptor_loop of
the PMT to register a unique and private attribute for association
with PID B. Any combination of the above methods may be used, as
deemed adequate and sensible. A common set of audio streams may
serve each case: 1) using only PID A 2) using both PID A and PID B.
The methods described above use a separate PID to carry additional
information. In those cases, the separate PID can optionally be
ignored by the decoder. In another alternative embodiment, a single
video PID may be used to carry both the base information and the
additional information, while still providing a way to optionally
reject the additional information. A separate packetized elementary
stream (PES) ID can be used such that a new PMT descriptor, which
would be allocated by MPEG, may designate one PES ID for the base
layer, and a different PES ID for the additional information, both
carried by the same PID. In this way, existing PES IDs may be
identified as base, and supplemental, without the need for new PES
IDs to be allocated. The decoder that needs only the base layer may
discard those PES packets whose ID does not match the ID designated
as the base layer in the PMT. The decoder that can use both may
simply not reject either. This approach is applicable to both
schemes: post-encoding-separation and
prior-encoding-separation.
[0089] The foregoing has broadly outlined some of the more
pertinent aspects and features of the present invention. These
should be construed to be merely illustrative of some of the more
prominent features and applications of the invention. Other
beneficial results can be obtained by applying the disclosed
information in a different manner or by modifying the disclosed
embodiments. Accordingly, other aspects and a more comprehensive
understanding of the invention may be obtained by referring to the
detailed description of the exemplary embodiments taken in
conjunction with the accompanying drawings, in addition to the
scope of the invention defined by the claims.
* * * * *