U.S. patent application number 12/264586 was filed with the patent office on 2009-05-07 for method and system to transport high-quality video signals.
Invention is credited to Ahmad Ansari, Pierre Costa, John Robert Erickson.
Application Number | 20090116494 12/264586 |
Document ID | / |
Family ID | 25498278 |
Filed Date | 2009-05-07 |
United States Patent
Application |
20090116494 |
Kind Code |
A1 |
Costa; Pierre ; et
al. |
May 7, 2009 |
Method and System to Transport High-Quality Video Signals
Abstract
Society of Motion Picture and Television Engineers (SMPTE) video
data is separated into first data and second data. A first signal
is formed based on the first data. A second signal is formed based
on the second data. The first signal is transported via a first
Optical Carrier 3 (OC-3) channel. The second signal is transported
via a second OC-3 channel.
Inventors: |
Costa; Pierre; (Austin,
TX) ; Erickson; John Robert; (Austin, TX) ;
Ansari; Ahmad; (Austin, TX) |
Correspondence
Address: |
AT & T Legal Department - BHGL;Attn: Patent Docketing Room 2A-207
One AT&T Way
Bedminster
NJ
07921
US
|
Family ID: |
25498278 |
Appl. No.: |
12/264586 |
Filed: |
November 4, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11499356 |
Aug 4, 2006 |
7447216 |
|
|
12264586 |
|
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|
|
09956475 |
Sep 18, 2001 |
7110412 |
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11499356 |
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Current U.S.
Class: |
370/395.6 ;
348/E7.094 |
Current CPC
Class: |
H04Q 11/0478 20130101;
H04L 2012/5654 20130101; H04L 2012/5658 20130101; H04N 7/22
20130101; H04L 2012/5605 20130101; H04L 2012/5664 20130101 |
Class at
Publication: |
370/395.6 ;
348/E07.094 |
International
Class: |
H04L 12/56 20060101
H04L012/56 |
Claims
1. A method comprising: separating a frame of Society of Motion
Picture and Television Engineers (SMPTE) video data into a first
subframe and a second subframe, wherein the first subframe
comprises even lines of active video and the second subframe
comprises odd lines of active video; transporting a first signal
that has been formed based on the first subframe via a first
Optical Carrier 3 (OC-3) channel; and transporting a second signal
that has been formed based on the second subframe via a second OC-3
channel.
2. The method of claim 1, further comprising: forming the first
signal based on the first subframe; and forming the second signal
based on the second subframe.
3. The method of claim 2, wherein forming the first signal
comprises: appending a first sequence number to the first subframe;
and encapsulating the first subframe and the first subframe number
into at least one asynchronous transfer mode (ATM) cell.
4. The method of claim 3, wherein forming the second signal
comprises: appending a second sequence number to the second
subframe; and encapsulating the second subframe and the second
subframe number into at least one ATM cell.
5. The method of claim 1, wherein the first subframe comprises
active video data and ancillary data, and the second subframe
comprises active video data and ancillary data.
6. The method of claim 1, wherein the SMPTE video data is SMPTE
259M video data.
7. A computer-readable storage medium comprising a set of
instructions to direct a processor to perform the acts of:
separating a frame of Society of Motion Picture and Television
Engineers (SMPTE) video data into a first subframe and a second
subframe, wherein the first subframe comprises even lines of active
video and the second subframe comprises odd lines of active video;
transporting a first signal that has been formed based on the first
subframe via a first Optical Carrier 3 (OC-3) channel; and
transporting a second signal that has been formed based on the
second subframe via a second OC-3 channel.
8. The computer-readable storage medium of claim 7, further
comprising a set of instructions to direct a processor to perform
acts of: forming the first signal based on the first subframe; and
forming the second signal based on the second subframe.
9. The computer-readable storage medium of claim 8, wherein forming
the first signal based on the first subframe comprises: appending a
first sequence number to the first subframe; and encapsulating the
first subframe and the first subframe number into at least one
asynchronous transfer mode (ATM) cell.
10. computer-readable storage medium of claim 8, wherein forming
the second signal comprises: appending a second sequence number to
the second subframe; and encapsulating the second subframe and the
second subframe number into at least one ATM cell.
11. A video processor operative to separate Society of Motion
Picture and Television Engineers (SMPTE) video data into first data
and second data, the video processor comprising: a first ATM
adaptation layer (AAL) operative to form a first signal based on
the first data and to couple the first signal to a first Optical
Carrier 3 (OC-3) channel, and a second AAL operative to form a
second signal based on the second data and to couple the second
signal to a second OC-3 channel.
12. The video processor of claim 11, wherein the first AAL is
further operative to append a first sequence number to at least a
portion of the first data and to encapsulate the first sequence
number and the at least a portion of the first data into at least
one asynchronous transfer mode (ATM) cell.
13. The video processor of claim 11, wherein the second AAL is
further operative to append a second sequence number to at least a
portion of the second data and to encapsulate the second sequence
number and at least a portion of the second data into at least one
ATM cell.
14. The video processor of claim 11, wherein the first and second
data are first and second subframes.
15. The video processor of claim 11, wherein the first data
comprises even lines of active video and the second subframe
comprises odd lines of active video.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 11/499,356 (still pending), filed Aug. 4,
2006, which is a continuation of U.S. patent application Ser. No.
09/956,475 (now U.S. Pat. No. 7,110,412), filed Sep. 18, 2001, the
entirety of each of which are hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to methods and systems for
transporting high-quality video signals.
BACKGROUND
[0003] The video industry has adopted the Society of Motion Picture
and Television Engineers (SMPTE) 259M (level C) standard almost
exclusively for high quality video in studio and production
applications. In some applications, a SMPTE 259M signal is to be
transported to a remote location, which may be several miles away
for example. Current methods of transporting SMPTE 259M signals or
other professional quality video signals to remote locations use
either dark fiber overlay networks or proprietary methods over very
high bandwidth pipes. For example, an OC-12 channel may be used to
transport an SMPTE 259M signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The invention is pointed out with particularity in the
appended claims. However, other features of the invention will
become more apparent and the invention will be best understood by
referring to the following detailed description in conjunction with
the accompanying drawings in which:
[0005] FIG. 1 is a block diagram of an embodiment of a system to
transport high-quality video;
[0006] FIG. 2 is a flow chart of an embodiment of a method
performed at a transmitter end;
[0007] FIG. 3 is a flow chart of an embodiment of a method
performed at a receiver end;
[0008] FIG. 4 illustrates the SMPTE 259M data structure;
[0009] FIG. 5 is a block diagram illustrating an embodiment of an
uncompressed signal based on a subframe of a SMPTE frame;
[0010] FIG. 6 is a schematic block diagram of an embodiment of a
video processor at the transmitter end;
[0011] FIG. 7 is a schematic block diagram of an embodiment of a
video processor at the receiver end;
[0012] FIG. 8 is a block diagram of an embodiment of a system to
provide timing information;
[0013] FIG. 9 is a block diagram of an embodiment of a system to
reconstruct the timing information at the receiver end; and
[0014] FIG. 10 is a block diagram depicting a packing method for
transmitting 10-bit word information using 8-bit bytes.
DETAILED DESCRIPTION OF THE DRAWINGS
[0015] Briefly, embodiments of the present invention provide an
improved process for transporting high-quality video. The process
includes separating the video data into two sets of data,
encapsulating each set of data into asynchronous transfer mode
(ATM) cells, and transporting two ATM cell-based bit streams over
dual, concatenated Optical Carrier 3 (OC-3) channels. Error
checking and/or correction is used to reduce the probability of
data errors during transport.
[0016] Embodiments of the present invention are described with
reference to FIG. 1, which is a block diagram of an embodiment of a
system to transport high-quality video, FIG. 2, which is a flow
chart of an embodiment of a method performed at a transmitter end
20, and FIG. 3, which is a flow chart of an embodiment of a method
performed at a receiver end 22.
[0017] As indicated by block 24, the method comprises separating
SMPTE video data 26, such as SMPTE 259M video data, into first
uncompressed data 30 and second uncompressed data 32. Preferably,
the act of separating the SMPTE video data comprises separating
each frame of the SMPTE video data into a first subframe and a
second subframe. The first subframe comprises even lines of active
video from the frame, and the second subframe comprises odd lines
of active video from the frame. In addition to active video, the
first subframe and the second subframe may further comprise
horizontal ancillary data, optional video data and/or vertical
ancillary data.
[0018] The SMPTE 259M standard is inherently suitable to separate
video data because of its field and frame-oriented data structure.
In addition, extraneous data can be eliminated since the timing
signals are not necessary to carry along a transport stream.
[0019] FIG. 4 illustrates the SMPTE 259M data structure. The data
structure comprises active video fields 34 and 36. The active video
fields 34 and 36 contain component pixel data. The active video
field 34 includes odd lines of active video from a frame, while the
active video field 36 includes even lines of active video from a
frame. Optional video fields 40 and 42 contain vertical blanking
interval (VBI) data and non-critical data. Horizontal ancillary
(HANC) data fields 44 and 46 contain audio, timing and control
information. Vertical ancillary (VANC) data fields 48 and 49
contain special user information. A clear delineation between the
fields is created by the inherent timing signals EAV 50 and SAV
52.
[0020] The aforementioned structure is exploited to separate the
SMPTE video data into two equal blocks. The first uncompressed data
includes data from the active video field 34, the HANC data field
44, and a portion of the data from the optional video field 40
and/or the VANC data field 48. The second uncompressed data
includes data from the active video field 36, the HANC data field
46, and a portion of the data from the optional video field 42
and/or the VANC data field 49.
[0021] Referring back to FIG. 2, the method comprises acts of
forming a first uncompressed signal based on the first uncompressed
data (block 54) and forming a second uncompressed signal based on
the second uncompressed data (block 56). The first uncompressed
signal is based on the each first subframe. The second uncompressed
signal is based on the each second subframe.
[0022] The act of forming the first uncompressed signal further
comprises appending a corresponding first sequence number to each
first subframe, and encapsulating each first subframe with its
corresponding first sequence number into at least one asynchronous
transfer mode (ATM) cell. Similarly, the act of forming the second
uncompressed signal further comprises appending a corresponding
second sequence number to each second subframe, and encapsulating
each second subframe with its corresponding second sequence number
into at least one ATM cell. The sequence numbers are appended to
each subframe since traffic in most ATM networks can take any of
several paths, each with a potentially different latency and cell
delay variation. The sequence numbers are used at the receiving end
22 to order reconstructed frames.
[0023] In one embodiment, each sequence number is defined by 20
bits. One bit of the sequence number is used to identify whether
the field is field 1 or field 2. Choosing 20 bits for the sequence
number field allows sequence numbers up to 2 (20-1)=524,288. For a
frame rate of 30 frames per second, the maximum video length for 20
sequence number bits is (524,288 frames)/((30 frames per
second)*(3600 seconds per hour)), which approximately equals 4.854
hours.
[0024] FIG. 5 is a block diagram illustrating an embodiment of an
uncompressed signal which results from the act of either block 54
or block 56 in FIG. 2. The uncompressed signal comprises a bit
stream including a sequence number 60, ancillary data 62, and
active video data 64 for a subframe from a first frame. Thereafter,
the bit stream includes a sequence number 70, ancillary data 72,
and active video data 74 for a subframe from a second frame. The
pattern of including a sequence number, ancillary data and active
video data for a subframe is repeated for each succeeding
frame.
[0025] The above-described encapsulation method distinguishes video
data (e.g. field/frame data) from ancillary data to facilitate the
SMPTE 259M video data being properly reconstructed at the receiver
end 22. Since timing relationships are well-defined in the SMPTE
259M standard, and since a fixed frequency of 270 Mbps is used,
logic at the receiver end 22 can add the proper timing signals.
[0026] The bandwidth required to transmit the above bit stream is
calculated as follows. With respect to the active video bandwidth,
each field has 244 active video lines. The number of words per line
is 720 pixels*2(Cr, Y, Cb)=1440. Since each word consists of 10
bits, the number of bits per line is (1440 words per line)*(10 bits
per word)=14,400. Thus, the total number of active video bits per
field is (14,400 bits per line)*(244 active video lines per
field)=3.5136 Mb. Since each frame is based on 2 fields, the total
number of active video bits per frame is (3.5136 Mb per field)*(2
fields per frame)=7.0272 Mb. For a frame rate of 30 frames per
second, the active video bit rate is (7.0272 Mb per frame)*(30
frames per second)=210.816 Mbps. Accounting for ATM overhead with a
cell tax of 1.09433, the total active video bandwidth is
1.09433*210.816 Mbps=230.7043 Mbps.
[0027] The bandwidth for the HANC data is determined as follows.
The HANC bit rate is 30 Mbps. Accounting for ATM overhead with a
cell tax of 1.09433, the HANC bandwidth is 1.09433*30 Mbps=32.8302
Mbps.
[0028] The bandwidth for the VANC/optional data is determined as
follows. Each frame has 20 lines allocated for VANC/optional data.
The 20 lines comprise any 10 lines selected from lines 1-20, and
any 10 lines selected from lines 264-283. Since the number of bits
per line is 14,400, the total number of VANC/optional bits per
frame is (14,400 bits per line)*(20 VANC/optional lines per
field)=288,000. For a frame rate of 30 frames per second, the
VANC/optional bit rate is (288,000 bits per frame)*(30 frames per
second)=8.64 Mbps. Accounting for ATM overhead with a cell tax of
1.09433, the VANC/optional bandwidth is 1.09433*8.64 Mbps=9.4550112
Mbps.
[0029] The total data rate is equal to the sum of the total active
video bandwidth, the HANC bandwidth and the VANC/optional
bandwidth. Thus, the total data rate is 230.7043 Mbps+32.8302
Mbps+9.4550112 Mbps, which equals 272.984612 Mbps. This is less
than the 299.52 Mbps bandwidth available on two OC-3 links. Since
the data is separated into two fields, the total data rate per
field is 272.984612 Mbps/2, which approximately equals 136.4923
Mbps.
[0030] Optionally, the act of forming the first uncompressed signal
further comprises adding a first ATM adaptation layer (AAL) with
either an error checking code or an error correcting code.
Similarly, the act of forming the second uncompressed signal may
optionally comprise adding a second ATM adaptation layer with
either an error checking code or an error correcting code. A block
coding algorithm such as Reed Solomon or another forward error
correcting (FEC) code may be used.
[0031] Referring back to FIGS. 1 and 2, the method comprises
transporting 80 the first uncompressed signal via a first OC-3
channel 82, and transporting 84 the second uncompressed signal via
a second OC-3 channel 86. The OC-3 channels 82 and 86 are provided
by an ATM network 90.
[0032] The adaptation layers may be added because of additional
bandwidth available on two OC-3 links beyond the 272.984612 Mbps
required by the two bit streams. Either AAL-1 with FEC or AAL-5
with FEC may be used. The former is less efficient but more robust,
and the latter is more efficient and slightly less robust. The
selection of which of these two adaptations to use may be dictated
by specifications of a specific application. Note that the FEC
process is symmetrical, requiring processing the inverse algorithm
at the receiver end 22.
[0033] Turning now to FIG. 3, a method performed at the receiver
end 22 comprises receiving the first uncompressed signal via the
first OC-3 channel (block 92), and receiving the second
uncompressed signal via the second OC-3 channel (block 94). As
described above, the first uncompressed signal comprises a bit
stream of a first plurality of ATM cells, and the second
uncompressed signal comprises a bit stream of a second plurality of
ATM cells. The ATM cells are extracted from the incoming bit
streams.
[0034] As indicated by blocks 96 and 100, the method optionally
comprises performing error checking based on the first uncompressed
signal, and performing error checking based on the second
uncompressed signal. An inverse FEC block code algorithm is used
for error checking and recovery. If an error is detected, the block
code may provide correction depending on which block code is used
and the type and number of errors.
[0035] As indicated by block 102, the method comprises extracting
each first subframe and its corresponding first sequence number
from the first plurality of ATM cells. As indicated by block 104,
the method comprises extracting each second subframe and its
corresponding second sequence number from the second plurality of
ATM cells. In these acts, the data payload is extracted from the
AAL-1 or AAL-5 encapsulation.
[0036] As indicated by block 106, the method comprises
reconstructing SMPTE video data 108, such as SMPTE 259M video data.
Each frame of the SMPTE video data is reconstructed based on a
first corresponding subframe represented within the first
uncompressed signal and a second corresponding subframe represented
within the second uncompressed signal. Further, the EAV and SAV
timing signals are added to reconstructed frames. The reconstructed
frames are ordered based on each first sequence number and each
second sequence number.
[0037] One approach to ordering the frames comprises using a buffer
management process to synchronize the arriving data based on the
sequence numbers. A modified leaky bucket (LB) algorithm or similar
technique can be used to synchronize the two fields. Optimization
can be performed by varying the limit parameter based on the LB
counter and the last compliance time. The arrival time is based on
the arrival of the sequence number. This allows for a fast
implementation in silicon, using the sequence number to direct data
to the appropriate buffers.
[0038] It is noted that some acts described with reference to FIGS.
2 and 3 need not be performed in the order shown in FIGS. 2 and 3.
Further, some of the acts may be performed concurrently. For
example, the act of transporting the first signal via the first
OC-3 channel typically is performed concurrently with the act of
transporting the second signal via the second OC-3.
[0039] Referring back to FIG. 1, the transmitter end 20 comprises a
video processor 110 which performs the method described with
reference to FIG. 2. FIG. 6 is a schematic block diagram of an
embodiment of the video processor 110 at the transmitter end 20.
Each video frame 120 within SMPTE 259M video data 122 is separated
into two active video subframes. A temporary buffer 124 stores one
of the two active video subframes. A temporary buffer 126 stores
the other of the two active video subframes. The temporary buffers
124 and 126 may have equal sizes. Ancillary data 130 within the
SMPTE 259M video data 122 is appended to outputs of the temporary
buffers 124 and 126. The resulting streams are applied to
first-in-first-out (FIFOs) 132 and 134. A sequence number is added
to the FIFO stream 132 by tagging logic 136. A sequence number is
added to the FIFO stream 134 by tagging logic 140. An AAL 142
applies FEC to the output of the tagging logic 136. An AAL 144
applies FEC to the output of the tagging logic 140. A physical
layer 146 couples the AAL 142 to the OC-3 channel 82 in FIG. 1. A
physical layer 150 couples the AAL 144 to the OC-3 channel 86 in
FIG. 1. The aforementioned components of the video processor 110
are directed by system control logic 152.
[0040] Referring back to FIG. 1, the receiver end 22 comprises a
video processor 158 which performs the method described with
reference to FIG. 3. FIG. 7 is a schematic block diagram of an
embodiment of the video processor 158 at the receiver end 22. A
physical layer 160 couples the OC-3 channel 82 in FIG. 1 to an AAL
162. A physical layer 164 couples the OC-3 channel 86 in FIG. 1 to
an AAL 166. The physical layers 160 and 164 extract ATM cells from
an incoming bit stream. The AALs 162 and 166 perform an inverse FEC
block code algorithm for error checking and/or correcting, and
extract the data payload from AAL-1/5 encapsulation.
[0041] Tagging logic 170 is responsive to the AAL 162 to order each
subframe based on its sequence number, and to remove the sequence
number. Tagging logic 172 is responsive to the AAL 166 to order
each subframe based on its sequence number, and to remove the
sequence number. The resulting synchronized buffers are indicated
by FIFOs 174 and 176. Ancillary data 180 is extracted from each
subframe. Temporary buffers 182 and 184 store the two active video
portions which, when combined with EAV and SAV signals, form a
video frame 186. The video frame 186 is in accordance with an SMPTE
standard such as SMPTE 259M. The aforementioned components of the
video processor 158 are directed by system control logic 190. The
system control logic 190, among other things, directs
synchronization of data from the two separate fields.
[0042] FIG. 8 is a block diagram of an embodiment of a system to
provide timing information in addition to the sequence number. The
timing information is based upon a first clock 200 and a second
clock 202. Preferably, the first clock 200 has a frequency of 90
kHz, and the second clock 202 has a frequency of 27 MHz.
[0043] A first counter 204 is responsive to the first clock 200. A
second counter 206 is responsive to the second clock 202.
Preferably, the first counter 204 is a 23-bit counter and the
second counter 206 is a 9-bit counter. The timing information has
an upper portion 210 comprising bits from the second counter 206,
and a lower portion 212 comprising bits from the first counter 204.
The timing information is encapsulated as described above for the
bit stream. The additional 32 bits keep the overall bandwidth
within the bandwidth limit of the two OC-3 links.
[0044] FIG. 9 is a block diagram of an embodiment of a system to
reconstruct the timing information at the receiver end. A clock
recovery module 214 outputs a first clock signal based on the lower
portion 212 of the received timing information, and a second clock
signal based on the upper portion 210. The clock recovery module
214 may be embodied using a phase-locked loop circuit. Preferably,
the first clock signal has a frequency of 90 kHz and the second
clock signal has a frequency of 27 MHz.
[0045] The clock signals can be useful in reducing jitter and
synchronizing data. The use of field/frame counters allow better
decisions to be made when reconstructing frames at the receiver. If
link errors occur, the receiver can perform a first check on field
number and decide what to do based thereupon. For example, the
receiver may decide to use a previous frame and wait for the next
consecutive frames to resynchronize.
[0046] FIG. 10 is a block diagram depicting a packing method for
transmitting 10-bit word information using 8-bit bytes. Four
consecutive pixel samples 220, 222, 224 and 226 are packed into
five consecutive bytes 230, 232, 234, 236 and 238.
[0047] Several embodiments including preferred embodiments of a
method and system to transport high-quality video signals have been
described herein.
[0048] The herein-described methods and systems facilitate high
bandwidth, real-time video signals to be transmitted over existing
ATM infrastructure. Use of two OC-3 links rather than one OC-12
connection translates into a significant savings in bandwidth.
[0049] It will be apparent to those skilled in the art that the
disclosed invention may be modified in numerous ways and may assume
many embodiments other than the preferred form specifically set out
and described above.
[0050] Accordingly, it is intended by the appended claims to cover
all modifications of the invention which fall within the true
spirit and scope of the invention.
* * * * *