U.S. patent application number 11/471221 was filed with the patent office on 2007-01-04 for latency handling for interconnected devices.
This patent application is currently assigned to U.S. PHILIPS CORPORATION. Invention is credited to Peter J. Lanigan, Nicoll B. Shepherd.
Application Number | 20070002886 11/471221 |
Document ID | / |
Family ID | 9883715 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070002886 |
Kind Code |
A1 |
Lanigan; Peter J. ; et
al. |
January 4, 2007 |
Latency handling for interconnected devices
Abstract
A data processing system comprises a cluster of devices (16)
interconnected for the communication of data in streams,
particularly digital audio and/or video data. One of the devices
(10) is a source device for at feast two data streams to be sent to
one or more other devices (12, 14) as destination devices of the
cluster. To enable synchronisation of the stream presentations by
the destination devices, some or all of the devices (10, 12, 14)
carry respective tables (11, 13, 15) identifying, for that device,
an identifier for each type of data stream that the device can
process together with the processing delay for that stream. The or
each such table is accessible via the cluster connection (18) to
whichever of the devices, at source, destination or in between for
the signal, is handling application of the necessary offsets.
Inventors: |
Lanigan; Peter J.; (Croydon,
GB) ; Shepherd; Nicoll B.; (Coulsdon, GB) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Assignee: |
U.S. PHILIPS CORPORATION
|
Family ID: |
9883715 |
Appl. No.: |
11/471221 |
Filed: |
June 20, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09759184 |
Jan 12, 2001 |
7136399 |
|
|
11471221 |
Jun 20, 2006 |
|
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Current U.S.
Class: |
370/432 ;
375/E7.019; 375/E7.022; 375/E7.271 |
Current CPC
Class: |
H04L 12/2805 20130101;
H04N 21/2368 20130101; H04N 21/4307 20130101; H04L 2012/2849
20130101; H04N 21/43632 20130101; H04N 21/23608 20130101; H04N
21/4344 20130101; H04N 21/4341 20130101 |
Class at
Publication: |
370/432 |
International
Class: |
H04J 3/26 20060101
H04J003/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 14, 2000 |
GB |
0000874.8 |
Claims
1. A data processing system comprising a cluster of devices
interconnected for the communication of data in streams wherein,
for at least two data streams to be sent to one or more devices as
destination devices of said cluster, at least one device of the
cluster comprises means arranged to apply a respective delay to at
least one of said at least two data streams in an amount determined
by differing signal path latencies for said at least two streams;
wherein at least some devices of the cluster maintain a respective
table, readable via said interconnection by other devices of said
cluster, each such table identifying one or more latencies for the
respective device, and the means arranged to apply a delay
operating to apply delays on the basis of table contents.
2. A system as claimed in claim 1, wherein each table identifies,
for its respective device, signal processing capabilities for that
device, together with the latency associated with each such
capability.
3. A system as claimed in claim 1, wherein one of said devices is a
source device for said at least two data streams to be sent to said
destination devices of said cluster, said source device including
said means arranged to apply a delay together with means arranged
to read data from said respective tables of the destination devices
and determine the respective delay to apply to at least one of said
at least two data streams.
4. A system as claimed in claim 3, wherein said source device
further comprises multiplexing means coupled with said means
arranged to apply a delay and arranged to combine said at least two
streams into a single data stream for transmission to said
destination devices.
5. A system as claimed in claim 2, wherein one or more table
entries is in the form of an algorithm requiring data from the
device reading the table to enable determination of the latency of
the device holding said table.
6. A system as claimed in claim 5, wherein the determination on the
basis of the algorithm is implemented by the device reading the
table, said device having downloaded the algorithm from the device
holding the table.
7. A system as claimed in claim 5, wherein the determination on the
basis of the algorithm is implemented by the device holding the
table, the results of the implementation being transmitted via said
interconnection to the device reading the table.
8. A system as claimed in claim 1, wherein all destination devices
maintain a respective table.
9. A system as claimed in claim 1, wherein said means arranged to
apply a delay comprises buffering means.
10. A system as claimed in claim 1, wherein said means arranged to
apply a delay comprises means arranged to selectively apply a delay
to reading of one or each of said data streams from a source
thereof.
11. (canceled)
12. (canceled)
Description
[0001] The present invention relates to systems composed of a
plurality of devices clustered for the exchange of audio and/or
video data and control messages via wired or wireless link and, in
particular although not essentially, to such systems where
different data components from a source device are to be routed to
respective and separate other devices of the system. The invention
further relates to devices for use in such systems.
[0002] Networking or interconnection of devices has long been known
and used, starting from basic systems where different system
functions have been provided by separate units, for example hi-fi
or so-called home cinema systems. A development has been the
so-called home bus systems where a greater variety of products have
been linked with a view to providing enhanced overall functionality
in for example domestic audio/video apparatus coupled with a home
security system and the use of telephone. An example of such a home
bus system is the domestic digital bus (D2B), the communications
protocols for which have been issued as standard IEC 1030 by the
International Electrotechnical Commission in Geneva, Switzerland.
The D2B system provides a single wire control bus to which all
devices are interfaced with messages carried between the various
devices of the system in a standardised form of data packet.
[0003] A particular problem that can occur with distributed systems
such as hi-fi and home cinema is loss of synchronisation between
different components required to be presented to a user
simultaneously, in particular for video images and an accompanying
soundtrack, or between different components of the soundtrack,
where the different components are to be handled by different
devices--for example in a home cinema set-up. This loss of
synchronisation may occur due differences in the effective lengths
of the transmission paths for the differing components resulting
in, or due to, different latencies in decoders or intermediate
processing stages for the different components.
[0004] One way to approach the synchronisation problem, where all
the components are decoded within a single device, is described in
U.S. Pat. No. 5,430,485 (Lankford et al) which describes a receiver
for decoding associated compressed video and audio information
components transmitted in mutually exclusive frames of data, each
with a respective presentation time stamp. A coarse synchronisation
is applied by selectively dropping frames of one or other of the
components and then fine tuning by adjusting the audio stream clock
frequency.
[0005] Another approach, this time closer to the source for
different components being sent out, is described in U.S. Pat. No.
5,594,660 (Sung et al) which provides an audio/video
decoder/decompressor for receiving and separating the components of
an encoded and compressed data stream. Within the
decoder/decompressor, Sung has means for breaking up a compound AV
stream and then applying an appropriate temporal offset to each
stream to achieve synchronisation of the outputs during playback.
The differential buffering by FIFO units follows the system decoder
but precedes the decoding of the audio or of the video.
[0006] Although handling the component delays with the components
still encoded generally involves less processing, handling of
synchronisation (particularly if done at source) can create its own
problems when it comes to determining just how much delay is to be
applied to each component stream.
[0007] It is accordingly an object of the present invention to
provide a networked system of devices including enabling means for
synchronising components intended to be presented synchronously to
a user of the system.
[0008] In accordance with the present invention there is provided a
data processing system comprising a cluster of devices
interconnected for the communication of data in streams wherein,
for at least two data streams to be sent to one or more devices as
destination devices of said cluster, at least one device of the
cluster comprises buffering means arranged to apply a respective
delay to at least one of said at least two data streams in an
amount determined by differing signal path latencies for said at
least two streams; wherein at least some devices of the cluster
maintain a respective table, readable via said interconnection by
other devices of said cluster, each such table identifying one or
more latencies for the respective device, and the means arranged to
apply delays applying delays on the basis of table contents. By the
use of respective tables, which are suitably (but not essentially)
carried by all destination devices, the determination of what delay
to apply to each data stream made be made more simply and greater
flexibility is introduced to the system in that changes to
processing arrangements may just require a table entry to be
altered, rather than a large-scale revision of the recorded
operational parameters typically held by networked devices.
[0009] Each table may identify, for its respective device, signal
processing capabilities for that device, together with the latency
associated with each such capability. Where one of the devices is a
source device for said at least two data streams to be sent to said
destination devices of said cluster, said source device may include
the means arranged to apply a delay together with means arranged to
read data from said respective tables of the destination devices
and determine the respective delay to apply to at least one of said
at least two data streams. In such an arrangement, the source
device may further comprise multiplexing means coupled with the
means arranged to apply a delay and arranged to combine said at
least two streams into a single data stream for transmission to
said destination devices.
[0010] Whilst simple figures for the respective delays may be held
in each table, one or more table entries may be in the form of an
algorithm requiring data from the device reading the table to
enable determination of the latency of the device holding said
table. For this, the determination on the basis of the algorithm
may be implemented by the device reading the table, said device
having downloaded the algorithm from the device holding the table:
alternatively, the determination may be implemented by the device
holding the table, with the results of the implementation being
transmitted via said interconnection to the device reading the
table.
[0011] The means arranged to apply a delay may suitably comprise
buffering means (i.e. a memory device with controls over the rates
of writing to, and reading from, such a device). Alternatively, the
means arranged to apply a delay may comprise means arranged to
selectively apply a delay to reading of one or each of said data
streams from a source thereof. In this latter option, the delay
means may be implemented by selective control over the reading of
the data streams from (for example) disc.
[0012] The present invention also provides a data processing
apparatus comprising the technical features of a source device in a
system as recited hereinabove and as claimed in the claims attached
hereto, to which the readers attention is now directed.
[0013] Further features and advantages of the present invention
will become apparent from reading of the description of preferred
embodiments of the invention, given by way of example only and with
reference to the accompanying drawings, in which:
[0014] FIG. 1 represents an arrangement of three interconnected
devices forming an audio/video cluster;
[0015] FIG. 2 represents a table of latency information as carried
by one of the devices in the cluster of FIG. 1;
[0016] FIG. 3 represents a configuration of source device suitable
to embody the present invention; and
[0017] FIG. 4 represents an alternative (wireless) interconnected
cluster suitable to embody the present invention.
[0018] A first arrangement of interconnected devices is shown in
FIG. 1, with three devices 10, 12, 14 forming a cluster 16 based
around a respective bus 18 supporting communication in accordance
with IEEE Standard 1394 connect and communications protocols. In
the following example, reference is made to IEEE 1394, and the
disclosure of the specification of this protocol is incorporated
herein by reference. As will be recognised by the skilled reader,
however, conformance with such protocol is not essential to the
operation of the present invention.
[0019] The devices in the cluster 16 comprise a source device 10
coupled via bus 18 to a pair of presentation devices, in this
example a television 12 for showing the image component of a
combined AV stream from the source, and an audio processor and
playback system 14 for reproducing the audio component of the AV
stream.
[0020] In order to synchronise the presentation to a user of the
audio and video components, a device on the network must arrange
for some stream components (in this example the audio component) to
be delayed relative to the others (in this case video). In the FIG.
1 example, if a data stream from the source 10 to the two
destination devices 12, 14 consists of MPEG2 video and AC3 audio,
where the processing delay for MPEG2 in the television 12 is 1.0
second, and the processing delay for AC3 audio in the audio
presentation device 14 is 0.1 seconds, the audio signal must be
delayed by (1.0-0.1)=0.9 seconds at some point along its signal
path to achieve synchronisation. One technique for applying this
delay is described in our co-pending commonly-assigned application
entitled "Interconnection of Audio/Video Devices" and will be
briefly described hereinafter with respect to FIG. 3. In order to
be able to arrange for these delays, the system must have some
means for determining the processing delays for the various types
of data stream.
[0021] In order to enable application of the appropriate delay to
counter latency in a matching stream, particularly for those
devices supporting more than one processing capability (e.g. MPEG2
and DV; AC3 and MP3), each device in the cluster 10, 12, 14 is
provided with a respective internal or remotely stored look-up
table 11, 13, 15. In this table (an example of which is given in
FIG. 2 for the television 12 from FIG. 1) there will be one entry
for each type of stream that a device can process. The entry will
consist of, at least, an identifier for the type of stream, and a
processing delay for that stream. Other information about the
stream may be contained in the table, as required.
[0022] In certain circumstances the system may support changes to
the specified delays in response to user input varying one or other
of the preset audio parameters. The notification for such changes
will generally be in the form of a protocol-supported notification
and the extent to which some or all devices of the cluster detect
and record the effects of the change against their particular
parameters as stored in their respective table will depend on the
extent to which they follow the protocol. This also applies to
their ability to read updated tables from other devices of the
cluster.
[0023] A single type of stream may have different processing delays
if, for example, the device has different processing delays for
various ranges of bit rates for that type of stream. Also, as shown
by the entry for MPEG7 stream types, an entry may consist of an
algorithm to determine the delay. For example, if the delay was 0.1
seconds for every megabit per second of incoming data, the formula
of (0.1*.chi.) seconds, where .chi. is the number of megabits per
second, could be stored. With an algorithm in the table, it is
either packaged such as to be available for downloading by a device
seeking to determine delays, or the enquiring device may be
required to submit parameter values (e.g. .chi.) to the device
holding the algorithm in its table, which device would then
calculate the delay and return the value to the enquiring device.
The table may be accessed by some form of read transaction (e.g.
"read" operations conforming to IEEE 1394 protocols), a command
protocol (e.g. AV/C), a remote method invocation protocol (e.g.
request messages according to the Home Audio/Video interoperability
standard--HAVi--based around IEEE1394), various Java.TM. RMI
procedures or some other method.
[0024] As mentioned above, and described in greater detail in our
co-pending application, one possible configuration for the source
device 10 comprises an audio stream buffer 20 and a video stream
buffer 22 for receiving separate input components from a remote
signal source 24. Under the direction of a controlling processor
30, which reads the processing latencies from the tables (not
shown) for destination devices 12, 14, the buffers are used to
apply a respective delay to at least one of the two data streams to
combat the differing processing latencies in the video 12 and audio
14 destination devices. Also under the direction of the processor
30, a multiplexer stage 32 combines the temporally offset audio and
video from the respective buffers into a single data stream for
transmission via the 1394 bus 18.
[0025] Whilst the signals in the respective buffers 20, 22 may
simply be read out and recombined, the source device optionally
further comprises data processing means interposed in the signal
path between the buffers 20, 22 and the multiplexer 32. As shown,
this further data processing means may take the form of an audio
signal processor ASP 34 on the output to the audio signal buffer
and a video signal processor VSP 36 on the output to the video
signal buffer.
[0026] The first and second data streams (audio and video) may be
encoded according to a first communications protocol such as MPEG1
or 2, and the destination devices 12, 14 are each provided with a
respective decoder 40, 42 operating according to the said
protocol.
[0027] From reading the present disclosure, other modifications and
variations will be apparent to persons skilled in the art,
including equivalents and features which are already known in the
field of bus-connected and cordless communication systems and
components and which may be used instead of or in addition to
features already disclosed herein. For example, as shown by FIG. 4,
the source 58 may comprise an optical or magnetic disk reader and,
instead of a digital data bus, the data channel from source 60 to
destination devices 62, 64, 66 may be a wireless communications
link 68 for which each of the destination devices is provided with
at least a receiver and the source device is provided with at least
a transmitter. The system may comprise many more devices than
illustrated herein including, for example, two or more source
devices, and some devices of the system may have the technical
features of both source and destination (for example a video
cassette record and playback deck) with the appropriate
source/destination behaviour being selected in dependence on the
context.
[0028] In the foregoing we have described a data processing system
that comprises a cluster of devices interconnected for the
communication of data in streams, particularly digital audio and/or
video data. One of the devices is a source device for at least two
data streams to be sent to one or more other devices as destination
devices of the cluster. To enable synchronisation of the stream
presentations by the destination devices, some or all of the
devices carry respective tables identifying, for that device, an
identifier for each type of data stream that the device can process
together with the processing delay for that stream. The or each
such table is accessible via the cluster connection to whichever of
the devices, at source, destination or in between for the signal,
is handling application of the necessary offsets.
* * * * *