EP1330925A1 - Method for synchronizing digital signals - Google Patents
Method for synchronizing digital signalsInfo
- Publication number
- EP1330925A1 EP1330925A1 EP01980601A EP01980601A EP1330925A1 EP 1330925 A1 EP1330925 A1 EP 1330925A1 EP 01980601 A EP01980601 A EP 01980601A EP 01980601 A EP01980601 A EP 01980601A EP 1330925 A1 EP1330925 A1 EP 1330925A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- signal
- signals
- time
- values
- synchronization
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
- H04N21/43—Processing of content or additional data, e.g. demultiplexing additional data from a digital video stream; Elementary client operations, e.g. monitoring of home network or synchronising decoder's clock; Client middleware
- H04N21/4302—Content synchronisation processes, e.g. decoder synchronisation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N5/00—Details of television systems
- H04N5/04—Synchronising
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N17/00—Diagnosis, testing or measuring for television systems or their details
- H04N17/004—Diagnosis, testing or measuring for television systems or their details for digital television systems
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
- H04N21/41—Structure of client; Structure of client peripherals
- H04N21/426—Internal components of the client ; Characteristics thereof
Definitions
- bit rate reduction coding techniques such as the method defined in ISO / IEC 13918 MPEG-2, and digital modulation techniques allow in particular to offer a greater number of services to the end user.
- ⁇ o the signals restored after decoding are no longer identical to the originals.
- the constraints imposed, in terms of bit rate or bandwidth available for transmission, as well as the content of the signal imply the appearance, at low bit rate or under difficult transmission conditions, of characteristic degradations.
- E and S Several methods exist for achieving time synchronization of any two digital signals, designated by E and S. All of them aim at matching elements, that is to say portions, of these signals.
- the basic element may be an image; similarly, for an audio sequence, it can be a sample.
- the existing methods can be divided into three approaches. 0
- the most common approach implements a correlation on the complete decoded signals. It consists in comparing the two signals E and S to be synchronized, based on their content. Indeed, assuming that the content of the signals evolves significantly between two consecutive elements, the comparison of the 5 signals E and S shows a great similarity of the signals only in the case where the elements of these are in correspondence. In all other cases, there is less similarity.
- An example of application of this principle to moving images consists in evaluating the variance of the error image E - S, which passes through a minimum when the images of the two video sequences are in correspondence.
- a correlation between the two images is made according to the relation (2) below.
- Each pixel being at the same spatial position (x, y) in the images of the two sequences, r ( ⁇ ) is maximum when the signals are time synchronized.
- the parameter ⁇ gives the time offset to be taken into account on one of the signals to obtain synchronization.
- a similar formula (1) applies to the case of audio signals.
- T is an arbitrary duration
- the main disadvantage of this type of method is the need for constantly evolving content. Depending on the type of signals analyzed, this assumption is not always true. The content of the signals therefore has a direct influence on the performance of the method. Furthermore, the implementation thereof can be complex in terms of computing capacity, particularly in the case of video signals or over long periods. audio signal periods. Furthermore, to use this type of approach on complete decoded signals, it is necessary that the two signals E and S are available at the same point: it is a very strong constraint, which it is not possible to satisfy for certain applications such as monitoring the quality of digital television signals in an operational system.
- a second known approach implements synchronization by time marks.
- RT time markers
- the process is based only on two series of time references RT, extracted from the signals according to any suitable extraction method.
- the RT marks being, for example, numbers of increasing value over time
- synchronization is carried out simply by selecting, for each RT time mark of a sequence, the closest time mark in the series of the other sequence.
- phase shift ⁇ is induced by the digital memories present in the decoder.
- This phase shift ⁇ is constant as long as the stream is not interrupted, but it takes a different value if we change the decoder, or the bit stream, or even only if we interrupt and then resume the same bit stream.
- the value of the phase shift can be of an order of magnitude at least equal to the duration of the largest signal element. For example, when the decoded signals contain video ( Figure 2), the phase shift can be of several images.
- This approach has the disadvantage of having a precision limited on the one hand by the precision of the values of the time reference marks RT, and on the other hand by the need that these reference points are transmitted synchronously to the perceptible or useful content of the signals.
- it only provides coarse synchronization for digital bit rate reduction systems.
- its implementation is very simple.
- a third class of synchronization methods aims to overcome the need for significant and permanent variation in the content of the signals in order to obtain good performance with the correlation methods. For this, there is the possibility of modifying the content of the signals, so as to insert there specific information aiming to optimize the reliability of the correlation. One possibility is to insert particular patterns in the images.
- This approach therefore corrects a defect in correlation approaches, but introduces a modification of the signals, which represents a major constraint incompatible with many applications, including monitoring the quality of digital television signals in an operational system.
- the method according to the invention aims to ensure precise time synchronization, while allowing simple implementation, without introducing any modification to the two signals to be synchronized.
- the main functionality consists in evaluating the exact offset between the two signals. Thereafter, the knowledge of this offset will be used to correct the synchronization fault.
- the basic idea of the present invention is to define a hybrid approach between the use of time marks and a correlation approach.
- the method advantageously exploits a characteristic parameter extracted from the signals to be synchronized, instead of all of the signals.
- the method is naturally integrated into a system for monitoring the quality of digital audio and / or video signals, in particular in digital television over an operational broadcasting network, but it is applicable whenever a time synchronization between two signals must be performed.
- the method according to the invention is easily integrated into a standard coding system with reduction in bit rate for digital television such as MPEG-2, or of coding of sound.
- the invention thus relates to a method for synchronizing a first and a second digital signal having digital elements to be matched, based on time marks, characterized in that it implements: a) preliminary synchronization of the two digital signals using time marks, by matching recognized time marks of the same value in the first (E) and in the second; (S) digital signal, b) fine synchronization from a characteristic parameter (PE, PS) of said digital elements, calculated for each of said first (E) and second (S) digital signals.
- Preliminary synchronization can be achieved by matching successive values of the time marks of said two digital signals as best as possible.
- the method can be characterized in that the preliminary synchronization implements: ai) a selection of a time frame (RTEj) of the first signal and a time frame (RTS j ) of the second signal and a calculation of the difference between the values of these two time marks. a2) If this difference is not minimal, a correspondence of the time marks (RTE, RTS) of the first (E) and the second (S) signal by shift (d) between the indices (i, j) of the marks temporal (RTE, RTS) of the first (E) and second (S) signal, this offset (d) corresponding to the observed difference.
- the preliminary synchronization advantageously implements the determination of an average value of the difference between the values of two successive time marks, this determination being preferably carried out before a-i.
- the method is advantageously characterized in that fine synchronization is carried out: b1) by associating with a series of successive time marks of the first (E) and of the second (S) signal, a series of values of a parameter characteristic of the signal, these values being denoted PE ⁇ for the value of the characteristic parameter associated with the time frame RTE (i) of the first signal (E), and PS ;, ) for the value of the characteristic parameter associated with the time frame RTS (i ) of the second signal ( S); b2) by comparing said series of values for the first (E) and the second (S) so as to match the time marks [RTE (i), RTE (i- ⁇ 0 )] of the first (E) and the second
- b 2 can be achieved by correlation.
- FIG. 1 illustrates the problem of synchronization of two digital signals
- FIG. 2 illustrating the phase shift likely to occur between the time marks and a signal, for example video
- FIG. 3 illustrates an approximate evaluation of the offset between two signals
- FIG. 4 represents the evolution of a parameter P extracted from the content of a sequence of images, this parameter being associated with the time references RT,
- FIGS. 5a and 5b illustrate for two signals to be synchronized, the evolution of the parameter P respectively before and after synchronization
- the first step of the method according to the invention is a preliminary synchronization by exploitation of time marks.
- This first step uses the two series of time references RT E , and RTs from the sequences E and S respectively to be synchronized. It consists in finding, for a value RTs (j) of the series RTs, the closest value in the series RT E (i) and the offset to be applied to one of the series to synchronize. For this, two approaches are proposed:
- the first step determines the average value P RT between two successive time marks (if this value is not known). It is estimated by examining, in one of the two series RT s (j) 20 or RT E (i), the difference between the values of two successive time marks. This difference is not necessarily constant, due to the limited precision of the numbers RT s (j) or RT E (i), for example integers. Consequently, the operation is repeated on a sufficient number of differences, to calculate the average difference.
- the second step is the prediction itself.
- the average difference between two successive time marks being known, the number d of time marks to be skipped in order to be synchronized can be predicted from the difference between the values of the marks RTsG) and RT E ((i).
- the third step makes it possible to predict the value of the time reference sought.
- FIG. 3 illustrates the evaluation of the offset d between the two sequences.
- the rough synchronization process by predictive search for the three-step shift is summarized below: a) the difference P RT between two successive time marks is constant. We can estimate it from several pairs of successive time marks:
- RT E and RT S is not necessarily zero. It can have a residual value lower than P RT . In this case, we consider that the difference is minimal and that the RT E and RT S series are matched. At the end of this phase, the two sequences E and S to be synchronized can be matched.
- the method implements a function for correcting the indices of the time markers, by adding or subtracting d from the indices i or j:
- the two sequences are now synchronized as best as possible, based on the time marks.
- Two effects limit the precision of this synchronization: on the one hand, the fact that the time reference sequences RT E and RT S are not identical, on the other hand the existence of a random phase shift between the signals and the time marks.
- the second synchronization step uses correlation to remove the uncertainties inherent in the previous step. 1.
- the method extracts from each signal element a characteristic parameter P.
- the evolution of the signal is replaced by the evolution of the characteristic parameter P, synchronous with the series of time references.
- a characteristic parameter can for example be extracted from a video sequence by any method.
- Figure 4 gives an example of the changes in the P parameter and the arrival times of the time marks.
- a correlation procedure is carried out on the parameter P, so as to find the exact correspondence between the two sequences. It is a question of knowing if the signal element represented by the reference RTsG ') e the parameter PsG') correspond to the signal element represented by the reference RT E (i) and the parameter P E (i), or to another element in the neighborhood T of P E (i).
- the purpose of the method is to provide an offset value ⁇ between the two series P E and Ps.
- the parameters P E and Ps can be subject to prior normalization by (3).
- the correction function is then the same as for the coarse synchronization phase.
- G ( ⁇ ) being a correlation function for example provided by one of relations (1), (4) or (5), SeuilValid being a validity threshold determined experimentally. In the case where this relation is not verified, it is considered that the fine synchronization process has failed.
- the signals E and S are obtained by decoding the corresponding bit streams by the decoders PDEC1 and PDEC2.
- RT time marks respectively for E and S, are extracted by the PERT1 and PERT2 blocks.
- PSGR Coarse Synchronization Processor
- the decoded signals E and S are used to extract the characteristic parameters therefrom by an external annex process, in the blocks PCPA1 and PCPA2. This information is used to achieve fine synchronization, performed by the PSFI processor.
- the method proposed by the invention is very useful in the application to a digital television broadcasting network. Indeed, in such a context, it is generally not possible to have the two sequences E and S in the same place. Therefore, it is not possible to use a conventional correlation approach.
- the interest of the proposed system comes from the use of parameters characteristic of the signals, which are materialized by easily transportable numbers, in order to achieve fine synchronization.
- Example of operation The table below illustrates the operation of the process in the case where the difference between two successive time references RT being constant, it is possible to transmit the value of the time reference RTE only all the N parameters PE.
- N 15.
- Coarse synchronization based on time marks has been achieved: after compensation for the offset d existing between the two series of values, we can see that the values of the two series are close. Then, the parameters P corresponding to the time marks are used to perform fine synchronization.
- the proposed method is relatively simple to implement and it can find multiple applications in the field of digital television.
- the proposed method can be applied to the resynchronization of signals before and after crossing certain special equipment, for example coder cascades and / or transcoders.
- the invention applies to any digital system, since the introduction of phase shifts is a characteristic of these systems.
- An advantage of the method according to the invention is that it is not necessary to have the complete signal E to synchronize a digital signal received S with the signal E, for example in order to carry out an evaluation of the quality. It suffices in fact to have the time references RT E of the reference signal, as well as the corresponding values of the parameter P. Under these conditions, it will be possible to calculate the parameter P for each of the digital elements, for example each of the images, of the signal received S so that the desired synchronization can then be carried out.
- the transmission of the time references RT E and of the corresponding parameters P of the reference signal E can for example be carried out using a service channel incorporated in the digital transmission multiplex, without modifying the transmitted signal.
- the invention makes it possible to relate the images of the reference signal E, with the images of the degraded signal S by using the parameters representative of the quality of the images.
- the quality of the images of signal S could have been degraded by transmission hazards and / or by the presence of coders or decoders in the transmission chain.
- the evaluation of the quality can then be carried out by comparison of the parameters representative of the quality of the images of the reference signal E and of the degraded signal S.
- the parameter P is liable to be subjected to degradations due to transmission, but it is observed in practice that at the degradation levels generally observed in transmission networks, synchronization can be carried out using the method according to the invention.
- the method makes it possible to verify that it is well preserved, so as to be able to remedy as necessary disturbances such as interruption of bit stream, change of bit stream, change decoder, etc. , by resynchronizing the two digital signals E and S.
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FR0013508 | 2000-10-23 | ||
FR0013508A FR2815805B1 (en) | 2000-10-23 | 2000-10-23 | METHOD FOR SYNCHRONIZING DIGITAL SIGNALS |
PCT/FR2001/003239 WO2002035855A1 (en) | 2000-10-23 | 2001-10-19 | Method for synchronizing digital signals |
Publications (1)
Publication Number | Publication Date |
---|---|
EP1330925A1 true EP1330925A1 (en) | 2003-07-30 |
Family
ID=8855593
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP01980601A Withdrawn EP1330925A1 (en) | 2000-10-23 | 2001-10-19 | Method for synchronizing digital signals |
Country Status (5)
Country | Link |
---|---|
US (1) | US7561601B2 (en) |
EP (1) | EP1330925A1 (en) |
CA (1) | CA2423861C (en) |
FR (1) | FR2815805B1 (en) |
WO (1) | WO2002035855A1 (en) |
Families Citing this family (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6459818B1 (en) * | 1999-03-01 | 2002-10-01 | University Of Rochester | System for recovery of degraded images |
DE102004042166A1 (en) * | 2004-08-31 | 2006-03-16 | MAX-PLANCK-Gesellschaft zur Förderung der Wissenschaften e.V. | Image processing device and corresponding operating method |
KR101224165B1 (en) * | 2008-01-02 | 2013-01-18 | 삼성전자주식회사 | Method and apparatus for controlling of data processing module |
US8205148B1 (en) | 2008-01-11 | 2012-06-19 | Bruce Sharpe | Methods and apparatus for temporal alignment of media |
EP2866448B1 (en) | 2010-07-30 | 2016-03-30 | Deutsche Telekom AG | Method and apparatus for temporally synchronizing the input bit stream of a video decoder with the processed video sequence decoded by the video decoder |
WO2017092007A1 (en) * | 2015-12-03 | 2017-06-08 | SZ DJI Technology Co., Ltd. | System and method for video processing |
US11321904B2 (en) | 2019-08-30 | 2022-05-03 | Maxon Computer Gmbh | Methods and systems for context passing between nodes in three-dimensional modeling |
US11714928B2 (en) | 2020-02-27 | 2023-08-01 | Maxon Computer Gmbh | Systems and methods for a self-adjusting node workspace |
US11373369B2 (en) | 2020-09-02 | 2022-06-28 | Maxon Computer Gmbh | Systems and methods for extraction of mesh geometry from straight skeleton for beveled shapes |
Citations (3)
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US5446492A (en) * | 1993-01-19 | 1995-08-29 | Wolf; Stephen | Perception-based video quality measurement system |
EP0838960A2 (en) * | 1996-10-28 | 1998-04-29 | Elop Electro-Optics Industries Ltd. | System and method for audio-visual content verification |
US6092040A (en) * | 1997-11-21 | 2000-07-18 | Voran; Stephen | Audio signal time offset estimation algorithm and measuring normalizing block algorithms for the perceptually-consistent comparison of speech signals |
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IT1237668B (en) * | 1989-10-31 | 1993-06-15 | Telettra Lab Telefon | SYSTEM AND MULTIPLATOR / DEMULTIPLATOR FOR THE TRANSMISSION / RECEPTION OF DIGITAL TELEVISION INFORMATION. |
US5467139A (en) * | 1993-09-30 | 1995-11-14 | Thomson Consumer Electronics, Inc. | Muting apparatus for a compressed audio/video signal receiver |
US5430485A (en) * | 1993-09-30 | 1995-07-04 | Thomson Consumer Electronics, Inc. | Audio/video synchronization in a digital transmission system |
US5642171A (en) * | 1994-06-08 | 1997-06-24 | Dell Usa, L.P. | Method and apparatus for synchronizing audio and video data streams in a multimedia system |
US5603016A (en) * | 1994-08-03 | 1997-02-11 | Intel Corporation | Method for synchronizing playback of an audio track to a video track |
US5874997A (en) * | 1994-08-29 | 1999-02-23 | Futuretel, Inc. | Measuring and regulating synchronization of merged video and audio data |
US5594660A (en) * | 1994-09-30 | 1997-01-14 | Cirrus Logic, Inc. | Programmable audio-video synchronization method and apparatus for multimedia systems |
US5598352A (en) * | 1994-09-30 | 1997-01-28 | Cirrus Logic, Inc. | Method and apparatus for audio and video synchronizing in MPEG playback systems |
US5805602A (en) * | 1995-09-25 | 1998-09-08 | Bell Atlantic Network Services, Inc. | Network monitoring system for cell delay variation |
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US6262776B1 (en) * | 1996-12-13 | 2001-07-17 | Microsoft Corporation | System and method for maintaining synchronization between audio and video |
JP3063838B2 (en) * | 1997-10-02 | 2000-07-12 | 日本電気株式会社 | Audio / video synchronous playback apparatus and method |
US6351471B1 (en) * | 1998-01-14 | 2002-02-26 | Skystream Networks Inc. | Brandwidth optimization of video program bearing transport streams |
SE517547C2 (en) * | 1998-06-08 | 2002-06-18 | Ericsson Telefon Ab L M | Signal synchronization in signal quality measurement |
JP2000092348A (en) * | 1998-09-10 | 2000-03-31 | Mitsubishi Electric Corp | Frame synchronizer |
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ATE270796T1 (en) * | 1999-07-15 | 2004-07-15 | Infineon Technologies Ag | METHOD FOR ESTIMATING THE CHANNEL PULSE RESPONSE OF A CELLULAR CHANNEL |
US6429902B1 (en) * | 1999-12-07 | 2002-08-06 | Lsi Logic Corporation | Method and apparatus for audio and video end-to-end synchronization |
FR2849328A1 (en) * | 2002-12-20 | 2004-06-25 | St Microelectronics Sa | METHOD AND DEVICE FOR SYNCHRONIZING THE PRESENTATION OF AUDIO FRAMES AND / OR VIDEO FRAMES |
-
2000
- 2000-10-23 FR FR0013508A patent/FR2815805B1/en not_active Expired - Fee Related
-
2001
- 2001-10-19 US US10/344,912 patent/US7561601B2/en not_active Expired - Lifetime
- 2001-10-19 WO PCT/FR2001/003239 patent/WO2002035855A1/en active Application Filing
- 2001-10-19 EP EP01980601A patent/EP1330925A1/en not_active Withdrawn
- 2001-10-19 CA CA2423861A patent/CA2423861C/en not_active Expired - Fee Related
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US5446492A (en) * | 1993-01-19 | 1995-08-29 | Wolf; Stephen | Perception-based video quality measurement system |
EP0838960A2 (en) * | 1996-10-28 | 1998-04-29 | Elop Electro-Optics Industries Ltd. | System and method for audio-visual content verification |
US6092040A (en) * | 1997-11-21 | 2000-07-18 | Voran; Stephen | Audio signal time offset estimation algorithm and measuring normalizing block algorithms for the perceptually-consistent comparison of speech signals |
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Title |
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See also references of WO0235855A1 * |
STEIN G P: "Tracking from multiple view points: self-calibration of space and time", PROCEEDINGS OF THE 1999 IEEE COMPUTER SOCIETY CONFERENCE ON COMPUTER VISION AND PATTERN RECOGNITION, JUNE 23-25, 1999; FORT COLLINS, COLORADO, IEEE, THE INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS, INC, US, vol. 1, 23 June 1999 (1999-06-23), pages 521 - 527, XP010347696, ISBN: 978-0-7695-0149-9 * |
Also Published As
Publication number | Publication date |
---|---|
WO2002035855A1 (en) | 2002-05-02 |
CA2423861A1 (en) | 2002-05-02 |
CA2423861C (en) | 2010-09-21 |
FR2815805A1 (en) | 2002-04-26 |
US7561601B2 (en) | 2009-07-14 |
US20030179740A1 (en) | 2003-09-25 |
FR2815805B1 (en) | 2005-09-02 |
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