EP0986915A1 - Transmission video codee en mpeg-2 dans des reseaux mta - Google Patents

Transmission video codee en mpeg-2 dans des reseaux mta

Info

Publication number
EP0986915A1
EP0986915A1 EP98917867A EP98917867A EP0986915A1 EP 0986915 A1 EP0986915 A1 EP 0986915A1 EP 98917867 A EP98917867 A EP 98917867A EP 98917867 A EP98917867 A EP 98917867A EP 0986915 A1 EP0986915 A1 EP 0986915A1
Authority
EP
European Patent Office
Prior art keywords
bit rate
encoder
data
mpeg
buffer
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.)
Ceased
Application number
EP98917867A
Other languages
German (de)
English (en)
Inventor
Per Tholin
Gunnar Bahlenberg
Erik Dillner
Magnus Johansson
Lis-Marie Ljunggren
Harry Tonvall
Per-Ola Wester
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Telia AB
Original Assignee
Telia AB
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Telia AB filed Critical Telia AB
Publication of EP0986915A1 publication Critical patent/EP0986915A1/fr
Ceased legal-status Critical Current

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
    • H04N21/434—Disassembling of a multiplex stream, e.g. demultiplexing audio and video streams, extraction of additional data from a video stream; Remultiplexing of multiplex streams; Extraction or processing of SI; Disassembling of packetised elementary stream
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T9/00—Image coding
    • G06T9/007—Transform coding, e.g. discrete cosine transform
    • 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]
    • H04N21/20—Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
    • H04N21/23—Processing of content or additional data; Elementary server operations; Server middleware
    • H04N21/236—Assembling of a multiplex stream, e.g. transport stream, by combining a video stream with other content or additional data, e.g. inserting a URL [Uniform Resource Locator] into a video stream, multiplexing software data into a video stream; Remultiplexing of multiplex streams; Insertion of stuffing bits into the multiplex stream, e.g. to obtain a constant bit-rate; Assembling of a packetised elementary stream

Definitions

  • the present invention relates to variable bit rate MPEG-2 encoders and decoders, particulariy encoders and decoders adapted for use with ATM, together with methods of encoding and decoding MPEG-2 data having a variable bit rate and systems for transmitting MPEG-2 data with a variable bit rate
  • MPEG-2 or ISO/IEC IS 13818, which is the official name for the MPEG-2 standard, is a key standard for high quality audiovisual communication and distribution
  • ISO/IEC IS 13818 which is the official name for the MPEG-2 standard
  • MPEG-2 for coding and multiplexing, for example, the new ITU-T Rec H 310 which sets out a terminal specification for broadband audiovisual communication over ATM
  • VBR which must comply with a traffic contract, is not easily implemented in a MPEG-2 encoder
  • the present invention provides, inter alia, a way of realising VBR in a
  • MPEG-2 system layer multiplexer which has been adapted for ATM. This can be used to provide a particularly simple implementation of a VBR MPEG-2 encoder having good jitter control and, at the same time, eliminates the need for a special "cell shaping" function in order to fulfil a traffic contract.
  • VBR variable bit rate
  • CBR constant bit rate
  • the nominal buffer level must be allowed to vary in time as the bit rate varies in order to keep the delay constant in the receiver; and the nominal bit rate is not known.
  • the present invention can be used in encoders, or terminals, for audiovisual communication, or distribution, based on MPEG-2 over ATM. Although this technique is primarily intended for use with MPEG-2 decoders which manage variable bit rate, for example, ATM-adapted MPEG-2 decoders operating with
  • VBR VBR.
  • the technique is not, however, limited to ATM transmission technology, but can be used for any transmission technology which supports VBR.
  • a telecommunications transmission system adapted for the transmission of MPEG-2 data streams, over a transmission network, with a variable bit rate including an encoder and decoder, characterised in that said encoder has data reading means, for reading data blocks from a video buffer, a bit rate within a block being constant and time slots between blocks having a variable duration.
  • Said decoder may have a reception buffer for receiving incoming MPEG-2 data, timing recovery means arranged to extract a current bit rate from a MPEG-2 protocol system layer, calculation means for calculating a nominal buffer level and recovery means for adaptively recovering deviations from said nominal bit rate.
  • a telecommunications transmission system adapted for the transmission of MPEG- 2 data streams, over a transmission network, with a variable bit rate including an encoder and decoder, characterised in that said decoder has a reception buffer for receiving incoming MPEG-2 data, timing recovery means arranged to extract a current bit rate from a MPEG-2 protocol system layer, calculation means for calculating a nominal buffer level for said reception buffer and recovery means for adaptively recovering deviations from said nominal bit rate
  • Said encoder may have data reading means, for reading data blocks from a video buffer, a bit rate within a block being constant and time slots between blocks having a variable duration
  • Said transmission network may be an ATM transmission network and said encoder and decoder may be adapted to operate with ATM
  • an encoder adapted to encode MPEG-2 data for transmission over an ATM network with a vanable bit rate, characterised in that data reading means are provided for reading data blocks from a video buffer, a bit rate within a block being constant and time slots between blocks having a variable duration
  • an encoder adapted to encode MPEG-2 data for transmission over an ATM network with a variable bit rate, characterised in that said encoder includes a system layer multiplexer adapted to empty a video encoder buffer by reading data blocks therefrom, at a bit rate which is constant within a block
  • Said system layer multiplexer may be adapted to control time intervals between said blocks in response to signals transmitted thereto by a regulator means
  • Said system layer multiplexer may generate an AAL payload flow which meets criteria specified by a traffic contract
  • Said regulator means may select time intervals between said blocks in dependence on an input signal indicative of said video data buffer's contents
  • Said bit rate may be substantially equal to one eighth of a network bit clock over which said MPEG-2 data is to be transmitted
  • Said encoder may include a programmable counter adapted to count down from a value, corresponding to the separation of two consecutive cells, to zero, and, in a latter part of a counting cycle, a cell may be transmitted
  • Said regulator means may be adapted to measure network load and bandwidth requirements for a given application and to determine the separation of two consecutive cells in dependence thereon
  • Said regulator means may be adapted to negotiate available bandwidth with a network over which said MPEG-2 data is to be transmitted
  • ATM cells may be transmitted in accordance with AAL1 , said programmable counter may be adapted to count from 52 to zero, a header may be transmitted when said counter has values between 52 and 47 and MPEG-2 data may be transmitted when said counter has values between 46 and zero
  • Flag means may be provided and arranged to set a flag, when said counter is zero, and reset said flag prior to reading out cells
  • a method of encoding MPEG-2 data for transmission over an ATM network with a variable bit rate characterised by reading data blocks from a video buffer, a bit rate within a block being constant and time slots between blocks having a variable duration
  • a video encoder buffer may be emptied by reading data blocks therefrom at a bit rate which is constant within a block.
  • Time intervals between said blocks may be controlled in response to signals transmitted by a regulator means.
  • An AAL payload flow may be generated which meets criteria specified by a traffic contract.
  • Time intervals between said blocks may be selected in dependence on said video data buffer's contents.
  • PCR fields may be located early in said blocks thereby maintaining alignment between transport packets and data blocks.
  • Said bit rate may be set substantially equal to one eighth of a network bit clock for a network over which said MPEG-2 data is to be transmitted.
  • Network load and bandwidth requirements may be measured for a given application and the separation of two consecutive cells may be determined in dependence thereon.
  • Available bandwidth may be negotiated with a network over which said MPEG-2 data is to be transmitted.
  • ATM cells may be transmitted in accordance with AAL1.
  • a decoder adapted to decode MPEG-2 data transmitted with a variable bit rate, characterised in that said decoder has a reception buffer for receiving incoming MPEG-2 data, timing recovery means arranged to extract a current bit rate from a MPEG-2 protocol system layer, calculation means for calculating a nominal buffer level and recovery means for adaptively recovering deviations from said nominal bit rate.
  • Said MPEG-2 data may have been transmitted over an ATM network and said decoder may be adapted to operate with ATM.
  • Said deviations, from a nominal bit rate, of the rate of emptying said buffer may be controlled by a phase locked loop.
  • Said nominal buffer level may be permitted to vary in time as said variable bit rate varies.
  • Said calculation means may operate on a bit rate immediately preceding said current bit rate, and said current bit rate, to calculate a nominal buffer level.
  • Said nominal buffer level may be used as a reference for adaptively recovering deviations from a current nominal bit rate by means of said phase locked loop.
  • Said nominal buffer level may vary, in a period where said nominal buffer level changes from an old to a new value, in the form of a ramp, either up, or down, between periods where said nominal buffer level is substantially constant.
  • Bit rate information may be extracted from outgoing data from said buffer and said bit rate information may be used to determine when said nominal bit rate is changed
  • a seventh aspect of the present invention there is provided a method of decoding MPEG-2 data for transmission with a variable bit rate, characterised by:
  • a phase locked loop may be used to control said deviations, from a nominal value, of the buffer level of said reception buffer.
  • a nominal buffer level may be calculated from an immediately preceding bit rate and said current bit rate.
  • Bit rate information may be extracted from outgoing data from said buffer and said bit rate information may be used to determine when said nominal bit rate is changed.
  • a system for transmitting MPEG-2 data with a variable bit rate including an encoder, a decoder and an ATM network characterised in that:
  • said encoder is an encoder as described in any preceding paragraph; and/or
  • said encoder operates according to a method as described in any preceding paragraph.
  • said decoder is an decoder as described in any preceding paragraph;
  • said decoder operates according to the method as described in any preceding paragraph.
  • a MPEG-2 terminal for transmitting/receiving MPEG-2 data with a variable bit rate, including an encoder, a decoder and an ATM network characterised in that
  • said encoder is an encoder as described in any preceding paragraph, and/or
  • said encoder operates according to a method as described in any preceding paragraph, and/or
  • said decoder is an decoder as described in any preceding paragraph, and/or
  • said decoder operates according to the method as described in any preceding paragraph
  • Figure 1 illustrates a process of reading data, block-by-block, from a video buffer with a variable bit rate
  • Figure 2 illustrates the variation with time of a programmable counter's contents with constant block and cell distance
  • Figure 3 illustrates the variation with time of a programmable counter's contents with variable block and cell distance.
  • VBR Special traffic classes are defined for VBR ATM transmission, namely
  • the MPEG-2 video encoding technique supports VBR.
  • VBR Video Broadcast Rate Average
  • VBR such as, a more uniform picture quality and shorter delay.
  • MPEG-2 specifications which define packeting, multiplexing and synchronisation, include support for VBR.
  • An encoder operating with VBR requires a control mechanism to continuously calculate a current data rate on the basis of a number of different input signals.
  • the data rate is a continuously variable function of time and can be different for each bit produced by an encoder. This ideal solution would be difficult to implement in a real encoder since the bit clock, which empties the video buffer, would, in principle, be required to vary continuously.
  • a VBR implementation of a MPEG-2 encoder can be substantially simplified by using a fixed clock frequency, selected in dependence on the highest data rate to be handled by the encoder, instead of a continuously varying transmission clock Data is then read out of the video buffer, in blocks, at the fixed clock frequency
  • the variation in bit rate is achieved by varying the interval between data blocks
  • the instantaneous rate will be burst-like with varying lengths of time slot between bursts, in which the bit rate is zero
  • the bit rate can be varied from a maximum value, on the right of Figure 1 , where the bursts are continuous, i e no intervening time slots between data blocks, to a much lower bit rate on the left of Figure 1 , in which there are substantial time slots between data blocks
  • a constant data rate is achieved within a data block, which can be varied from data block to data block.
  • the size of data blocks is kept comparatively small, e g equivalent to the size of an ATM cell, there are no restrictions imposed by the use of a step-wise block-by-block variation in bit rate compared with a continuous va ⁇ ation in bit rate.
  • the use of a step-wise va ⁇ ation in bit rate based on data blocks corresponding to the size of ATM cells, fits very well with the implementation of VBR in a MPEG-2 encoder adapted for use with ATM MPEG-2 supports VBR in the form of a "piecewise constant rate". This means that the byte stream has a constant byte rate between either:
  • a traffic contract is established when a VC (Virtual Channel) is established, such a traffic contract can be modelled by a "leaky bucket", see for example the ATM Forum's description of VBR.
  • the encoder To comply with the traffic contract, the encoder must supervise the following three parameters:
  • the present invention provides VBR in a MPEG-2 encoder through the action of the system layer multiplexer which empties the video encoder buffer block-by-block at a bit rate R.
  • B 0 is selected to be equal to 47 bytes, since this is the SAR-PDU (Segmentation and Reassembly Protocol Data Unit) payload size in the simplest case
  • the interval between two consecutive blocks is controlled by a multiplexer which, in turn, gets information from a regulator
  • the multiplexer therefore becomes the "rate master" in the system and other elements of the system adapt their processing rate to that set by the multiplexer
  • the multiplexer can, while the video buffer is being emptied, create a cell flow, strictly speaking an AAL payload flow, which meets the parameter values specified in the traffic contract No following "cell shaping" is needed provided that sequential steps in the AAL are implemented as pipe-lines with fixed delays
  • R is preferably selected to have a comparatively high value because this gives a low self induced jitter in the case where a plurality of different channels are multiplexed together, each with its own VCI
  • control mechanism used to select the data rate, uses the degree of fill of the video buffer as an input signal, allowance must be made for rapid changes of the signal du ⁇ ng the short period when a data block is read out of the video buffer
  • the gradient in buffer filling, as a function of time increases as the selected value of R increases This does not cause any practical difficulties, but it does have implications for the design of the regulator
  • the multiplexer and the AAL, etc data is transmitted in the form of blocks which always have an internal bit rate of R This need not cause jitter problems Provided alignment between transport packets and data blocks is maintained, i e so that PCR fields always occur early in the blocks the self induced jitter amplitude can be kept to an acceptably low level
  • the multiplexer generates a "piece- wise constant cell rate", which is referred to as PCCR in this patent specification
  • the control mechanism for PCCR operates with a clock frequency which is preferably, but not necessarily, selected as the bit clock of the network divided by eight, i.e. the clock rate corresponds to the network "byte clock” This rate is used to select the number of network clock cycles that will separate each cell
  • This mechanism includes a programmable counter which counts from the value "cell distance”, see Figure 2, to zero The "cell distance” is the distance between two consecutive cell starts. During the latter part of the counting cycle the cell is placed on the channel for transmission
  • the cell distance value can be changed and this in turn enables the distance between cells to be varied
  • the value of the cell distance is decided in a separate regulator which can measure the load on the network and bandwidth requirements of the application to be used On the basis of this data, the regulator negotiates, with the network, the bandwidth that will be made available - traffic contract
  • the case of variable block and cell distance is illustrated in Figure 3
  • the number of bits the counter contains depends on how low a bit rate, i.e the size of the maximal distance between cells, can be achieved For instance, if the maximal channel rate is 155Mb ⁇ t/s and the encoder needs to utilize 1 5 Mbit/s, then the distance will be
  • cell distance (cell size x 155)/1 5 expressed as a number of network clock cycles (byte oriented transmission)
  • the nominal buffer level must be allowed to vary in time as the bit rate vanes in order to keep the delay constant in the receiver
  • a buffer in the receiver is filled with incoming MPEG-2 data
  • the piece-by-piece constant bit rate Is extracted from incoming data by the system layer of the MPEG2 protocol This may be executed, for example, by means of the parameter programjnux_rate, see ISO/IEC IS13818-1
  • the nominal buffer level is calculated on the basis of this information and the preceding bit rate
  • the nominal buffer level will typically adopt the form of a ramp up, or down which changes to a constant level when all data which was transmitted with the old rate has left the buffer
  • the calculated nominal level can then be used as reference for the adaptive recovery of the deviation from the nominal bit rate by means of a PLL, or similar arrangement
  • the bit rate information from outgoing data is also extracted
  • This technique can be regarded as an extension of 'Adaptive Clock", which enables it to function with VBR, as well as CBR.
  • An implementation of this technique in an ATM-adapted MPEG-2 decoder can, therefore, utilize the same hardware as that used for an AAL1 Adaptive Clock. This means that separate AAL1 implementations for VBR and CBR are not needed.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Discrete Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Data Exchanges In Wide-Area Networks (AREA)
  • Compression Or Coding Systems Of Tv Signals (AREA)

Abstract

L'invention concerne un système de transmission de télécommunications conçu pour la transmission de trains de données MPEG-2 à un débit binaire variable. Ce système comprend un codeur et un décodeur. Le décodeur comprend un multiplexeur de couche système conçu pour vider un tampon de décodeur vidéo par lecture de ses blocs de données, avec un débit binaire constant dans un bloc. Le décodeur autorise un débit binaire variable (VBR) dans un multiplexeur de couche système MPEG-2 conçu pour un mode MTA, et représente une application particulièrement simple d'un décodeur VBR MPEG-2 ayant une bonne commande de gigue. Le décodeur rend superflue une fonction 'formation de cellule' spéciale en vue d'accomplir un contrat de trafic. Pour rétablir le rythme binaire dans le décodeur MPEG-2, les données sont temporairement mémorisées dans un tampon de réception. Par lecture continue de l'écartement du niveau tampon, c'est-à-dire du niveau de remplissage du tampon par des données, de sa valeur nominale, il est possible de commander, dans ce tampon, l'écartement du débit de vidage du tampon du débit binaire nominal, par une boucle à phase asservie (PLL) ou un système similaire.
EP98917867A 1997-04-16 1998-04-08 Transmission video codee en mpeg-2 dans des reseaux mta Ceased EP0986915A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE9701415A SE519917C2 (sv) 1997-04-16 1997-04-16 Förbättringar av,eller med avseende på,överföring av MPEG-2- data med variabel bithastighet
SE9701415 1997-04-16
PCT/SE1998/000648 WO1998047293A1 (fr) 1997-04-16 1998-04-08 Transmission video codee en mpeg-2 dans des reseaux mta

Publications (1)

Publication Number Publication Date
EP0986915A1 true EP0986915A1 (fr) 2000-03-22

Family

ID=20406592

Family Applications (1)

Application Number Title Priority Date Filing Date
EP98917867A Ceased EP0986915A1 (fr) 1997-04-16 1998-04-08 Transmission video codee en mpeg-2 dans des reseaux mta

Country Status (5)

Country Link
EP (1) EP0986915A1 (fr)
EE (1) EE9900491A (fr)
NO (1) NO994939L (fr)
SE (1) SE519917C2 (fr)
WO (1) WO1998047293A1 (fr)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6412013B1 (en) * 1998-10-23 2002-06-25 Koninklijke Philips Electronics N.V. System for controlling data output to a network
US7013318B2 (en) * 2002-05-29 2006-03-14 Raytheon Company Method and system for encapsulating cells
US7376141B2 (en) 2002-12-17 2008-05-20 Raytheon Company Method and system for encapsulating variable-size packets
EP1843587A1 (fr) 2006-04-05 2007-10-10 STMicroelectronics S.r.l. Methode de conversion de la fréquence trame d'un signal vidéo numérique et appareil correspondant

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5287182A (en) * 1992-07-02 1994-02-15 At&T Bell Laboratories Timing recovery for variable bit-rate video on asynchronous transfer mode (ATM) networks
FR2693864B1 (fr) * 1992-07-17 1994-08-26 Thomson Csf Procédé et dispositif de synchronisation d'un décodeur connecté à un réseau de transmission asynchrone, notamment de type ATM.
US5511054A (en) * 1993-03-31 1996-04-23 Sony Corporation Apparatus and method for multiplexing encoded data signals and recording medium having multiplexed signals recorded thereon
US5561466A (en) * 1993-06-23 1996-10-01 Nec Corporation Video and audio data multiplexing into ATM cells with no dummy cell used and ATM cell demultiplexing
CA2146801C (fr) * 1994-05-27 1999-11-02 Barin Geoffry Haskell Restitution des signaux de synchronisation pour les signaux video a debit binaire variable dans les reseaux a mode de transfert asynchrone (mta)

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9847293A1 *

Also Published As

Publication number Publication date
WO1998047293A1 (fr) 1998-10-22
NO994939L (no) 1999-12-16
SE9701415D0 (sv) 1997-04-16
SE519917C2 (sv) 2003-04-22
NO994939D0 (no) 1999-10-11
EE9900491A (et) 2000-06-15
SE9701415L (sv) 1998-10-17

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