EP0891673A1 - Commande de tampon dans un systeme de transmission de donnees codees - Google Patents

Commande de tampon dans un systeme de transmission de donnees codees

Info

Publication number
EP0891673A1
EP0891673A1 EP97915597A EP97915597A EP0891673A1 EP 0891673 A1 EP0891673 A1 EP 0891673A1 EP 97915597 A EP97915597 A EP 97915597A EP 97915597 A EP97915597 A EP 97915597A EP 0891673 A1 EP0891673 A1 EP 0891673A1
Authority
EP
European Patent Office
Prior art keywords
buffer
data
encoder
rate
bitrate
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Withdrawn
Application number
EP97915597A
Other languages
German (de)
English (en)
Inventor
Michael Richard Joseph Budge
John Jordan
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.)
Synamedia Ltd
Original Assignee
NDS Ltd
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 NDS Ltd filed Critical NDS Ltd
Publication of EP0891673A1 publication Critical patent/EP0891673A1/fr
Withdrawn legal-status Critical Current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]
    • H04N21/20—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
    • H04N21/234—Processing of video elementary streams, e.g. splicing of video streams or manipulating encoded video stream scene graphs
    • H04N21/23406—Processing of video elementary streams, e.g. splicing of video streams or manipulating encoded video stream scene graphs involving management of server-side video buffer
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/146—Data rate or code amount at the encoder output
    • H04N19/152—Data rate or code amount at the encoder output by measuring the fullness of the transmission buffer
    • 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
    • H04N21/2365—Multiplexing of several video streams
    • 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
    • H04N21/2365—Multiplexing of several video streams
    • H04N21/23655—Statistical multiplexing, e.g. by controlling the encoder to alter its bitrate to optimize the bandwidth utilization
    • 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
    • H04N21/24—Monitoring of processes or resources, e.g. monitoring of server load, available bandwidth, upstream requests
    • H04N21/2401—Monitoring of the client buffer
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding

Definitions

  • This invention relates to improvements in data transmission
  • a typical system for transmitting and/or receiving digital data may allow several video, audio and associated services to be multiplexed, sent over a
  • bitrate of data through individual channels or encoders is varied depending on the overall resources available
  • bitrate can be allocated to maximise picture quality for the group.
  • the present invention addresses the problems of managing the data within encoder and decoder buffers for systems that are operating both in
  • bitrate of the system whilst preserving picture quality, and preventing decoder buffer overflow and underflow.
  • the output of data is delayed by a time period dependant on the time taken for the data to enter the encoder and leave the decoder buffers.
  • this time period is set to the time stamp of the decoder.
  • apparatus for transmitting data in a digital data transmission system comprising monitoring means for monitoring the rate of data input to an encoder buffer to determine the decoder buffer requirements downstream of the encoder buffer; and a controller for controlling the encoder buffer in response to the monitoring step to delay a change in the rate of data output from the encoder by a predetermined time period relative to any change in rate of data input to the encoder buffer.
  • Figure 1 is a schematic diagram of a broadcasting system according to the invention.
  • Figure 2 is a diagram of encoder and decoder buffers
  • Figure 3 is a diagram for illustrating the features of the encoder buffer
  • Figure 4 is a diagram for illustrating how to achieve seamless bitrate changes according to a first embodiment of the present invention
  • Figure 5 is a diagram for illustrating buffer management in a statistical multiplexing system
  • Figure 6 is a diagram for illustrating the effect on buffer occupancy of different frame types
  • Figure 7 is a graph for showing the relationship between the encoder pre-quantisation scaling parameter and linear quality.
  • Figure 8 is a diagram for illustrating how to achieve seamless bitrate changes according to a second embodiment of the present invention.
  • the broadcasting system is illustrated in Figure 1 and includes a statistical multiplexing system 10.
  • the statistical multiplexing system may be as described in the above mentioned co-pending application or may be any other type of statistical multiplexing system.
  • a signal 12 such as a video signal is encoded by one of a plurality of encoders 14 and passes through the statistical multiplexing system and a transmission signal 16 is generated.
  • the video signal will be compressed by the encoder
  • the transmission signal is then transmitted to a receiver 18 where it is decoded back into a video signal by one of a plurality of decoders 20.
  • This video signal may then either be displayed for viewing or re-transmitted to another receiver, if necessary.
  • the transmission from the transmission end to the receiver end is via a satellite 22.
  • the encoders and decoders each include a buffer 13 and 23 respectively which are described in greater detail below.
  • the system in figure 1 shows a statistical multiplexing (Stat Mux) system.
  • Stat Mux statistical multiplexing
  • An MPEG receiver or decoder buffer is limited to 1.8Mbits or greater in size. This rate buffer can sustain a certain amount of bitrate variation. However it cannot support an unlimited variation of bitrate without an
  • the present invention provides a technique for improving the range of seamless bitrate changes by managing the encoder rate buffer so that the receiver buffer limits are not infringed.
  • FIG. 2 shows the encoder and decoder rate buffers 24 and 27 respectively.
  • the MPEG standard specifies that the maximum receiver rate buffer size is 1.8 Mbit.
  • the encoder buffer itself comprises two parts, a rate buffer 25 and a storage area 26 below the rate buffer. This storage area is referred to herein as the stuffing buffer and has an upper level which is referred to as the stuffing level.
  • the stuffing level is equivalent to the virtual floor of the rate buffer which will be described in greater detail below.
  • the rate buffer is the part of the encoder buffer used to smooth the arrival of data. In the case of compressed video data the data arrives at a 'bursty' rate.
  • the rate buffer is provided in the encoder to smooth this bursty data into a near constant stable output bitrate. A feedback mechanism exists from the rate buffer to the video
  • the quantisation factor The higher the occupancy, the higher is the mapping.
  • the timestamp is associated with a given frame of data and is
  • the decoder time stamp is selected
  • decoder buffers The total amount of data in the encoder and decoder buffers.
  • decoder rate buffer empties and vice versa.
  • encoder rate buffer is the same as that of the decoder buffer, to prevent
  • the total amount of data in the system at any point in time can also be any other data in the system at any point in time.
  • the total amount of data is equal to the buffer space available in both the rate
  • stuffing buffer capacity (dt s delay x bitrate) - 1.8Mbit
  • dt s delay can be varied by the user or by a control computer within the system, however it is preferred that this variable is left
  • the present invention provides a so called seamless bitrate
  • the minimum bitrate is given by:
  • buffer size is limited to a maximum of 1.8M bit, then:
  • bitrates can be achieved.
  • capacity of the stuffing buffer can be
  • the encoder buffer 24 includes the two sections previously identified, namely the rate buffer 25 and the 'stuffing buffer' 26.
  • the encoder rate buffer is provided with a virtual floor 54 and ceiling 56.
  • the whole of the rate buffer is typically fixed in absolute size, but is capable of
  • FIGs 4a ⁇ 4b, 4c and 4d illustrates one embodiment for carrying out the function of the seamless bitrate change.
  • the rate of data in is equal to the rate of data out. It will of course be appreciated that this may not be the case, since neither the receiver buffer limits and their effects, or the effect of the quantisation factor on data in are being taken into consideration.
  • FIG 4a normal levels of the rate buffer (RB) and stuffing buffer (SB) are shown.
  • the data is at a quantisation factor of Q a within the rate buffer. If the incoming data changes it may be necessary to transmit data to the decoder at a higher bitrate. If this higher bitrate is greater than that which can be achieved instantly, then it will be necessary to increase the capacity of the stuffing buffer.
  • the rate buffer slides up the encoder buffer, thereby increasing the capacity of the stuffing buffer. Since in this example the data level remains unchanged, the effect of this is that the quantisation factor will lower. In other words Q a > Q b , although the total amount of data in the system is the same. As the requirements for still higher bitrates occur the rate buffer slides still further up the encoder buffer, making the stuffing buffer still
  • the rate buffer can gradually slip down to be in
  • buffer has a finite size; a seamless bitrate change is required (i.e. no visual
  • the buffer time delay is generally already allocated and cannot be varied or controlled for buffer
  • the Stat Mux system will initialise the buffer levels in
  • residual data in the encoder can also inhibit the bitrate swing. Typically about
  • the bitrate that creates this initial level will be determined by the Multiplexer code. Assuming the buffer delay is fixed by time stamping then the decoder and encoder levels can be calculated. For example, in a system in which the Stat Mux computer decides that 8Mbit/s is the best estimate for bitrate and T is 0.2s, then the buffer levels would be as shown in Figure 5.
  • the bitrate B could jump from a maximum bitrate of 11.5Mbit/s to a minimum of 4.5Mbit/s as is described above.
  • bitrate A is the bitrate of data entering the encoder or rate buffer
  • bitrate B is the bitrate from the rate buffer to the variable buffer
  • bitrate C is the bitrate leaving the encoder or variable buffer.
  • the encoder buffer is controlled such that the amount of data leaving the rate buffer is always equal to the amount of data entering the rate buffer. In other words bitrate A is equal to bitrate B.
  • bitrate A is always changing and so therefore is bitrate B.
  • the changes made to bitrate B occur instantly as bitrate A changes in dependence on the source of the material broadcast.
  • bitrate C In order to ensure that the decoder or receiver buffer 90 does not underflow or overflow bitrate C cannot change instantly in dependence on bitrate A and/or B. If it did there would be a good chance that the decoder would either overfill or underfill, in either case causing the decoder to fail. Bitrate C must be controlled to ensure that there is not too much or too little data transmitted to the receiver buffer In the present embodiment this is done by delaying the change in bitrate of C. A typical delay implemented would be the time stamp period dt s . In other words bitrate C lags bitrate A (or B) by one time stamp period.
  • time stamp period is the time from which the data is 'inserted' into the encoder buffer, to the time it is 'removed' from the decoder buffer for decoding.
  • time stamp delay is the total time the date is in the system illustrated herein.
  • the present invention establishes a predictive track which aims to keep Q p the same and brings the
  • the predictive track results in a triangular waveform for the encoder buffer occupancy, which is shown in Figure 6.
  • the solid line shows the target track and the two dotted line show higher and lower Q p tracks. If the level strays
  • This tracking scheme for calculating Q p suits both Stat Mux and fixed rate systems.
  • the scheme handles the stabilisation of Q p within a frame, allowing the Stat Mux to stabilise Q p across multiple frames.
  • each pair may be operated as described above.
  • the operation of one pair of encoder and decoder buffers may be influenced by operation of another pair. This may be particularly the case when the two pairs are in the same Stat Mux group and bitrate is restricted.
  • the main controlling factor on operation of the system is the fact that the incoming data is the driving force.
  • the system works on a predictive basis and adjustments are made in response to the incoming data and the prediction of what will occur downstream. All data input into the system must be managed and caused to pass therethrough with the minimum degradation of quality At the decoder end there is a finite restriction for space and it is essential in the present invention to deal with the problems this may create before the system collapses.
  • the system is capable of predicting the problems which will result at the receiver end and manipulate the data in the transmitter end in such a way that the problems are prevented
  • the system can operate as an open loop system By predicting the value of Q P of the video signal being provided to the encoder it is possible to estimate whether the decoder buffers are going to experience underflow or overflow If either are likely to happen the encoder data is manipulated in such a way that the expected underflow or overflow are prevented
  • the above described techniques provide seamlessly changing bitrates in an MPEG video encoder across an unlimited range of values
  • a narrow range of bitrates can be achieved instantly using a control computer such as the MCC (Multiplex Control Computer) or the like and a wider range that are not instant rely on having a variable size stuffing buffer and a movable rate buffer
  • the non instant bitrate changes rely on the bitrate being changed incrementally and also an accompanying incremental adjustment to the stuffing buffer.

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Compression Or Coding Systems Of Tv Signals (AREA)
  • Communication Control (AREA)

Abstract

L'un des aspects de l'invention concerne un procédé permettant de modifier le débit des données dans un système de transmission de données numériques, qui comprend le contrôle du débit d'entrée dans un tampon de codeur pour déterminer les besoins du tampon du décodeur en aval; et la commande du tampon de codeur en réponse à l'étape de contrôle, de façon à retarder une modification du débit de sortie des données depuis le codeur d'une durée prédéfinie à partir de n'importe quelle modification du débit d'entrée des données dans le tampon codeur. Cette technique prédictive satisfait aux exigences d'une modification instantanée du débit binaire sans rupture de continuité. Une modification du débit binaire sans rupture de continuité implique qu'il n'y ait, au niveau du récepteur, ni interruption dans le décodage du flux binaire, ni artefacts anormaux. Donc, pour modifier sans rupture de continuité le débit binaire, la capacité du tampon du récepteur ne doit être ni surpassée ni soupassée, et le décalage du l'horodatage dans le flux binaire (le retard du tampon de débit) doit rester constant, de façon que le récepteur n'ait besoin ni de gagner ni de sauter des trames.
EP97915597A 1996-04-04 1997-04-04 Commande de tampon dans un systeme de transmission de donnees codees Withdrawn EP0891673A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GBGB9607162.6A GB9607162D0 (en) 1996-04-04 1996-04-04 Improvements in or relating to the transmission of data
GB9607162 1996-04-04
PCT/GB1997/000948 WO1997038532A1 (fr) 1996-04-04 1997-04-04 Commande de tampon dans un systeme de transmission de donnees codees

Publications (1)

Publication Number Publication Date
EP0891673A1 true EP0891673A1 (fr) 1999-01-20

Family

ID=10791637

Family Applications (1)

Application Number Title Priority Date Filing Date
EP97915597A Withdrawn EP0891673A1 (fr) 1996-04-04 1997-04-04 Commande de tampon dans un systeme de transmission de donnees codees

Country Status (4)

Country Link
EP (1) EP0891673A1 (fr)
JP (1) JP2001502125A (fr)
GB (1) GB9607162D0 (fr)
WO (1) WO1997038532A1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6061399A (en) * 1997-05-28 2000-05-09 Sarnoff Corporation Method and apparatus for information stream frame synchronization
WO2000003544A1 (fr) * 1998-07-10 2000-01-20 Koninklijke Philips Electronics N.V. Modification du debit binaire
US7145912B1 (en) 2000-03-23 2006-12-05 Tut Systems, Inc. Demultiplexing a statistically multiplexed MPEG transport stream into CBR single program transport streams
EP1783945A3 (fr) * 2000-10-13 2014-09-03 Sony Corporation Système de contrôle de qualité, système de transmission et récepteur des communications de données
EP2557788A1 (fr) * 2002-11-29 2013-02-13 Sony Corporation Appareil de codage et procédé

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0670663A1 (fr) * 1994-03-02 1995-09-06 Laboratoires D'electronique Philips S.A.S. Procédé et dispositif de codage de signaux numériques représentatifs d'une séquence d'images
US5534937A (en) * 1994-04-14 1996-07-09 Motorola, Inc. Minimum-delay jitter smoothing device and method for packet video communications
ES2150013T3 (es) * 1994-12-28 2000-11-16 Koninkl Philips Electronics Nv Gestion de almacenamiento intermedio en sistemas de compresion variable de transferencia de bits.
US5619341A (en) * 1995-02-23 1997-04-08 Motorola, Inc. Method and apparatus for preventing overflow and underflow of an encoder buffer in a video compression system

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9738532A1 *

Also Published As

Publication number Publication date
GB9607162D0 (en) 1996-06-12
JP2001502125A (ja) 2001-02-13
WO1997038532A1 (fr) 1997-10-16

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