GB2242097A - Buffer synchronisation in a variable transmission rate codec - Google Patents

Buffer synchronisation in a variable transmission rate codec Download PDF

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Publication number
GB2242097A
GB2242097A GB9100983A GB9100983A GB2242097A GB 2242097 A GB2242097 A GB 2242097A GB 9100983 A GB9100983 A GB 9100983A GB 9100983 A GB9100983 A GB 9100983A GB 2242097 A GB2242097 A GB 2242097A
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Prior art keywords
buffer
decoder
coder
transmission rate
changes
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Granted
Application number
GB9100983A
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GB2242097B (en
GB9100983D0 (en
Inventor
Nicholas Dominic Wells
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British Broadcasting Corp
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British Broadcasting Corp
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Publication of GB2242097A publication Critical patent/GB2242097A/en
Priority to GB9401783A priority Critical patent/GB2274041B/en
Application granted granted Critical
Publication of GB2242097B publication Critical patent/GB2242097B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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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, manipulating MPEG-4 scene graphs
    • H04N21/23406—Processing of video elementary streams, e.g. splicing of video streams, manipulating MPEG-4 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
    • H04N21/23614—Multiplexing of additional data and 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]
    • H04N21/40—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
    • H04N21/4348—Demultiplexing of additional data and 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]
    • H04N21/40—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
    • H04N21/44—Processing of video elementary streams, e.g. splicing a video clip retrieved from local storage with an incoming video stream, rendering scenes according to MPEG-4 scene graphs
    • H04N21/44004—Processing of video elementary streams, e.g. splicing a video clip retrieved from local storage with an incoming video stream, rendering scenes according to MPEG-4 scene graphs involving video buffer management, e.g. video decoder buffer or video display 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

Landscapes

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

Abstract

In order to synchronise buffer delays between coder and decoder buffers in a transmission system, e.g. an HDTV system, a signal representing the coder buffer occupancy Bc(r) is transmitted to the decoder with the picture signal. The transmission rate R or changes DELTA R in the transmission rate is summed or integrated at the cooler up to a point in time t1 at which picture information is written into the cooler buffer and a signal representing the resulting sum or integral is transmitted to the decoder with the picture signal. The decoder buffer occupancy Bd(r) is adjusted in response to the signals transmitted with the picture signal to adjust the delay through the decoder buffer and synchronise it with the delay through the cooler buffer. Underflow or overflow at the decoder buffer is also avoided.

Description

BUFFER RESYNCHRONISATION The present invention relates to a buffer resynchronisation strategy for a bit-rate reduction codec in which the transmission bit-rate may vary, for example, an HDTV (high definition television) oontribution codec.
An HDTV contribution codec has been proposed which consists of six 17 Mbit/s television codecs in parallel. Using this arrangement, it is envisaged that the available bit rate of 140 Mbit/s is shared rtynamically between the six codecs according to the needs of each picture area.
The dynamic allocation of bit rate between the codecs introduces complications in that it mLst be ensured that the delays through the buffer stores associated with each codec are synchronised, particularly in the presence of transmission errors.
In accordance with the invention, there is provided a method of synchronising buffer delays between coder and decoder buffers in a transmission system in which a signal representing the ooder buffer occupancy Bc(r) is transmitted to the decoder with the picture signal; changes R in the transmission rate R being hummed at the coder up to a point in time t1 at which picture information is written into the coder buffer and a signal representing the resulting sum transmitted to the decoder with the picture signal;; and the decoder buffer occupancy Bd(r) being adjustable in response to the signal representing the coder buffer occupancy and in response to the signal representing the said sum to thereby adjust the delay through the decoder buffer and synchronise it with the delay through the oDder buffer.In a preferred method according to the invention, the buffer occupancy Bd(r) is adjusted so as to meet the condition Bc(r,tl) + Bd (r,t2) = B - y1 + Y2 = Y2'-Y1' where
and
where B is the buffer size of both the coder and decoder buffers, R is the transmission rate, tl is the time at which picture information is written into the coder buffer, and t2 is the time at which the same picture information is read from the decoder buffer.
The invention also provides a method of regulating operation of a decoder buffer in a transmission system, in which changes in the transmission rate R and in the coder buffer occupancy Bc are monitored at the coder and the transmission rate adjusted in response to the said changes to avoid underflow or overflow at the decoder buffer.
In a further aspect, the invention provides means for putting the methods outlined above into effect.
A method in accordance with the invention will now be described in detail, by way of example, with reference to the drawings, in which: Figures l(a) and l(b) illustrate buffer addressing in a variable bit-rate coding system for a constant transmission rate; Figure 2(a) is a redrawing of Figures l(a) and l(b) for the case in which the coder buffer read address and decoder buffer write address are the same; Figure 2(b) illustrates buffer addressing with a non-constant transmission rate; and Figure 3 illustrates coder and decoder buffer addressing and shows regions of buffer underflow and overflow.
Synchronisation problems can arise for both fixed and variable transmission rates.
At the coder, with a fixed transmission rate, the data is written into the transmission buffer at a variable rate and read out at a constant rate. This is illustrated in Figure la. At the decoder, the data is written into the buffer at a constant rate and read out at a variable bit rate as shown in Figure Ib.
From the Figure, it can be seen that, if Bc(r) is the coder buffer occupancy at the time when the picture point r is written into the coder buffer and Bd(r) is the decoder buffer occupancy at the time when the same point r is read fran the decoder buffer, then Bc(r) + Bd(r) = const (1) and T = Tc + Td = (BcLr) + Bd(r))/R = Const/R (2) where R is the transmission bit rate and T the delay through the buffers.
If the coder and decoder buffers are the same size, B, then the delay through the buffers is given by T 5 B/R, which is a constant dependent on the transmission rate.
In order to be able to set the correct buffer occupccy (and hence overall delay) in the decoder, for example, after loss of synchronisation because of errors, the coder buffer occupancy is measured periodically at a known point in the picture and transmitted with that picture information. At the time when this picture information is read out from the decoder buffer, along with the corresponding decoder buffer occupancy, the decoder buffer occupancy is measured and caanpared with the expected value of (B-Bc(r)). If there is a discrepancy, the rate of reading from the buffer is increased or decreased as appro2riate such that the buffers are synchronised at some later point in the picture when the buffer occupancy is again checked.
Since the overall delay T = B/R, it might be thought that, for a variable transmission rate R, changes in the transmission rate R might result in changes in the delay T through the codec. This would create abvious problems for the synchronisation of six codecs in parallel if the rate, R, for each codec is different and changing.
Iwever, we have appreciated that this is not necessarily the case, as will be illustrated using Figure 2. Figure 2a is a redrawing of Figures la and Ib in which it is assumed, for otwnience and without loss of generality, that the coder buffer read address and the decoder buffer write address are the same. It can clearly be seen that the overall delay through the buffer pair is a constant.
In Figure 2b, it is assumed that the transmission rate is increased by an amount A R for a time 25T. It can be seen that the delay through the buffer pair remains unchanged as the shorter time that information is in the coder buffer is compensated by an increased delay in the decoder buffer.
However, a problem arises if it is necessary to resynchronise the decoder buffer. The coder buffer occupancy at the time of writing and the decoder occupancy at the time of reading are no longer related by the equation Bc(r) + Bd(r) = B.
If tl is the time at which the information at a particular point (e.g. the start of a stripe) is written into the coder buffer and t2 is the time that this information is read out from the decoder buffer, then Bc(r,t1) + Bd(r,t2) = B - Y1 + Y2 = y2'-y1' where
and
and where # R(t) is the change in transmission rate from the default rate Thus, for the decoder to be able to reset or to check its buffer read address the values of yl(tl) and y2(t2) or y11(t1) and y21(t2) must be known at the decoder.
Assuming that the transmission rate is changed only at the time when a new stripe of blocks is written into the coder buffer (or at a time as close to this as allowed by the transmission multiplex), then y1(tl) (or y11(t1)) can be calculated by accumulating the sum #n #R(stripe n).tstripe (or #nR(stripe n).tstripe) where tstripe is one stripe interval. In order to avoid the problem of knowing when to reset this sum, the accumulation could use appropriate irodiilo arithmetic.
With the assumption made above, the transmission rate at the input to the decoder buffer is changing at times corresponding closely to starts of stripes at the coder. Therefore, by monitoring the transmission rate changes at the input to the decoder buffer, the decoder can also calculate an accumulating sum of these changes.
The time t2 at which a 'start-of-stripe' is read from the decoder buffer is not necessarily co-timed with a start-of-stripe at the coder and hence with a change in R. However, an appropriate correction in the calculation of y2(t2) or y2,(t2) could be made taking into account this timing difference. Alternatively, the overall delay could be fixed such that these events were co-tinfil At the decoder, the value of the accumulating sum will need to be synchronised with that at the coder.This can be achieved, for example, by sending periodically the value of the sum yl(t1) and setting y2(t1)=yl(tl). The value of yl(t1) must be sent occasionally, therefore, as part of the transmission MUX together with the ch > unge cf transmission rate infarmation, It is possible to make changes in the transmission rate R such that the decoder buffer can overflow or underflow. This is illustrated in Figure 3. Buffer overflow occurs when the transmission rate is increased such that the buffer write address starts to overwrite information which has not yet been read from the buffer. Similarly, decoder buffer underflow can occur when the transmission rate is reduced and the read address catches up with the write address.
Decoder buffer underflow and overflow can be avoided by performing appropriate calculations at the coder. For example, Figure 3 shows that to avoid decoder overflow the coder must ensure that at any time, t
i.e.
To avoid underflow, the coder must also ensure that at any time t
i.e.
Therefore, the coder must know the total delay, T, through the buffers and must record and store buffer occupancies and values of the integrated transmission rate change for a period equal to this delay. The coder can then perform the checks described in equations (3) and (4).
Thus, two problems caused by the dynamic allocation of the bit rate between individual codecs runing in parallel in an HDTV codec have been addressed. These are (a) delay checking and synchronisation for the individual decoders, and (b) decoder buffer underflow and overflow.
These can be overcome to a large extent by a method according to the invention, in which: 1) The integral of the transmission rate or change in transmission rate is transmitted in the video MUX along with the buffer occupancy at the start of each stripe. The integral can be calculated modulo 2N where N is suitably large.
2) The decoder calculates the integral of the transmission rate or of the change in transmission rate at the input to the decoder buffer. This result can then be sampled as each stripe is read out of the buffer and appropriate corrections made for the exact output timing.
3) The e accumulation of the transmission rate or transmission rate change is sent periodically as part of the transmission MUX in order to reset the corresponding accumulating sum in the decoder.
4) The coder records and stores past values of the buffer occupancy and the accuitiilated transmission rate or transmission rate changes in order to check for and prevent decoder buffer overflow and underflow.

Claims (26)

1. A method of synchronising buffer delays between coder and decoder buffers in a transmission system in which a signal representing the coder buffer occupancy Bc(r) is transmitted to the decoder with the picture signal; the transmission rate or changes AR in the transmission rate R is surtrted or integrated at the coder up to a point in time tl at which picture information is written into the coder buffer and a signal represerxting the resulting sum or integral is transmitted to the decoder with the picture signal; and the decoder buffer occupancy Bd(g) being adjustable in response to the signal representing the coder buffer occupancy and in response to the signal representing the said sum or integral to thereby adjust the delay through the decoder buffer and synchronise it with the delay through the coder buffer.
2. A method according to claim 1 in which the signal representing the coder buffer occupancy is transmitted at intervals and the coder buffer occupancy adjusted each time such a signal is received at the decoder.
3. A method according to claim 1 or 2 in which a signal representing the said sum or integral is re-calculated and transmitted at intervals, the buffer occupancy at the decoder buffer being adjustable each time such a signal is received at the decoder,
4. A method according to claim 3 in which the said sum is recalculated and the said signal transmitted as each picture stripe is written to the coder buffer.
5. A method according to any preceding claim in which the transmission rate R or changes tiR in the transmissian rate R are monitored at the input of the decoder buffer and the rate or changes in the rate hummed up to a point in time t2 at which the picture information written into the coder buffer at time tl is read from the decoder buffer and the buffer occrqwlcy at the decoder buffer is adjustable in response to the said sum
6.A method according to claim 5 in which the buffer occupancy Bd(r) at the decoder buffer is adjustable so as to meet the condition Bc(r,tl) + Bd(r,t2) = B Y1 + Y2 = y2 -Y1 where
and
7. A method according to any preceding claim in which changes in the transmission rate R and in the coder buffer occupancy Bc are monitored at the coder and the transmission rate is adjustable in response to the said changes to avoid underflow or overflow at the decoder buffer.
8. A method of regulating operation of a decoder buffer in a transmission system, in which changes in the transmission rate R and in the coder buffer occupancy Bc are monitored at the coder and the transmission rate is adjustable in response to the said changes to avoid underflow or overflow at the decoder buffer.
9. A method according to claim 7 or 8 in which the transmission rate or changes iSR R in the transmission rate are monitored over a period T equal to the sum of the delays at the coder and decoder buffers.
10. A method according to claim 9 in which the transmission rate is adjusted to meet the condition
at time t, so as to avoid overflow at the decoder buffer.
11. A method according to claim 9 or 10 in which the transmission rate is adjusted to meet the condition
at time t so as to avoid underflow at the decoder buffer.
12. A method of synchronising buffer delays between coder and decoder buffers in a variable transmission rate codec, the method being substantially as hereinbefore described.
13. A method of regulating operation of a decoder buffer in a variable transmission rate codec, the method being substantially as hereinbefore described.
14. In a transmission system, means for synchronising buffer delays between coder and decoder buffers including means for transmitting a signal representing the coder buffer occupancy Bc(r) to the decoder with the picture signal; surtrting means for surritting the transmission rate R or changes A R in the transmussiDn rate R at the coder up to a point in time tl at which picture information is written into the coder buffer and for providing a signal representing the resulting sum to the means for transmitting; and means for adjusting the decoder buffer occupancy Bd(g) in response to the signal representing the coder buffer occupancy and in response to the signal representing said sum to thereby adjust the delay through the decoder buffer and synchrDnise it with the delay through the coder buffer.
15. ASxlratus according to claim 14 in which the signal representin the coder buffer occupancy is transmitted at intervals and the coder buffer occupancy adjusted each time such a signal is received at the decoder.
16. Apparatus according to claim 15 in which a signal representing the said sum is re-calculated and transmitted at intervals, the buffer occupancy at the decoder buffer being adjustable each time such a signal is received at the decoder.
17. Apparatus according to claim 16 in which the said sum is recalculated and the said signal transmitted as each picture stripe is written to the coder buffer.
18. Apparatus according to any of claims 14 to 17 including means for monitoring the transmission rate or changes b R in the transmission rate R at the input of the decoder buffer and for sutrrtiing the changes up to a point in time t2 at which the picture information written into the coder buffer at time tl is read from the decoder buffer; the means for adjusting the buffer occupancy at the decoder buffer being responsive to the said sum.
19. Apparatus according to claim 18 in which the buffer occupancy Bd(r) at the decoder buffer is adjusted so as to meet the condition Bc(r,t1) + Bd(rtt2) = B-y1 + Y2 = Y1 where
and
20. Apparatus according to any of claims 14 to 19 including means for monitoring changes in the transmission rate R and in the coder buffer occupancy Bc at the coder, and means for adjusting the transmission rate in response to the said changes to avoid underflow or overflow at the decoder buffer.
21. In a transmission system, means for regulating operation of a decoder buffer including means for ironitoring changes in the transmission rate R and in the coder buffer Occupancy Bc at the coder, and means for adjusting the transmission rate in response to the said changes to avoid underflow or overflow at the decoder buffer.
22. Apparatus according to claim 20 or 21 in which the transmission rate or changes R in the transmission rate are monitored over a period T equal to the sum of the delays at the coder and decoder buffers.
23. Apparatus according to claim 22 in which the transmission rate is adjusted to meet the condition
at time t, so as to avoid overflow at the decoder buffer.
24. Apparatus according to claim 2 or 23 in which the transmission rate is adjusted to meet the condition
at time t, so as to avoid underflow at the decoder buffer.
25. Apparatus for synchronising buffer delays between coder and decoder buffers in a variable transmission rate codec, the apparatus being substantially as hereinbefore described.
26. Apparatus for regulating operation of a deer buffer in a variable transmission rate codec, the apparatus being substantially as hereinbefore described.
GB9100983A 1990-01-19 1991-01-16 Buffer resynchronisation Expired - Fee Related GB2242097B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9401783A GB2274041B (en) 1990-01-19 1994-01-31 Buffer regulation

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9001295A GB9001295D0 (en) 1990-01-19 1990-01-19 Buffer resynchronisation

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GB9100983D0 GB9100983D0 (en) 1991-02-27
GB2242097A true GB2242097A (en) 1991-09-18
GB2242097B GB2242097B (en) 1994-09-14

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GB9100983A Expired - Fee Related GB2242097B (en) 1990-01-19 1991-01-16 Buffer resynchronisation

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0515101A2 (en) * 1991-05-23 1992-11-25 AT&T Corp. Buffer control for variable bit-rate channel
EP0517273A2 (en) * 1991-06-07 1992-12-09 Alcatel Espacio S.A. Method and device to regulate the output bit rate in variable bit rate video coders
WO1996017492A2 (en) * 1994-12-02 1996-06-06 Philips Electronics N.V. Encoder system level buffer management
WO1996017490A2 (en) * 1994-12-02 1996-06-06 Philips Electronics N.V. Audio/video timing discrepancy management
GB2307151A (en) * 1995-11-10 1997-05-14 British Broadcasting Corp Digital coding of video signals
WO1997039587A1 (en) * 1996-04-12 1997-10-23 Snell & Wilcox Limited Method and apparatus for looping of compressed video bitstreams
GB2315391A (en) * 1996-07-15 1998-01-28 Plessey Telecomm Data transfer over intermediate link with a higher data rate, keeping the sum of the input and output queues at a fixed value
GB2347326A (en) * 1999-02-26 2000-08-30 Mitel Inc Text-to-speech converter
GB2357674A (en) * 1999-10-26 2001-06-27 Snell & Wilcox Ltd Compressed bitstreams

Citations (1)

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Publication number Priority date Publication date Assignee Title
GB2181926A (en) * 1985-09-17 1987-04-29 Codex Corp Network data flow control

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2787599B2 (en) * 1989-11-06 1998-08-20 富士通株式会社 Image signal coding control method

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2181926A (en) * 1985-09-17 1987-04-29 Codex Corp Network data flow control

Cited By (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0515101A2 (en) * 1991-05-23 1992-11-25 AT&T Corp. Buffer control for variable bit-rate channel
EP0515101A3 (en) * 1991-05-23 1993-06-30 American Telephone And Telegraph Company Buffer control for variable bit-rate channel
EP0517273A2 (en) * 1991-06-07 1992-12-09 Alcatel Espacio S.A. Method and device to regulate the output bit rate in variable bit rate video coders
ES2038897A2 (en) * 1991-06-07 1993-08-01 Alcatel Espacio Sa Method and device to regulate the output bit rate in variable bit rate video coders.
EP0517273A3 (en) * 1991-06-07 1994-01-05 Alcatel Espacio Sa
WO1996017492A2 (en) * 1994-12-02 1996-06-06 Philips Electronics N.V. Encoder system level buffer management
WO1996017490A2 (en) * 1994-12-02 1996-06-06 Philips Electronics N.V. Audio/video timing discrepancy management
WO1996017492A3 (en) * 1994-12-02 1996-08-29 Philips Electronics Nv Encoder system level buffer management
WO1996017490A3 (en) * 1994-12-02 1996-08-29 Philips Electronics Nv Audio/video timing discrepancy management
CN1113542C (en) * 1994-12-02 2003-07-02 皇家菲利浦电子有限公司 Encoder system level buffer management
WO1997017809A1 (en) * 1995-11-10 1997-05-15 British Broadcasting Corporation Digital coding
GB2307151A (en) * 1995-11-10 1997-05-14 British Broadcasting Corp Digital coding of video signals
WO1997039587A1 (en) * 1996-04-12 1997-10-23 Snell & Wilcox Limited Method and apparatus for looping of compressed video bitstreams
AU715613B2 (en) * 1996-04-12 2000-02-03 Snell & Wilcox Limited Method and apparatus for looping of compressed video bitstreams
US6229851B1 (en) 1996-04-12 2001-05-08 Snell & Wilcox Limited Method and apparatus for looping of compressed video bitstreams
GB2315391A (en) * 1996-07-15 1998-01-28 Plessey Telecomm Data transfer over intermediate link with a higher data rate, keeping the sum of the input and output queues at a fixed value
GB2315391B (en) * 1996-07-15 2000-10-25 Plessey Telecomm Communication links for transmission of data in fixed size packets
GB2347326A (en) * 1999-02-26 2000-08-30 Mitel Inc Text-to-speech converter
US6546366B1 (en) 1999-02-26 2003-04-08 Mitel, Inc. Text-to-speech converter
GB2347326B (en) * 1999-02-26 2004-04-14 Mitel Inc Text-to-speech converter
GB2357674A (en) * 1999-10-26 2001-06-27 Snell & Wilcox Ltd Compressed bitstreams
GB2357674B (en) * 1999-10-26 2003-12-10 Snell & Wilcox Ltd Compressed bitstreams

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Publication number Publication date
GB2242097B (en) 1994-09-14
GB9001295D0 (en) 1990-03-21
GB9100983D0 (en) 1991-02-27

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