+

WO1997017809A1 - Digital coding - Google Patents

Digital coding Download PDF

Info

Publication number
WO1997017809A1
WO1997017809A1 PCT/GB1996/002771 GB9602771W WO9717809A1 WO 1997017809 A1 WO1997017809 A1 WO 1997017809A1 GB 9602771 W GB9602771 W GB 9602771W WO 9717809 A1 WO9717809 A1 WO 9717809A1
Authority
WO
WIPO (PCT)
Prior art keywords
buffer
coder
bit rate
decoder
size
Prior art date
Application number
PCT/GB1996/002771
Other languages
French (fr)
Inventor
Peter Ashley Sarginson
Original Assignee
British Broadcasting Corporation
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 British Broadcasting Corporation filed Critical British Broadcasting Corporation
Priority to EP96938327A priority Critical patent/EP0860085A1/en
Publication of WO1997017809A1 publication Critical patent/WO1997017809A1/en

Links

Classifications

    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06FELECTRIC DIGITAL DATA PROCESSING
    • G06F5/00Methods or arrangements for data conversion without changing the order or content of the data handled
    • G06F5/06Methods or arrangements for data conversion without changing the order or content of the data handled for changing the speed of data flow, i.e. speed regularising or timing, e.g. delay lines, FIFO buffers; over- or underrun control therefor
    • G06F5/10Methods or arrangements for data conversion without changing the order or content of the data handled for changing the speed of data flow, i.e. speed regularising or timing, e.g. delay lines, FIFO buffers; over- or underrun control therefor having a sequence of storage locations each being individually accessible for both enqueue and dequeue operations, e.g. using random access memory
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/115Selection of the code volume for a coding unit prior to coding
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134Methods 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
    • H04N19/146Data rate or code amount at the encoder output
    • H04N19/152Data rate or code amount at the encoder output by measuring the fullness of the transmission buffer
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/184Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being bits, e.g. of the compressed video stream
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/189Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding
    • H04N19/192Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding the adaptation method, adaptation tool or adaptation type being iterative or recursive
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/60Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
    • H04N19/61Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding in combination with predictive coding
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/20Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
    • H04N21/23Processing of content or additional data; Elementary server operations; Server middleware
    • H04N21/234Processing of video elementary streams, e.g. splicing of video streams or manipulating encoded video stream scene graphs
    • H04N21/23406Processing of video elementary streams, e.g. splicing of video streams or manipulating encoded video stream scene graphs involving management of server-side video buffer
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/40Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
    • H04N21/43Processing 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
    • H04N21/44Processing of video elementary streams, e.g. splicing a video clip retrieved from local storage with an incoming video stream or rendering scenes according to encoded video stream scene graphs
    • H04N21/44004Processing of video elementary streams, e.g. splicing a video clip retrieved from local storage with an incoming video stream or rendering scenes according to encoded video stream scene graphs involving video buffer management, e.g. video decoder buffer or video display buffer
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134Methods 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
    • H04N19/146Data rate or code amount at the encoder output
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding

Definitions

  • This invention relates to digital coding and in the most important example to the coding of video signals for transmission or otherwise.
  • the digital broadcast channels currently being specified for use within Europe and elsewhere each have sufficient digital capacity to accommodate a number of independent television services bound together in a "multiplex".
  • the video component For a television service, it is usual for the video component to be compressed using a video compression algorithm such as that known as PEG-2 . Despite the use of video compression it will generally be the case that the encoded video data stream occupies the majority of the bit- rate allocated to that service.
  • a video compression algorithm such as that known as PEG-2 .
  • the ability to subsequently change the video bit rate allocations of services sharing a multiplex is attractive to a broadcaster for the various reason.
  • space may be relinquished to accommodate an additional service.
  • a service that is no longer required may be dropped from the multiplex and its digital capacity may be reassigned to those services remaining thereby increasing their video bit rates and thence their subjective picture quality.
  • Service video bit rates may be reassigned dynamically according to programme content or other criteria. For example, bit-rate may be borrowed from a service carrying visual material that is easy to encode (e.g. a news reader talking in front of an otherwise stationary set) and used to help boost the video bit rate (and hence picture quality) of a service carrying more difficult programme material (e.g. a sports sequence - with fast action and camera pans).
  • a digital television broadcast receiver contains a video decoder whose function is to reverse the encoding process performed by the video coder in order to recover the original picture.
  • An important part of a video decoder is the "decoder buffer" which is used to store coded video data prior to decoding. Study of the behaviour of the decoder buffer shows that a sustained change in the bit rate assigned to the video component of an on-air service will almost certainly lead to overflow or underflow of the buffer. Either condition is highly undesirable and will result in corruption of the decoded picture and may require a complete reset of the decoder in order to recover from the situation.
  • the present invention consists in one aspect in a method of making a sustainable change to the output data rate of a coder without at any time causing overflow or underflow of the buffer of a decoder to which the coder is directly or indirectly connected by means of modifying the upper and lower limits of permitted coder buffer occupancy before, during and after a change in bit rate such that at all times the following equations are satisfied:
  • the present invention consists in a method of coding a signal at a controllable bit rate in a coder having a coder buffer, the coded signal being adapted for decoding in a decoder having a decoder buffer, comprising the steps of testing whether a desired bit rate change falls within acceptable limits; imposing buffer occupancy constraints upon the coder buffer in dependence upon the desired bit rate change; and implementing the bit rate change.
  • the step of testing whether a desired bit rate change falls within acceptable limits comprises comparing the ratio ⁇ r/r of the desired bit rate change ⁇ r to the original bit rate r, with fixed limits which are typically
  • the size of the coder buffer B c is greater than the size of the decoder buffer B d , and said fixed limits are BJB d and -1 .
  • the step of implementing the bit rate change is delayed after the attainment of said buffer occupancy constraints by a time interval not less than the buffer delay T.
  • the step of testing whether a desired bit rate change falls within acceptable limits comprises comparing the coder buffer occupancy ratio at a ⁇ earlier time spaced by a time interval, with a time integral over said interval of the bit rate increased by the desired bit rate change.
  • Figure 1 is a block diagram of a prior art broadcast chain proposal incorporating coding and multiplexing
  • Figure 2 is a graph illustrating the relationship between the occupancy of coder and decoder buffers
  • Figure 3 is a graph similar to Figure 2, illustrating decoder buffer overflow resulting from a step increase in bit rate;
  • Figure 4 is a graph similar to Figure 2, illustrating decoder buffer underflow resulting from a step decrease in bit rate:
  • Figure 5 is a graph showing permitted coder buffer occupancy versus change in bit rate in one arrangement according to the present invention.
  • Figure 6 is a block diagram illustrating one embodiment of the present invention.
  • Figures 7 & 8 are flow charts illustrating "loose” and “tight” coupling control procedures, respectively, for the apparatus of Figure 6;
  • Figure 9 is a graph of permitted coder buffer occupancy versus change in bit rate in a modified arrangement according to the present invention.
  • Input video is compressed by a video coder (10) according to a video compression algorithm such as that known as MPEG-2.
  • the video coder generates a variable number of bits per input video picture depending on the picture content.
  • the variable bit rate output from the video coder is converted to a fixed bit rate in the coder buffer (12).
  • the coder buffer is a first- in-first-out memory device enabling data to enter the buffer at a variable bit rate and be removed at a fixed bit rate determined by the multiplexer (14).
  • a feedback system is employed to prevent the coder buffer becoming too full (a condition known as "overflow") or empty (a condition known as "underflow").
  • the coded video data is delivered along with other programme components via the digital broadcast channel to a demultiplexer (16).
  • the demultiplexer extracts the coded video and delivers it at a fixed bit rate to the decoder buffer (18).
  • the video decoder (20) decodes pictures at regular intervals determined by the television standard being used (e.g. 25 pictures per second). However, because each picture is represented by a variable amount of data, this necessarily means that the video decoder must read a variable amount of data per picture period from the decoder buffer.
  • the decoder buffer adapts the fixed bit rate video from the demultiplexer to the variable bit rate needs of the video decoder. Reconstructed video is output from the video decoder.
  • Figure 2 shows how the positions (addresses) of the write and read pointers within the coder and decoder buffers vary with time. It is usual for the coder buffer size, B c and the decoder buffer size, j9,to be equal.
  • the buffers are "circular" meaning that when a write or read pointer reaches address (B - 1), it is automatically reset to address 0 upon the next address increment. This is reflected in the labelling of the vertical axis in Figure 2.
  • Variable bit-rate data is input to the coder buffer.
  • the coder buffer write address does not increment linearly with time.
  • Data is read from the coder buffer at a fixed bit rate and so the coder buffer read address does increment lineariy with time.
  • Data read from the coder buffer is transferred via the multiplexer, broadcast channel and demultiplexer to the decoder buffer. This transfer process will take a fixed and finite time, however, in this analysis for the sake of clarity and without loss of generality, the transfer time is ignored and the coder buffer read address and decoder buffer write address are assumed to be equal for all time, t
  • Figure 2 it is shown that data read from coder buffer address n is instantaneously transferred and written into decoder buffer address n.
  • coder will generally contain a sophisticated internal control system to prevent the coder buffer becoming too full (overflow) or too empty (underflow). So long as the control system achieves this goal it is certain that the decoder buffer will also never overflow or underflow.
  • bit rate i.e. the rate at which data is transferred from coder buffer to decoder buffer
  • Figure 3 illustrates the effect of a sustained increase in bit rate on the reference system.
  • the point where the decoder read address curve crosses the minimum decoder read address limit represents the onset of decoder buffer overflow.
  • For increases in bit rate of 100% or more it will be found to be quite impossible to draw a coder write address curve that does not result in decoder buffer overflow.
  • For increases in bit rate less than 100% it will be found possible to devise a coder write address curve that does not cause decoder buffer overflow but only by constraining the permitted range of coder buffer occupancy towards the higher end of the coder buffer. Such constraints are undesirable and may be impossible to achieve in a practical system.
  • Figure 4 illustrates the effect of a sustained decrease in bit rate on the reference system.
  • the point where the decoder read address curve crosses the decoder write address line represents the onset of decoder buffer underflow.
  • buffer underflow will generally be the result of a decrease in bit rate, it is always possible to devise a coder write curve that does not cause decoder buffer overflow. However, to achieve this it is necessary to constrain the coder buffer occupancy towards the lower end of the coder buffer. Again, such constraints are undesirable and may be impossible to achieve in a practical system.
  • the reason a sustained change in bit rate may lead to decoder buffer overflow or underflow is as follows: It is essential that the buffer delay, 7 * , remains constant regardless of any changes in bit rate, otherwise temporal distortion of the decoded video will occur.
  • the buffer delay is made up of two components. They are the time taken for an item of data to propagate through the coder buffer, T c and the time taken for the item of data to propagate through the decoder buffer, 7 " ,.
  • Bo a is the coder buffer occupancy at time t, .
  • Boont is the decoder buffer occupancy at time t,. ( ⁇ r + r) is the bit rate
  • Bo dt2 (r * A ⁇ T - Bo ⁇ [5]
  • the present invention provides a novel method of controlling a video coder such that sustained changes in bit rate may be achieved over a limited range - subject to certain constraints - without causing interruption of the decoded video.
  • equation [4] shows that limited, sustained changes in bit rate may be accommodated without causing overflow or underflow of the decoder buffer provided that the coder buffer occupancy is constrained to a reduced range.
  • equations [1], [2] and [3] apply and assuming that the original bit rate, r is changed by an amount, ⁇ r , then the constrained range of permitted coder buffer occupancy, Bo c is given by:
  • the coder controller has a means to convey instructions to the video coder and a means of receiving messages returned from the coder.
  • the "demand clock generator” block (64) effectively sets the actual output bit rate of the video coder under the direction of the coder controller.
  • the coder controller and the demand clock generator may form part of the multiplexer and the data passed from the coder to the coder controller may be incorporated into the coded video data stream. It is possible to devise control procedures for the coder controller that facilitate a sustained change in the output bit rate of the video coder whilst ensuring that equations [9] & [10] are always satisfied and hence without causing overflow or underflow of the decoder buffer. Two examples of these are given in the flowcharts of Figures 7 and 8. They are referred to as “loosely coupled” and “tightly coupled” respectively.
  • Control procedures as illustrated in Figure 7 permit a fairly "loose" coupling between coder and controller meaning that the dialogue between coder and coder controller is quite relaxed, permitting the use of low data rate connections. Such a control procedure may be especially useful in situations where the coder is physically remote from the coder controller.
  • coder buffer occupancy is constrained as follows
  • Figure 9 is a graph of permitted coder buffer occupancy plotted against ( ⁇ r/r) for a coder possessing a large buffer. It is apparent that the range of possible bit rates has been increased when compared to Figure 5 which shows the equivalent graph for a coder with buffer of size, fl . Also apparent and of special importance is the fact that for operation at bit rates in the range:
  • flosky TM is the maximum permitted buffer occupancy.
  • flo ⁇ is the minimum permitted buffer occupancy.
  • a coder possessing a large buffer can support sustained changes in its output bit rate without causing overflow or underflow of the decoder buffer and without requiring a reduction in the range of coder buffer occupancy.
  • the coder buffer is with advantage at least twice the size of the decoder buffer and, with further advantage, at least four times the size of the decoder buffer, in MPEG-2, there is defined the VBV (Virtual Buffer Verifier) buffer.
  • a coder buffer size is preferably at least twice and more preferably four times the size of the VBV buffer.
  • Equations [9] and [10] are still valid for a coder possessing a large coder buffer and must be satisfied at all times if overflow and underflow of the decoder buffer is to be avoided.
  • a control procedure designed to facilitate the adjustment of the output bit rate of a coder possessing a large coder buffer must ensure that equations [9] and [10] are satisfied before, during and after the change of bit rate.
  • control procedures are possible including enhancements of the "loosely coupled” and "tightly coupled” procedures presented earlier.
  • a further possibility is to avoid the use of a step change in bit rate but instead to change the bit rate slowly from one value to another whilst at the same time slowly changing the values of Bo ⁇ and Bo ⁇ , in such a way as to ensure that equations [9] and [10] are satisfied at all times.
  • Bo Bo condition Decoder buffer occupancy. (Units : bits). flo rt , Coder buffer occupancy at time, f,. (Units : bits). flo ⁇ Decoder buffer occupancy at time, ⁇ . (Units : bits).
  • BO ⁇ T Coder buffer occupancy at time, (t-T). (Units : bits). o ⁇ , Maximum permitted coder buffer occupancy. (Units : bits). o ⁇ Minimum permitted coder buffer occupancy. (Units : bits). r Nominal bit rate. (Units : bits per second).

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Theoretical Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Compression Or Coding Systems Of Tv Signals (AREA)

Abstract

The bit rate of an MPEG-2 or other digital coder can be varied without causing buffer underflow or overflow in a downstream decoder by controlling coder buffer occupancy and by employing an oversized coder buffer.

Description

DIGITAL CODING
This invention relates to digital coding and in the most important example to the coding of video signals for transmission or otherwise.
The digital broadcast channels currently being specified for use within Europe and elsewhere each have sufficient digital capacity to accommodate a number of independent television services bound together in a "multiplex".
It is a technically trivial matter to divide the total digital capacity of a multiplex into fixed bit-rate fractions each assigned to one service.
For a television service, it is usual for the video component to be compressed using a video compression algorithm such as that known as PEG-2 . Despite the use of video compression it will generally be the case that the encoded video data stream occupies the majority of the bit- rate allocated to that service.
The ability to subsequently change the video bit rate allocations of services sharing a multiplex is attractive to a broadcaster for the various reason. By lowering the video bit rate of existing services within a multiplex, space may be relinquished to accommodate an additional service. A service that is no longer required may be dropped from the multiplex and its digital capacity may be reassigned to those services remaining thereby increasing their video bit rates and thence their subjective picture quality. Service video bit rates may be reassigned dynamically according to programme content or other criteria. For example, bit-rate may be borrowed from a service carrying visual material that is easy to encode (e.g. a news reader talking in front of an otherwise stationary set) and used to help boost the video bit rate (and hence picture quality) of a service carrying more difficult programme material (e.g. a sports sequence - with fast action and camera pans).
Ideally, it should be possible to make such adjustments whilst the multiplex is "on-air" and without causing any interruption of the received services. Unfortunately, for reasons that will be described, it is technically very difficult (and often impossible) to make sustained changes to service video bit rates without upsetting the video decoder in the receiver. (It is always possible to drop a group of services from a multiplex and then re- introduce the group with a different assignment of bit-rates but this will clearly cause an interruption of the affected services at the receiver).
The reason for the difficulty is as follows: A digital television broadcast receiver contains a video decoder whose function is to reverse the encoding process performed by the video coder in order to recover the original picture. An important part of a video decoder is the "decoder buffer" which is used to store coded video data prior to decoding. Study of the behaviour of the decoder buffer shows that a sustained change in the bit rate assigned to the video component of an on-air service will almost certainly lead to overflow or underflow of the buffer. Either condition is highly undesirable and will result in corruption of the decoded picture and may require a complete reset of the decoder in order to recover from the situation.
It is an object of this invention to provide an improved approach to coding which addresses this problem.
Accordingly, the present invention consists in one aspect in a method of making a sustainable change to the output data rate of a coder without at any time causing overflow or underflow of the buffer of a decoder to which the coder is directly or indirectly connected by means of modifying the upper and lower limits of permitted coder buffer occupancy before, during and after a change in bit rate such that at all times the following equations are satisfied:
f
}(r * Ar ).dt < Bd + Bo^^ t-τ
Figure imgf000004_0001
ln another aspect, the present invention consists in a method of coding a signal at a controllable bit rate in a coder having a coder buffer, the coded signal being adapted for decoding in a decoder having a decoder buffer, comprising the steps of testing whether a desired bit rate change falls within acceptable limits; imposing buffer occupancy constraints upon the coder buffer in dependence upon the desired bit rate change; and implementing the bit rate change.
Preferably, the step of testing whether a desired bit rate change falls within acceptable limits, comprises comparing the ratio Δr/r of the desired bit rate change Δr to the original bit rate r, with fixed limits which are typically
1 and -1 .
Advantageously, the size of the coder buffer Bc is greater than the size of the decoder buffer Bd , and said fixed limits are BJBd and -1 .
Suitably, the step of implementing the bit rate change is delayed after the attainment of said buffer occupancy constraints by a time interval not less than the buffer delay T.
Alternatively, the step of testing whether a desired bit rate change falls within acceptable limits, comprises comparing the coder buffer occupancy ratio at aπ earlier time spaced by a time interval, with a time integral over said interval of the bit rate increased by the desired bit rate change.
The invention will now be described by way of example, with reference to the accompanying drawings, in which:-
Figure 1 is a block diagram of a prior art broadcast chain proposal incorporating coding and multiplexing;
Figure 2 is a graph illustrating the relationship between the occupancy of coder and decoder buffers;
Figure 3 is a graph similar to Figure 2, illustrating decoder buffer overflow resulting from a step increase in bit rate; Figure 4 is a graph similar to Figure 2, illustrating decoder buffer underflow resulting from a step decrease in bit rate:
Figure 5 is a graph showing permitted coder buffer occupancy versus change in bit rate in one arrangement according to the present invention;
Figure 6 is a block diagram illustrating one embodiment of the present invention;
Figures 7 & 8 are flow charts illustrating "loose" and "tight" coupling control procedures, respectively, for the apparatus of Figure 6;
Figure 9 is a graph of permitted coder buffer occupancy versus change in bit rate in a modified arrangement according to the present invention;
The invention can usefully be described with respect to the "reference system" shown in Figure 1. Such systems are well known especially within the field of digital television broadcasting.
Input video is compressed by a video coder (10) according to a video compression algorithm such as that known as MPEG-2. The video coder generates a variable number of bits per input video picture depending on the picture content. The variable bit rate output from the video coder is converted to a fixed bit rate in the coder buffer (12). The coder buffer is a first- in-first-out memory device enabling data to enter the buffer at a variable bit rate and be removed at a fixed bit rate determined by the multiplexer (14). A feedback system is employed to prevent the coder buffer becoming too full (a condition known as "overflow") or empty (a condition known as "underflow"). The coded video data is delivered along with other programme components via the digital broadcast channel to a demultiplexer (16). The demultiplexer extracts the coded video and delivers it at a fixed bit rate to the decoder buffer (18). The video decoder (20) decodes pictures at regular intervals determined by the television standard being used (e.g. 25 pictures per second). However, because each picture is represented by a variable amount of data, this necessarily means that the video decoder must read a variable amount of data per picture period from the decoder buffer.
Thus, the decoder buffer adapts the fixed bit rate video from the demultiplexer to the variable bit rate needs of the video decoder. Reconstructed video is output from the video decoder.
In systems of the type described by this reference system, there is a relationship between the occupancy (fullness) of the coder and decoder buffers and this may be illustrated on a diagram as shown in Figure 2.
Figure 2 shows how the positions (addresses) of the write and read pointers within the coder and decoder buffers vary with time. It is usual for the coder buffer size, Bc and the decoder buffer size, j9,to be equal.
Bc = Bd = B [1]
The buffers are "circular" meaning that when a write or read pointer reaches address (B - 1), it is automatically reset to address 0 upon the next address increment. This is reflected in the labelling of the vertical axis in Figure 2.
Variable bit-rate data is input to the coder buffer. Thus the coder buffer write address does not increment linearly with time. Data is read from the coder buffer at a fixed bit rate and so the coder buffer read address does increment lineariy with time. Data read from the coder buffer is transferred via the multiplexer, broadcast channel and demultiplexer to the decoder buffer. This transfer process will take a fixed and finite time, however, in this analysis for the sake of clarity and without loss of generality, the transfer time is ignored and the coder buffer read address and decoder buffer write address are assumed to be equal for all time, t Thus, in Figure 2, it is shown that data read from coder buffer address n is instantaneously transferred and written into decoder buffer address n. The video coder and the video decoder must process the same number of pictures per unit time, otherwise the decoded video will suffer temporal distortion ("playback" of the decoded video will be too slow or too fast). Therefore there must exist a fixed delay between a picture being coded in the video coder and subsequently decoded at the video decoder. Pursuing this line of reasoning to its conclusion it can be shown that there must exist a fixed delay between data being written into the coder buffer and the same data being read from the decoder buffer. This delay is shown as the "buffer delay, 7 " in Figure 2. The presence of this fixed delay enables the following important conclusions to be reached concerning the relationship between the coder buffer and the decoder buffer illustrated in Figure 2:
1. The shape of the coder write address and decoder read address curves are identical except that they are separated in time by an amount equal to the buffer delay, T.
If
t2 - i = T [2]
the coder buffer occupancy at time t„ Bo*, and the decoder buffer occupancy at time f, BoM when added together will equal the buffer size fl.
Bo^ + Bodt2 = B [3]
Thus, there is a complementary relationship between the coder buffer occupancy at time t, and the decoder buffer occupancy at time f.: If the coder buffer is π% full at time fT I the decoder buffer will be (100-π)% full at time t,.
The complementary relationship between coder and decoder buffer occupancies may be exploited as follows. A coder will generally contain a sophisticated internal control system to prevent the coder buffer becoming too full (overflow) or too empty (underflow). So long as the control system achieves this goal it is certain that the decoder buffer will also never overflow or underflow.
Unfortunately, this is no longer the case if the bit rate (i.e. the rate at which data is transferred from coder buffer to decoder buffer) is changed and this is illustrated in Figures 3 and 4.
Figure 3 illustrates the effect of a sustained increase in bit rate on the reference system. The point where the decoder read address curve crosses the minimum decoder read address limit represents the onset of decoder buffer overflow. For increases in bit rate of 100% or more, it will be found to be quite impossible to draw a coder write address curve that does not result in decoder buffer overflow. For increases in bit rate less than 100% it will be found possible to devise a coder write address curve that does not cause decoder buffer overflow but only by constraining the permitted range of coder buffer occupancy towards the higher end of the coder buffer. Such constraints are undesirable and may be impossible to achieve in a practical system.
Figure 4 illustrates the effect of a sustained decrease in bit rate on the reference system. The point where the decoder read address curve crosses the decoder write address line represents the onset of decoder buffer underflow. Although buffer underflow will generally be the result of a decrease in bit rate, it is always possible to devise a coder write curve that does not cause decoder buffer overflow. However, to achieve this it is necessary to constrain the coder buffer occupancy towards the lower end of the coder buffer. Again, such constraints are undesirable and may be impossible to achieve in a practical system.
The reason a sustained change in bit rate may lead to decoder buffer overflow or underflow is as follows: It is essential that the buffer delay, 7* , remains constant regardless of any changes in bit rate, otherwise temporal distortion of the decoded video will occur. The buffer delay is made up of two components. They are the time taken for an item of data to propagate through the coder buffer, Tc and the time taken for the item of data to propagate through the decoder buffer, 7",. Referring to Figure 2:
τ = τc + τd = Bo<» + Bo<« [4]
where:
Boa, is the coder buffer occupancy at time t, . Bo„ is the decoder buffer occupancy at time t,. (Δr + r) is the bit rate
re-arranging for Bo„:
Bodt2 = (r * AήT - Bo^ [5]
Thus if T is kept constant, an increase in the bit rate (i.e. Δr > 0) will result in a higher decoder buffer occupancy at time f, than would be observed for the same value of coder buffer occupancy when operating at the original bit rate (i.e. Δr = 0) . The increase in decoder buffer occupancy makes decoder buffer overflow likely (or certain) particularly if the bit rate is increased by a large amount or the coder buffer occupancy is low. Similarly, a decrease in the bit rate (i.e. Δr < 0) will result in a lower decoder buffer occupancy compared to that resulting from operation at the original bit rate and thus decoder buffer underflow is likely.
In one aspect, the present invention provides a novel method of controlling a video coder such that sustained changes in bit rate may be achieved over a limited range - subject to certain constraints - without causing interruption of the decoded video.
Further consideration of equation [4] will show that limited, sustained changes in bit rate may be accommodated without causing overflow or underflow of the decoder buffer provided that the coder buffer occupancy is constrained to a reduced range. Applied to the reference system of Figure 1 where equations [1], [2] and [3] apply and assuming that the original bit rate, r is changed by an amount, Δr , then the constrained range of permitted coder buffer occupancy, Boc is given by:
B > Bo„ ≥ B Δr Δr ≥ 0 [6]
fl (1 + AL) > Boc ≥ 0 Δr ≤ 0 [7]
There is shown in Figure 5 a graph of permitted coder buffer occupancy if underflow or overflow of the decoder buffer is to be prevented during a sustained change of bit-rate. It is apparent from this graph that the range over which the bit rate may be changed is limited to the range:
-1 < ( — ) < 1 [8] r
i.e. Between 0 and twice the original bit rate. Operation towards the extremes of this range requires severe limitation of the range of permitted coder buffer occupancy and this may be impossible to achieve in a practical video coder. However, for small changes in bit rate the limitation of coder buffer occupancy range may be acceptable. The following are general equations which must always be satisfied if decoder buffer overflow and underflow are to be avoided. They are based on the work of Dr N.D. Wells in GB-B-2 2420 97, to which reference is directed.
To avoid decoder buffer overflow at time f the following relationship must be satisfied:
t f(r + Ar ).dt < Bd + flo, -Kt-T) [9] t-τ
Similarly, to avoid decoder buffer underflow at time, f, the following relationship must be satisfied:
/(r + Δr ).Λ > floc(/.7) [10] t-τ
It can be shown that in order to guarantee that these equations are satisfied during a change of bit rate, it is necessary for the coder to attain the constrained buffer occupancy range a time T before the bit rate is changed (where T is the buffer delay). Once the bit rate has assumed the new value, the coder must maintain its buffer occupancy within the constrained range until the bit rate is restored to the original value (Δr = 0 ). Using an approach according to this invention, it is possible to control an otherwise conventional video coder such that sustained changes in its output bit rate may be made without causing underflow or overflow of the decoder buffer. A possible implementation is shown in Figure 6.
In Figure 6, the output bit rate of the video coder (60) may be freely varied over the range defined by equation [8]. The "coder controller" block
(62) is responsible for orchestrating the bit rate changes in such a way as to prevent overflow or underflow of the decoder buffer. The coder controller has a means to convey instructions to the video coder and a means of receiving messages returned from the coder. The "demand clock generator" block (64) effectively sets the actual output bit rate of the video coder under the direction of the coder controller.
Note that in a digital television broadcast system such as shown in Figure 1 , the coder controller and the demand clock generator may form part of the multiplexer and the data passed from the coder to the coder controller may be incorporated into the coded video data stream. It is possible to devise control procedures for the coder controller that facilitate a sustained change in the output bit rate of the video coder whilst ensuring that equations [9] & [10] are always satisfied and hence without causing overflow or underflow of the decoder buffer. Two examples of these are given in the flowcharts of Figures 7 and 8. They are referred to as "loosely coupled" and "tightly coupled" respectively.
Control procedures as illustrated in Figure 7 permit a fairly "loose" coupling between coder and controller meaning that the dialogue between coder and coder controller is quite relaxed, permitting the use of low data rate connections. Such a control procedure may be especially useful in situations where the coder is physically remote from the coder controller.
The loose coupling procedure operates as follows. It is assumed that the coder is initially operating at its original bit rate (Δr = 0). When a change in bit rate is desired, the coder controller (62) instructs the coder (60) to attain the appropriate constrained buffer occupancy range as determined by equations [6] and [7]. This may be achieved by modifying the maximum and minimum permitted buffer occupancy limit parameters in the coder's internal buffer control system. On achieving stable operation within the constrained range, the coder informs the coder controller. To ensure that equations [9] and [10] are satisfied under all conditions, the controller must now wait a time, T before instructing the demand clock generator to implement the new bit rate. To return subsequently to the original bit rate (Δr = 0), the coder controller (62) simply instructs the demand clock generator (64) to restore the original bit rate and informs the coder (60) that the constraints on buffer occupancy may be removed. (It is possible to extend this basic procedure to permit changes from one bit rate to another without returning to the original bit rate as an intermediate step). In contrast, control procedures as illustrated in Figure 8 require a
"tighter" coupling between coder and controller meaning that the coder continually passes data to the controller and a fairly high bandwidth connection is required to support this. The advantage of this type of procedure is that the controller may instantaneously change the bit rate, that is to say there is no need to wait a time, T .
In the tightly coupled control procedure, data is continually conveyed from the coder to the controller such that at any moment, the amount by which the bit rate may be increased or decreased (without causing overflow or underflow of the decoder buffer) is known. For any time, t , this may be determined by observing the coder buffer occupancy over the previous time period, T . Application of equations [9] & [10] will enable the available range of bit rate variation to be determined. This calculation may be performed by the coder or by the controller. In the former case, it is the available range of bit rate variation that is continually conveyed to the controller and in the latter case it is the instantaneous buffer occupancy (or something closely related to it) that is continually conveyed to the controller.
Many variations and combinations of the two basic control procedures are possible.
In a second aspect of this invention, it has been recognised by the present inventor that the range of possible bit rates may be greatly increased and the constraints on buffer occupancy range may be reduced, if the video coder is fitted with a "coder buffer" of greater than conventional size.
Thus far, it has been assumed that the coder and decoder buffers are of equal size, fl . Now consider a video coder possessing a buffer of size, flc where fl, > fl . Consideration of equation [4] will show that for such a coder sustained changes in bit rate without causing overflow or underflow of the decoder buffer may be accommodated over the following extended range:
.?• > > -ι [11] fl r
provided that the coder buffer occupancy is constrained as follows
Bc > Bo0 ≥ B £ B,
> — Δr ≥ B r f - 1 [12] l
fl 1 0 [13]
Figure imgf000015_0001
fl 1 + L \ > Bon ≥ 0 Δr < 0 [14]
Figure 9 is a graph of permitted coder buffer occupancy plotted against (Δr/r) for a coder possessing a large buffer. It is apparent that the range of possible bit rates has been increased when compared to Figure 5 which shows the equivalent graph for a coder with buffer of size, fl . Also apparent and of special importance is the fact that for operation at bit rates in the range:
Figure imgf000016_0001
the range of coder buffer occupancy is not reduced, i.e:
- B0cmln = B [16]
where: flo„ is the maximum permitted buffer occupancy. flo^ is the minimum permitted buffer occupancy.
Thus, a coder possessing a large buffer can support sustained changes in its output bit rate without causing overflow or underflow of the decoder buffer and without requiring a reduction in the range of coder buffer occupancy. The coder buffer is with advantage at least twice the size of the decoder buffer and, with further advantage, at least four times the size of the decoder buffer, in MPEG-2, there is defined the VBV (Virtual Buffer Verifier) buffer. According to the present invention, a coder buffer size is preferably at least twice and more preferably four times the size of the VBV buffer.
Equations [9] and [10] are still valid for a coder possessing a large coder buffer and must be satisfied at all times if overflow and underflow of the decoder buffer is to be avoided. Thus a control procedure designed to facilitate the adjustment of the output bit rate of a coder possessing a large coder buffer must ensure that equations [9] and [10] are satisfied before, during and after the change of bit rate.
A variety of control procedures are possible including enhancements of the "loosely coupled" and "tightly coupled" procedures presented earlier.
A further possibility is to avoid the use of a step change in bit rate but instead to change the bit rate slowly from one value to another whilst at the same time slowly changing the values of Bo^ and Bo^, in such a way as to ensure that equations [9] and [10] are satisfied at all times.
A glossary of the symbols used in this description and the accompanying drawings and claims is for reference set out below:-
t, t„ t, Moments in time. (Units : seconds).
7 Buffer delay. (Units : seconds). Generally 7 = _B_. r Bc Size of coder buffer. (Units : bits) fl. Size of decoder buffer. (Units : bits) fl Nominal buffer size. (Units : bits). In this document Bc ≥ B = B„. Boc Coder buffer occupancy. (Units : bits).
Bo„ Decoder buffer occupancy. (Units : bits). flort, Coder buffer occupancy at time, f,. (Units : bits). floΛ Decoder buffer occupancy at time, ζ. (Units : bits).
BO^T, Coder buffer occupancy at time, (t-T). (Units : bits). o^, Maximum permitted coder buffer occupancy. (Units : bits). o^ Minimum permitted coder buffer occupancy. (Units : bits). r Nominal bit rate. (Units : bits per second).
Δr Offset from nominal bit rate. (Units : bits per second). May be positive or negative.

Claims

1. A method of making a sustainable change to the output data rate of a coder without at any time causing overflow or underflow of the buffer of a decoder to which the coder is directly or indirectly connected by means of modifying the upper and lower limits of permitted coder buffer occupancy before, during and after a change in bit rate such that at all times the following equations are satisfied:
t
Figure imgf000018_0001
t
Figure imgf000018_0002
2. A coder incorporating a buffer of size greater than is required for operation at a single fixed output data rate in order to permit sustained changes to be made to its output data rate over a greater range of possible data rates when compared to a coder incorporating a buffer of the size required for operation at a single fixed output data rate, the coder comprising means for controlling the upper and lower limits of permitted coder buffer occupancy before, during and after a change in bit rate such that at all times the following equations are satisfied: t
Figure imgf000019_0001
t
Figure imgf000019_0002
3. A method of coding a signal at a controllable bit rate in a coder having a coder buffer, the coded signal being adapted for decoding in a decoder having a decoder buffer, comprising the steps of testing whether a desired bit rate change falls within acceptable limits; imposing buffer occupancy constraints upon the coder buffer in dependence upon the desired bit rate change; and implementing the bit rate change.
4. A method according to Claim 3, wherein the coder buffer size is at least twice the nominal decoder buffer size.
5. A method according to Claim 4, wherein the coder buffer size is at least four times the nominal buffer size.
6. A method according to any one of Claims 3 to 5, wherein the step of testing whether a desired bit rate change falls within acceptable limits, comprises comparing the ratio Δr/r of the desired bit rate change Δr to the current bit rate r, with fixed limits.
7. A method according to Claim 6, wherein said fixed limits are 1 and -1.
8. A method according to Claim 6, where the size of the coder buffer B is greater than the size of the decoder buffer Bd , and wherein said fixed limits are BJBύ and -1 .
9. A method according to any one of Claims 6 to 8, wherein the step of implementing the bit rate change is delayed after the attainment of said buffer occupancy constraints by a time interval not less than the buffer delay T.
10. A method according to any one of Claims 3 to 5, wherein the step of testing whether a desired bit rate change falls within acceptable limits, comprises comparing the coder buffer occupancy ratio at an earlier time spaced by a time interval, with a time integral over said interval of the bit rate increased by the desired bit rate change.
11. A method according to Claim 10, wherein the step of testing utilises the following inequality:
Bd +
Figure imgf000020_0001
> /(r + Aή.dt > flo, c(f-7) t-T
where Boe(t_η is the coder buffer occupancy at time t-T , Bd is the size of the decoder buffer and T is the buffer delay.
12. A method according to any one of Claims 3 to 5, wherein for a desired bit rate increase of Δr from a current bit rate of r , the coder buffer occupancy is constrained to be greater than or equal to the proportion Δr/r of the coder buffer size.
13. A method according to any one of Claims 3, 4, 5 or 12, wherein for a desired bit rate decrease of Δr from a current bit rate of r , the coder buffer occupancy is constrained to be less than the proportion (1+Δr/r) of the coder buffer size.
14. A method of coding a signal at a controllable bit rate in a coder having a coder buffer, the coded signal being adapted for decoding in a decoder having a decoder buffer, wherein the size of the coder buffer exceeds that of the decoder buffer and wherein buffer occupancy constraints are imposed upon the coder buffer in dependence upon the desired bit rate change.
PCT/GB1996/002771 1995-11-10 1996-11-11 Digital coding WO1997017809A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP96938327A EP0860085A1 (en) 1995-11-10 1996-11-11 Digital coding

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9523042.1 1995-11-10
GB9523042A GB2307151A (en) 1995-11-10 1995-11-10 Digital coding of video signals

Publications (1)

Publication Number Publication Date
WO1997017809A1 true WO1997017809A1 (en) 1997-05-15

Family

ID=10783690

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1996/002771 WO1997017809A1 (en) 1995-11-10 1996-11-11 Digital coding

Country Status (3)

Country Link
EP (1) EP0860085A1 (en)
GB (1) GB2307151A (en)
WO (1) WO1997017809A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114185512A (en) * 2021-11-01 2022-03-15 荣耀终端有限公司 Sensor data processing method, electronic device and readable storage medium

Families Citing this family (40)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2323754B (en) * 1997-01-30 2002-03-20 Peter Graham Craven Lossless compression using iir prediction filters
GB2331678A (en) * 1997-11-25 1999-05-26 Daewoo Electronics Co Ltd Controlling data flow in a synchronous data compression system
EP0972408A2 (en) * 1998-02-03 2000-01-19 Koninklijke Philips Electronics N.V. Method of switching of coded video sequences and corresponding device
US6023233A (en) * 1998-03-20 2000-02-08 Craven; Peter G. Data rate control for variable rate compression systems
KR100728509B1 (en) * 1998-07-10 2007-06-15 코닌클리케 필립스 일렉트로닉스 엔.브이. Data compression apparatus and method for controlling same, computer readable recording medium and video encoding apparatus control method
US6546366B1 (en) 1999-02-26 2003-04-08 Mitel, Inc. Text-to-speech converter
US8266657B2 (en) 2001-03-15 2012-09-11 Sling Media Inc. Method for effectively implementing a multi-room television system
US6263503B1 (en) 1999-05-26 2001-07-17 Neal Margulis Method for effectively implementing a wireless television system
JP4331835B2 (en) 1999-09-22 2009-09-16 パナソニック株式会社 Image data transmission method
US7707614B2 (en) 2004-06-07 2010-04-27 Sling Media, Inc. Personal media broadcasting system with output buffer
US8346605B2 (en) 2004-06-07 2013-01-01 Sling Media, Inc. Management of shared media content
US9998802B2 (en) 2004-06-07 2018-06-12 Sling Media LLC Systems and methods for creating variable length clips from a media stream
US8099755B2 (en) 2004-06-07 2012-01-17 Sling Media Pvt. Ltd. Systems and methods for controlling the encoding of a media stream
US7769756B2 (en) 2004-06-07 2010-08-03 Sling Media, Inc. Selection and presentation of context-relevant supplemental content and advertising
US7975062B2 (en) 2004-06-07 2011-07-05 Sling Media, Inc. Capturing and sharing media content
US7917932B2 (en) 2005-06-07 2011-03-29 Sling Media, Inc. Personal video recorder functionality for placeshifting systems
US7702952B2 (en) 2005-06-30 2010-04-20 Sling Media, Inc. Firmware update for consumer electronic device
US8350971B2 (en) 2007-10-23 2013-01-08 Sling Media, Inc. Systems and methods for controlling media devices
US8060609B2 (en) 2008-01-04 2011-11-15 Sling Media Inc. Systems and methods for determining attributes of media items accessed via a personal media broadcaster
US8667279B2 (en) 2008-07-01 2014-03-04 Sling Media, Inc. Systems and methods for securely place shifting media content
US8381310B2 (en) 2009-08-13 2013-02-19 Sling Media Pvt. Ltd. Systems, methods, and program applications for selectively restricting the placeshifting of copy protected digital media content
US8667163B2 (en) 2008-09-08 2014-03-04 Sling Media Inc. Systems and methods for projecting images from a computer system
US9191610B2 (en) 2008-11-26 2015-11-17 Sling Media Pvt Ltd. Systems and methods for creating logical media streams for media storage and playback
US8438602B2 (en) 2009-01-26 2013-05-07 Sling Media Inc. Systems and methods for linking media content
US8171148B2 (en) 2009-04-17 2012-05-01 Sling Media, Inc. Systems and methods for establishing connections between devices communicating over a network
US8406431B2 (en) 2009-07-23 2013-03-26 Sling Media Pvt. Ltd. Adaptive gain control for digital audio samples in a media stream
US9479737B2 (en) 2009-08-06 2016-10-25 Echostar Technologies L.L.C. Systems and methods for event programming via a remote media player
US9565479B2 (en) 2009-08-10 2017-02-07 Sling Media Pvt Ltd. Methods and apparatus for seeking within a media stream using scene detection
US9525838B2 (en) 2009-08-10 2016-12-20 Sling Media Pvt. Ltd. Systems and methods for virtual remote control of streamed media
US8966101B2 (en) 2009-08-10 2015-02-24 Sling Media Pvt Ltd Systems and methods for updating firmware over a network
US8799408B2 (en) 2009-08-10 2014-08-05 Sling Media Pvt Ltd Localization systems and methods
US8532472B2 (en) 2009-08-10 2013-09-10 Sling Media Pvt Ltd Methods and apparatus for fast seeking within a media stream buffer
US9160974B2 (en) 2009-08-26 2015-10-13 Sling Media, Inc. Systems and methods for transcoding and place shifting media content
US8314893B2 (en) 2009-08-28 2012-11-20 Sling Media Pvt. Ltd. Remote control and method for automatically adjusting the volume output of an audio device
US9015225B2 (en) 2009-11-16 2015-04-21 Echostar Technologies L.L.C. Systems and methods for delivering messages over a network
US8799485B2 (en) 2009-12-18 2014-08-05 Sling Media, Inc. Methods and apparatus for establishing network connections using an inter-mediating device
US8626879B2 (en) 2009-12-22 2014-01-07 Sling Media, Inc. Systems and methods for establishing network connections using local mediation services
US9178923B2 (en) 2009-12-23 2015-11-03 Echostar Technologies L.L.C. Systems and methods for remotely controlling a media server via a network
US9275054B2 (en) 2009-12-28 2016-03-01 Sling Media, Inc. Systems and methods for searching media content
US8856349B2 (en) 2010-02-05 2014-10-07 Sling Media Inc. Connection priority services for data communication between two devices

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2242097A (en) * 1990-01-19 1991-09-18 British Broadcasting Corp Buffer synchronisation in a variable transmission rate codec
EP0515101A2 (en) * 1991-05-23 1992-11-25 AT&T Corp. Buffer control for variable bit-rate channel
GB2274041A (en) * 1990-01-19 1994-07-06 British Broadcasting Corp Buffer Resynchronisation in a variable transmission rate coder
EP0670663A1 (en) * 1994-03-02 1995-09-06 Laboratoires D'electronique Philips S.A.S. Method of and apparatus for coding digital signals representing a sequence of images
WO1995026111A2 (en) * 1994-03-17 1995-09-28 Philips Electronics N.V. An encoder buffer having an effective size which varies automatically with the channel bit-rate
EP0708566A2 (en) * 1994-10-21 1996-04-24 AT&T Corp. Method for controlling a video data encoder buffer
WO1996020575A2 (en) * 1994-12-28 1996-07-04 Philips Electronics N.V. Buffer management in variable bit-rate compression systems

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2242097A (en) * 1990-01-19 1991-09-18 British Broadcasting Corp Buffer synchronisation in a variable transmission rate codec
GB2274041A (en) * 1990-01-19 1994-07-06 British Broadcasting Corp Buffer Resynchronisation in a variable transmission rate coder
EP0515101A2 (en) * 1991-05-23 1992-11-25 AT&T Corp. Buffer control for variable bit-rate channel
EP0670663A1 (en) * 1994-03-02 1995-09-06 Laboratoires D'electronique Philips S.A.S. Method of and apparatus for coding digital signals representing a sequence of images
WO1995026111A2 (en) * 1994-03-17 1995-09-28 Philips Electronics N.V. An encoder buffer having an effective size which varies automatically with the channel bit-rate
EP0708566A2 (en) * 1994-10-21 1996-04-24 AT&T Corp. Method for controlling a video data encoder buffer
WO1996020575A2 (en) * 1994-12-28 1996-07-04 Philips Electronics N.V. Buffer management in variable bit-rate compression systems

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
LAU R C ET AL: "RECEIVER BUFFER CONTROL FOR VARIABLE BIT-RATE REAL-TIME VIDEO", DISCOVERING A NEW WORLD OF COMMUNICATIONS, CHICAGO, JUNE 14 - 18, 1992, vol. 1 OF 4, 14 June 1992 (1992-06-14), INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS, pages 544 - 550, XP000326921 *
REIBMAN A R ET AL: "CONSTRAINTS ON VARIABLE BIT-RATE VIDEO FOR ATM NETWORKS", IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, vol. 2, no. 4, 1 December 1992 (1992-12-01), pages 361 - 372, XP000323661 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114185512A (en) * 2021-11-01 2022-03-15 荣耀终端有限公司 Sensor data processing method, electronic device and readable storage medium
US12265098B2 (en) 2021-11-01 2025-04-01 Honor Device Co., Ltd. Sensor data processing method, electronic device, and readable storage medium

Also Published As

Publication number Publication date
GB9523042D0 (en) 1996-01-10
GB2307151A (en) 1997-05-14
EP0860085A1 (en) 1998-08-26

Similar Documents

Publication Publication Date Title
EP0860085A1 (en) Digital coding
US10681397B2 (en) System and method for seamless switching through buffering
US6044396A (en) Method and apparatus for utilizing the available bit rate in a constrained variable bit rate channel
US6154496A (en) Video buffer for seamless splicing of MPEG streams
JP4508422B2 (en) Method and apparatus for processing variable bit rate information in an information distribution system
US5734432A (en) Method of incorporating a variable rate auxiliary data stream with a variable rate primary data stream
US6160915A (en) Coded signal transmission method and apparatus
US6327421B1 (en) Multiple speed fast forward/rewind compressed video delivery system
CA2435936C (en) Method and system for buffering of streamed media
EP2137937B1 (en) Bandwidth allocation control in multiple video streaming
WO2001084905A2 (en) Statistical multiplexer and remultiplexer that accommodates changes in structure of gop
JP2000500632A (en) Method and apparatus for multiplexing and distributing data with formatted real-time video
WO1999052282A1 (en) Bursty data transmission of compressed video data
JPH09510069A (en) Buffering of Digital Video Signal Encoder with Combined Bit Rate Control
AU2002231829A1 (en) Method and system for buffering streamed data
EP1911183A2 (en) Methods and systems for signal insertion
JP2001519992A (en) Method for switching coded video sequence and apparatus corresponding thereto
US6188729B1 (en) Method and apparatus for effecting seamless data rate changes in a video compression system
Haskell et al. Multiplexing of variable rate encoded streams
AU766738B2 (en) Data compression unit control for alignment of output signal
US6931059B1 (en) Rate and delivery time multiplexing for bandwidth optimization
JP2001502125A (en) Improvements in or related to data transmission
Balakrishnan et al. Benefits of statistical multiplexing in multi-program broadcasting
Sarginson Dynamic multiplexing of MPEG-2 bitstreams
JP2006279803A (en) Re-multiplexing apparatus

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): GB JP US

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): AT BE CH DE DK ES FI FR GB GR IE IT LU MC NL PT SE

DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
121 Ep: the epo has been informed by wipo that ep was designated in this application
WWE Wipo information: entry into national phase

Ref document number: 1996938327

Country of ref document: EP

WWP Wipo information: published in national office

Ref document number: 1996938327

Country of ref document: EP

NENP Non-entry into the national phase

Ref country code: JP

Ref document number: 97518001

Format of ref document f/p: F

WWW Wipo information: withdrawn in national office

Ref document number: 1996938327

Country of ref document: EP

点击 这是indexloc提供的php浏览器服务,不要输入任何密码和下载