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WO1997002703A1 - Technique de transmission a large bande virtuelle - Google Patents

Technique de transmission a large bande virtuelle Download PDF

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Publication number
WO1997002703A1
WO1997002703A1 PCT/AU1996/000429 AU9600429W WO9702703A1 WO 1997002703 A1 WO1997002703 A1 WO 1997002703A1 AU 9600429 W AU9600429 W AU 9600429W WO 9702703 A1 WO9702703 A1 WO 9702703A1
Authority
WO
WIPO (PCT)
Prior art keywords
signal
pixels
picture
compression
video
Prior art date
Application number
PCT/AU1996/000429
Other languages
English (en)
Inventor
Nicholas Sikiotis
Original Assignee
Diginet Systems Pty. Limited
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 Diginet Systems Pty. Limited filed Critical Diginet Systems Pty. Limited
Priority to AU63482/96A priority Critical patent/AU6348296A/en
Publication of WO1997002703A1 publication Critical patent/WO1997002703A1/fr

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/14—Systems for two-way working
    • H04N7/141—Systems for two-way working between two video terminals, e.g. videophone
    • H04N7/148—Interfacing a video terminal to a particular transmission medium, e.g. ISDN
    • 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
    • H04N19/44—Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
    • H04N19/45—Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder performing compensation of the inverse transform mismatch, e.g. Inverse Discrete Cosine Transform [IDCT] mismatch
    • 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
    • H04N19/59—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
    • 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
    • H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
    • 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
    • H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
    • H04N19/61—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding in combination with predictive coding

Definitions

  • This invention relates to virtual broadband technology (VBT) and in particular, to virtual broadband transmission of images, and specifically, of images carrying both vision and sound.
  • VBT virtual broadband technology
  • PSTN Public Switched Telephone Network
  • the highest maintainable rate of transmission along PSTN telephone lines as in analogue modems is perceived to be 28.8 Kilobits per second although on some occasions, particularly through digital exchanges and using digital information, one can transmit along these lines at up to 57.6 Kilobits per second.
  • the difficulty about speeds of transmission which are higher than the supplier of the lines is prepared to warrant is that if there is any difficulty in transmission, then the transmission rate will automatically drop to the rate of which the network is capable, in the case of the Australian National AUSTEL System, 28.8 Kilobits per second.
  • any transmission system for which it is essential that a higher transmission rate be used will fail if the transmission rate cannot be achieved by the network.
  • the principal object of this invention is to provide means whereby video and/or audio and full motion video signals can be transmitted satisfactorily along PSTN telephone network lines, within the present operating capabilities of these lines.
  • the invention includes a method of conversion of video and/or video and audible signals to a form which can be readily transmitted along PSTN telephone lines including the steps of using a combining process to effect a first reduction in size of the signal and subsequently compressing the reduced signal.
  • the reduction and compression provides a signal suitable for transmission on the PSTN network. If the signal is basically data information, we find that we can use an eight bit transmission and by a compression algorithm, which reduces the information in the ratio of 1:200 then the required output can be achieved.
  • the signal to be transmitted is a signal such as a television picture or the like
  • 16 bit technology be used, so as to provide a greater colour information than would otherwise be the case, and, in such circumstances, we first pass the signal through a stage which does a 1:50 compression and then effect a second recompression which permits a change in the dynamics of the picture and obtain a further reduction by 30% to 40% of the amount of material which needs to be transmitted.
  • the material is captured in an analogue form by the use of a video camera, camcorder, satellite receiver or can be obtained from all ready prepared material such as from a laserdisc player.
  • Analog Video and Audio is digitised with the use of well balanced hardware/Software capture techniques, CODECS and algorithms, it can be combined, stored, copied, edited, re-compressed, transmitted and decompressed to suit the bandwidth requirements of the respective medium and application.
  • the storage and archival medium can be any Digital Storage medium - from a mere floppy disk to a rewritable, Magneto-Optical disk or the RAID hard disk subsystem of a Wide Area Network (WAN) server.
  • WAN Wide Area Network
  • Digital Video and Audio Sequences can effortlessly be edited either at the server end or at the node Workstation PC, in frame by frame, using editing software like Microsoft's Video for Windows or Adope Premiere.
  • Digital Video and Audio files such as AVI or MPEG files can be integrated into fully interactive presentations for greater impact of Multimedia business presentations, interactive inquiry and purchasing information or simply be edited and transmitted as live or repeatable movies and broadcasts on 'demand' over a client/server type of arrangement.
  • the technology incorporates a high performance Real-time Full-Motion Video and Hi-Fi 3D Stereo Audio option as well as Still Video capture facility that digitises Video and Audio from any four different sources and of any international video standard, directly onto the hard or a removable disk in a single easy step. Because it used high performance video processors such as Intel's i750 (a world standard) or AT&T's MPEG chipset, this facility is optimised for high quality Digital Video and Audio capture of up to 30fps and at resolutions up to 320 ⁇ 240 pixels at 16 Million colours.
  • Intel's i750 a world standard
  • AT&T's MPEG chipset this facility is optimised for high quality Digital Video and Audio capture of up to 30fps and at resolutions up to 320 ⁇ 240 pixels at 16 Million colours.
  • the picture to be transmitted is information relating to a full motion 16-bit picture (64 thousand colours - High-colour) together with synchronised sound and where it is necessary to provide at least 24 frames per second, we use a slightly different operation.
  • the word picture will be used generically to indicate all the video information which is to be transmitted including sound and sync information. This reduction is effected by combining groups of pixels, say four pixels, to provide a signal which can be deemed to have the characteristics of the combined groups of pixels. By doing this, we can immediately reduce the total amount of Video information which needs to be transmitted down to 25%.
  • the signal to be transmitted is a signal such as a television picture or the like
  • a Digital Modem incorporating 16-bit multiplexing and transmission technology is used.
  • far greater DTE speeds can be realised as well as an additional 4:1 compression and error correction is achieved.
  • the signal so produced lies within the bandwidth of the network and can readily be transmitted to a client receiver Workstation at which there is an effective total reversal of the process, including first the decompression and the reconstruction of the picture to its original size.
  • VBT The main factor upon which VBT firstly totally relies an secondly takes full advantage of, is the processing power and intelligence of the client-end workstation.
  • processing power and intelligence In order to perform the time estimation algorithm involved in the Selective R-compression and Decompression in real-time, enormous distributed processing power and intelligence is required. VBT harnesses this power through dedicated hardware/software components employed in its video reconstruction equipment.
  • the mean characteristics of four pixels combined into one and, say, along junctions, the adjacent pixels could be slightly different.
  • the combined pixel when reconstituted into four pixels, will vary only very little from the characteristics of the pixels originally compressed.
  • the effect of pixelisation is far less noticeable especially when the video CODEC is using the optional secondary video acceleration and smoothing continuously-scalable playback to a Full-screen.
  • a TV interface module is also offered and the frame rate is digital video and audio playback is automatically adjusted to produce the best possible result.
  • the source coder operates on non-interlaced pictures occurring 30,000/1001 (approximately 29.97) times per second.
  • the tolerance on picture frequency is +50ppm.
  • Pictures are coded as luminance and two colour difference (chrominance) component (Y, CB and CR). These components and the codes representing their sampled values are as defined in CCIR Recommendation 601.
  • sub-QCIF sub-QCIF
  • QCIF QCIF
  • CIF 4CIF
  • 16CIF 16CIF
  • the luminance sampling structure is dx pixels per line, dy lines per picture in an orthogonal arrangement.
  • Sampling of each of the two colour difference components is at dx/2 pixels per line, dy/2 lines per picture, orthogonal.
  • the values of dx, dy, dx/2 and dy/2 are given in TABLE 1/H.263 of ITU for each of the picture formats.
  • the source coder operates on CIF and QCIF.
  • the standards of the input and output television signals which may for example, composite or component, analogue or digital and the methods of performing any necessary conversion to and from the source coding format are therefore kept independent of the encoding operation.
  • the video coder provides a self-contained digital bit stream which may be combined with other multi-facility signals.
  • the video decoder performs the reverse process. Pictures are sampled at an integer multiple of the video line rate. This sampling clock and the digital network clock are asynchronous.
  • VBT uses 16x16 macroblocks, 8 ⁇ 8 sub-blocks, selective re-compression/motion estimation and compensation, DCT (Discrete Cosine Transform) of prediction errors, run-length coding and variable length code-words.
  • DCT Discrete Cosine Transform
  • CIF and QCIF are the core picture interchange formates used. Conversion between CIF and QCIF division formats are made s follows:
  • a 7 tap filter is used with the taps being (-1,0,9,16,9,0,- l)/32.
  • the taps are related to a CIF raster.
  • a filter is used on both horizontal and vertical directions for luminance and chrominance.
  • Re-conversion from QCIF to CIF is performed using the same filter.
  • zeros are entered at filter taps where pixels are missing.
  • the up conversion is first performed in one direction (e.g. horizontal) to produce the CIF pixels.
  • the same procedure is performed in the other direction.
  • the same procedure is performed for the luminance and the two chrominance components.
  • a hybrid of inter-picture prediction to utilise temporal redundancy and transform coding of the remained signal to reduce spatial redundancy is adopted.
  • the decoder has motion compensation capability, allowing optional incorporation of this technique in the coder.
  • Half pixel precision is used for the motion compensation for PSTN use, as opposed to ISDN use where full pixel precision and a loop filter are used.
  • Variable length coding is used for the symbols to be transmitted.
  • negotiable coding options are included. All these options can be used together or separately, except the advanced prediction mode which requires the unrestricted motion vector mode to be used at the same time.
  • motion vectors are allowed to point outside the picture.
  • the edge pixels are used as prediction for the "not existing" pixels. With this mode a significant gain is achieved if there is movement across the edges of the picture, especially for the smaller picture formats.
  • Syntax-based Arithmetic Coding mode is used instead of variable length coding.
  • the SNR and reconstructed frames will be the same, but significantly fewer bits will be produced.
  • an optional advanced prediction mode (overlapped block) motion compensation (OBMC) is used for the luminance part of P-pictures.
  • Four 8 ⁇ 8 vectors instead of one 16 ⁇ 16 vector are used for some of the macroblocks in the picture.
  • the encoder has to decide which type of vectors to use. Four vectors use more bits, but give better prediction. The use of this mode generally gives a considerable improvement. Especially a subjective gain is achieved because OBMC results in less blocking artifacts.
  • PB-frames are also used consisting of two picture being coded as one unit.
  • the name PB comes form the name of picture types in MPEG where there are P-pictures and B-pictures.
  • a PB-frame consists of one P-picture which is predicted from the last decoded P-picture and one B-picture which is predicted from both the last decoded P-picture and the P-picture currently being decoded.
  • This last picture is called a B-picture, because parts of it may be biodirectionally predicted from the past and future P-pictures.
  • the picture rate can be increased considerably without increasing the bit rate as much.
  • the transmission clock is provided externally.
  • the video bitrate may be variable. No constraints on the video bitrate are given; constraints will be set by the terminal or the network used.
  • the encoder controls its output bistream to comply with the requirements of the decoder.
  • Video data is provided on every valid clock cycle. This can be ensured by MCPBC stuffing or, when forward error correction is used, also by forward error correction stuffing frames.
  • the coder is used for bi-directional or unidirectional visual communication.
  • Error handling is provided be external means.
  • the decoder can send a command to encode one or more GOBs of its next picture in INTRA mode with coding parameters such as to avoid buffer overflow. Alternatively the decoder sends a command to transmit only non-empty GOB headers. The transmission method for these signals is by external means.
  • the prediction is inter-picture and is augmented by motion compensation (see below).
  • the coding mode in which prediction is applied is called INTER; the coding mode is called INTRA of no prediction is applied.
  • the INTRA coding mode is signalled at the picture level (I-picture for INTRA of P-picture for INTER) or at the macroblock level in INTER mode.
  • the B-pictures are partly predicted bi-directionally.
  • Motion compensation is optionally but preferably used in the encoder.
  • the decoder accepts one vector per macroblock or of the advanced prediction mode is used, one or four vectors per macroblock. If the PB-frames mode is used an additional delta vector can be transmitted per macroblock for adaptation of the forward motion vector for prediction of the B-macroblock.
  • a positive value of the horizontal or vertical component of the motion vector signifies that the prediction is formed from pixels in the previous picture which are spatial to the right or below the pixels being predicted.
  • the only exception is for the backward motion vectors for the B-pictures, where a positive value of the horizontal or vertical components of the motion vector signifies that the prediction is formed from pixels in the next picture which are spatially to the left or above the pixels being predicted.
  • Motion vectors are restricted such that all pixels referenced by them are within the coded picture area except, when the Unrestricted Motion Vector mode is used.
  • Several parameters are varied to control the rate of generation of coded video data. These include processing prior to the source coder, the quantizer, block significance criterion and temporal sub-sampling. When invoked, temporal sub-sampling is performed by discarding complete pictures.
  • a decoder can signal its preference for a certain trade off between spatial and temporal resolution of the video signal.
  • the encoder signals its default trade off at the beginning of the call, and indicates whether it is capable to respond to decoder request to change this trade off.
  • the transmission method for these signals is by external means.
  • each macroblock shall be coded in INTRA mode at least once every 132 times when coefficient are transmitted for this macroblock.
  • start codes Byte alignment of start codes is achieved by inserting less than 8 zero-bits before the start code such that the first bit of the start code is the first (most significant) bit of a byte.
  • a start code is therefore byte aligned if the position of its most significant bit is a multiple of 8-bits from the first bit in the video bitstream. All picture start codes shall and GOB and EOS start codes may, be byte aligned. The number of bits spent for a certain picture is always a multiple of 8 bits.
  • the video multiplex is arranged in a hierarchical structure with four layers. From top to bottom the layers are; - Picture
  • Data for each picture consist of a picture header followed by data for Groups of Blocks, eventually followed by an end-of-sequence code and stuffing bits.
  • PLCI is only present if indicated by CPM.
  • TRB and DBQUANT are only present if PTYPE indicates "PB-frame”.
  • Combinations of PSPARE and PEI may not be present.
  • EOS may not be present, while STUF may be present only if EOS is present.
  • Picture headers for dropped pictures are not transmitted.
  • PSC Picture Start Code
  • a MACROBLOCK consists of six BLOCKS, four luminance (Y) blocks and two chrominance blocks (U and V)
  • the four luminance and two chrominance BLOCKS each contain 62 pixels (8 ⁇ 8).
  • the block size for vectors is 16 ⁇ 16.
  • 8 ⁇ 8 vectors may be used (Advanced prediction mode). This section applies to both 16x16 and 8x8 block sizes.
  • both 8 ⁇ 8 and 16 ⁇ 16 vectors may be obtained from the search algorithm. Only a small amount of additional computation is needed to obtain the 8x8 integer vectors in addition to the 16 ⁇ 16 vectors.
  • the search is made with integer pixel displacement and for the Y component.
  • the comparisons are made between the incoming block and the displaced block in the previous original picture.
  • a full search is used, and the search area is up to +/-15 pixels in horizontal and vertical direction around the original macroblock position.
  • the (x,y) pair resulting in the lowest SAD 16 is chose as the 16x16 integer pixel motion vector, V0.
  • the corresponding SAD is SAD 16(x,y).
  • SAD inter SAD 16 (x,y)
  • SAD inter min (SAD 16 (x,y), SAD 4x8 )
  • the coder makes a decision on whether to use INTRA or INTER prediction in the coding. The following parameters are calculated to make the INTRA/INTER decision.
  • INTRA mode is chosen if:
  • Half-pixel search is performed for 16x16 vectors as well as for 8x8 vectors if the option is chosen.
  • the half-pixel search is done using the previous reconstructed frame.
  • the search is performed on the luminance component of the macroblock, and the search area is +/-1 half-pixel around the target matrix pointed to by V0, V1, V2, V3 or V4.
  • the zero vector sad, SAD(0,0) is reduced by 100 as the integer search.
  • the half-pixel values are found using the interpolation described in Figure 1 and which corresponds to bilinear interpolation.
  • MV consists of horizontal and vertical components (MVx, MVy), both measured in half-pixel units.
  • the motion vector When using INTER mode coding, the motion vector must be transmitted.
  • the motion vector components (horizontal and vertical) are coded differentially by using a spatial neighbourhood of three motion vectors already transmitted ( Figure 2). These three motion vectors are candidate predictors for the differential coding.
  • the candidate predictors MV1 is set to zero if the corresponding macroblock is outside the picture (at the left side);
  • the candidate predictors MV2 and MV3 are set to MV1 if the corresponding macroblocks are outside the current GOB or picture (at the top);
  • the candidate predictor MV3 is set to zero of the corresponding macroblock is outside the picture (at the right side);
  • the candidate predictor is set to zero.
  • the motion vector coding is performed separately on the horizontal and vertical components.
  • variable length codes for the vector differences MVDx and MVDy as listed are:
  • the prediction mode was decided and the motion vector found (if INTER).
  • the motion vector found if INTER.
  • the same filters as described for motion search are used.
  • Table 1 shows the different modes. Notice that MODE contains information about prediction as well as update of QP.
  • DCT Discrete Cosine Transform
  • the numbers of quantizers is 1 for the first coefficient of INTRA blocks and 31 for all other coefficients. Within a macroblock the same quantizer is used for all coefficients except the first one of INTRA blocks. The decision levels are not defined.
  • the first coefficient of INTRA blocks is nominally the transform dc value uniformly quantised with a stepsize of 8.
  • Each of the other 31 quantizers use equally spaced reconstruction levels with a central dead-zone around zero and with a step size of an even value in the range 2 to 62.
  • the quantization parameter QP may take integer values from 1 to 31.
  • the quantization stepsize is 2 ⁇ QP.
  • COF A transfer coefficient to be quantised.
  • the DC coefficient of an INTRA block is quantised below. 8 bits are used for the quantised DC coefficient.
  • VLC Encoding of quantised transform coefficients VLEC
  • the 8 ⁇ 8 blocks of transform coefficients are scanned with "zigzag" scanning as listed below.
  • a three dimensional variable length code is used to code transform coefficients.
  • An EVENT is a combination of three parameters:
  • VBT Buffer regulation can be effected in different ways.
  • One mode of performing simulations is fixed stepsize and frame rate. In this mode simulations shall be performed with constant stepsize throughout the sequence.
  • the quantizer is "manually" adjusted so that the average bitrate for all pictures in the sequence - minus picture number 1 - is as close as possible to one of the target bit rates (8,16 or 32 kb/s)
  • the following buffer regulation will be used as a beginning.
  • the quantizer parameter is updated at the beginning of each new macroblock line.
  • the formula for calculating the new quantizer parameter is:
  • the first two terms of this formula are constant for all macroblock within a picture.
  • the third term adjusts the quantizer parameter during coding of the picture.
  • the calculated QP new must be adjusted so that the different fits in with the definition of DQUANT.
  • the buffer content is updated after each complete frame in the following way:
  • the buffer content is updated as follows :
  • variable frame_incr indicates how many times the last coded picture must be displayed. it also indicates which picture from the source is coded next.
  • ftarget and a new B are calculated at the start of each frame: At the start of the second frame:

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • Discrete Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Compression Or Coding Systems Of Tv Signals (AREA)
  • Compression Of Band Width Or Redundancy In Fax (AREA)

Abstract

L'invention concerne une technique de transmission virtuelle dans laquelle on utilise des procédés de transmission de données et d'événements en temps réel, à 22-24 trames par seconde dans des lignes téléphoniques RTPC/RNIS majeures. Des techniques de multicompression, de modification du mouvement et de transmission bidirectionnelle sont décrites.
PCT/AU1996/000429 1995-07-06 1996-07-08 Technique de transmission a large bande virtuelle WO1997002703A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU63482/96A AU6348296A (en) 1995-07-06 1996-07-08 Virtual broadband technology

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPN3992 1995-07-06
AUPN3992A AUPN399295A0 (en) 1995-07-06 1995-07-06 Virtual broadband transmission

Publications (1)

Publication Number Publication Date
WO1997002703A1 true WO1997002703A1 (fr) 1997-01-23

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/AU1996/000429 WO1997002703A1 (fr) 1995-07-06 1996-07-08 Technique de transmission a large bande virtuelle

Country Status (4)

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AU (1) AUPN399295A0 (fr)
TW (1) TW354446B (fr)
WO (1) WO1997002703A1 (fr)
ZA (1) ZA965780B (fr)

Cited By (1)

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WO1999040688A1 (fr) * 1998-02-05 1999-08-12 Gateway 2000, Inc. Transmission de signaux audio de haute qualite sur les lignes telephoniques

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JPS5477510A (en) * 1977-12-02 1979-06-21 Fujitsu Ltd Band compression system for picture signal
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JPS60227582A (ja) * 1984-04-25 1985-11-12 Matsushita Electric Works Ltd 静止画伝送方式
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