CA2026766C - Method for multiplexing an audio signal and an analogue video signal and sound still picture distribution system - Google Patents

Abstract

The method for multiplexing a sound signal into an analog video signal comprises an amplitude dynamic, in which the sound signal is multiplied in a useful part of the analog video signal corresponding to a video image, the method comprises the following steps: digitizes the sound signal and bitrate compression techniques are used to obtain a sequence of digital coding expressions; the sequence of digital coding expressions is temporarily stored for sequentially extracting coding sub-expressions at a frequency related to a line frequency of the video signal, each digital coding sub-expression comprising a predetermined number of binary elements which are functions of the amplitude dynamics of the video signal; each extracted digital coding sub-expression is converted into analog form in order to provide analog samples whose amplitude level is proportional to the quantification of the digital coding sub-expression considered; an amplitude modulation of the analog samples is imposed in the useful part of the video signal to provide a composite signal having the same format as a video signal. The method according to the invention is used for the production of an interactive system for the distribution of fixed sound images.

Description

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METHOD FOR MULTIPLEXING A SOUND SIGNAL
IN AN ANALOGUE VIDEO SIGNAL AND SYSTEM
DISTRIBUTION OF SOUND STILL IMAGES.
The field of the invention is that of methods for multiplexing a sequence signal sound inside a video image signal analog.
More particularly, the invention relates to a new method for multiplexing a signal of sound sequences sampled and multiplexed by pulse amplitude modulation in the lines useful video image signal.
This new process is part of the signal transmission techniques compatible with current equipment and takes into account specifics of existing transmission media.
The known methods of multiplexing a audio signal with image signal analog video use the techniques of digitization of sound samples and multiplexing ! of a signal in the logic state corresponding to the digital quantification of each sound sample with analog video image signal by distribution ~ temporal in the useful lines of it 'J 25 (pulse modulation and coding).
However, these coding techniques known limit signal transport capabilities `analog video image in terms of duration of sequences sound inserted by useful line of the image signal, these limitations being mainly due to the process of coding of sound samples.
Consequently, the objective of the invention is to overcome this drawback and including significantly increasing the duration of sound sequences inserted in each useful line of the c ~ analog video image signal by optimizing v the use of signal amplitude dynamics , ~, .,.

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video image for coding sound samples, this duration should be of the order of 8 seconds of sound phone quality per image frame for one channel for transmitting an analog video image signal 5 has a base bandwidth of 5 megahertz and a amplitude dynamics less than 50 dB.
This objective is achieved using a method for multiplexing an analog sound signal in an analog video signal with a 10 amplitude dynamics, in which the sound signal is multiplexed into a useful part of the video signal analog corresponding to a video image, characterized in that:
- we digitize the sound signal and use 15 flow compression techniques to achieve sequence of digital coding expressions;
- we temporarily store the sequence of numeric coding expressions to extract sequentially numeric sub-expressions of ~ 20coding at a frequency related to a frequency ; video signal line, each digital subexpression ~! coding with a predetermined number of elements ~ binaries based on signal amplitude dynamics `` j video;
', 25- we convert to analog form chague `numeric coding sub-expression extracted for provide analog samples whose level : of amplitude is proportional to the quantification of the digital coding sub-expression considered;
`30- an amplitude modulation of the analog samples in the useful part of the signal `video to provide a composite signal having the same ~; format as a video signal.
In this way, if the period of ! `~ '35 sound samples modulated in the video signal by : pulse amplitude modulation is 160 `nanoseconds, which is compatible with :,.
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3 2026766 characteristics of existing video channels, it is possible to encode 8 seconds of sound (32 kilobits / second per video frame; G 721) or 4 seconds of sound (64 kilobits / second per video frame;
G 711), a video image signal frame representing 1/50 second in "Pal-Secam" mode).
`` According to another characteristic of the invention, each digital coding sub-expression preferably contains four binary elements.
lQ Preferably, according to a characteristic of the invention, each numerical coding expression contains a number of binary elements multiple of - four and the extraction step of the sub-expressions digital coding includes a segmentation step of the digital expression coding into subexpressions digital coding and scheduling of sub-`numeric coding expressions.
In this way, although limited by the ~ amplitude dynamics of the video image signal, we can 3 20 increase the resolution of the digital samples of the , sound sequence signal. In addition, a margin of ~ I noise security can always be ; ~ canned.
The invention also relates to a system interactive still image distribution implementing the coding method according to ~~ the invention, in which we transmit simultaneously by ; ~ the same video transmission channel of the elements `, <b of still images and sound signal elements of sound sequences associated with still images.
We already know interactive distribution of sound images.
However, the major drawback of these known systems is that the transport of images and its this done in separate ways. Furthermore, these known systems are not compatible with the mode diffuse ~.
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4 2 02 As a result, another goal of the invention is to propose an interactive system of distribution of fixed sound images using a single video transmission channel capable of providing 25 simultaneously viewing images per second with at least 8 seconds of sound (telephone quality CCITT standard G 721) associated with each of the images fixed.
This objective is achieved using a interactive still image distribution system with sound broadcasting the still images associated with sound sequences via a network of video communication to a plurality of terminals reception, characterized in that it includes:
- the first means of memorizing a plurality of sets of digitized image elements, - second means for storing a plurality of sequences of signal coding expressions digitized sound sequences, each image being associated with a sound sequence, - extraction means connected to the first ~ and second storage means for extracting from ! Alternative alternatively a set of image elements of a digitized image corresponding to an image frame ~ 25 and a series of coding expressions corresponding to . ~ a sound sequence of a predetermined duration, . ' - digital conversion means analog connected to said storage means for . convert to ~ analog form alternatively ; 30 the set of picture elements and the following coding expressions, . - video coding means connected to ..: means of digital to analog conversion to provide a composite analog video image signal comprising "35 alternately a frame of picture elements and a . frame of coding expressions.
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5 20 267 66 Preferably, according to a characteristic of the interactive still image distribution system according to the invention the reception terminal understands S - analog conversion means digital to digitally convert the signal analog video frame into element components image, ~ - referral means connected to the means of `. 10 analog to digital conversion, controlled by a frame signal to isolate a set of elements digitized image of an image frame and a suite coding expressions of a digitized sound sequence . associated, multiplexed in the adjacent image frame, - storage means linked to `referral means for storing alternately ; j depending on the frame signal command, the set : picture elements and the sequence of coding expressions, ~ - digital conversion means . ~. 20 analog connected to the storage means for deliver an analog sound signal from the sequence of coding expressions.
The invention will be better understood using of the description which will follow in a preferential realization of the invention given as illustrative and not limiting and attached drawings wherein :
- Figure 1 shows schematically . ~ an interactive still image distribution system . 30 sound systems, - Figure 2 shows schematically ~ a device for multiplexing sound sequences in '. an analog video signal according to the invention in ; which the sound sequence signal is digitized on four binary elements, - Figure 3 shows schematically . . .
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corresponding to that of FIG. 2, in which the audio sequence signal is digitized to eight binary elements, - Figure 4 shows schematically .a terminal for the decoding of the sound signal multiplexed in the video channel according to the invention.
As shown in Figure 1, the interactive still image distribution system sonorisees has a server site consisting of a part of a telematic server 220 connected by the network switched telephone 210 to a plurality of terminals telematics 200 and secondly an audio server-visual 230 connected by a video communication network, for example the broadband network 270, has a plurality video reception terminals for sound images 280, 290 associated with the plurality of terminals l telematics 200.
j The audio-visual server 230 is elsewhere connected to a base storage means ~ 20 documentary of still images 230 stored in the form Digital Yi (for example as an image pixel ~ ij coded in color components on twelve binary elements o including four for the red component (R), guatre for the green component (V), four for the component blue (B) or coded as luminance (Y) and ; chrominance (D2, DB) on twelve binary elements including seven for the luminance component (Y) and five for ; the chrominance component (DR / DB)) and has means ; ~ storage of a documentary base of sequences :; 30 sounds 250 stored also in digital form (for example - example 50U5 the form of digital samples of the sampled sound signal coded on four elements .: binaries corresponding to sound quality telephone).
3S At each still image of the base . documentary of images is associated with a sound sequence of the documentary base of sound sequences serving as "
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still image comment. The image being fixed, we transmits through the video ~ -communication channel using a "Pal-Secam" 260 encoder connected to the audio server - visual only one frame of image per image, the second frame being used for insertion by multiplexing of the associated sound sequence.
Viewing a still image sounded by a user is carried out in the manner next. The user communicates with the telematic server 220 using the terminal telematics 200 to provide it with its code personal identification as well as the the fixed image that he wishes to view on the video reception 290.
The audiovisual server 230 comprising a memory plan of still images with sound powered by storage facilities for document databases 240, 250 met permanently update the memory plan of still images with sound ~ depending on the information it provides the telematics server. In addition, each still image loaded into memory plan contains in coded form the identification code of the user wishing to view.
The audiovisual server then broadcasts the ~ 25 still images with sound by cyclically reading the plan ; memory. The transmitted video image signal includes coded for a still image with a frame `image related to image information and a frame - "pseudo-imag ~ e" relating to information from the multiplexed sound sequence in the video signal. This `composite video signal is received by a terminal 280 `connected to the 2gO image reception video station for decode the image information contained in a ~ picture frame and multiplexed sound information - 35 in an adjacent image frame. The still image is identified at terminal 280 by recognition user code and is displayed at the extension . ~.

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video image reception 290, while - decoded sound information is delivered to the user as a comment for the still image displayed.
We will now describe the sound signal multiplexing process ~ re in the signal analog video which is transmitted by the server audiovisual 230 with reference to Figures 2 and 3.
As shown in Figure 2, the signal sound sequences is applied to the input of a analog to digital converter 10 to be sampled at a sampling frequency of eight KH2 for example.
The amplitude level of each sound sample can be coded in a known manner on 12 binary elements defining a level of `l resolution determined.
An analog video image signal is ; composed of a succession of image lines of duration useful time of 52 microseconds. the amplitude dynamics of the ~.
analog video signal is around 50 dB. Account ~, given this amplitude dynamic and according to the law of quantification, we can differentiate sixteen levels signal amplitude in the part of the signal corresponding to the useful line of a video image ~ 25 while ensuring a sufficient margin of safety vis--to noise. ~ a safety margin thus obtained is 24 dB. Therefore, the amplitude level of a pulse modulated in the useful line of the image signal analog video can correspond to a value of -`30 quantization expressed on four binary elements.
- ~ Before analog conversion digital signal of sound sequences, we perform flow compression using either a logarithmic algorithm, i.e. an algorithm of the type "ADPCM"("ADAPTATIVE DIFFERENTIAL PULSE CODE
- MODULATION ") to obtain at the output of the converter 10 :., , ~
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a series of coding expressions comprising 4 elements representative binaries of sound samples.
The sequence of coding expressions is then stored in a temporary storage means 20 whose capacity is such that the continuity of the sound sequence is assured.
Temporary memory 20 therefore contains a series of coding expressions expressed on 4 binary elements. We extract sequentially from the ; 0 temporary memory 20, in the order of their memorization, each coding press has a frequency equal to or less than 3 times the line frequency of the logical video signal to attack a 60 digital resolution znalog converter , 4 bits and whose conversion frequency is greater than 12 MHz.
The analog digital converter 60 can be of type "AD9 / 02" of "ANALOG DEVICES". The digital to analog converter 60 delivers 23 analog pulses or samples whose amplitude is proportional to the quantification of expressions coding. analog samples are substituted to the color components of the video image for be multiplexed into the video imase signal `~ analog by a sequential coder 40 of the" PAL- type SEC ~ - NTSC "or analog ~: a for their broadcast on a vi_eo transmission channel.
In a referential way, multiplexing sound sequences c_ns the analog video signal is done a screen of im ~ e on two, the second frame being reserved for coda ~ e image elements of a still image to broadcast CG__2 described above.
A multip7exer 30 is coupled between the ~ temporary memory 20 _t digital converter , ~ ~ analog 60. the multip'exeur 30 is connected at input a c ~ i a memory 50 of digital image (pixels) ~; corresponding to either the RGB color components or . "~

10 2 ~ 26r ~ 6 to the luminance and chrominance components, coded on twelve binary elements. Synchronized Multiplexer 30 on a frame rate of video image restored alternatively to converters 60 either sound samples, i.e. picture elements a each image frame. in this way we use the same channels of multiplexer 60 for coding the images and sound sequences. We can see that in a way advantageous, the capacity of the temporary memory 20 will correspond to the memorization of a sequence coding expressions to insert into a frame ; video image. This frame memory can be ; made up of "N43" RAM components 256 C "from" NEC ".
- 15 In the case of the distribution system of still images with sound, coding expressions - relating to the signal of sound sequences are previously stored in the storage means 230 and therefore the sound sequence signal is not not digitized in real time. Similarly, memory temporary 20 may have a capacity of 128 kilos 4-bit words to allow distribution of 25 - frames per second with 8 seconds for each of telephone quality sound sequence.
Advantageously, a time base 70 constituting means of extraction, connected has temporary memory 20 of coding expressions and has the picture element memory 50 for selecting from alternatively one or the other of the memories in ~ 30 function of a frame synchronization signal.
- At the output of the analog converter digital 10, the sound sequence signal can be digitized as a series of expressions by `coding comprising eight binary elements by a process` ~
scanning and compression reduction -; bit rate of logarithmic law type A type G711 of `" CCITT ". This coding expression cannot be . ~, , .

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directly multiplexed in impulse form in the video image signal given the dynamic of limited amplitude of the latter. The expressions of coding thus obtained are stored in the memory temporary 20, as described above, in the form bytes. At the output of the temporary memory 20, we performs a segmentation of the coding expression into two coding sub-expressions each with four corresponding bits respectively at the high and low weights of the expression of coding. This segmentation is obtained using two shift registers 25.26, for example, powered by temporary memory 20. these shift registers, 25, 26 operate in such a way as to successively supply the multiplexer 30 a first coding sub-expression ; issued by the corresponding register 25 for example to the most significant bits of the coding expression and a second coding sub-expression issued by the register 26 corresponding to the least significant bits of the coding expression, each subexpression of `coding with four binary elements. In this case, the shift registers operate at a ~ `frequency half the line frequency.
Each of the coding sub-expressions 25 thus obtained is supplied as previously to digital to analog converter 60 to be ~ 'multiplexed into the video image signal. We will be able to advantageously code in the video image signal coding expressions resulting from the digitization of a sound signal whose size in binary elements is `, greater than 8 binary elements by applying the same ~ `process.
; According to this method, each expression of coding coded on eight binary elements we do match a couple of analog samples from the pulse signal type delivered by the converter digital analog 60 whose cumulative level . ~. ,, '; ~

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~ 20 ~ 67 ~ 6 amplitude corresponds to the quantification of the coding expression.
Advantageously the expression of coding will include a number of binary elements multiple of four to facilitate treatment at level of segmentation.
Analog video image signal provided by the encoder 40 includes a su ~ assignment of frames alternately corresponding to a frame image and a pseudo-image frame, the frame of pseudo-image including sound samples multiplexed.
This analog video image signal "composite" is received by a terminal 280 connected to the station 290 video image viewing reception as visible in figure 1.
The role of terminal 280 is to restore on the one hand the picture elements inserted in a first frame and the multiplexed sound elements in a second adjacent frame.
The received composite video image signal has the input of terminal 280 is decoded into components RGB colors by a 140 "Pal-Secam" decoder by `example, as visible in figure 4.
`~ 25 RGB signals are digitized by ^ 160 digital analog converters that deliver a series of four-bit binary words. Following binary words is segmented into two consecutive frames of binary words, one corresponding to an image frame, The other corresponding to a pseudo-image frame, the segmentation being controlled by a multiplexer 130 of the `type" 74 157 "of" TEXAS INSTRUMENTS "forming means `~ referral. the multiplexer 130 is powered by a even / odd frame signal supplied by a base time 100 of the video synchronization extractor type . "LM 1881" from "NS". Pointed digital data ~ by the multiplexer 130 are stored respectively ., ' ~, ~

2 0 ~ 6 in an image frame memory 150 for which concerns the picture elements and a soundtrack memory 120 for coding expressions relating to a sound sequence. In a way preferential, the size of the image frame memory 150 is 256 kilobytes and the size of the memory soundtrack is 128 kilos 4-bit words.
The time base 100 connected to the memory of frame 120 sound authorizes a writing of expressions of coding in memory 120 at a frequency of 6 MHz half the pixel frequency, which corresponds to a 160 nanosecond sample period and allows a reading of the coding expressions contained in the sound frame memory 120 has a sampling frequency 8 KHz sound, which are supplied to a decoder ', 110.
In the case of a transmission of sound samples corresponding to an expression `of coding expressed on eight binary elements, the `, 20 out of four coding sub-expressions binary elements delivered by converters analog digital 60 are placed sequentially in the sound frame memory, the corresponding bytes to coding expressions are serialized for supply a sound decoder encoder with 110 filtering type "TCR 2913" from "TEXAS INSTRUMENTS" which converts `in analog form the coding expressions and delivers a corresponding analog sound signal.
The use of frame memories 150, 120 has the advantage of "freezing" the content of a image, i.e. an image frame and a sound frame and ~ to be able to repeat the sequence as much as necessary ; sound.
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~ 2 ~ 7 ~: 3 each numeric coding sub-expression in two digital video image elements (pixels).
Thus, in the storage means 230, each numeric coding sub-expression is duplicated in two memory words corresponding to two digital video image elements to overcome signal restitution performance sound.
Of course, we can plan to write each numeric coding sub-expression in more than two memory words. However, the ability to transport of the video channel.
A particular problem of the process of multiplexing according to the invention resides in the fact increase the video signal correlation rate due to significant variations in the amplitude level of the successive analog samples. To stay compatible with a video coding system of the type SECAM, the bandwidth of the luminance signal must be of the order of 2.5 MHz. To respect the band - passing of the luminance signal, a interpolation between the numeric sub-expressions of ~ adjacent coding. Interpolation consists of replacing ;; the value of one of the numeric sub-expressions of coding written in doublets of pixels by a J mean value of amplitude level corresponding to the mean amplitude levels of two sub-Adjacent numeric coding expressions. This operation amounts to performing digital filtering which `~ 30 makes it possible to attenuate the folding spectra of ; frequencies that cause interference between - analog sound samples in the video signal.
as an extension of this improvement we can perform a double interpolation when each sub-coding expression is written in three pixels to further increase the quality of restitution of the sound signal.
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. Of course, the invention is not `limited to the example above and we can . advantageously provide other variants without this is outside the scope of the invention.
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Claims (8)

1. A process for multiplexing a sound signal analog in an analog video signal having a amplitude dynamics in which the sound signal is multiplied in a useful part of the video signal corresponding to a video image, characterized in that:
- we digitize the sound signal and use flow compression techniques to get a sequel digital coding expressions;
- we temporarily store the expression sequence digital coding to sequentially extract digital coding sub-expressions at a frequency in relation to a line frequency of the video signal, each digital coding subexpression with number predetermined binary elements depending on the dynamics amplitude of the video signal;
- each sub- is converted into analog form numeric coding expression extracted to provide analog samples with amplitude level proportional to a quantification of the sub-expression digital coding considered;
- an amplitude modulation of the samples is imposed analog in the useful part of the video signal for providing a composite signal having a video signal format. 2. A method according to claim 1, in which each of the coding digital sub-expressions has four binary elements. 3. A method according to claim 2, in which each of the numerical coding expressions comprises a number of bits multiple of four and in which step where we temporarily store the following of numeric coding expressions to extract the sub-digital coding expressions includes a step of segmentation of each numeric coding expression into digital coding and scheduling sub-expressions digital coding sub-expressions. 4. A method according to claim 1, 2 or 3, wherein each numeric coding sub-expression is inscribed in a plurality of digital picture elements video. 5. A method according to claim 4, in which said plurality of digital video picture elements includes two digital video image elements. 6. A method according to claim 4, in which one associated with each numerical sub-expression of coding at least one numeric coding sub-expression interpolated. 7. Interactive image distribution system sound systems broadcasting still images associated with sound sequences via a video network communication to a plurality of reception terminals, characterized in that it comprises:
- first means of memorizing a plurality sets of digitized image elements, - second means for storing a plurality of sequences of coding expressions of a sequence signal digital sound, each image being associated with a sequence sound, - extraction means connected to the first and second storage means for alternative extraction a set of image elements of a scanned image corresponding to an image frame and a series of expressions coding corresponding to a sound sequence of a duration predetermined, - digital to analog conversion means connected to said storage means for converting into analog alternatively the set of elements images and the sequence of coding expressions, - video coding means connected to the means of digital to analog conversion to provide a signal composite analog video image comprising alternately a frame of picture elements and a frame of coding expressions. 8. The system of claim 7, wherein a reception terminal includes:
- analog-to-digital conversion means for digitally convert analog video image signal into picture element components, - referral means connected to the means of analog to digital conversion, controlled by a signal frame to isolate a set of digitized image elements an image frame and a sequence of coding expressions an associated digitized sound sequence, multiplexed in an adjacent image frame, - storage means connected to the means switch to memorize alternately according to a frame signal control, the set of picture elements and the sequence of coding expressions, - digital to analog conversion means connected to the storage means for delivering an audible signal analog from the sequence of coding expressions.