Abstract:
A method and apparatus for compressing and restructuring video signals are provided to promote the usefulness of a video channel, resulting in the efficacy of accommodating more video programs in a single video channel. Several video compressing and restructuring devices are used to directly compress multiple digital video data streams which are then integrated by a multiplexer. Each of the video compressing and restructuring devices comprises a plurality of video compressors for compressing the video codes of the digital video data stream, and a multiplexer for integrating the video codes having been compressed by the video compressor. Each video compressor comprises a trancoder for properly adjusting quantization scale for further compressing video signals. Based on the present invention, video signals are directly compressed with simple method and apparatus of low cost, leading to the realizing of an analogy Video-On-Demand system (approximate to a Video-On-Demand system).

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to a method and apparatus for video compression and reformatting, and particularly to a method and apparatus for enabling existing video channels to accommodate the transmission of more video programs.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is getting more and more important to tackle the problem that the signal flow capacity and communication quality of a video transmission systems are always limited by channel bandwidth. This is because of the bulk of data contained in video signal and the higher communication quality required by video transmission. Although the number of video channels allowable for cable TV is more than 120, only very few remain available given that some are prohibited or are not suitable for using, resulting in extreme difficulty for acquiring channels for new video programs and new medium broadcast companies. Due to the limited number of channels available for application, the increase of number of the programs in a single channel shall be a good option for expanding the number of broadcast programs which, however, is limited by channel bandwidth, leading to a necessity of digital signal compression technology.  
           [0003]    Shown in FIG. 1 is a conventional digital video signal transmission and receiving system in which 8 video programs are merged by multiplexing technology into a single video channel for transmission. As shown in FIG. 1, the system comprises a sending station  100  for sending processed video programs which are then transmitted through cable  200  to a receiving site to be received by STB (set-top-box)  300  thereat and delivered therefrom to users.  
           [0004]    In sending station  100 , a network management and control unit  110  is used to manage and control a subscriber management unit  112 , a multiplex management unit  114 , a conditional access unit  116 , a multiplex and sever  118 , and a 8:1 multiplexer  120 ; the input of  110  is connected to an electronic program guide  122  and a scheduler/trafficker  124  according to which a tape/archive  126  provides programs to be sent directly or through an encoder  128  to a multiplex and sever  118  which also receives a live video source  130  processed by a real-time encoder  132 . Multiplex and sever  118  in turn sends a video signal to be processed by the 8:1 multiplexer  120  for merging into a single channel and then being processed by a modulator  140  in order to transmit through cable  200 .  
           [0005]    STB  300  receives, through a cable interface  302 , from cable  200  a signal which has frequency reduced by a tuner  304  and is then demodulated by a demodulator  306  into a MPEG2 video signal consisting of 8 programs, and is demultiplexed afterwards by a 1:8 demultiplexer  308  into individual video signals for being applied to a bus  310  connecting a Direct Random Access Memory (DRAM)  312  and a flash memory  314  for saving data. Based on the system, the video programs selected by users are retrieved and saved in a DRAM  316  while the others are ignored. The signals contained in DRAM  316  are decoded by MPEG2 decoder  318 , with digital video signals (digital video data stream) and digital audio signals individually inputted to a video digital-to-analog converter  320  and an audio digital-to-analog converter  322  to be respectively converted into analog video signals and analog audio signals for outputting to an ordinary TV for displaying. The 1:8 demultiplexer  308  also connects a infrared ray receiver (IR)  324  which is used by users to select a desired program through a remote controller.  
           [0006]    Given that the bandwidth of a channel for current TV systems is about 6 Mhz with transmission speed at about 27 Mbps, and that a MPEG2 system is adopted, the digital signals will usually be provided (by most of MPEG2 Encoder, for example) with an average output speed of 3.3 Mbps. With 3.3 Mbps×8=26.4 Mbps&lt;27 Mbps (equation 1), it can be seen at most 8 programs can be accommodated in a channel, e.g., only 8 programs can be broadcast simultaneously through one channel even though a MPEG2 system is used, thereby the number of increased programs is far beyond significant given that the number of available channels is so limited.  
           [0007]    [0007]FIG. 2 shows a video signal obtained from MPEG2 compression, most of which are distributed in a small range of bandwidth, with scarce explosion  402  and swiftly moving rapid pan of high detail  404 , implying feasible further compression.  
           [0008]    [0008]FIG. 3(A) and FIG. 3(B) illustrate encoding and decoding algorithm of MPEG2. As can be seen in FIG. 3(A), a MPEG encoder comprises a discrete cosine transform unit  502 , a quantizer  504 , and a variable length encoder  506 . Usually a video signal is converted through the three devices into a bit stream (digital video data stream) to be sent to user sites through a modulator and transmission medium. To reduce the bulk of signal flows,, many frames in MPEG2 system are transmitted on the basis of the difference between two successive frames, therefore a MPEG2 encoder further comprises a motion compensation unit  512  and a motion estimation unit. Due to the need that the two devices must operate with video signal data, a dequantizer  516  and an inverse discrete cosine transform unit  518  are further required. The final output is a MPEG2 bit stream (digital video data stream).  
           [0009]    [0009]FIG. 3(B) illustrates the operation algorithm of a decoder, which reverses the operation shown in FIG. 3(A), i.e., the MPEG2 bit stream (digital video data stream) outputted by the encoder in FIG. 3(A) is inputted to the decoder in FIG. 3(B), and processed by a variable length decoder  522 , a dequantizer  524 , and an inverse discrete cosine transform unit  526 , as well as a motion compensation unit  528 , to eventually obtain a restored video signal as its output.  
           [0010]    When proceeding quantization, the bulk of video data signal may be reduced by lowering quantization level. Although lowered quantization level naturally reduces quantized data signal, it leads to a drawback that the quality of video frames is lowered.  
           [0011]    Paik suggested, in U.S. Pat. No. 5,216,503, a multi-channel video compression system using a statistical multiplexer to integrate multiple video programs in a conventional video channel. To avoid the unnecessary waste resulting from too big instant bandwidth of a single program, a buffer controller is used to generate, when the total bandwidth of these programs exceeds system capacity, a signal for requesting the quantizer to adjust quantization level so that the bandwidth is lowered.  
           [0012]    When the aforementioned patent was filed, digital video signal standard had not been established, therefore its quantizer was designed for digitizing video signal (similar to MPEG). Nowadays some digital video signal standards such as ISO/IECJTCI/SC29/WG11 for MPEG2 have been established, thereby most of the video contents are processed according to these standards, resulting in a necessity of converting digital video contents into analog contents if the aforementioned patent is to be applied, leading to the need of extra decoding devices and extremely long operating time.  
           [0013]    It can be seen now that a practicable method and apparatus for integrating multiple programs in a conventional video channel can be adopted only if it fits the existing video system and maintains the quality of video frames. The requirement, however, is beyond the capacity of conventional arts.  
         SUMMARY OF THE INVENTION  
         [0014]    An object of the present invention is to provide a method and apparatus for integrating multiple video programs in a video channel.  
           [0015]    When bandwidth is extremely limited, digital video signal is further compressed according to the present invention under the condition that it is not to be sensed by the eyes of human being, leading to more efficient utilization of existing channels. It is therefore another object of the present invention to provide a method and apparatus for compressing and restructuring video signals.  
           [0016]    Another further object of the present invention is to promote operation efficiency of a video system by enabling a single channel to accommodate more video programs.  
           [0017]    The other further object of the present invention is to provide a method and apparatus for directly compressing video signals to realize a real time video system.  
           [0018]    Furthermore, digital video signals (digital video data stream) can be directly compressed according to the present invention to enable a single channel to accommodate more video programs, therefore it is also an object of the present invention to provide a video compressor and a method for compressing digital video data, as well as a trancoder and associated method for compressing digital video data.  
           [0019]    The trancoder suggested by the present invention is characterized in that a better quantization scale can be achieved by determining a new quantization scale when quantizing data. It is therefore also another object of the present invention to provide a neural network quantization scale predictor for determining an optimum quantization scale.  
           [0020]    The compression of digital video signal suggested by the present invention is characterized in that the quantization level for the areas of a video frame which are less sensitive to human eyes is reduced while the quantization level for those which are sensitive to human eyes is maintained  
           [0021]    In an embodiment of the present invention, multiple digital video compressing and restructuring devices (or called Q-mux) are used to directly compress digital video signals (digital video data stream) which are then integrated by a multiplexer; each digital video compressing and restructuring device has a multiplexer to restructure digital codes (digital codes of the multiple digital video signals) having been compressed by video compressors (or called Q-presser); each video compressor comprises at least a trancoder to reduce the quantization level for the areas of a frame which are less sensitive to human eyes, in order to further compress digital video signal.  
           [0022]    The present invention may best be understood through the following description with reference to the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 shows a conventional video transmission and receiving system wherein 8 video programs are merged in a single channel.  
         [0024]    [0024]FIG. 2 shows video signal bandwidth distribution of a conventional MPEG2.  
         [0025]    [0025]FIG. 3 shows an encoder and decoder of MPEG2, among which FIG. 3(A) shows the encoder and FIG. 3(B) shows the decoder.  
         [0026]    [0026]FIG. 4 illustrates, on the basis of video bandwidth distribution, the video compression algorithm suggested by the present invention.  
         [0027]    [0027]FIG. 5 illustrates an embodiment of the present invention allowing up to 24 video programs to be accommodated in a single channel.  
         [0028]    [0028]FIG. 6 illustrates an embodiment of a trancoder suggested by the present invention.  
         [0029]    [0029]FIG. 7 illustrates an embodiment of a quantization scale predictor suggested by the present invention, which is achieved by a neural network of 3 layers.  
         [0030]    [0030]FIG. 8 shows an embodiment of a video transmission and receiving system suggested by the present invention.  
         [0031]    [0031]FIG. 9 shows an embodiment of a video-on-demand analogy system (approximate to a video-on-demand system) suggested by the present invention.  
       Reference Numerals  
       [0032]    [0032] 100  sending station  
         [0033]    [0033] 110  network management and control unit  
         [0034]    [0034] 112  subscriber management unit  112   
         [0035]    [0035] 114  multiplex management unit  
         [0036]    [0036] 116  conditional access unit  116   
         [0037]    [0037] 118  multiplex and sever  118   
         [0038]    [0038] 120   8 : 1  multiplexer  120   
         [0039]    [0039] 122  electronic program guide  122   
         [0040]    [0040] 124  scheduler/trafficker  124   
         [0041]    [0041] 126  tape/archive  126   
         [0042]    [0042] 128  encoder  
         [0043]    [0043] 130  live video source  130   
         [0044]    [0044] 132  real-time encoder  132   
         [0045]    [0045] 140  modulator  
         [0046]    [0046] 200  cable  
         [0047]    [0047] 300  STB (SET-TOP-BOX)  
         [0048]    [0048] 302  cable interface  
         [0049]    [0049] 304  tuner  304   
         [0050]    [0050] 306  demodulator  
         [0051]    [0051] 308  demultiplexer  
         [0052]    [0052] 310  bus  
         [0053]    [0053] 312  Direct Random Access Memory (DRAM)  
         [0054]    [0054] 314  flash memory  
         [0055]    [0055] 316  DRAM  
         [0056]    [0056] 318  MPEG2 decoder  
         [0057]    [0057] 320  video digital-to-analog converter  
         [0058]    [0058] 322  audio digital-to-analog converter  
         [0059]    [0059] 324  infrared ray receiver (IR)  
         [0060]    [0060] 402  explosion  
         [0061]    [0061] 404  rapid pan of high detail  
         [0062]    [0062] 502  discrete cosine transform unit  
         [0063]    [0063] 504  quantizer  
         [0064]    [0064] 506  variable length encoder  
         [0065]    [0065] 512  motion compensation unit  
         [0066]    [0066] 516  dequantizer  
         [0067]    [0067] 518  inverse discrete cosine transform unit  
         [0068]    [0068] 522  variable length decoder  
         [0069]    [0069] 524  dequantizer  
         [0070]    [0070] 526  inverse discrete cosine transform unit  
         [0071]    [0071] 528  motion compensation unit  
         [0072]    [0072] 601 - 608  digital video compressing and restructuring devices (or called Q-mux)  
         [0073]    [0073] 611 - 613  video compressors  
         [0074]    [0074] 621  trancoder  
         [0075]    [0075] 622  input buffer  
         [0076]    [0076] 623  output buffer  
         [0077]    [0077] 624  disc drives (computer disc drives)  
         [0078]    [0078] 625  high speed network  
         [0079]    [0079] 631  multiplexer  
         [0080]    [0080] 640  Ethernet network switch (etherswitch)  
         [0081]    [0081] 650  8:1 multiplexe  
         [0082]    [0082] 700  trancoder  
         [0083]    [0083] 702  decoder  
         [0084]    [0084] 704  encoder  
         [0085]    [0085] 712  delay buffer  
         [0086]    [0086] 714  quantization scale predictor  
         [0087]    [0087] 716  variable length decoder  
         [0088]    [0088] 718  dequantizer  
         [0089]    [0089] 720  quantizer  
         [0090]    [0090] 722  variable length encoder  
         [0091]    [0091] 802  input layer  
         [0092]    [0092] 804  concealed layer  
         [0093]    [0093] 806  output layer  
         [0094]    [0094] 901 - 908  digital video compressing and restructuring devices  
         [0095]    [0095] 910  multiplexer  
         [0096]    [0096] 912  modulator  
         [0097]    [0097] 914  frequency multiplier (frequency raiser)  
         [0098]    [0098] 916  cable  
         [0099]    [0099] 918  set-top-box  
         [0100]    [0100] 920  TV set  
         [0101]    [0101] 930  digital video compressing and restructuring device  
         [0102]    [0102] 931  video tape  
         [0103]    [0103] 932  compact disc (CD)  
         [0104]    [0104] 933  digital video disc (DVD)  
         [0105]    [0105] 934  disc (hard or floppy)  
         [0106]    [0106] 935  cable system  
         [0107]    [0107] 936  satellite antenna  
         [0108]    [0108] 937  satellite  
         [0109]    [0109] 938 - 939  satellite antenna  
         [0110]    [0110] 940  head-end  
         [0111]    B1.B2 bit stream (digital video data stream)  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0112]    According to the present invention, digital video contents are directly compressed and multiple video programs are merged into a single video channel. It can be seen from FIG. 4 that most of video bandwidth ranges below 1 Mbps therefore further exploitation of bandwidth can be achieved by further compressing digital video signals (digital video data stream).  
         [0113]    [0113]FIG. 5 shows an embodiment of the present invention, which comprises 8 digital video compressing and restructuring devices  601 - 608  each including 3 video compressors, such as 3 video compressors  611 - 613  included in  601 , each of video compressors  611 - 613  has a trancoder  621  and buffers connected to its input and output. For example, video compressor  611  includes trancoder  621  for converting video codes of 3.3 Mbps or higher transmission speed into video codes of 1.1 Mbps. Trancoder  621  has its input and output respectively connected to input buffer  622  and output buffer  623  each with a memory capacity of 1 Mb for temporarily saving video signals. The digital video signals (digital video data stream) retrieved from disc drives  624  are compressed by trancoder  621  to become video codes of 1.1 Mbps. The video compressor may also receive digital video signals (digital video data stream) from another kinds of sources such as that video compressor  613  receives digital video signals (digital video data stream) from high speed network  625  and compresses the received digital video signals (digital video data stream).  
         [0114]    3 video compressor  611 - 613  output signals to be integrated by multiplexer  631  to form signals of 3.3 Mbps. 8 digital video compressing and restructuring devices  601 - 608  output signals to be sent to 8:1 multiplexe  650  through etherswitch  640 , and then integrated step by step to form digital video signals (digital video data stream) of 27 Mbps to be outputted.  
         [0115]    Each video compressor in the embodiment compresses video signals into video codes of 1.1 Mbps, each of digital video compressing and restructuring devices  601 - 608  has 3 video compressors and has output of 3.3 Mbps, outputs of 8 digital video compressing and restructuring devices  601 - 608  fit right in a channel of 27 Mbps, thereby a single channel can accommodate up to (3×8=)24 video programs which are 3 times what a conventional system can provide, allowing cable TV companies to have optimum arrangement in facing clients and video program providers, in order to maximize the number of programs while minimize the number of channels.  
         [0116]    It shall be known by those who are skilled in the art that the video compressor and the video compressing and restructuring device suggested by the present invention are not limited by the aforementioned embodiments. Their configuration or design, as well as constituent number can be modified to adapt to system requirements, which are not beyond the scope of the present invention.  
         [0117]    A preferred embodiment of the hardware for the present invention is that a digital video compressing and restructuring device comprises a mother board and 3 pieces of Single Board Personal Computer (SBPC); the mother board comprises Central Processing Unit (CPU), Read Only Memory, (ROM), Random Access Memory (RAM), disc drives, and high speed network interface; each SBPC comprises CPU. ROM, RAM; 8:1 multiplexe  650  can be made of a CPU (or a computer).  
         [0118]    A preferred embodiment of the trancoder is shown in FIG. 6( a ) and FIG. 6( b ). FIG. 6( a ) briefly illustrates trancoder  700  comprising decoder  702  for decoding inputted bit stream (digital video data stream) B 1  and encoder  704  for receiving the bit stream (digital video data stream) decoded by decoder  702  and encoding it into bit stream (digital video data stream) B2. Detailed description of trancoder  700  is shown in FIG. 6( b ) where delay buffer  712  adjusts inputted bit stream (digital video data stream) B 1  and generates an overflow signal according to its overflow status; quantization scale predictor  714  estimates, based on nonlinear algorithm, optimum quantization scale according to the current overflow status and the video signal segment to be outputted immediately; variable length decoder  716  restores the signal produced by a variable length encoder to numeral codes; dequantizer  718  restores quantized signal; quantizer  720  proceeds another quantization according to the outputs of quantization scale predictor  714  and dequantizer  718 ; its output is processed by variable length encoder  722  to provide bit stream (digital video data stream) B 2  as an output.  
         [0119]    The trancoder is characterized in that the parts of video signal which are to be well sensed by human eyes are less compressed while those which are to be less sensed by human eyes are more compressed, in order to achieve maximum compression while maintain frame quality in the range human eyes can tolerate.  
         [0120]    The compression can be easily done by software in a personal computer for meeting most requirements for video display quality. The algorithm for compressing data in the present invention is to determine a new quantization scale when quantizing data, i.e., relatively rough quatitization scale is given to the complicated parts (the parts with roughness not easily sensed by human eyes) of a frame, while relatively fine quantization scale is given to the plain parts (the parts with roughness easily sensed by human eyes) of a frame.  
         [0121]    In the operation of MPEG2 compression, image processing is done on the basis of basic unit (Macroblock; MB) which comprises 8×8 Pixels. The image signal contained in a MB is processed by a discrete cosine transformation to become a transformation coefficient C ij ; quantization is one of several main steps in the MPEG compression of video signals. If transformation coefficient C ij  is divided by quantization step size, and then an operation of making integers is applied, quantization levels L ij  are obtained below  
                 L     i   ,   j       =     int              [       α   ·     C     i   ,   j             q   s          ω     i   ,   j           ]       ,   i   ,     j   =   1     ,   …              ,   8           (equation  2)                               
 
         [0122]    where q s  is quantization scale, and is an integer ranging from 1 to 31 in MPEG2; ω ij  is a quantization matrix for applying different weighting of processing to the transformation of different locations, the weighting is established through observation by human eyes; practically, however, the higher frequency the transformation coefficient is associated with, the less sensitivity it has to human eyes, and the corresponding locations in the matrix have bigger coefficient (less fine), while the locations corresponding to a transformation coefficient associated with lower frequency have smaller matrix value which leads to finer quantization step size, here a is a quantization constant, and is assigned to equal 2 4 .  
         [0123]    Each video frame having a necessity of bit rate trancoding shall have its frame type remain unchanged, and have the number of its total bits and each average quantization scale as well as the number of corresponding bits recorded. Take I Frame for example, assume the number of bits of a temporarily recorded frame is B Prev  bits, the bit rate of inputted video signals is R 1  Mbps, and the bit rate of outputted video signals is R 2  Mbps, the desired number of bits (T bits) of trancoded output for the frame is obtained according to the ratio between the bit rates as follows,  
             T   =         R   2       R   1       ·     B   prev               (equation  3)                               
 
         [0124]    the number T is the desired number of bits set before the frame is trancoded, and is theoretically an ideal number of bits of the trancoded output for the frame. The object of controlling bit rate is to make the number of bits of the trancoded output for the frame approximate the desired number of bits.  
         [0125]    After calculating the desired number of bits fir a frame, the Complexity estimation C j  of each MB of the frame is then computed, and the desired number of bits (T mb bits) of each MB is allocated according to the Complexity estimation C j  of the MB, as shown below,  
                 T   j   mb     =         C   j         C   1     +     C   2     +   …              +     C   m            T       ,     1   ≦   j   ≦   m             (equation  4)                               
 
                 C   j   1     =       q   j     ?     B   prev         ,     j   =   1     ,   …              ,   m           (equation  5)                               
 
         [0126]    where nm is the number of all MBs in the frame, T is the desired number of all bits in the frame. Computation of C i   j  is shown by equation 5 where q j  is the quantization scale of the j th MB of an inputted frame, B prev   j  is the number of the bits which are in the inputted frame and are enclosed by the MB. Because the input to the trancoder is MPEG2 video signals, the encoded data for inputted video signals can be known when proceeding trancoding, and higher efficiency and accuracy can be thus achieved by setting desired number of bits according to the Complexity estimation C j  of each MB.  
         [0127]    Whenever the trancoding for a MB is completed during the process of trancoding, the overflow coefficient of virtual buffer shall be updated as shown by equation 6 below,  
           d   i   j = d   i   0 + B   mb   j-1 − T   mb   j-1   (equation 6) 
         [0128]    where d i   j  is the overflow coefficient of virtual buffer when trancoding the j th row, B mb   j-1  is the number of bits of the output for the (j-1) th row, T j- 1 mb  is the desired number of bits computed by equation 4 for the (j-1) th row.  
         [0129]    It can be seen from equation 6 that d i   j  is successively accumulated. In case the number (B mb ) of bits of the trancoded output for each row before the (j-1) th row exceeds the computed desired number T mb , d j   i  will gradually become bigger until Quantization scale gets so big that the number of outputted bits starts to be smaller than desired number of bits. This is the time the overflow coefficient begins to fall off.  
         [0130]    In equation 6, d i   0  is the initial value of overflow coefficient for I frame, the initial value in the beginning is  
               d   0   i     =       q   seed     ·     γ   31               (equation  7)                               
 
         [0131]    where γ is the value obtained through dividing bit rate by the number of frames per second, i.e.,  
             γ   =     2   ·     bit_rate   frame_rate               (equation  8)                               
 
               q   seed     =       q   1     ·     exp              [         R   1     -     R   2       β     ]               (equation  9)                               
 
         [0132]    where q1 is the quantization scale of the first MB of the first frame, β is a coefficient related to q1 and is used as the initial value of the overflow coefficient for next I frame. For P frame and B frame, the steps before computing overflow coefficient are the same as those for I frame.  
         [0133]    For each MB, the quantization scale predictor suggested by the present invention can be used to obtain in advance the q i   opt  (Optimal Quantization scale) given that the current overflow coefficient d i-1  and its desired number T mb   i  of bits are known. The predication based on d i-1  and T i   mb , is usually not good enough, because the predication for best q i   opt  based on current d i-1  and T 1   mb  may heavily affect the q i+1   opt  for next MB, such as the case T i+1   mb  becomes verse large while d I  is not big enough, resulting in a poor scale to quantize T i   mb  for q i+1   opt  . Observation of more T j   mb (j&gt;1) will be more proper for determining relatively suitable q i   opt . It must also be noted that the relations between q i   opt  and d i-1 , T i   mb  , T i+1   mb , . . . are nonlinear, and therefore the computation for the predication can be based only on experienced formula associated with complicated computation and accompanied with inaccuracy It is therefore an object of the present invention to provide a neural network workable with learning approach in order to better define the relations between q i   opt  and d i-1 , T i   mb , T I+1   mb , . . . ,.  
         [0134]    [0134]FIG. 7 shows a preferred embodiment of a neural network which is a 3 layer of Multi-Layer Perceptron (MLP). It comprises an input layer  802 , a concealed layer  804 , and an output layer  806 . Try each of various different values for d i-1 , T mb   i-1 , . . . , to find, by human experimentation, a q i   opt  for best frame performance, and then train the neural network according to these values. Due to its Generalization capability, the neural network can make optimum predication for various cases. It must be noted that the output value of the neural network ranges between 0 and 1, thereby the outputted q i   opt  appears as a normalized value which must be multiplied by a constant.  
         [0135]    [0135]FIG. 8 shows an application example of the cable TV broadcasting and receiving system suggested by the present invention. Configured on broadcasting site are 8 digital video compressing and restructuring devices  901 - 908  forming a single channel through multiplexer  910 , with video output fed to cable  916  through modulator  912  and frequency multiplier  914 , for users to retrieve video programs from set-top-box  918  on remote site and display the programs on TV set  920 . The operation of set-top-box  918  is the same as the set-top-box  300  shown in FIG. 1.  
         [0136]    The present invention&#39; feature of enabling a single channel to accommodate many programs contributes significantly to the establishment of a Video On Demand (VOD) system. FIG. 9 shows an analogy Video On Demand system (NVOD) provided by the present invention, in which a digital video compressing and restructuring device  930  as that shown in FIG. 5 is configured on broadcasting site, and  24  video programs are merged into a single channel. There can be various options for the source of the video programs, among which are video tape  931 , Compact Disc (CD)  932 , compressed video signals, digital video disc (DVD)  933 , and floppy disc  934  containing compressed image, etc. After being integrated by digital video compressing and restructuring device  930 , and broadcast through cable system  935  or through satellite antenna  936  as well as uplink satellite  937 , these programs can be directly received by users through satellite antenna  938 , or received by cable TV service companies through satellite antenna  939  and then fed to cable system  935  via headend  940 . Because 24 programs can be merged in a channel, if a hot program is broadcast through a sub-channel every 2.5 minutes, by considering 2.5 minutes×24=60 minutes (equation 10), it can be seen that the broadcasting of a movie based on a NVOD provided by the present invention can proceed with original video signals of one copy.  
         [0137]    While the invention is described in terms of what are presently considered to be the most practical and preferred embodiments, it must be understood that the invention is not limited to the disclosed embodiment. On the contrary, it is to cover various modifications and similar arrangements included within the spirit and scope of the following claims which are to be accorded with the broadest interpretation to encompass all modifications and similar structures based thereon.