Abstract:
An output coding apparatus includes a coder for coding an inputted bitstream to an error correction and/or detection code composed of information bits and check bits; and a bitstream assembling section for assembling an outputted bitstream by inserting a synchronization code at any one of a plurality of synchronization code insertion positions previously determined in the outputted bitstream, arranging the information bits at any desired positions of the bitstream, and by arranging the check bits at positions other than the synchronization code insertion positions in the bitstream. Therefore, when the coding apparatus is combined with a resynchronization method using both an error correction and/or detection code and a synchronization code, it is possible to solve a problem caused by pseudo-synchronization or synchronization-loss pull-out or step-out due to erroneous detection of the synchronization code.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a system for transmitting and/or storing information through a medium of high error rate such as radio transmission path, and more specifically to a coding and/or decoding apparatus for coding a bitstream obtained by a high efficiency compression coding to an error correction and/or detection code and for transmitting and/or storing the coded bitstream.  
         [0002]     In a system for transmitting audio and/or video signals via radio transmission path after the signals have been compression-coded at a high efficiency to reduce the signal quantity as small as possible, for instance as with the case of radio TV telephone, portable information terminal, digital TV broadcasting system, etc., since the error rate of the transmission path is relatively high, it is important to transmit the obtained bitstream in as high a quality as possible.  
         [0003]     When the bitstream is transmitted and/or stored via a medium of high error rate as described above, an error correction code such as BCH code, RS code, convolution code, etc. has been so far widely adopted as means for reducing the error rate. On the other hand, as means for detecting an error on the reception side, an error detecting code such as check sum, CRC, etc. are used. In these error correction and/or error detection methods, error is corrected and/or detected by adding excessive (redundant) bits to information to be transmitted and/or stored in accordance with a prescribed rule and further by checking whether the transmitted and/or stored bitstream abides by the same rule when decoded.  
         [0004]     However, in the above-mentioned method such that the bitstream obtained by high efficiency compression coding is further coded to an error correction and/or detection code and then transmitted and/or stored, there exists a problem in that it is difficult to combine this method with a resynchronization method for recovering a synchronization when synchoronization-loss occured due to an erroneous bistream word caused by the transmission and/or storage medium. Here, as the above-mentioned synchronization restoring method, there has been widely used such a method of inserting a unique word (referred to as synchronization code or start-code) decodable uniquely (unconditionally) and of resuming decoding operation, in case of synchronization-loss, from a time point when the synchronization code is detected again.  
         [0005]     In order to form the synchronization code as a code word decodable unequivocally, it is necessary to construct the code word in combination with another code word in such a way that a bit pattern the same as that of the synchronization code will not appear. In the case of the general error correction and/or detection coding method, however, it is difficult to construct the code word in such a way that a specific bit pattern will not appear. On the other hand, when the bit pattern the same as the synchronization code appear, pseudo-synchronization may occur due to an erroneous detection of the synchronization code.  
         [0006]     To overcome this problem, conventionally, the following method has been so far used: after the error correction and/or detection coding has been executed, the presence of the bit pattern the same as that of the synchronization code is checked in the bitstream; when the same bit pattern exists, stuffing bits .are inserted into the pattern in accordance with a prescribed rule; and the inserted stuffing bits are removed in accordance with the same prescribed rule by the decoding apparatus in order to prevent the pseudo-synchronization. In this method, however, when the bitstream having an error is transmitted and/or stored, since there exists a possibility that the stuffing bits are also inserted erroneously, there still exists another problem in that an additional synchronization-loss or pseudo-synchronization may occur.  
         [0007]     Further, when the bitstream is coded for error correction and/or detection and further the synchronization code is inserted, in the conventional method, since many insertion bits must be added to the bitstream at the last portion of a synchronization block sandwiched between two synchronization codes in order to compensate for a remainder of the information bits to be coded for error correction and/or detection, there arises another problem in that the coding efficiency is lowered.  
         [0008]     On the other hand, in order to increase the error correction and/or detection capability, although it may be considered to increase the redundancy of the information to be transmitted and/or stored, in this case, however, the number of necessary bits increases when the same quantity of the information is transmitted. Therefore, when the error correction and/or detection capability is simply increased, there arises another problem in that a transmission path of higher transmission rate is required or that the number of bits of information to be stored is increased. Further, when the transmission rate or the storage capacity is the same, the quantity of information to be transmitted and/or stored decreases with increasing redundancy. As a result; in the case where audio and video information are compression-coded at a high efficiency and then transmitted and/or stored, if the redundancy is simply increased to Increase the error resistance, as far as the transmission and/or storage rate is the same, since the information must be compression-coded down to a lesser information quantity, there causes another problem in that the audio quality and picture quality both deteriorate.  
         [0009]     To overcome the above-mentioned problems, as the method of obtaining a high error resistance in spite of a lesser redundancy, there exists a method referred to as hierarchical coding. In this method, the audio or picture information compression-coded at a high efficiency is classified according to the degree of error which deteriorates the audio quality or the picture quality; the error correction and/or detection code of a high redundancy and thereby a high error correction and/or detection capability is adopted for the information with more importance and a large error influence; and the error correction and/or detection coding of a low redundancy and thereby a low error correction and/or detection capability is adopted for the information with less importance and a small error influence. In this method, it is possible to increase the error resistance in spite of a relatively small averaged redundancy, as compared with when a correction and/or detection code is used uniformly for all the information in the same redundancy.  
         [0010]     For instance, in the case of the coding method such that motion compensation prediction and the orthogonal transform are combined with each other (which is widely adopted for compression-coding moving picture information at high efficiency); that is, in the case of the coding method such that the motion compensation prediction is executed for the inputted moving picture video signals, and the predicted residual is orthogonal-transformed (e.g., discrete cosine transform (DCT)), the error correction and/or detection code of strong error correction and/or detection capability is used for the motion vector information or low-order coefficients of the orthogonal transform coefficients of the prediction residual signals (because these information deteriorates picture quality largely in case an error occurs); and the error correction and/or detection code of weak error correction and/or detection capability is used for high-order coefficients of the orthogonal transform coefficients of the prediction residual signals (because these information exerts a relatively small influence upon the picture quality).  
         [0011]     To realize the above-mentioned hierarchical coding, it is necessary to switch the error correction and/or detection codes of different error correction and/or detection capabilities midway in the outputted bitstream. As the method of switching the error correction and/or detection codings of different error correction and/or detection capabilities, there exists such a method that header information indicative of the sort of the error correction and/or detection code is added to the bitstream.  FIG. 1  shows an example of a bitstream in which the error correction and/or detection codes are switched by adding header information. In more detail, in this example, two sorts of the error correction and/or detection codes FETC 1  and FEC 2  are switched. In each of the headers  1101  to  1104 , header information indicative of the sort of the error correction and/or detection code and a number of code word is inserted. Therefore, the coding apparatus arranges the code word coded for error correction and/or detection after each header information, and the decoding apparatus decodes the header information; and the decoding apparatus decodes the header information and after that the error correction and/or detection code in accordance with the decoded header information.  
         [0012]     However, in the above-mentioned method of switching the error correction and/or detection codes by adding the header information, however, there arises a problem in that the number of bits of the bitstream to be transmitted and/or stored increases due to the addition of the header information. In the case where audio or video signals are compression-coded, since some bits are used for the header information, the number of bits used for the compression-coding audio or video signals is inevitably reduced, with the result that the audio quality and/or the picture quality inevitably deteriorates.  
         [0013]     As described above, when the error correction and/or detection coding is executed for a bitstream obtained by compression-coding moving picture signals, since any bit pattern is generated, in the case where the error correction and/or detection coding is combined with the synchronization method using the unique word as synchronization code, there exists a pseudo-synchronization due to erroneous detection of the synchronization code. Further, when the stuffing bits are inserted to prevent the pseudo-synchronization, there arises another problem in that the synchronization-loss and the pseudo-synchronization occur due to erroneous insertion of the stuffing bits.  
         [0014]     Further, when the bitstream is coded for error correction and/or detection and further the synchronization code is inserted, in the conventional method, since a relatively large number of bits must be inserted to compensate for the remainder of the information bits to be coded for error correction and/or detection at the last portion of the synchronization block, there arises a problem in that the coding efficiency deteriorates.  
         [0015]     Further, in the case of the coding and/or decoding apparatus in which the error correction and/or detection codes of different error correction and/or detection capabilities are switched by adding header information, since the number of bits to be transmitted and/or stored increases due to the addition of the header information, when audio or video signals are compression-coded at a high efficiency and then transmitted and/or stored, the information quantity used for audio or video information inevitably decreases, with the result there exists a problem in that the audio quality and the video quality both deteriorate.  
       SUMMARY OF THE INVENTION  
       [0016]     With these problems in mind, therefore, it is the first object of the present invention to provide a coding and/or decoding apparatus, which can solve such a problem as pseudo-synchronization or synchronization-loss due to erroneous detection of the synchronization code, when combined with the resynchronization method which uses both the error correction and/or detection code and the synchronization code.  
         [0017]     Further, the second object of the present invention is to provide a coding and/or decoding apparatus which can increase the coding efficiency by reducing the number of bits inserted at the last portion of the synchronization block, when combined with the resynchronization method which uses both the error correction and/or detection code and the synchronization code.  
         [0018]     Further, the third object of the present invention is to provide a coding and/or decoding apparatus, which can improve the information quality by reducing the number of bits of the bitstream to be transmitted and/or stored, without adding header information indicative of the sort of the error correction and/or detection code, in the case when bitstream obtained by compression-coding audio and video signals are coded by switching a plurality of sorts of error correction and/or detection codes and then transmitted and/or stored.  
         [0019]     To achieve the above-mentioned object, the first aspect of the coding apparatus according to the present invention provides a coding apparatus, comprising: coding means for coding an inputted bitstream to an error correction and/or detection code composed of information bits and check bits; and bitstream assembling means for assembling an outputted bitstream by inserting a synchronization code at any one of a plurality of synchronization code insertion positions previously determined in the outputted bitstream, arranging the information bits at any desired positions of the bitstream, and by arranging the check bits at positions other than the synchronization code insertion positions in the bitstream.  
         [0020]     Further, the first aspect of the present invention provides a decoding apparatus, comprising: synchronization code detecting means for detecting a synchronization code from a bitstream coded to an error correction and/or detection code composed of information bits and check bits, at each of a plurality of previously determined synchronization code insertion positions thereof; bitstream disassembling means for disassembling the bitstream to extract the information bits of the error correction and/or detection code and the check bits of the error correction and/or detection code arranged at positions other than the synchronization code insertion positions; and decoding means for decoding the error correction and/or detection code on the basis of the information bits and the check bits extracted by said code disassembling means.  
         [0021]     In the first aspect of the present invention, since the synchronization code is arranged at each of a plurality of predetermined synchronization code insertion positions in the output bitstream and further since the check bits of the error correction and/or detection code are arranged at positions other than the synchronization code insertion positions, even if the bit pattern the same as that of the synchronization code is included in the check bits, there exists no possibility that the synchronization code is detected erroneously. Therefore, it is unnecessary to use a specific error correction and/or detection code to prevent a specific bit pattern form being formed or to insert bits to protect the synchronization pattern after having been coded to the error correction and/or detection code. As a result, it is possible to increase not only the degree of freedom of selection of the usable error correction and/or detection codes but also to improve the resistance against error, because there exists no possibility that the new erroneous synchronization detection occurs due to mixture of the erroneous insertion bit.  
         [0022]     Further, the second aspect of the present invention provides a coding apparatus, comprising: bitstream converting means for converting an inputted bitstream other than a synchronization code arranged at each of a plurality of synchronization code insertion positions previously determined in an outputted bitstream, in such a way that a Hamming distance from the synchronization code exceeds a predetermined value; coding means for coding the bitstream converted by said bitstream converting means to an error correction and/or detection code composed of information bits and check bits; and bitstream assembling means for assembling an outputted bitstream by inserting a synchronization code at any one of a plurality of the synchronization code insertion positions previously determined in the outputted bitstream, arranging the information bits at any desired positions of the bitstream, and by arranging the check bits at positions other than the synchronization code insertion positions in the bitstream.  
         [0023]     Further, the second aspect of the present invention provides a decoding apparatus, comprising: synchronization code detecting means for detecting a synchronization code at each of previously determined synchronization code insertion positions, from a bitstream coded to an error correction and/or detection code composed of information bits and check bits and further including the inserted synchronization codes; bitstream disassembling means for disassembling the bitstream, to extract the information bits of the error correction and/or detection code and the check bits of the error correction and/or detection code arranged at positions other than the synchronization code insertion positions; decoding means for decoding the error correction and/or detection code on the basis of the information bits and the check bits extracted by said code disassembling means; and bitstream converting means for converting the bitstream other than the synchronization code arranged at each of the synchronization code insertion positions, which is decoded by said decoding means and further converted in such a way that a Hamming distance from the synchronization code in the bitstream exceeds a predetermined value, to the original bitstream.  
         [0024]     In the second aspect of the present invention, since the bit train arranged at the synchronization code insertion position is converted in such a way that the Hamming distance from the synchronization code exceeds a predetermined value and further since the bit train is reversely converted by the decoding processing, the bit pattern the same as that of the synchronization code will not be included in the bit train, so that it is possible to prevent the erroneous detection of the synchronization code. Further, when the bit train is converted in such a way that the Hamming distance between the synchronization code and the bitstream other than the synchronization code exceeds a predetermined value, even if an error is mixed with the bitstream, since the synchronization code can be discriminated from the bitstream other than the synchronization code, it is possible to reduce the possibility that the synchronization code is detected erroneously.  
         [0025]     Further, since the above-mentioned conversion and/or reverse conversion processing is executed at the synchronization code insertion positions, it is possible to reduce the overhead, as compared with the prior art method such that the conversion and/or reverse conversion processing is executed all over the bitstream. In addition, in the case of the bitstream inputted to the coding apparatus, it is unnecessary to execute the conversion processing or to use a special code word, so that the bit pattern the same as that of the synchronization code can be prevented from being formed. In particular, in the case where a variable code length coding apparatus in which different code word tables are switched in use is connected to the input side of the coding apparatus according to the present invention, when the code word table is formed in such a way that the bit pattern the same as that of the synchronization code will not be formed by the variable length coding apparatus, there exists a problem in that the coding efficiency is inevitably reduced. In the present invention, however, since the coding apparatus and/or decoding apparatus as described above is used, it is possible to eliminate this problem.  
         [0026]     Further, the third aspect of the present invention provides a coding apparatus, comprising: coding means for coding an inputted bitstream to an error correction and/or detection code; synchronization code inserting means for inserting synchronization codes into the inputted bitstream; deciding means for deciding the number of information bits to be coded to the error correction and/or detection code and arranged immediately before the synchronization code of the bitstream; and said coding means forming the error correction and/or detection code arranged immediately before the synchronization code as a degenerative code adaptively degenerated on the basis of the number of bits decided by said deciding means.  
         [0027]     Further, the third aspect of the present invention provides a decoding apparatus, comprising: decoding means for decoding a bitstream coded to an error correction and/or detection code and further including inserted synchronization codes; synchronization code detecting means for detecting the synchronization codes arranged in the bitstream; deciding means for deciding the number of information bits coded to the error correction and/or detection code and arranged immediately before the synchronization code detected by said synchronization code detecting means; and said decoding means decoding the bitstream by deciding whether the error correction and/or detection code arranged immediately before the synchronization code is a degenerative code or not on the basis of the number of the information bits decided by said deciding means.  
         [0028]     In the third aspect of the present invention, since a degenerative code (whose number of bits is degenerated to a small number of bits required to code the information bits remaining at the last portion of the one synchronization period (block) is used for the error correction and/or detection code arranged immediately before the synchronization code, it is unnecessary to use many insertion bits to fill the remainder of the information bits at the last portion of the synchronization block, with the result that the coding efficiency can be increased.  
         [0029]     Further, the fourth aspect of the present invention provides a coding apparatus, comprising: coding means for coding an inputted bitstream including a plurality of sorts of information to different error correction and/or detection codes; and switching means for switching the sorts of the error correction and/or detection codes according to the sort of the information included in the bitstream.  
         [0030]     Further, the fourth aspect of the present invention provides a decoding apparatus, comprising: decoding means for decoding a bitstream coded to error correction and/or detection codes of different sorts according to information sort, to form original information; and means for deciding the sort of the error correction and/or detection code on the basis of the information sort formed by said decoding means, the decided sort being transmitted to said decoding means.  
         [0031]     In the fourth aspect of the present invention, when the coding and/or decoding is executed by switching the error correction and/or detection codes according to the sort thereof, since the error correction and/or detection code is switched on the coding apparatus side according to the sort of information of the bitstream inputted to the coding apparatus, and since the error correction and/or detection code is switched on the decoding apparatus side by deciding the sort of the error correction and/or detection code on the basis of the decoded information (i.e., the same code as that used on the coding side), any header information indicative of the sort of the error correction and/or detection code is not required (being different from the prior art method), so that it is possible to eliminate the overhead due to the header information. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]      FIG. 1  is an illustration showing an example of a bitstream obtained by the prior art error correction and/or detection code switch coding apparatus.  
         [0033]      FIG. 2  is a block diagram showing an embodiment of the moving picture compression coding apparatus according to the present invention;  
         [0034]      FIG. 3  is a diagram for assistance in explaining the multiplexing syntax adopted by a multiplexer of the moving picture compression coding apparatus shown in  FIG. 2 ;  
         [0035]      FIG. 4  is a block diagram showing an output coding apparatus of the moving picture compression coding apparatus shown in  FIG. 2 ;  
         [0036]      FIG. 5  is an illustration showing an example of an outputted bitstream outputted by the moving picture compression coding apparatus shown in  FIG. 2 ;  
         [0037]      FIG. 6  is an illustration showing an example of a synchronization code;  
         [0038]      FIG. 7  is a block diagram showing the error correction and/or detection switching coder of the output coding apparatus shown in  FIG. 4 ;  
         [0039]      FIG. 8  is a block diagram showing the bitstream assembler of the output coding apparatus shown in  FIG. 4 ;  
         [0040]      FIG. 9  is a block diagram showing an embodiment of the moving picture compression decoding apparatus according to the present invention;  
         [0041]      FIG. 10  is a block diagram showing an input decoding apparatus of the moving picture compression decoding apparatus shown in  FIG. 9 ; and  
         [0042]      FIG. 11  is a block diagram showing a bitstream disassembler of the input decoding apparatus shown in  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0043]     Embodiments of the present invention will be described hereinbelow with reference to the attached drawings.  
         [0044]      FIG. 2  is a block diagram showing an embodiment of the moving picture coding apparatus provided with an error correction and/or detection switching function according to the present invention, which is combined with a compression coding apparatus using motion compensation adaptive prediction and discrete cosine transform coding (one of orthogonal transform codings). Here, the coding method in which both the motion compensation adaptive prediction and discrete cosine transform coding are combined with each other is disclosed in detail by Document: by Hiroshi YASUDA, “International Standard of Multimedia Coding”, published by Maruzen, June 1991, for instance. Therefore, only the operation thereof will be briefly explained hereinbelow. Further, as the error correction and/or detection code used in this embodiment, such a code as the BCH code in which the information bits are separated from the check bits is assumed to be used.  
         [0045]     In  FIG. 2 , moving picture signals  131  to be coded are inputted in unit of frame. The inputted moving picture signals  131  are processed for motion compensation adaptive prediction in unit of small region (e.g., macro block). In more detail, a motion vector between inputted moving picture signals  131  and video signals already coded and locally decoded and further stored in a frame memory is detected by a motion compensation adaptive predictor  101 . Further, predicted signals  132  are formed by compensation prediction on the basis of the detected motion vector. In this motion compensation predictor  101 , a preferable prediction mode to be used for coding is selected from both the motion compensation prediction coding and the intra-frame coding (the inputted moving picture signal  131  is coded as it is without forming any prediction signal), and the prediction signals corresponding to the selected mode are outputted.  
         [0046]     The outputted prediction signals are inputted to a subtracter  103 , and prediction residual signals  133  obtained by subtracting the prediction signals  132  from the inputted moving picture signals  131  are outputted. The outputted prediction residual signals  133  are discrete-cosine transformed (DCTed) in unit of constant size block by a discrete cosine transform section  104 , so that DCT coefficients can be formed. The formed DCT coefficients are quantized by a quantizer  105 . The DCT coefficient signals quantized by the quantizer  105  are branched into two. One is variable-length coded by a first variable length coder  106 . Further, the other is dequantized by a dequantizer  107 , and further reversely discrete-cosine transformed by a inverse discrete cosine transform section  108 . The output of the inverse discrete cosine transform section  108  is added to a prediction signal  132  by an adder  109  to form local decoded signals. The formed local decoded signals are stored in a frame memory  102 .  
         [0047]     On the other hand, the prediction mode and the motion vector information decided by the motion compensation adaptive predictor  101  are variable-length coded by a second variable length coder  110 . The variable length codes outputted by the first and the second variable length coders  106  and  110  are multiplexed by a multiplexer  111 .  
         [0048]     From the multiplexer  111 , a bitstream  201  of the multiplexed variable length codes, an FEC sort ID (identification) signal  202  indicative of a sort of the corresponding error correction and/or detection code, and a synchronization code insertion request signal  203  for requesting an insertion of a synchronization code is outputted.  
         [0049]     These signals of the bitstream  202 , the FEC sort ID signal  202 , and the synchronization code insertion request signal  203  are inputted to an output coding apparatus  200 . The output coding apparatus  200  codes the bitstream  201  by switching a plurality of error correction and/or detection codes of different sorts, to form a final output bitstream  205 . Here, the output coding apparatus  200  corresponds to the coding apparatus according to the present invention.  
         [0050]      FIG. 3  shows a flow of signals multiplexed by the multiplexer  111 . Here, the multiplexing is executed in unit frame to be coded. First, the picture synchronization code  301  is multiplexed. When the picture synchronization code  301  is multiplexed, the synchronization code insertion request signal  203  is outputted from the multiplexer  111  to the coding apparatus  200 , so that the coding apparatus  200  can know that the multiplexed code word is a synchronization code. Successively, a picture header  302  indicative of one of various coding modes of the coded frame is multiplexed upon the bitstream  201 . Further, prediction mode information  303  indicative of the prediction mode of the motion compensation adaptive predictor MC at each region is multiplexed. Further, motion vector information  304  and the DCT coefficients (referred to as residual DCT coefficients)  305  of the prediction residual signals are multiplexed. Here, when the picture header  302 , the prediction mode information  303 , the motion vector information  304 , and the residual DCT coefficients  305  are multiplexed, the FEC sort ID signal  202  indicative of the sort of the error correction and/or detection code is outputted in correspondence to each of the multiplexed signals.  
         [0051]     Here, an error correction and/or detection code of high correction and/or detection capability is used for the picture header  302 , the prediction mode information  303  and the motion vector information  303 , because these information deteriorate picture quality largely when an error is mixed therewith. On the other hand, in the case of the residual DCT coefficients  305 , even if error is mixed therewith, since the picture quality can be prevented from being deteriorated largely by detecting the error and by setting the residual to zero, an error correction and/or detection code of high correction and/or detection capability is not used; that is, it is sufficient to detect only an error of the residual DCT coefficients  305 .  
         [0052]      FIG. 4  is a block diagram showing the output coding apparatus  200  shown in  FIG. 2 . The output coding apparatus  200  is composed of a bit inserter  211 , an error correction and/or detection switching coder  212 , and a bitstream assembler  213 . Further,  FIG. 5  shows an example of the output bitstream  205  formed by the output coding apparatus  200 . The bitstream  205  is composed of a picture synchronization code PSC, a picture header PH, prediction mode information MODE, motion vectors MV, error correction and/or detection code check bits CHK, residual DCT coefficients COEF, and stuffing (insertion) bits STUFF. The output bitstream  205  has the following features:  
         [0053]     (1) The picture synchronization code PSC is inserted into any one of the synchronization code insertion positions as shown by arrows and arranged at constant intervals (for each sync_period bits). The length of the sync_period is determined larger than the maximum length of the synchronization code PSC and the maximum length of the check bit CHK. Further, the check bits CHK are arranged each being shifted so as to be arranged immediately before the synchronization code insertion position.  
         [0054]     (2) The error correction and/or detection code arranged at the last portion of one frame (i.e., at the last portion of one synchronization period sandwiched between the two synchronization codes PSC) is a punctured code such that only the finally remaining information bits are coded. Further, in order to shift the position of the check bit CHK (e.g., the check bit CHK 6  in the example shown in  FIG. 5 ,) a necessary number of the stuffing bites STUFF are inserted.  
         [0055]     (3) The FEC sort ID signal indicative of the sort and the number of the error correction and/or detection codes is not arranged n the output bitstream  205  shown in  FIG. 5 .  
         [0056]     In the output bitstream  205  as shown in  FIG. 5 , since the positions of the check bits CHK are shifted as explained in item (1) above, the check bit CHK is not inserted at any of the synchronization code insertion positions shown by the arrows in  FIG. 5 , with the result that there exists no possibility that the pseudo-synchronization occurs by the check bits CHK. Further, in the case of the error correction and/or detection coding at the last of the frame, although many stuffing bits must be inserted at the last of the frame in the prior art method, since the punctured code is used for the last of the frame as explained by item (2) above, it is possible to reduce the number of the insertion (stuffing) bits. In addition, since the header information indicative of the sort and the number of error correction and/or detection code is not included in the output bitstream  205  as explained by item (3) above, it is possible to reduce the code quantity for the header information.  
         [0057]     The construction and the operation of the output coding apparatus  200  (shown in  FIG. 4 ) for forming the output bitstream  205  will be described in more detail hereinbelow in relation between the bitstream  201  shown in  FIG. 3  outputted by the multiplexer  111  and the output bitstream  205  shown in  FIG. 5 .  
         [0058]     When the synchronization code  301  is multiplexed by the multiplexer  111 , the synchronization code insertion request signal  203  is outputted as already explained. Here, the synchronization code  301  is composed of sync — 0_len bits of “0”, one bit of “1”, and sync_nb_len bits of “xxxxx” indicative of the sort of the synchronization code  301 , as shown in  FIG. 6 . In response to the synchronization code  301  and the synchronization code insertion request signal  203  outputted by the multiplexer  111 , the output coding apparatus  200  outputs the synchronization code (PSC) of the output bitstream  205  from the bitstream assembler  213 .  
         [0059]     Here, as shown in  FIG. 5 , since the synchronization code  301  (PSC) can be inserted at only the synchronization code insertion positions arranged at sync_period intervals of the output bitstream  205 , when the last position of the output bitstream  205  already formed is not arranged at the synchronization code insertion position, the stuffing bits STUFF (as described later) are inserted in such a way that the synchronization code  301  can be arranged at the synchronization code insertion position.  
         [0060]     After the synchronization code  301  has been outputted to the output bitstream  205 , the picture header  302 , the prediction mode information  303 , the motion vector information  304 , and the residual DCT coefficients  305  are coded as follows: First, bits are inserted into the bitstream  201  outputted by the multiplexer  111  by the bit inserter  211  in order to prevent the generation of the pseudo-synchronization. In other words, when a bit pattern the same as that of the code word of the synchronization code  301  exists in the output bitstream  205 , since the synchronization code  301  cannot be decoded unequivocally, bits are inserted according to the necessity. For instance, if the synchronization code  301  is a code word in which the sync — 0_len bits of “0” are arranged continuously as shown in  FIG. 6 , it is possible to prevent the pseudo-synchronization by inserting “1” in such a way that “0” will not be continued beyond the sync — 0_len bits in the bitstream, except at the synchronization code  301 .  
         [0061]     Here, since the synchronization code  301  is inserted at only the synchronization code insertion position as already explained, it is sufficient when the bit “1” is inserted at only the synchronization insertion positions, respectively for prevention of the pseudo-synchronization. Here, a count value  221  indicative of the total number of bits of the output bitstream  205  so far formed is outputted by the bitstream assembler  213 , and further the bit inserter  211  decides as to whether further bit insertion is necessary or not on the basis of the count value  221  of the bit inserter  211 . Here, when the count value  221 , that is, the total bit number of the output bitstream  205  so far formed is denoted by total_len, the number of “1” in the bitstream  201  is counted in a bit block (interval) of 
 
0&lt;total_len mod sync_period≦sync — 0_len 
 
         [0062]     where A mod B denotes a remainder obtained when A is divided by B.  
         [0063]     Here, if there exists no bit of “1” in this bit interval, one bit of “1” is inserted.  
         [0064]     Further, in order to reduce the possibility that the synchronization code  301  is detected erroneously, bit are inserted as follows:  
         [0065]     Here, in order to detect the synchronization code  301  even if an n-bit error is mixed with the synchronization code  301 , it is necessary to decide the code word having a Hamming distance less than n from the true synchronization code, as the synchronization code, by use of an input decoding apparatus of the moving picture decoding apparatus (described later). In this case, however, if the above-mentioned decision is made by leaving the bitstream other than the synchronization code  301  as it is, since there exists the case where a bit pattern having a Hamming distance less than n exists in the bitstream other than the synchronization code  301 , when existing at the synchronization code insertion position, this bit pattern is erroneously decided as the synchronization code  301 .  
         [0066]     To overcome this problem, the bit inserter  211  inserts bits into the bitstream  201  as follows: the bitstream other than the synchronization code arranged at each of the synchronization code insertion positions in the bitstream  201  is converted in such a way that the Hamming distance thereof from the synchronization code  301  becomes a value larger than 2*n+1. In more detail, the number (=n0) of “1” is counted in the bit block (interval) of 
 
0&lt;total_len mod sync_period≦sync — 0_len−(2*N+1) 
 
         [0067]     Here, if n0 is less than (2*N+1), ((2*n+1)−n0) bits of “1” are inserted into the bitstream  201 .  
         [0068]     After the bits have been inserted by the bit inserter  211  as described above, the bitstream  222  is inputted to the error correction and/or detection code switching coder  212 , together with he FEC sort ID signal  202  indicative of the sort of the error correction and/or detection code.  
         [0069]      FIG. 7  is a block diagram showing the error correction and/or detection code switching coder  212  shown in  FIG. 4 . A latch circuit  603  is a circuit for latching the FEC sort ID signal  202 , after the synchronization code has been outputted from the multiplexer  111  to the bitstream  201  and further the synchronization code insertion request signal  203  has been outputted. The latched signal  623  is supplied to an error correction and/or detection coder  604 .  
         [0070]     The error correction and/or detection coder  604  codes the bitstream  222  supplied by the bit inserter  211  for error correction and/or detection in accordance with the latched signal  623 ; that is, forms and outputs the information bits  631  and check bits  632 , respectively. Further, after the error correction and/or detection coding for one block has been completed, the error correction and/or detection coder  604  outputs a latch command signal  625  for commanding the latch circuit  603  to latch the succeeding FEC sort ID signal  202 . Therefore, on the basis of this latch command signal  625 , the latch circuit  603  latches the succeeding FEC sort ID signal  202  and supplies the latched signal to the error correction and/or detection coder  604  again.  
         [0071]     By repeating the above-mentioned operation, the output coding apparatus  200  codes the bitstream  222  (to which bits have been already inserted by the bit inserter  211 ) for error correction and/or detection, by switching the error correction and/or detection codes by the error correction and/or detection switching coder  212  in accordance with the FEC sort ID signal  202  supplied by the multiplexer  111 . Here, since the FEC sort ID signal  202  can be latched by the latch circuit  603  only when the error correction and/or detection coding of one block has been completed, the same error correction and/or detection code is kept applied until the FEC sort ID signal  202  is switched. For instance, in the case where the error correction and/or detection code of FEC 1  is used for the picture header  302  and the code of FEC 2  is used for the prediction mode information  303 , if the number of bits of the picture header  302  is shorter than that of the one-block information of FEC 1 , the FEC 1  code is kept used for the error correction and/or detection code of the succeeding prediction mode information  303  until reaching the bit number of FEC 1  information.  
         [0072]      FIG. 8  is a block diagram showing the bitstream assembler  213  shown in  FIG. 4 . The bitstream assembler  213  is composed of a counter  701  for counting the number of bits of the output bitstream  205 , a buffer  702  for storing the check bits  632  and the number of bits thereof temporarily, a switch  703  for switching the output bitstream  205 , and a switch controller  704  for controlling the switch  703 . When the synchronization code request signal  203  is inputted to the bitstream assembler  213 , the counter  701  is reset to a synchronization code length value sync_len, and counts up bits in sequence beginning from a bit just after the synchronization code until the succeeding synchronization code is inputted. Here, after the synchronization code has bee inputted, the switch  703  is activated in such a way that the information bits  631  can be kept outputted until the first check bit  632  is inputted. When the check bit  632  is inputted, the check bit  632  is stored in the buffer  702 , and the number of bits (check bit number)  711  is outputted from the buffer  702  to the switch controller  704 .  
         [0073]     On the basis of the check bit number  711  and the count value  221  of the counter  701 , the switch controller  704  controls the switch  703  to shift the check bit, that is, in such a way that the check bit  632  will not be outputted to the synchronization code insertion position, as already explained. For instance, when the count value  221  is denoted by bit_count and the check bit number  711  is denoted by check_len, if  
         [0074]     bit_count mod sync_period&lt;sync_period−check_len information bits  631  are outputted, and if  
         [0075]     sync_period−check_len≦total_bits mod sync_period&lt;sync_period  
         [0000]     the check bits  713  stored in the buffer  702  are outputted. After that, the above-mentioned processing is repeated by inputting the information bits  631  and the check bits  632 .  
         [0076]     Here, as already explained, since the output coding apparatus  200  uses the punctured code at the last portion of each frame as the error correction and/or detection code and further shifts the check bit position for bit insertion, the operation is somewhat different from the ordinary operation. In more detail, after having outputted the one-frame bitstream  201 , the multiplexer  111  first outputs the synchronization code insertion request signal  203  for the succeeding frame. In correspondence thereto, the error correction and/or detection coder  604  of the error correction and/or detection switching coder  212  shown in  FIG. 7  regards the insufficient portion of the information bits  631  of the error correction and/or detection code, as a bit pattern previously determined and outputted by an insertion (stuffing) bit generator  705 , and forms the error correction and detection code by use of the redundant code. Here, the bit pattern can be composed of only bits of “1” or “0” or a repetition of a specific pattern as “010101 . . .”.  
         [0077]     After having outputted the last bit of the information bits  631 , in the bitstream assembler  213  shown in  FIG. 8 , the switch  703  is switched from the bit generator  705  to the input side, to insert the insertion (stuffing) bit in such a way that the check bit  713  stored in the buffer  702  can be arranged just before the succeeding synchronization code. Here, when the count value  221  of the counter  701  obtained when the last information bit  631  of one frame has been outputted is denoted by total_len and the number of bits of the check bits  632  outputted lastly is denoted by last_check_len, the number of the insertion bits stuffing_len can be expressed as 
 
stuffing_len=sync_period−last_check_len−(total_len mod sync_period). 
 
         [0078]     Further, when the degenerative code is not used, the insufficient portion (info_len−last_info_len) from the normal information bits info_len in the last information bits last_info_len are inserted. In addition, bits must be inserted in order to shift the check bits. As a result, as compared with when the redundant code is used, it is necessary to insert the following additional bits as 
 
info_len−last_info_len+(info_len−last_info_len) mod sync_period 
 
         [0079]     After having outputted the information bits  631  and the insertion bits to the output bitstream  205  through the switch  703 , the bitstream assembler  213  is lastly switched to the check bits  731 , and outputs the switched check bits  713  to the output bitstream  205 .  
         [0080]     The moving picture decoding apparatus according to the present invention will be described hereinbelow.  
         [0081]      FIG. 9  is a block diagram showing the moving picture decoding apparatus which corresponds to the moving picture coding apparatus shown in  FIG. 2 . After having been passed through a transmission and/or storage system, the output bitstream  205  outputted by the moving picture coding apparatus shown in  FIG. 2  is inputted to an input decoding apparatus  800  as an input bitstream  205 ′. In the present invention, the input decoding apparatus  800  corresponds to the output decoding apparatus  200  according to the present invention.  
         [0082]     The input decoding apparatus  800  outputs a bitstream  801  obtained by decoding the error correction and/or detection code, a synchronization code detection signal  803 , and an error detection signal  804 , by switching the error correction and/or detection code on the basis of an FEC sort ID signal  802  indicative of the sort of the error correction and/or detection signal applied by the demultiplexer  811 . That is, the demultiplexer  811  inputs the bitstream  801 , the synchronization code detection signal  803 , and the error detection signal  804 , and outputs a prediction residual signal  841  and a notion compensation adaptive prediction information code  842 , separately.  
         [0083]     The prediction residual code  841  is inputted to the first variable length decoder  806 , and the motion compensation adaptive prediction information code  842  is inputted to a second variable length decoder  810 . Residual DCT coefficients  831  decoded by the first variable length decoder  806  are dequantized by a dequantizer  807 , inverse-DCTed by a inverse DCT section  808 , added to a motion compensation adaptive prediction signal  832  outputted by a motion compensation adaptive predictor  801  by an adder  809 , and then outputted as reconstructed picture signals  850 . The reproduced picture signals  850  are outputted from the decoding apparatus and further stored in a frame memory  820 . Further, the motion compensation adaptive prediction information decoded by the second variable length decoder  810  is inputted to a motion compensation adaptive predictor  801  to form motion compensation prediction signals  832 .  
         [0084]     The above-mentioned processing is executed to reproduce moving picture in correspondence to the moving picture coding apparatus shown in  FIG. 2 . Therefore, the serial processing executed by the dequantizer  807 , the inverse DCT section  608 , the adder  800  and the frame memory  820  as shown in  FIG. 9  is basically the same as the serial processing executed by the dequantizer  107 , the inverse DCT section  108 , the adder  109  and the frame memory  102  as shown in  FIG. 2 , although the realizing means are somewhat different from each other. Further, the processing of the first and second variable length decoders  806  and  810 , the demultiplexer  811  and the input decoding apparatus  800  are opposite to the processing of the first and second variable length decoders  106  and  110 , the multiplexer  111  and the output decoding apparatus  200 , respectively, excepting the case where an error injured the bitstream.  
         [0085]      FIG. 10  is a block diagram showing the input decoding apparatus  800  shown in  FIG. 9 . The input decoding apparatus  800  is composed of a synchronization detector  901  for detecting the synchronization code of the input bitstream  205 ′, a counter  902  for counting the number of bits of the input bitstream  205 ′, a bitstream disassembler  903  for disassembling the input bitstream  205 ′ into information bits  912  and check bits  913  and for outputting these bits separately, an error correction and/or detection decoder  904 , and an inserted stuffing bit remover  905 .  
         [0086]     The synchronization detector  901  detects the synchronization code at only the synchronization code insertion position on the basis of the count value  911  outputted by the counter  902 . For instance, when the interval between the two synchronization code insertion positions is denoted by sync_period; the count value  911  is dented by bit_count; and the length of the synchronization code is denoted by sync_len, the synchronization code is detected only when 
 
0&lt;bit_count mod sync_period≦sync_len 
 
         [0087]     Here, it is also possible to detect the synchronization code under consideration of the presence of an error in the synchronization code.  
         [0088]     Here, by the bit inserter  211  of the output coding apparatus  200  shown in  FIG. 4 , when the bitstream has been converted by inserting bits in such a way that the Hamming distance thereof from the synchronization code becomes 2*n+1 under consideration of an error less than n bits, even if the code having a Hamming distance less than n from the true synchronization code is decided as the synchronization code, as far as the erroneous bit is less than n bits, it is possible to prevent the synchronization code from being detected erroneously.  
         [0089]      FIG. 11  is a block diagram showing the bitstream disassembler  903  shown in  FIG. 10 . The input bitstream  205 ′ is switched to the information bits  1021  and the check bits  913  by a first switch  1002  controlled by a controller  1001  (described later). When the information bits  1021  are outputted from the first switch  1002 , the information bit length of the information bits  1021  are stored by a buffer  1004  via a second switch  1003 . A counter  1005  counts the number of the output bits from the second switch  1003 . The count value  1023  of the counter  1005  is compared with the information bit length  1024  outputted by an error correction and/or detection code (i.e., FEC) information output section  1007  by a comparator  1006 . When both match, the counter  1005  is reset, and the FEC sort ID signal  802  indicative of the sort of the error correction and/or detection code is latched by a latch circuit  1008 . Further, the information bits  912  are outputted from the buffer  1004 . Further, the output  914  of the latch circuit  1008  is inputted to the error correction and/or detection code information output circuit  1007  and further to the error correction and/or detection decoder  904  shown in  FIG. 10 .  
         [0090]     As already explained, the check bits of the error correction and/or detection code are shifted in position so as to be formed between the information bits of the error correction and/or detection code arranged backward in the bitstream  205 . Therefore, the controller  1001  controls the switch  1002  in such a way that these position-shifted check bits can be separated from the information bits. After the information bits of the one-block error correction and/or detection code have been inputted, the count value  1023  matches the information bit length  1024  in the comparator  1006 . In response to this match signal, the controller  1001  receives the check bit length  1025  from the error correction and/or detection information output circuit  1007  to calculate the check bit position inserted between the information bits. Here, when the count value  911  indicative of the number of inputted bits of the bitstream  205 ′ (obtained when the comparator  1006  outputs the match signal) is denoted by bit_count; and the check bit length is denoted by check_len, the check bit start position check_start is 
 
check_start=(bit_count/sync_period+1)*sync_period−check_len 
 
 and the check bit end position check_end is 
 
check_end=(bit_count/sync_period+1)*sync_period 
 
 That is, the controller  1001  controls the switch  1002  so that the check bits  913  can be outputted when the count value  911  lies between check_start and check_end. 
 
         [0091]     Further, since the error correction and/or detection coding is executed by the degenerative code at the last of one frame, a special processing is necessary. At the last of one frame, the synchronization detector  901  outputs a signal  803  indicative of that the synchronization code of the succeeding frame has been detected. In response to this signal, the controller  1001  calculates the position of the last error correction and/or detection check bit in the frame and the number of insufficient information bits. Here, the assumption is made that the count value  911  of the number of bits of the bitstream  205 ′ inputted when the last error correction and/or detection code of one frame is started to be inputted is denoted by pre_last_count; the count value  911  at a time when the one-frame bitstream  205 ′ has been inputted is denoted by total_count; the count value  911  at the processing is denoted by bit_count; the check bit length of the last error correction and/or detection code of one frame is denoted by last_check_len; and the check bit length of the second-last error correction and/or detection code is denoted by pre_last_check len. First, since the error correction code is a punctured code and further the bit is inserted, the overs and shorts of the information bits are calculated. Here, the number of information bits last_info_len of the last error correction and/or detection code of one frame included in the output bitstream  205  is 
 
last_info_len=total_count−last_check_len−pre_last_count−pre_last_check_len 
 
         [0092]     Then, when last_info_len is shorter than the information length info_len of the error correction code, the degenerative code is decided, so that the switch  1003  is switched so as to output the bit pattern from the insertion bit generator  1015  during the period between last_info_len and info_len of the count value  1023 , in order to supply the insufficient information bits due to the degenerative code. Here, the bit pattern outputted by the insertion bit generator  1015  is the same as that generated by the insertion bit generator  705  of the coder shown in  FIG. 8 .  
         [0093]     On the other hand, when last_info_len is longer than info_len, this information bit length is decided as inserted bits, and the bit portion of the count value more than info_len is not outputted as the information bits  912 . On the other hand, the switch  1002  is so controlled that the output bitstream  205  is outputted as the check bits, when the bit count of the check bits is 
 
total_count−check_len&lt;bit_count≦total_count 
 
         [0094]     The error correction and/or detection decoder  904  inputs the information bits  912  and the check bits  913  outputted by the bitstream disassembler  903 , decodes the error correction and/or detection code on the basis of the FEC sort ID signal  914  indicative of the sort of the error correction and/or detection code latched by the latch circuit  1008  shown in  FIG. 11 , and outputs the error-corrected bitstream  915  and the error-detected signals  804 .  
         [0095]     The error-corrected bitstream  915  is inputted to the insertion bit remover  905  to remove the insertion bits inserted by the bit inserter  211  of the output coding apparatus  200 , in order to prevent pseudo-synchronization signal from being generated. As already explained, since the bits are inserted at only the synchronization code insertion positions, the synchronization code insertion position can be decided on the basis of the count value  911  of the counter  902 .  
         [0096]     For instance, when the synchronization code word is that as shown in  FIG. 6  and further when the bits are inserted by the bit inserter  211  at “0000 . . .” portion of the first sync_len bits in such a way that the Hamming distance from the synchronization code is more than (2*n+1), the number (=n0) of “1” in (sync — 0_len−(2*n+1)) bits beginning from the synchronization code insertion position is counted, when n0 is less than 2*n+1, bits of (2*n+1−n0) are removed. Here, however, since the insertion bits are determined as “1”, when the bit decided by the insertion bit remover  905  as the insertion bit is “0”, this is regarded as that an error is mixed in the synchronization code insertion block. In this case, therefore, the error detection signal  804  is outputted.  
         [0097]     As described above, the bitstream  801  decoded by the input decoding apparatus  800  is reverse multiplexed by the reverse multiplexer  811 . In this operation, the code word multiplexed as shown in  FIG. 3  is separated and then outputted. Further, this reverse multiplexer  811  operates in linkage with the first and second variable length decoders  806  and  810 , respectively.  
         [0098]     In operation in  FIG. 9 , first when a synchronization code detection signal  803  is inputted from the output decoding apparatus  800 , the reverse multiplexer  811  is initialized for one-frame processing. Then, the reverse multiplexer  811  outputs the sort of the error correction and/or detection code corresponding to the picture header, as the FEC sort ID signal  802  indicative of the sort of the error correction and/or detection code, inputs the bitstream  801 , and decodes the picture header  302  to check whether there exists any error in the decoded picture header. When there exists no error, the reverse multiplexer  811  outputs the sort of the error correction and/or detection code corresponding to the prediction mode information  303  as the FEC sort ID signal  802 , inputs the bitstream  801 , multiplexes the prediction mode information, and then outputs the motion compensation adaptive prediction information code  842  to the second variable length decoder  810 .  
         [0099]     When having decoded all the prediction mode information (the motion compensation adaptive prediction information code  842 ), the second variable length decoder  810  outputs an end signal to the reverse multiplexer  811 . In response to this end signal, the reverse multiplexer  811  outputs the FEC sort ID signal indicative of the sort of the error correction and/or detection code corresponding to the motion vector information  304 , and starts the reverse multiplex processing of the motion vector information  304 . The reverse multiplexed motion vector information is outputted to the second variable length decoder  810  for decoding. After having decoded all the motion vector information, the second variable length decoder  810  outputs an end signal to the reverse multiplexer  811 . In response to this end signal, the reverse multiplexer  811  outputs the FEC sort ID signal indicative of the sort of the error correction and/or detection code corresponding to the residual DCT coefficient  305 , reversely multiplexes the residual DCT coefficients  305 , and outputs the reversely multiplexed results to the first variable length decoder  806 . The first variable length decoder  806  decodes the residual DCT coefficients  305 .  
         [0100]     As described above, the sort of the error correction and/or detection code is decided by the reverse multiplexer  811  in accordance with the multiplexing rule prescribed in the same way as with the case of the output coding apparatus  200 . Therefore, it is unnecessary to add the header information indicative of the sort of the error correction and/or detection code to the output bitstream  205 .  
         [0101]     In the error correction and/or detection decoder  904  shown in  FIG. 10 , there exists the case where a mixture of an error with the inputted bitstream  205 ′ can be detected by the error detection code. In addition, there exist the case where an erroneous bit insertion can be detected by the insertion bit remover  905 . In these error cases, the input decoding apparatus  800  outputs an error detection code  804 . Further, when a code word not stored in a variable length word table is detected in the variable length decoding processing, a mixture of an error is decided. Further, when the presence of a portion departing from the multiplexing rule is decided by the reverse multiplexer  811  during the reverse multiplexing processing, it is discriminated that an error is mixed. In these cases, in order to prevent the reproduced picture from being deteriorated largely, the input decoding apparatus  800  and the reverse multiplexer  811  execute the following processing:  
         [0102]     (1) When an error is detected in the residual DCT coefficient, the residual at the corresponding portion is set to zero. In this case, when the intra-coding mode is selected as the prediction mode, the reproduced picture signals can be predicted on the basis of the already reproduced frame or the reproduced video signals in the surrounding area.  
         [0103]     (2) When an error is detected in the prediction mode information and the motion vector, if it is possible to presume the prediction mode information or the motion vector information on the basis of the prediction mode information or the motion vector information existing in the surrounding area, these information can be used. If impossible, however, the reproduced picture signals are predicted on the basis of the reproduced picture signals in the already reproduced frame or existing in the surrounding area.  
         [0104]     (3) When an error is detected in the picture header, since the picture quality deteriorates largely when decoded as it is, the reproduced picture of the preceding frame is used as it is, as the reproduced picture of the present frame.  
         [0105]     In the above-mentioned processing in the items (1) to (3) above, when the error exerts a harmful influence upon the following code till the succeeding synchronization code, because the variable length coding is used, the similar processing as above is executed for the error-affected portion.  
         [0106]     In the above-mentioned description, an example where the synchronization code detector  901  detects the synchronization code at only the synchronization code insertion positions (for each sync_period bits) has been explained. However, there exists the case where a bit is lost or an erroneous bit is inserted according to the transmission and/or storage medium. In this case, the synchronization code is detected at the position other than the synchronization code insertion position, and the position where the synchronization code can be detected is decided as the synchronization code insertion position.  
         [0107]     Further, in the above description, although an example where the moving picture is high-efficiency compression-coded and then transmitted and/or stored has been explained by way of example, it is of course possible to apply the coding and decoding apparatus according to the present invention to the case where still picture or audio or other information are transmitted and/or stored. For instance, in the case where still picture signals are compression coded at a high efficiency by use of the orthogonal transform, it is preferable to switch the error correction and/or detection codes in such a way that the lower frequency components of the transform coefficients can be protected from error more securely. For instance, in the method of coding audio signals by modeling voice with a sound source and a sound path filter, it is preferable that the error correction and/or detection codes are switched in such a way that the pitch period and the sound path filter can be protected from error more securely.  
         [0108]     As described above, in the coding and decoding apparatus according to the present invention, since the synchronization code is inserted at only the synchronization code insertion position at regular intervals and further since the check bits of the error correction and/or detection code are shifted so as to be arranged at a position other than the synchronization code insertion position, even if the bit pattern the same as that of the synchronization code is formed in the check bits, the bit pattern the same as that of the synchronization code will not be formed at the synchronization code insertion position at which the synchronization code is detected, so that it is possible to perfectly eliminate the possibility that the synchronization is detected erroneously, from the principle standpoint.  
         [0109]     Further, when the bits are inserted into the bitstream arranged at the synchronization code insertion position in such a way as not to form the pseudo-synchronization, it is possible to eliminate such a prior art difficulty that the code word must be constructed in such a way that the bit pattern the same as that of the synchronization bits will not be formed.  
         [0110]     In addition, in the present invention, since the bits are inserted under consideration of erroneous synchronization code; that is, since the bit train arranged at the synchronization code insertion position is converted in such a way that the Hamming distance from the synchronization code exceeds a predetermined value and further reversely converted by the decoding apparatus, the bit pattern the same as that of the synchronization code will not be included in the bit train, so that it is possible to secure that an erroneous detection of the synchronization code can be prevented as far as the number of bits is less than a predetermined value. As a result, the possibility of the erroneous detection of the synchronization code can be reduced. Further, when the above-mentioned conversion is executed, even if an error is mixed with the bitstream, since it is possible to discriminate the synchronization code from the bitstream other than the synchronization code, it is possible to reduced the possibility that the synchronization code is detected erroneously.  
         [0111]     Further, since the error correction and/or detection coding is executed after the code word has been converted by bit insertion, the bit insertion can be protected from the error occurrence. Therefore, as compared with the prior art method such that the bits are inserted after the error correction and/or detection coding has been completed, it is possible to reduce the possibility that the erroneous bit insertion occurs. In addition, since the bit insertion is executed only at the synchronization code insertion position, an increase of the code quantity due to the bit insertion can be reduced, as compared with he prior art case where the bits are inserted all over the bitstream, with the result that the coding efficiency can be increased.  
         [0112]     Further, in the present invention, since the error correction and/or detection code immediately before the synchronization code is formed as a degenerative code, it is possible to reduce the number of insertion bits for compensating for the remainder of the information bits immediately before the synchronization code, as compared with the prior art coding apparatus, with the result that the coding efficiency can be further increased.  
         [0113]     Further, in the present invention, since the error correction and/or detection codes are switched in accordance with the multiplexing rule of the high efficiency compression coding apparatus for audio and video signals and according to the information sort of the inputted bitstream, and further since the error correction and/or detection codes are switched by deciding the sort of the error correction and/or detection code on the basis of the decoded information on the decoding apparatus side, it is unnecessary to add the header information indicative of the sort of the error correction and/or detection code and thereby the number of bits assigned to the audio or video high efficiency compression coding can be increased, with the result that it is possible to increase the quality of the audio and video information to that extent.