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A variable length code multiplexer multiplexes a plurality of input codes (102) including a variable length code into a multiplexed code (121) and outputs the multiplexed code (121). The multiplexer includes a forward direction multiplexing unit (22) for multiplexing the plurality of input codes (10

A variable length code multiplexer multiplexes a plurality of input codes (102) including a variable length code into a multiplexed code (121) and outputs the multiplexed code (121). The multiplexer includes a forward direction multiplexing unit (22) for multiplexing the plurality of input codes (102) one by one so that they are running in a forward direction from a head of the multiplexed code (121) to a tail of the multiplexed code (121), a backward direction multiplexing unit (23) for multiplexing the plurality of input codes (102) one by one so that they are running in a backward direction from the tail of the multiplexed code (121) to the head of the multiplexed code (121), and a selection unit (25) for selecting either the forward direction multiplexing unit (22) or the backward direction multiplexing unit (23) for each of the plurality of input codes (102).

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What is claimed is: 1. A variable length code multiplexer that multiplexes a plurality of input codes including a variable length code into a multiplexed code and outputs the multiplexed code, said multiplexer comprising: a forward direction multiplexing means for multiplexing a first subset of cod

What is claimed is: 1. A variable length code multiplexer that multiplexes a plurality of input codes including a variable length code into a multiplexed code and outputs the multiplexed code, said multiplexer comprising: a forward direction multiplexing means for multiplexing a first subset of codes from the plurality of input codes one by one so that the first subset of codes are running in a forward direction from a head of the multiplexed code to a tail of the multiplexed code; a backward direction multiplexing means for multiplexing a second subset of input codes from the plurality of input codes one by one so that they are running in a backward direction from the tail of the multiplexed code to the head of the multiplexed code; and a selection means for selecting to assign each of the plurality of input codes to either the first or second subset of codes, wherein the plurality of input codes includes variable length encoded band-by-band codes resulting from sound encoding, the selection means selects to assign each of the plurality of input codes to either the first or second subset of codes based on the input code's sequential placement within the plurality of input codes and the number of the input codes already multiplexed. 2. The variable length code multiplexer according to claim 1, wherein the tail of the multiplexed code is fixed. 3. The variable length code multiplexer according to claim 1, further comprising a code length calculation means for determining a total code length of the plurality of input codes, wherein said backward direction multiplexing means determines the tail of the multiplexed code based on the total code length determined by said code length calculation means. 4. The variable length code multiplexer according to claim 1, wherein said selection means alternately selects either said forward direction multiplexing means or said backward direction multiplexing means for each of the plurality of input codes. 5. The variable length code multiplexer according to claim 1, wherein said forward direction multiplexing means outputs a length of input codes which have already been multiplexed into the multiplexed code as an already-multiplexed code length, and said selection means selects either said forward direction multiplexing means or said backward direction multiplexing means based on the already-multiplexed code length from said forward direction multiplexing means. 6. The variable length code multiplexer according to claim 5, wherein when the already-multiplexed code length from said forward direction multiplexing means is less than a predetermined value, said selection means selects said forward direction multiplexing means. 7. A variable length code demultiplexer that demultiplexes a multiplexed code into a plurality of output codes including a variable length code and outputs the plurality of output codes, said demultiplexer comprising: a forward direction demultiplexing means for demultiplexing the multiplexed code into a first subset of the plurality of output codes one by one so that they are separated from respective areas of the multiplexed code running in a forward direction from a head of the multiplexed code to a tail of the multiplexed code; a backward direction demultiplexing means for demultiplexing the multiplexed code into a second subset of the plurality of output codes one by one so that they are separated from respective areas of the multiplexed code running in a backward direction from the tail of the multiplexed code to the head of the multiplexed code; and a selection means for selecting said forward direction demultiplexing means to demultiplex a first portion of the multiplexed code extending from the head into the first subset, and selecting said backward direction demultiplexing means to demultiplex a second portion of the multiplexed code extending from the tail into the second subset, wherein the plurality of output codes includes variable length encoded band-by-band codes resulting from sound encoding, the selection means selects either said forward or backward demultiplexing means for demultiplexing the next output code based on the number of output codes having already been demultiplexed from the multiplexed code. 8. The variable length code demultiplexer according to claim 7, wherein the tail of the multiplexed code is fixed. 9. The variable length code demultiplexer according to claim 7, further comprising a code length decoding means for determining a total code length of the multiplexed code, wherein said backward direction demultiplexing means determines the tail of the multiplexed code based on the total code length determined by said code length decoding means. 10. The variable length code demultiplexer according to claim 7, further comprising a means for determining a total code length of the multiplexed code based on an identification signal identifying boundaries of the multiplexed code for each frame, wherein said backward direction demultiplexing means determines the tail of the multiplexed code based on the total code length of the multiplexed code. 11. The variable length code demultiplexer according to claim 7, wherein said selection means alternately selects either said forward direction demultiplexing means or said backward direction demultiplexing means for each of the plurality of output codes. 12. The variable length code demultiplexer according to claim 7, wherein said forward direction demultiplexing means outputs a length of codes which have already been separated from the multiplexed code as an already-demultiplexed code length, and said selection means selects either said forward direction demultiplexing means or said backward direction demultiplexing means based on the already-demultiplexed code length from said forward direction demultiplexing means. 13. The variable length code demultiplexer according to claim 12, wherein when the already-demultiplexed code length from said forward direction demultiplexing means is less than a predetermined value, said selection means selects said forward direction demultiplexing means. 14. The variable length multiplexer of claim 1, wherein when a particular code from the first subset of codes is input to the forward direction multiplexing means, the forward direction multiplexing means multiplexes the particular code into the next available code location closest to the head of the multiplexed code; and when a particular code from the second subset of codes is input to the backward direction multiplexing means, the backward direction multiplexing means multiplexes the particular code into the next available code location closest to the tail of the multiplexed code. 15. The variable length multiplexer of claim 1, wherein the selecting unit assigns a first consecutive set of the plurality of input codes, which correspond to a protected area of the multiplexed code, to the first subset of codes. 16. The variable length multiplexer of claim 15, wherein the protected area corresponds to an area of the multiplexed code for which error correction coding is to be performed. 17. The variable length multiplexer of claim 1, wherein the selecting means selectively switches between the forward and backwards multiplexing means in such a manner that reduces the number of input codes affected by the occurrence of a bit error that occurs after the multiplexed code is output. 18. A system comprising the variable length multiplexer of claim 1, wherein the system further comprises a demultiplexer for demultiplexing the multiplexed code into a series of output codes, the demultiplexer including: a forward direction demultiplexing means adapted to demultiplex a segment at the head of the multiplexed code as a next output code; a backward direction demultiplexing means adapted to demultiplex a segment at the tail of the multiplexed code as a next output code; and a demultiplexer selecting means adapted to determine which of the forward and backward demultiplexing means demultiplexes the next output code in the series of output codes. 19. A variable length code multiplexer that multiplexes a plurality of input codes including a variable length code into a multiplexed code and outputs the multiplexed code, said multiplexer comprising: forward direction multiplexing unit for multiplexing a code to the next available location closest to the head of the multiplexed code; a backward direction multiplexing unit for multiplexing a code to the next available location closest to the tail of the multiplexed code; and a selector adapted to selectively input at least one of the input codes to the forward direction multiplexing unit and at least one of the input codes to the backward direction multiplexing unit, wherein the plurality of input codes includes variable length encoded band-by-band codes resulting from sound encoding, the selector selects to input each of the plurality of input codes to either the forward or backward direction multiplexing unit based on the input code's sequential placement within the plurality of input codes and the number of the input codes already multiplexed. 20. The variable length code multiplexer of claim 19, wherein the selector is adapted to selectively input the input codes in such a manner as to reduce the number of input codes affected by the occurrence of a bit error that occurs after the multiplexed code is output.