Abstract:
An object of the present invention is to easily and quickly decode a plurality of types of compressed audio data. A compressed audio data reproduction apparatus comprising a plurality of decoders configured to decode compressed audio data of respective exclusive compression forms, a compression form identifying portion configured to identify the compression form based on header information of the compressed audio data, and a selector configured to select the decoders corresponding to the compression form identified by said compression form identifying portion from said plurality of decoders.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the priority right under 35 U.S.C. 119 of Japanese Patent Application No. 81590/2000 filed in Japan on Mar. 23, 2000.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a compressed audio data reproduction apparatus and a compressed audio data reproducing method for extending and reproducing compressed audio data, and more particularly, it relates to a technique for reproducing a plurality of types of compressed audio data with compressed form different from one another.  
           [0004]    2. Related Background Art  
           [0005]    In recent years, with technical advantage and cost reduction of a computer, it has become possible to easily record, reproduce and process audio data with the computer. An amount of the audio data presented in forms such as CD is enormous. Therefore, a large number of audio compression forms have been proposed in which it is possible to highly compress data, while holding the same sound quality as that of CD. Examples of the forms include MPEG1 LAYER3 (MP3) and MPEG2 AAC (AAC).  
           [0006]    When the compressed audio data is reproduced with the computer, a conventional method identifies a file extension, and then executes an extension program for the extension, and then based on the result of the executed program, performs an extension processing of the compressed audio data.  
           [0007]    [0007]FIG. 1 is a block diagram showing a schematic constitution of a conventional compressed audio data reproduction apparatus. The apparatus of FIG. 1 can perform reproduction of compressed audio data of MP3 and the like, and reproduction of CD.  
           [0008]    The compressed audio data reproduction apparatus of FIG. 1 includes a data reader  2  for reading out compressed audio data stored in a portable recording medium  1  such as smart media, a controller  3  for controlling the entire system, a key input section  4  for selecting various functions, an LCD display  5  for displaying a music piece name and the like, an optical pickup  7  for reading information recorded in a CD  6 , a CD driver  8  for controlling the optical pickup  7 , an RF amplifier  9  for amplifying the information read by the optical pickup  7 , a CD processor  10  for carrying out a signal processing for an output of the RF amplifier  9 , a decoder  11  for decoding the compressed audio data or bit stream data from the CD, a D/A converter  12  for converting the decoded data to an analog sound signal, and a headphone amplifier  13  for outputting sound to a headphone.  
           [0009]    [0009]FIG. 2 is a block diagram showing an internal constitution of the controller  3  and decoder  11  of FIG. 1. The controller  3  of FIG. 2 includes a receiver  41  for receiving the compressed audio data, a file manager  42  for associating the data with a file type or another file, and a file extension identifier  43  for identifying the type of the data based on the extension of the data taken by the receiver  41 .  
           [0010]    Here, the file manager  42  is realized by utilizing a function of a FAT management or a DOS.  
           [0011]    On the other hand, the decoder  11  includes a decoder switch  44  for switching the decoder based on the extension identified by the file extension identifier, and a plurality of decoding sections  45  disposed for respective extensions.  
           [0012]    [0012]FIG. 3 is a block diagram showing the internal constitution of the decoder  11  in more detail. The decoder  11  of FIG. 3 includes the aforementioned decoder switch  44 , an MP3 decoder  45   a  for carrying out decoding (extension processing) of the compressed audio data with an MP3 form, an AAC decoder  45   b  for carrying out decoding of the compressed audio data with an AAC form, a CD input section  47  for extracting bit stream data from the CD processor  10 , and a signal switch  48  for switching output signals from the MP3 decoder  45   a , AAC decoder  45   b  and CD input section  47 .  
           [0013]    As described above, in the conventional method, since the FAT management or the file management function of the DOS is utilized to identify the type of the compressed audio data, there are problems that the internal constitution of the controller  3  shown in FIGS. 1 and 2 becomes complicated, and it also takes much time to reproduce the compressed audio data.  
           [0014]    Moreover, the file manager  42  shown in FIG. 2 can identify the type of the compressed data having the extension, but cannot identify the type of bit stream compressed data of CD or the like. Therefore, in the conventional method, a decoding processing of the compressed data having the extension is carried out separately from a decoding processing of bit stream compressed data, and this causes a problem that the system constitution becomes complicated.  
         SUMMARY OF THE INVENTION  
         [0015]    The present invention has been developed in consideration of this respect, and an object thereof is to provide a compressed audio data reproduction apparatus which can easily and quickly decode and reproduce a plurality of types of compressed audio data.  
           [0016]    To achieve the object, there is provided a compressed audio data reproduction apparatus comprising:  
           [0017]    a plurality of decoders configured to decode compressed audio data of respective exclusive compression forms;  
           [0018]    a compression form identifying portion configured to identify the compression form based on header information of the compressed audio data; and  
           [0019]    a selector configured to select the decoders corresponding to the compression form identified by said compression form identifying portion from said plurality of decoders.  
           [0020]    According to the present invention, since the header information of the compressed audio data is analyzed and the compression form is specified, optimum decoders can be selected for the compression form without utilizing a FAT management or a function of DOS. Therefore, the plurality of types of compressed audio data with compressed forms different from one another can easily and quickly be decoded and reproduced. Moreover, it is possible to carry out the decoding processing of the compressed audio data having the file extension such as MP3 in common with that of the bit stream compressed data such as CD. Therefore, the entire apparatus can be miniaturized, and a processing time required for reproduction can also be shortened. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a block diagram showing a schematic constitution of a conventional compressed audio data reproduction apparatus.  
         [0022]    [0022]FIG. 2 is a block diagram showing an internal constitution of a controller and decoder of FIG. 1.  
         [0023]    [0023]FIG. 3 is a block diagram showing the internal constitution of the decoder in more detail.  
         [0024]    [0024]FIG. 4 is a block diagram showing a schematic constitution of an embodiment of a compressed audio data reproduction apparatus according to the present invention.  
         [0025]    [0025]FIG. 5 is a block diagram showing an internal constitution of a decoder of FIG. 4.  
         [0026]    [0026]FIG. 6 is a diagram showing a data constitution of compressed audio data.  
         [0027]    [0027]FIG. 7 is a diagram showing breakdown of a header section. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    A compressed audio data reproduction apparatus according to the present invention will concretely be described hereinafter with reference to the drawings.  
         [0029]    [0029]FIG. 4 is a block diagram showing a schematic constitution of an embodiment of the compressed audio data reproduction apparatus according to the present invention. In FIG. 4, constituting components common to those of FIG. 1 are denoted with the same reference numerals, and different respects will mainly be described hereinafter.  
         [0030]    The compressed audio data reproduction apparatus of FIG. 4 includes a data reader  2  for reading out compressed audio data stored in a portable recording medium  1  such as smart media, a controller  3   a  for controlling the entire system, a key input section  4  for selecting various functions, an LCD display  5  for displaying a music piece name and the like, an optical pickup  7  for reading information recorded in a CD  6 , a CD driver  8  for controlling the optical pickup  7 , an RF amplifier  9  for amplifying the information read by the optical pickup  7 , a CD processor  10  for performing a signal processing based on an output of the RF amplifier  9 , a decoder  11   a  for decoding the compressed audio data or bit stream data from the CD, a D/A converter  12  for converting the decoded data to an analog sound signal, and a headphone amplifier  13  for outputting sound to a headphone.  
         [0031]    In the compressed audio data reproduction apparatus of FIG. 4, the type of the compressed audio data can be identified and the data can be decoded regardless of the FAT management or control of the DOS. Concretely, internal constitutions of the controller  3   a  and decoder  11   a  are different from conventional constitutions.  
         [0032]    [0032]FIG. 5 is a block diagram showing the internal constitution of the decoder  11   a  of FIG. 4. The decoder  11   a  of FIG. 5 includes a receiver  21  for taking the compressed audio data read via the data reader  2  and bit stream data from the CD  6 , a header information analyzer (compression form identifying portion)  22  for analyzing header information of the taken data, a decoder switch (selector)  23  for switching a decoding processing based on a header analysis result, and a plurality of decoding sections  24  corresponding to respective exclusive compression forms.  
         [0033]    [0033]FIG. 6 is a diagram showing a data constitution of the compressed audio data. As shown in FIG. 6, the compressed audio data is constituted of a plurality of frames (packets), and each frame includes a header section  31  in which data type and other information are stored, a management information section  32  in which bit allotment information and the like are stored, and a data main body  33 .  
         [0034]    [0034]FIG. 7 is a diagram showing breakdown of the header section  31 . As shown in FIG. 7, information such as ID, layer, protection bit, bit rate, and sampling frequency are stored in the header section  31 .  
         [0035]    For example, in case of MP3, since the ID is “1” and the layer is “3”, “1” is stored in the ID of the header section  31 , and “01” is stored in the layer. Moreover, in case of AAC, “1” is stored in the ID of the header section  31 , and “00” is stored in the layer. Therefore, when the ID and layer of the header section  31  are detected, MP3 and AAC can be identified.  
         [0036]    Operation of the compressed audio data reproduction apparatus of FIG. 4 will next be described. When the reproduction of the compressed audio data is instructed via the key input section  4 , the data reader  2  reads the compressed audio data stored in the portable recording medium  1  and transmits the data to the decoder  11   a.    
         [0037]    The decoder  11   a  analyzes the header section  31  of the compressed audio data and identifies the compression form. As described above, the MP3 and AAC can be identified by the ID and layer of the header section  31 . Moreover, even when the data is compressed in other compression forms (e.g., ATRAC3, TWIN-VQ, WMA and the like), the information indicating the compression form is stored in the header section  31 . Therefore, the compression form can be specified by detecting the information. Additionally, depending upon a compression form, a frame constitution of FIG. 6 is sometimes different from that of FIG. 7. Even in this case, the compression form can be specified by forming the frame constitution inherent in each compression form in a database.  
         [0038]    When the compression form is identified, the decoder  11   a  selects the decoding section  24  for the compression form and performs the decoding (extension processing) of the compressed audio data.  
         [0039]    On the other hand, in case of reproducing the CD  6 , similarly as the conventional method, the CD processor  10  generates the bit stream data based on bit information read by the optical pickup  7 .  
         [0040]    Similarly as the compressed audio data, the bit stream data is inputted to the receiver  21 . In case of the bit stream data, since the header information does not exist, the predetermined decoder la is selected, and the extension processing is performed.  
         [0041]    After the data subjected to the extension processing is converted to the analog sound signal by the D/A converter  12 , sound is outputted via the headphone amplifier  13 .  
         [0042]    Thus, in the present embodiment, since the header information of the compressed audio data is analyzed and the compression form is identified, different from the conventional method, the compression form can be identified without utilizing the file management function of DOS or the like, and the constitution of the controller  3   a  can be simplified. Moreover, since the compressed audio data having the extension and the bit stream data from the CD or the like can similarly be processed, the constitution of the decoder  11   a  can also be simplified. Therefore, the system can be miniaturized, a burden of an operating system (hereinafter referred to as OS) is reduced, and time required for the reproduction of the compressed audio data can therefore be shortened.  
         [0043]    In the aforementioned embodiment, MP3 or AAC has been described as one example of the compressed audio data, but the type of the compressed audio data to be reproduced is not particularly limited. That is, all types of compressed audio data having the information on the compression form in the header section  31  can be an object of the present invention.  
         [0044]    Moreover, in the aforementioned embodiment, the example for utilizing the smart media as one example of the portable recording medium  1  has been described, but the concrete type and form of the portable recording medium  1  are not particularly limited.  
         [0045]    Moreover, the example in which the reproduction of the compressed audio data and the reproduction of the CD are possible has been described with reference to FIG. 4, but the CD reproduction function may be omitted.