Abstract:
An AV data conversion apparatus has a verification file confirmation means ( 11 ) for reading an AV data file ( 101 ) containing AV data including video information and audio information, and a verification file ( 102 ) for the AV data file, and confirming if the AV data file and verification file mutually correspond; a plurality of stream conversion means ( 13 ) for changing the AV data to a specific format; and a conversion method determining means ( 12 ) for selecting from among the plural stream conversion means at least one stream conversion means for changing the AV data to the specific format based on verification file content.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an AV data conversion apparatus and method for converting AV data compressed according to the MPEG standard, for example, to data conforming to the VR format and recording the converted AV data to an optical disc.  
         [0003]     2. Description of Related Art  
         [0004]     DVD-RAM and similar optical disc drives record AV data such as MPEG-encoded AV data according to the industry-standard Video Recording (VR) format for recording AV data. Files for storing AV data according to the VR format are called “VRO files”, and conform to the MPEG standard. Some limitations are, however, applied to the MPEG standard in this case so that disc content can be edited in real time. This means that not all MPEG files are interchangeable with VRO files, and data conversion, including changing the pack size, to conform to the VR format is needed in order to record an MPEG file that is not compliant with the VR format.  
         [0005]      FIG. 19  is a block diagram of a conventional AV data converter for converting MPEG or other AV data to VR format data and then recording the resulting VR data. The AV data converter shown in  FIG. 19  reads an MPEG-format data file  101  that is non-compliant with the VR format, converts the MPEG data file  101  to VR-compliant VRO data file  107  and IFO data file  108 , and records the converted files to an optical disc  50 . To accomplish this, the AV data converter has an MPEG demultiplexer  61 , video decoder  91 , VR video encoder  92 , audio decoder  81 , VR audio encoder  82 , VR multiplexer  62 , and VR stream information detector  14 .  
         [0006]     The MPEG demultiplexer  61  splits the read MPEG data file into a video elementary stream  601  and an audio elementary stream  602 . The video decoder  91  then decodes the video elementary stream  601  into decoded video data  901 , and the VR video encoder  92  then converts and re-encodes the decoded video data  901  to VR video stream  902 .  
         [0007]     The audio decoder  81  likewise decodes the audio elementary stream  602  to acquire decoded audio data  801 , and the VR audio encoder  82  then converts and re-encodes the decoded audio data  801  to VR audio stream  802 .  
         [0008]     The VR multiplexer  62  then multiplexes the VR video stream  902  and VR audio stream  802  to a program stream compliant with the VR format, that is, VR-compliant MPEG data  106 .  
         [0009]     The VR stream information detector  14  then acquires the management information such as the stream VOBU (Video OBject Unit) information required by the VR format from this VR-compliant MPEG data  106 . The VR stream information detector  14  then generates and records VR-compliant VRO data file  107  and IFO data file  108  to optical disc  50 .  
         [0010]     The operation of this AV data converter is described next.  
         [0011]     When the AV data converter reads MPEG data file  101 , the MPEG demultiplexer  61  demultiplexes the MPEG data file  101  into the video elementary stream  601  and audio elementary stream  602 . The video elementary stream  601  is input to the video decoder  91  whereby it is decoded and converted to decoded video data  901 . The decoded video data  901  is then passed to the VR video encoder  92 , which converts it to a VR video elementary stream  902 , that is, a video elementary stream defined by the VR format. The audio elementary stream  602  demultiplexed from the MPEG data file  101  by the MPEG demultiplexer  61  is similarly applied to the audio decoder  81  whereby it is decoded and converted to decoded audio data  801 . This decoded audio data  801  is then converted by the VR audio encoder  82  to a VR audio elementary stream  802 , that is, an audio elementary stream defined by the VR format.  
         [0012]     The VR multiplexer  62  then multiplexes the VR video elementary stream  902  and VR audio elementary stream  802  to output VR-compliant MPEG data  106  to the VR stream information detector  14 . VRO data file  107  and IFO data file  108  are then generated using the stream VOBU and other management information detected by the VR stream information detector  14  from the VR-compliant MPEG data  106 .  
         [0013]     A problem with this AV data converter of the prior art is that because all data in the read MPEG data file is decoded and all decoded data is then encoded according to the VR format, conversion takes a long time.  
         [0014]     Another problem is that the original image quality and sound quality may not be retained in the converted AV data file depending upon the encoding conditions, and information is therefore lost.  
         [0015]     Yet another problem is that because decoding and encoding are applied even when there is an error or other problem in the MPEG data file, a non-standard or corrupted data file that does not comply with the VR format is created and a noncompliant disc is produced.  
       SUMMARY OF THE INVENTION  
       [0016]     The present invention is directed to solving these problems, and an object of the invention is to provide an AV data conversion apparatus and method capable of quickly converting AV data with little loss of image quality or sound quality, and preventing creation of noncompliant discs.  
         [0017]     To achieve this object, an AV data conversion apparatus according to the present invention has a verification file confirmation means for reading an AV data file containing AV data including video information and audio information, and a verification file for the AV data file, and confirming if the AV data file and verification file match; a plurality of stream conversion means for changing the AV data to a specific format; and a conversion method determining means for selecting from among the plural stream conversion means at least one stream conversion means for changing the AV data to the specific format based on verification file content.  
         [0018]     A stream conversion method for converting an AV data file to a VR-format AV data file can thus be easily selected by creating and appending to the AV data file a verification file denoting the compatibility level of the AV data file with the VR format. This verification file can be created and appended to the AV data file at the time the AV data file is created. The verification file confirmation means confirms the correlation between the AV data file and verification file, and the stream conversion method determining means evaluates AV data file compatibility with the VR format based on the compatibility information contained in the verification file to select the appropriate stream conversion means.  
         [0019]     The selected stream conversion means then re-encodes only the data that is not compliant with the VR format. Because VR-compliant data is thus not re-encoded, the conversion operation is fast with very little loss of image or sound quality.  
         [0020]     Preferably, the AV data conversion apparatus reads a verification file containing AV data attributes from when the AV data file was created. The verification file confirmation means comprises an AV data attribute extraction means for extracting AV data attributes from the read AV data file, and a comparison means for comparing the AV data attributes extracted by the AV data attribute extraction means with the AV data attributes contained in the verification file. The stream conversion means converts the AV data to the specified format only when the comparison means confirms an attribute match.  
         [0021]     If the verification file confirmation means determines that the AV data file does not conform to the verification file, stream conversion by the stream conversion means is prohibited and creating a disc that does not comply to the standard is prevented at an early stage in the process.  
         [0022]     Yet further preferably, the AV data conversion apparatus of this invention reads a verification file containing VenderID information for uniquely identifying a device or software that created the AV data file, and the stream conversion means determines at least one stream conversion means based on VenderID information.  
         [0023]     By pre-registering in the stream conversion means which conversion means is best for each VenderID, the best conversion means for a given AV data file can be selected based on the VenderID information in the verification file. Compatibility of an AV data file with the VR format depends upon the device or software used to create the AV data file. It is therefore desirable to set a VenderID for each device or software program, and correlate each VenderID to VR format compliance.  
         [0024]     When the verification file confirmation means cannot read the verification file, the AV data conversion apparatus of this invention further preferably creates a verification file containing AV data attributes acquired by the AV data attribute extraction means and specific VenderID information corresponding to the AV data attributes.  
         [0025]     This aspect of the invention creates a new verification file corresponding to the AV data attributes of the AV data file when the verification file cannot be read so that even AV data files for which there is no associated verification file can be converted.  
         [0026]     A further aspect of the invention is an AV data conversion method having a first step of reading an AV data file containing AV data including video information and audio information, and a verification file for the AV data file; a second step of selecting at least one stream conversion method from among plural stream conversion methods for changing the AV data to the specific format based on verification file content; and a third step of converting the AV data to a specific format by means of the at least one selected stream conversion method.  
         [0027]     This method of the invention evaluates compliance with the VR format based on compatibility information contained in the verification file, and selects a stream conversion method appropriate to the compliance level indicated in the verification file. As a result, only data that is not compliant with the VR format is re-encoded, and VR-compliant data is not re-encoded. AV data files can therefore be converted quickly with little loss of video or sound quality.  
         [0028]     Preferably, this AV data conversion method also has, after the first step and before the second step, a fourth step of confirming if the AV data file and verification file mutually correspond.  
         [0029]     If the AV data file is determined to be a corrupt file not corresponding to the verification file, subsequent stream conversion is stopped and creating a non-standard disc can be prevented at an early stage in the process.  
         [0030]     Yet further preferably, this AV data conversion method reads a verification file containing AV data attributes from when the AV data file was created. In addition, the fourth step further comprises a fifth step for extracting the AV data attributes when the AV data file was created from the read AV data file, and a sixth step for comparing the AV data attributes extracted by the fourth step with the AV data attributes contained in the verification file. The third step converts the AV data to the specified format only when a comparison result from the sixth step confirms an attribute match.  
         [0031]     Creating a non-standard disc can thus be prevented at an early stage in the process because conversion by the stream conversion means is prohibited when the result of the fourth step is that the AV data file is an illegal AV data file not conforming to the verification file.  
         [0032]     Yet further preferably, this AV data conversion method reads a verification file containing VenderID information uniquely identifying a device or software that created the AV data file, and the second step selects the conversion method based on this VenderID information.  
         [0033]     By pre-registering in the stream conversion means which conversion means is best for each VenderID, the best conversion method for a given AV data file can be selected based on the VenderID information in the verification file.  
         [0034]     An AV data conversion method according to another aspect of the invention has a first step of reading an AV data file containing AV data including video information and audio information; a second step of extracting AV data attributes from the read AV data file; a third step of creating a verification file corresponding to the extracted AV data attributes; a fourth step of selecting at least one stream conversion method from among plural stream conversion methods for changing the AV data to the specific format based on verification file content; and a fifth step of converting the AV data to the specific format by applying the at least one selected stream conversion method.  
         [0035]     This aspect of the invention creates a new verification file corresponding to the AV data attributes of the AV data file when the verification file cannot be read so that even AV data files for which there is no associated verification file can be converted.  
         [0036]     A further aspect of the invention is a computer-readable recording medium storing an AV data conversion program of this invention for executing on a computer the steps of the AV data conversion method. The recording medium could be an optical recording medium, magnetic recording medium, semiconductor recording medium, or other type recording medium.  
         [0037]     An AV data conversion program according to the present invention is a program for executing on a computer the steps of an AV data conversion method according to this invention. This AV data conversion program can be distributed on a recording medium or over the Internet or other digital communication medium.  
         [0038]     It will thus be apparent that an AV data conversion apparatus according to the present invention decodes and encodes only data that is compatible with the VR format based on a VenderID or other information contained in a verification file. As a result, the present invention can convert AV data faster and with less loss of image quality or sound quality when compared with a conventional AV data conversion system that decodes and encodes all data.  
         [0039]     Producing a non-compliant disc can also be prevented at an earlier stage in the process because information contained in the verification file and information contained in the AV data file are compared, and data file conversion is stopped if an error is detected in the AV data file.  
         [0040]     Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]     The present invention will become readily understood from the following description of preferred embodiments thereof made with reference to the accompanying drawings, in which like parts are designated by like reference numeral, and in which:  
         [0042]      FIG. 1  is a block diagram of an AV data conversion apparatus according to a first embodiment of the present invention;  
         [0043]      FIG. 2  is a block diagram showing an example of an AV data conversion apparatus according to a first embodiment of the invention;  
         [0044]      FIG. 3  is a block diagram showing the configuration of the video capturing means shown in  FIG. 2 ;  
         [0045]      FIG. 4  is a flow chart describing operation of the AV data conversion apparatus according to a first embodiment of the invention;  
         [0046]      FIG. 5A  is a schematic diagram of information contained in a VR-compatibility verification file;  
         [0047]      FIG. 5B  shows steps executed by the VR verification file confirmation means;  
         [0048]      FIG. 6A  is an example of a stream conversion means compatibility table;  
         [0049]      FIG. 6B  describes the stream conversion method determining means;  
         [0050]      FIG. 7  is a block diagram describing operation of the 0-th stream conversion means  51 ;  
         [0051]      FIG. 8  is a block diagram describing operation of the 1st stream conversion means  13   a;    
         [0052]      FIG. 9  is a block diagram describing operation of the 2nd stream conversion means  13   b;    
         [0053]      FIG. 10  is a block diagram describing operation of the 3rd stream conversion means  13   c;    
         [0054]      FIG. 11  is a block diagram describing operation of the 4th stream conversion means  13   d;    
         [0055]      FIG. 12  is a detailed block diagram of the loss-of-synchronization detection means and audio data correction means shown in  FIG. 11 ;  
         [0056]      FIG. 13  is a block diagram describing operation of the 5th stream conversion means  13   e;    
         [0057]      FIG. 14  is a block diagram describing operation of the 6th stream conversion means  13   f;    
         [0058]      FIG. 15  is a block diagram describing operation of the 7th stream conversion means  13   g;    
         [0059]      FIG. 16  is a block diagram describing operation of the 8th stream conversion means  13   h;    
         [0060]      FIG. 17  is a block diagram of an AV data conversion apparatus according to a second embodiment of the invention;  
         [0061]      FIG. 18  is a flow chart of the operation of the AV data conversion apparatus according to the second embodiment of the invention; and  
         [0062]      FIG. 19  is a block diagram of an AV data conversion apparatus according to the prior art. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0063]     Preferred embodiments of the present invention are described below with reference to the accompanying figures. Note that like reference numerals in the figures denote identical components or components performing identical actions and operations.  
       Embodiment 1  
       [0064]      FIG. 1  is a block diagram of an AV data conversion apparatus according to a first embodiment of the present invention. As shown in  FIG. 1 , this AV data conversion apparatus reads an MPEG data file  101  and a VR-compatibility verification file  102  corresponding to the MPEG data file  101 , and produces VR-format VRO file  107  and IFO file  108  through a stream conversion operation. As will also be known from  FIG. 1 , this AV data conversion apparatus has a VR-compatibility verification file confirmation means  11 , stream conversion method determining means  12 , stream conversion unit  13  containing at least one stream conversion means, and VR stream information detector  14 .  
         [0065]     The IFO file is a management information file containing information relating to the recorded MPEG stream. This information includes, for example, the size and total number of GOP (data compression unit) objects, the size of each recorded data block, and the video signal resolution. The IFO file also contains the results of simple editing operations based on the VR format.  
         [0066]     The operation of each component of the AV data conversion apparatus is described next.  
         [0067]     The VR-compatibility verification file confirmation means  11  first confirms whether the MPEG data file  101  conforms to the VR-compatibility verification file  102 . The VR-compatibility verification file is paired with an MPEG data file and is used to verify the MPEG data file, and includes MPEG data video attributes and audio attributes, and information about the compatibility of MPEG data contained in the MPEG data file with the VR format.  
         [0068]     If the VR-compatibility verification file confirmation means  11  verifies that the MPEG data file is compatible with the VR format (referred to below as “VR compliant”), the VR-compatibility verification file confirmation means  11  outputs the verified MPEG stream data  103  to the stream conversion unit  13 , and outputs the MPEG verification data  104  acquired from the VR-compatibility verification file  102  to the stream conversion method determining means  12 .  
         [0069]     Based on the MPEG verification data  104 , the stream conversion method determining means  12  determines the best stream conversion means of the stream conversion unit  13 , and applies stream conversion means identifier  105  to the stream conversion unit  13 .  
         [0070]     In this embodiment of the invention the stream conversion unit  13  includes first stream conversion means  13   a,  second stream conversion means  13   b,  and third conversion means  13   c,  each performing a different stream conversion function. Which of these stream conversion means is used to convert the MPEG data file is selected based on the stream conversion means identifier  105 . The stream conversion unit  13  then converts the verified MPEG stream data  103  to VR-compliant MPEG stream data  106 , that is, an MPEG data stream that is compatible with the VR format.  
         [0071]     The VR stream information detector  14  then detects the stream VOBU and other management information required by the VR format from the VR-compliant MPEG data, and generates VR-compliant VRO file  107  and IFO file  108 .  
         [0072]     The functions of the present invention shown in  FIG. 1  can be rendered by a computer program executed by a personal computer, for example.  FIG. 2  is a block diagram showing the configuration of a personal computer  10  for executing the method of the present invention by means of a CPU  1 , memory  2 , hard disk drive  3 , DVD-RAM drive  4 , and video capture device  5 . The CPU  1  reads and runs a computer program stored in memory  2  or hard disk drive  3 . This computer program is typically distributed via a recording medium, but could be distributed via a digital communication network. The configuration of the video capture device  5  is described next with reference to  FIG. 3 .  
         [0073]     The video capture device  5  has an A/D converter  6 , encoder  7 , and VR-compatibility verification file generator  8 . The A/D converter  6  converts video input to the video capture device  5  to digital image data, and the encoder  7  then MPEG-encodes the digital image data to output MPEG data file  101 . The VR-compatibility verification file generator  8  also generates VR-compatibility verification file  102  containing information about the compatibility of the MPEG data file  101  with the VR format. Compatibility with the VR format depends on the characteristics of the encoder  7 . These characteristics differ according to the manufacturer and system design of the encoder  7 . As a result, this embodiment of the invention adds a VenderID identifying the encoder  7  manufacturer as the compatibility information in the VR-compatibility verification file  102 . It will be obvious to one with ordinary skill in the related art that this VenderID shall not necessarily identify the manufacturer, and could instead be a unique ID determined by the characteristics of the encoder  7 . The encoder  7  could further be either a software or a hardware construction, and the VenderID predetermined for each encoder  7  or video capture device  5  can be added to the VR-compatibility verification file  102 . The VenderID could also be added according to the output MPEG data file  101 .  
         [0074]     The personal computer  10  acquires the MPEG data file  101  and VR-compatibility verification file  102  from the video capture device  5 . The MPEG data file  101  is written to memory  2 , and the program run by the CPU  1  converts the MPEG stream data  103  contained in the MPEG data file  101  to VR-compliant MPEG data  106  which is then written to DVD-RAM by the DVD-RAM drive  4 , producing a VR-format optical disc  50 . It should be noted that the personal computer  10  of this embodiment has a video capture device  5 , but the video capture device  5  is not required as long as there is means for acquiring a MPEG data file  101  and VR-compatibility verification file  102  set. There could, for example, be a network connection enabling the AV data conversion method described above to be executed using an MPEG data file  101  and paired VR-compatibility verification file  102  acquired from another device on the network.  
         [0075]     The present invention can also be rendered in a DVD recorder having the construction shown in  FIG. 2  built in. In this case the program run by the CPU  1  can be stored to memory  2  or hard disk drive  3 . The memory  2  could be ROM (read-only memory) or RAM (random access memory), and the program could be stored in a ROM device. This ROM device could be flash memory, and the program recorded to flash memory can be overwritten with a program obtained from a communication network or recording medium.  
         [0076]     The AV data conversion method of this invention is described step by step next with reference to  FIG. 4 .  
         [0077]     (a) The VR-compatibility verification file confirmation means  11  first reads MPEG data file  101  and VR-compatibility verification file  102  (S 11 ).  
         [0078]     (b) The VR-compatibility verification file confirmation means  11  then gets the MPEG verification information from the read VR-compatibility verification file  102  (S 12 ).  
         [0079]     (c) Whether the MPEG data file  101  matches the VR-compatibility verification file  102  is then verified based on the content of the MPEG verification information (S 13 ).  
         [0080]     (d) If the MPEG data file  101  and VR-compatibility verification file  102  match, the stream conversion method determining means  12  selects the stream conversion unit  13  from the stream conversion means correspondence table based on the VenderID contained in the MPEG verification information (S 14 ). For example, if the VenderID is Vender_C, second stream conversion means  13   b  is selected by referencing the table shown in  FIG. 6A , and third conversion means  13   c  is selected if the VenderID is Vender_D. If the VenderID in the MPEG verification information is not found in the stream conversion means correspondence table, the process ends as shown in  FIG. 6 ( b ).  
         [0081]     (e) The selected stream conversion unit  13  then applies the VR conversion process to the MPEG stream data  103  in the MPEG data file  101  (S 15 ).  
         [0082]     (f) The VR stream information detector  14  then acquires the VOBU and other management information required by the VR format from the VR-compliant MPEG data  106 , and generates the VR-compliant VRO file  107  and IFO file  108  (S 16 ).  
         [0083]     The original MPEG data file  101  is thus output as VR-compliant MPEG stream data  106  as a result of these steps.  
         [0084]     The AV data conversion method described above can also be executed as a computer program.  
         [0085]     Operation of an AV data conversion apparatus according to this embodiment of the invention is described next with reference to the flow chart in  FIG. 4 .  
         [0086]     The VR-compatibility verification file confirmation means  11  first reads the MPEG data file  101  and VR-compatibility verification file  102  (S 11 ).  
         [0087]     Based on the content of the read VR-compatibility verification file  102 , the VR-compatibility verification file confirmation means  11  then verifies if the MPEG data file  101  corresponds to the VR-compatibility verification file  102  (S 12 , S 13 ).  
         [0088]     The operation of the VR-compatibility verification file confirmation means  11  at this time is described in detail with reference to  FIG. 5 . As shown in  FIG. 5A , the VR-compatibility verification file  102  is composed of, for example, MPEG file information denoting the file name and file size, a VenderID denoting the type of system that produced the MPEG file, video attributes indicating the resolution and other attributes of the video content, and audio attributes indicating such information as the audio bitrate. Note that the file information, video attributes, and audio attributes are collectively referred to as the AV data attributes.  
         [0089]      FIG. 5  ( b ) describes operation of the VR-compatibility verification file confirmation means  11 . As shown in  FIG. 5  ( b ) this VR-compatibility verification file confirmation means  11  is composed of an MPEG information acquisition means  21 , MPEG file information comparison means  22 , video attribute comparison means  23 , and audio attribute comparison means  24 .  
         [0090]     The MPEG information acquisition means  21  gets the file information, video attributes, and audio attributes from the AV data attributes of the MPEG data file. The MPEG file information comparison means  22  then determines if the filename, size, date, and other file attributes of the MPEG data file match the file information of the MPEG data file. The video attribute comparison means  23  likewise determines if the video resolution and other video attributes match, and the audio attribute comparison means  24  determines if the audio bitrate and other audio attributes match.  
         [0091]     The VR-compatibility verification file  102  contains the MPEG file information, VenderID, video attributes, and audio attributes at specific locations in a known file format.  
         [0092]     The MPEG information acquisition means  21  gets the MPEG file information, video attributes, and audio attributes from the MPEG data file. The MPEG file information comparison means  22  determines if the MPEG file information acquired from the MPEG data file matches the MPEG file information of the VR-compatibility verification file, and stops the stream conversion process if a match is not confirmed. The video attribute comparison means  23  determines if the video attributes acquired from the MPEG data file match the video attributes of the VR-compatibility verification file, and stops the stream conversion process if a match is not confirmed. The audio attribute comparison means  24  likewise determines if the audio attributes from the MPEG data file match the audio attributes of the VR-compatibility verification file (S 13 ), and stops the stream conversion process if a match is not confirmed. The stream conversion process thus continues and MPEG verification information storing the MPEG stream data and VenderID is output only if all information matches.  
         [0093]     The MPEG verification information output from the VR-compatibility verification file confirmation means  11  is input to the stream conversion method determining means  12 . Operation of the stream conversion method determining means  12  is described next with reference to  FIGS. 6A and 6B .  
         [0094]      FIG. 6A  shows a sample stream conversion means correspondence table. This stream conversion means correspondence table records which conversion process should be run for a particular VenderID in the VR-compatibility verification file.  FIG. 6B  describes the operation of the stream conversion method determining means  12 .  
         [0095]     The stream conversion method determining means  12  references the stream conversion means correspondence table  31 , and the VenderID comparison means  32  compares the VenderID in the VR-compatibility verification file with the VenderIDs in the stream conversion means correspondence table  31 .  
         [0096]     When the MPEG verification information is input to the stream conversion method determining means  12 , the stream conversion means is selected from the stream conversion means correspondence table based on the VenderID contained in the MPEG verification information (S 14 ). Using the stream conversion means correspondence table shown in  FIG. 6  by way of example, second stream conversion means  13   b  is selected if the VenderID is Vender_C, and third conversion means  13   c  is selected if the VenderID is Vender_D. Likewise, third stream conversion means  13   c  and sixth stream conversion means  13   f  are selected if the VenderID is Vender_E, fourth stream conversion means  13   d  is selected if Vender_F, fifth stream conversion means  13   e  is selected if Vender_G, sixth stream conversion means  13   f  is selected if Vender-H, seventh stream conversion means  13   g  if Vender_I, and eighth stream conversion means  13   h  is selected if Vender_J. Processing stops as shown in  FIG. 6  ( b ) if the VenderID contained in the MPEG verification information is not found in the stream conversion means correspondence table.  
         [0097]     The stream conversion method determining means  12  then inputs the stream conversion means selection to the stream conversion unit  13 . Using the selected stream conversion means  13   a  to  13   h,  the stream conversion unit  13  applies the appropriate conversion process to the verified MPEG stream data  103  (S 15 ).  
         [0098]     Operation of the stream conversion unit  13  is described in detail next with reference to  FIG. 7  to  FIG. 16 .  
         [0099]     If stream conversion is unnecessary because the input verified MPEG stream data  103  is highly compliant with the VR format, the stream conversion unit  13  selects the 0-th stream conversion means  51 . This situation corresponds to a VenderID of Vender_B in the table shown in  FIG. 6A . The 0-th stream conversion means  51  then outputs the input verified MPEG stream data  103  as VR-compliant MPEG stream data  106  without further processing as shown in  FIG. 7 .  
         [0100]     If the input verified MPEG stream data  103  is VR format compliant on the video and audio elementary stream level but not compatible on the multiplex level, the stream conversion unit  13  selects first stream conversion means  13   a  (equivalent to a VenderID of Vender_A in  FIG. 6 ). This first stream conversion means  13   a  is described with reference to  FIG. 8 .  
         [0101]     The first stream conversion means  13   a  has an MPEG demultiplexer  61  and VR multiplexer  62 . The MPEG demultiplexer  61  demultiplexes the verified MPEG stream data  103  into the video elementary stream  601  and audio elementary stream  602 . The VR multiplexer  62  then combines the video elementary stream  601  and audio elementary stream  602  to the VR-compliant MPEG stream data  106  of a VR program stream.  
         [0102]     The MPEG demultiplexer  61  of the first stream conversion means  13   a  demultiplexes the input verified MPEG stream data  103  into the video elementary stream  601  and audio elementary stream  602 . The VR multiplexer  62  then converts these elementary streams to the VR format by, for example, converting the pack size to 2048 bytes, and thus outputs VR-compliant MPEG stream data  106 .  
         [0103]     It will thus be apparent from  FIG. 8  that when the input verified MPEG stream data  103  is compatible with the VR format on the video and audio elementary stream level, the first stream conversion means  13   a  converts the verified MPEG stream data  103  to VR-compliant MPEG stream data  106  by simply multiplexing the elementary streams without decoding or encoding the streams.  
         [0104]     If the input verified MPEG stream data  103  is compatible with the VR format on the video and audio elementary stream level except for some selected flags, the stream conversion unit  13  selects second stream conversion means  13   b  (equivalent to a VenderID of Vender_C in  FIG. 6 ). Operation of the second stream conversion means  13   b  is described next with reference to  FIG. 9 .  
         [0105]     As shown in  FIG. 9 , the second stream conversion means  13   b  is composed of MPEG demultiplexer  61 , VR multiplexer  62 , video stream correction means  71 , and audio stream correction means  72 . The video stream correction means  71  corrects the video elementary stream  601  so that it is compatible with the VR format on the video elementary stream level, and thus outputs corrected video elementary stream  701 . The audio stream correction means  72  corrects the audio elementary stream  602  so that it is compatible with the VR format on the audio elementary stream level, and thus outputs corrected audio elementary stream  702 .  
         [0106]     The second stream conversion means  13   b  thus splits the input verified MPEG stream data  103  into video elementary stream  601  and audio elementary stream  602  by means of MPEG demultiplexer  61 . The video stream correction means  71  then changes or deletes particular flags in the video elementary stream  601  according to the VR format, and the audio stream correction means  72  likewise changes or deletes particular flags in the audio elementary stream  602  according to the VR format. The VR multiplexer  62  then converts the MPEG-2 program stream conforming to the VR format to 2048-byte packs, for example, and outputs VR-compliant MPEG stream data  106 .  
         [0107]     The second stream conversion means  13   b  runs a conversion process for cases in which the values of only some flags in the video and audio of the input MPEG data file are incompatible with the VR format. If only the display resolution of the MPEG data is not compatible with the VR format, for example, the MPEG data can be converted to VR-format stream data by changing only the data relating to the display resolution contained in the video elementary stream isolated by the demultiplexer, and full decoding and encoding are therefore not necessary.  
         [0108]     If the input verified MPEG stream data  103  is VR-compliant on the video elementary stream level, the stream conversion unit  13  selects the third stream conversion means  13   c  (corresponding to a VenderID of Vender_D in  FIG. 6 ). Operation of the third stream conversion means  13   c  is described with reference to  FIG. 10 .  
         [0109]     As shown in  FIG. 10  the third stream conversion means  13   c  has a MPEG demultiplexer  61 , VR multiplexer  62 , audio decoder  81 , and VR audio encoder  82 . The audio decoder  81  decodes the audio elementary stream  602  and outputs decoded audio data  801 . The VR audio encoder  82  then encodes the decoded audio data  801  to VR-format VR audio elementary stream  802 .  
         [0110]     The input verified MPEG stream data  103  is demultiplexed by the MPEG demultiplexer  61  of the third stream conversion means  13   c  to video elementary stream  601  and audio elementary stream  602 . The audio elementary stream  602  is then decoded by the audio decoder  81 . The decoded audio data  801  is then encoded by the VR audio encoder  82  to a VR audio elementary stream  802  as defined by the VR format. The VR multiplexer  62  then converts the VR-compliant MPEG-2 program stream to 2048-byte packs, for example, and outputs VR-compliant MPEG stream data  106 .  
         [0111]     If only the audio portion of the input MPEG data file  101  is incompatible with the VR format, a VR-compliant MPEG stream data  106  can be output by re-encoding only the audio portion instead of re-encoding all data.  
         [0112]     If the input verified MPEG stream data  103  is VR compliant at the video elementary stream level but AV synchronization is off, the stream conversion unit  13  selects the fourth stream conversion means  13   d  (equivalent to a VenderID of Vender_F in  FIG. 6A ). Operation of the fourth stream conversion means  13   d  is described next with reference to  FIG. 11 .  
         [0113]     As shown in  FIG. 11  the fourth stream conversion means  13   d  has MPEG demultiplexer  61 , VR multiplexer  62 , audio decoder  81 , VR audio encoder  82 , loss-of-synchronization detector  83 , and audio data correction means  84 . The loss-of-synchronization detector  83  compares video time information  803  and audio time information  806  to detect any offset in the video and audio playback times, and outputs audio correction information  804  denoting how much to correct the audio data. The audio data correction means  84  then adjusts the data size of the decoded audio data  801  according to the correction specified by the audio correction information  804 , and outputs AV-synchronization-corrected audio data  805 . The audio component of the AV-synchronization-corrected audio data  805  is corrected to resynchronize the video and audio.  
         [0114]     The MPEG demultiplexer  61  of the fourth stream conversion means  13   d  demultiplexes the input verified MPEG stream data  103  into the video elementary stream  601  and audio elementary stream  602 , and outputs AV synchronization data  803 ,  806  containing a Presentation Time Stamp (PTS), that is, time information for synchronizing video and audio playback. Based on the AV synchronization data  803 ,  806 , the loss-of-synchronization detector  83  detects any offset between the video and audio, and outputs audio correction information  804 . Based on this audio correction information  804 , the audio data correction means  84  adjusts the data size of the decoded audio data  801 , and outputs AV-synchronization-corrected audio data  805 , that is, the audio data after correcting it to synchronize with the video. This AV-synchronization-corrected audio data  805  is then encoded by the VR audio encoder  82  to a VR audio elementary stream  802 . The VR multiplexer  62  then multiplexes the data according to the VR format and outputs VR-compliant MPEG stream data  106 .  
         [0115]     When re-encoding the audio part of input MPEG data file  101  could cause a loss of synchronization between the video and audio, the MPEG data file  101  can be converted to synchronized VR-format data by increasing or decreasing the audio data according to the video data.  
         [0116]     This synchronization correction method is described in further detail with reference to  FIG. 12 .  FIG. 12  is a detailed block diagram of the loss-of-synchronization detector  83  and audio data correction means  84 .  
         [0117]     (1) The MPEG demultiplexer  61  demultiplexes the input verified MPEG stream data  103  into the video elementary stream  601  and audio elementary stream  602 . The MPEG demultiplexer  61  also outputs AV synchronization information  803  containing the PTS or other time information enabling synchronized playback of the video and audio.  
         [0118]     (2) The loss-of-synchronization detector  83  then acquires the total video frame count (time equivalent) as the AV synchronization information  803  (S 01 ).  
         [0119]     (3) The average difference between the video and audio is then calculated for a predetermined period. The offset between this average and the difference between the video and audio is then calculated (S 02 ). This step is necessary because the average difference calculated in the first predetermined period will vary according to the current environment.  
         [0120]     (4) Whether this difference exceeds a specified threshold value is then determined (S 03 ). If the difference exceeds the threshold value, the audio correction information  804  is sent to the audio data correction means  84 .  
         [0121]     (5) The audio data correction means  84  acquires the decoded audio data  801   a  and audio data size (time-equivalent)  806  from the audio decoder  81  (S 04 ).  
         [0122]     (6) The loss-of-synchronization detector  83  acquires the audio correction information  804  from the loss-of-synchronization detector, and calculates the required audio data correction (S 05 ).  
         [0123]     (7) If the audio data correction required for decoded audio data  801   b  is a non-zero value, the audio data size is increased or decreased accordingly (S 06 ). Adjusting the audio data at once can cause the audio to skip or sound unnatural after conversion is completed, and a gradual adjustment in the audio data size is therefore desirable. The data is downsampled at specified intervals in order to reduce the amount of data, and data is duplicated at specified intervals to gradually increase the amount of audio data. This operation continues until the specified desired audio data correction is achieved.  
         [0124]     Note that this synchronization correction method is described in further detail in International Application PCT/JP02/05108 (WO 02/097817), incorporated herein by reference.  
         [0125]     (8) AV-synchronization-corrected audio data  805  corrected to synchronize with the video stream is output to the VR audio encoder  82 .  
         [0126]     (9) The VR audio encoder  82  then encodes the AV-synchronization-corrected audio data  805  to a VR audio elementary stream  802 .  
         [0127]     (10) The VR multiplexer  62  then converts the video elementary stream  601  and VR audio elementary stream  802  to conform to the VR format, thereby outputting VR-compliant MPEG stream data  106 .  
         [0128]     If the verified MPEG stream data  103  is VR-compliant at the audio elementary stream level but not at the video elementary stream level, the stream conversion unit  13  selects the fifth stream conversion means  13   e  (equivalent to a VenderID of Vender_G in the correspondence table shown in  FIG. 6A ). This fifth stream conversion means  13   e  is described next with reference to  FIG. 13 .  
         [0129]     As shown in  FIG. 13  the fifth stream conversion means  13   e  is composed of a MPEG demultiplexer  61 , VR multiplexer  62 , video decoder  91 , and VR video encoder  92 . The video decoder  91  decodes the video elementary stream  601  and outputs decoded video data  901 . The VR video encoder  92  encodes the decoded video data  901  and outputs VR video elementary stream  902 .  
         [0130]     The MPEG demultiplexer  61  of fifth stream conversion means  13   e  demultiplexes the input verified MPEG stream data  103  to video elementary stream  601  and audio elementary stream  602 . The video decoder  91  then decodes the video elementary stream  601 . The VR video encoder  92  then encodes the decoded video data  901  to a VR video elementary stream  902 . The VR multiplexer  62  then converts the VR video elementary stream  902  according to the VR format, and outputs VR-compliant MPEG stream data  106 .  
         [0131]     An MPEG data file in which only the video component is not compliant with the VR format can thus be converted to a VR-compliant AV data stream by re-encoding only the video portion rather than re-encoding all data.  
         [0132]     If the input verified MPEG stream data  103  is compatible with the VR format at the audio elementary stream level but audio synchronization is lot, the stream conversion unit  13  selects the sixth stream conversion means  13   f  (corresponding to a VenderID of Vender_H in the correspondence table shown in  FIG. 6A ). This sixth stream conversion means  13   f  is described below with reference to  FIG. 14 .  
         [0133]     As shown in  FIG. 14 , the sixth stream conversion means  13   f  is composed of a MPEG demultiplexer  61 , VR multiplexer  62 , video decoder  91 , VR video encoder  92 , loss-of-synchronization detector  93 , and video data correction means  94 .  
         [0134]     The loss-of-synchronization detector  93  compares the audio time information  903  and video time information  906  to detect the difference between the video and audio playback times, and outputs video data correction information  904  denoting the required video data correction. The video data correction means  94  then adjusts the video data size according to the video correction indicated by the video data correction information  904 , and outputs AV-synchronization-corrected video data  905 . The video data of the AV-synchronization-corrected video data  905  is adjusted to synchronize the video with the audio. It should be noted that the detailed operation of the loss-of-synchronization detector  93  and video data correction means  94  is the same as the operation of the audio data correction means, and further description thereof is thus omitted.  
         [0135]     The MPEG demultiplexer  61  of the sixth stream conversion means  13   f  demultiplexes the verified MPEG stream data  103  into the video elementary stream  601  and audio elementary stream  602 , and outputs AV synchronization information  903 ,  906  including a PTS or other time information enabling synchronized playback of the video and audio.  
         [0136]     The loss-of-synchronization detector  93  detects a loss of synchronization between the video and audio based on the AV synchronization information  903 ,  906 , and outputs video data correction information  904 . Based on this video data correction information  904 , the video data correction means  94  adjusts the size of the decoded video data  901 , and outputs AV-synchronization-corrected video data  905 , which has been corrected for synchronization with the audio. This AV-synchronization-corrected video data  905  is encoded by the VR video encoder  92  to a VR video elementary stream  902 . The VR multiplexer  62  then converts the video and audio to output VR-compliant MPEG stream data  106 .  
         [0137]     This method of the invention can thus convert an input MPEG data file to a VR-compliant data file free of synchronization errors by adjusting the video data size to the audio data when synchronization between the video and audio can be lost by re-encoding the video portion of an input MPEG data file.  
         [0138]     When both the video elementary stream and audio elementary stream of the input verified MPEG stream data  103  are incompatible with the VR format, the stream conversion unit  13  selects seventh stream conversion means  13   g  (corresponding to a VenderID of Vender_I in the correspondence table shown in  FIG. 6A ). This seventh stream conversion means  13   g  is described further with reference to  FIG. 15 .  
         [0139]     The seventh stream conversion means  13   g  is composed of MPEG demultiplexer  61 , VR multiplexer  62 , audio decoder  81 , VR audio encoder  82 , video decoder  91 , and VR video encoder  92 .  
         [0140]     The audio decoder  81  decodes the audio elementary stream  602  and outputs decoded audio data  801 . The VR audio encoder  82  encodes the decoded audio data  801  and outputs VR audio elementary stream  802 . The video decoder  91  decodes video elementary stream  601  and outputs decoded video data  901 . The VR video encoder  92  encodes decoded video data  901  and outputs VR video elementary stream  902 .  
         [0141]     The MPEG demultiplexer  61  of seventh stream conversion means  13   g  demultiplexes the input verified MPEG stream data  103  to video elementary stream  601  and audio elementary stream  602 . The video decoder  91  then decodes the video elementary stream  601 , and the audio decoder  81  decodes the audio elementary stream  602 . The decoded video data  901  is encoded to a VR video elementary stream  902  by the VR video encoder  92 , and the decoded audio data  801  is encoded to a VR audio elementary stream  802  by the VR audio encoder  82 . The VR multiplexer  62  then converts these elementary streams to the VR format, and outputs VR-compliant MPEG stream data  106 .  
         [0142]     If neither the video nor the audio portion of the input MPEG data file  101  is compatible with the VR format, the MPEG data file  101  can thus be converted to VR-format data by re-encoding both the video and audio portions.  
         [0143]     If the input verified MPEG stream data  103  is not compatible with the VR format on either the video or audio elementary stream level, and a loss of synchronization is also detected in the AV data, the stream conversion unit  13  selects the eighth stream conversion means  13   h  (equivalent to a VenderID of Vender_J in the correspondence table shown in  FIG. 6A ). This eighth stream conversion means  13   h  is described next with reference to  FIG. 16 .  
         [0144]     The MPEG demultiplexer  61  of this eighth stream conversion means  13   h  demultiplexes the input verified MPEG stream data  103  to video elementary stream  601  and audio elementary stream  602 , and outputs AV synchronization information  803  including the PTS enabling synchronous audio and video playback.  
         [0145]     Based on the AV synchronization data  803 , the loss-of-synchronization detector  83  detects a difference between the audio and video playback times, and outputs audio correction information  804 . Based on the audio correction information  804 , the audio data correction means  84  adjusts the decoded audio data  801  and outputs AV-synchronization-corrected audio data  805 , that is, the decoded audio data  801  corrected for video synchronization. The VR audio encoder  82  then encodes this AV-synchronization-corrected audio data  805  to a VR audio elementary stream  802 .  
         [0146]     The video elementary stream  601  is likewise decoded by the video decoder  91 . The decoded video data  901  is then encoded by the VR video encoder  92  to a VR video elementary stream  902 . The VR video elementary stream  902  is then converted to a VR video stream, and VR-compliant MPEG stream data  106  is output.  
         [0147]     When neither the video nor audio portions of the input MPEG data file  101  is compatible with the VR format and the video and audio may go out of synchronization, VR-format data with no loss of synchronization can be output by re-encoding the video and audio, and then adjusting the audio to the video data size.  
         [0148]     The stream conversion unit  13  thus selects one of the stream conversion means  0  to  8 , and converts the input MPEG data stream using the selected stream conversion means. The VR stream information detector  14  then gets the VOBU and other management information required by the VR format from the VR-compliant MPEG stream data  106 . A VR-compliant VRO file and IFO file are then created (S 16 ).  
         [0149]     It should be noted that the stream conversion means is determined based on the VenderID information by the stream conversion method determining means  12  in the embodiment described above, but the stream conversion means could be determined based on AV data attributes such as the MPEG file information, video information, and audio information. In this case a correspondence table relating the AV data attributes and stream conversion means can be used instead of the stream conversion means correspondence table shown in  FIG. 6A .  
         [0150]     Compatibility between the MPEG data file  101  and VR format is described next. MPEG files can be encoded according to various specifications. An MPEG data file  101  that is VR compliant is therefore described below.  
         [0151]     The video elementary stream of an MPEG title is compatible with the VR format only for NTSC (PAL) resolutions of 720×480 (720×576), 704×480 (760×576), 352×480 (352×576), 352×240 (352×288), 544×480 (544×576), and 480×480 (480×576). The video elementary stream is also compatible with the VR format only when the video bitrate is 9.8 Mbps or less (MPEG-2), or 1.856 Mbps or less (MPEG-1).  
         [0152]     The audio elementary stream is compatible with the VR format only if the audio compression method is AC3, MPEG-1, MPEG-2, or LPCM; the sampling frequency is 48 kHz; the channel is channel 1 (1 ch) through 8 (8 ch); and the bitrate is 64 Kbps/80 Kbps/96 Kbps/112 Kbps/128 Kbps/10 Kbps/192 Kbps/224 Kbps/256 Kbps/320 Kbps/384 Kbps/448 Kbps/748 Kbps (LPCM)/1536 Kbps (LPCM).  
         [0153]     Compatibility with VR format multiplexing is described next. The conditions for VR compatibility are that the pack size is fixed at 2048 bytes and the playback time from one system header to the next system header (VOBU) is at least 0.4 second and 1 second or less. All video and audio data must be completely contained in one VOBU, and the bitrate must be 10.08 Mbps or less for VR format compliance.  
       Embodiment 2  
       [0154]     An AV data conversion apparatus according to a second embodiment of the invention is described next. The first embodiment described above assumes the existence of a VR-compatibility verification file for the MPEG data file being processed. This second embodiment of the invention applies to a process used when a VR-compatibility verification file corresponding to the MPEG data file  101  does not exist.  
         [0155]      FIG. 17  is a block diagram showing the configuration of an AV data conversion apparatus according to a second embodiment of the invention. Like parts are identified by like reference numerals in  FIG. 1  and  FIG. 17 , and further description thereof is thus omitted here.  FIG. 18  is a flow chart showing the operation of this second embodiment. Steps identified by the same reference numeral in  FIG. 4  and  FIG. 18  perform the same operation, and further description thereof is this omitted here.  
         [0156]     As shown in  FIG. 17  this AV data conversion apparatus has an MPEG information acquisition means  21 , a virtual VR-compatibility verification file generator  41 , and a VR-compatibility file confirmation means  42 . The MPEG information acquisition means  21  acquires file information and video and audio attribute data from the MPEG data file. The virtual VR-compatibility verification file generator  41  then creates a VR format verification file based on the attributes acquired by the MPEG information acquisition means  21 .  
         [0157]     The operation of an AV data conversion apparatus according to this second embodiment of the invention is described below with reference to the flow chart shown in  FIG. 18 .  
         [0158]     The VR-compatibility file confirmation means  42  first reads the MPEG data file and corresponding VR-compatibility verification file. If the VR-compatibility verification file is found, operation is the same as described in the first embodiment (S 22 , S 23 , S 13  to S 16 ), and further description thereof is thus omitted. If the VR-compatibility verification file cannot be read because there is no VR-compatibility verification file corresponding to the MPEG data file  101 , for example, the MPEG information acquisition means  21  gets the AV data attributes including video attributes such as the file size, file creation date, the video resolution, and other video file information, and audio attributes such as the audio bitrate.  
         [0159]     In addition to the file information, video information, and audio attributes acquired by the MPEG information acquisition means  21 , the virtual VR-compatibility verification file generator  41  adds a virtual VenderID to these AV data attributes, and creates a VR-compatibility verification file such as shown in  FIG. 5  (S 25 ). The virtual VenderID assigned here is a reserved VenderID such as Vender_X.  
         [0160]     The stream conversion method determining means  12  then selects stream conversion means X as the stream conversion means corresponding to Vender_X (S 14 ). This stream conversion means X corresponds to seventh stream conversion means  13   g  or eighth stream conversion means  13   h  described in the first embodiment above, and encodes both the video and audio (S 15 ).  
         [0161]     The stream conversion unit  13  then applies stream conversion as described in the first embodiment, and the VR stream information detector  14  creates the VRO file and IFO file output as a VR format file (S 16 ).  
         [0162]     It is therefore possible to convert an MPEG data file to a VR format file by creating a virtual VR-compatibility verification file when only a MPEG data file is present.  
         [0163]     The present invention can also be rendered as a computer program. This program can also be distributed via an electrical communications medium or recording medium so that the invention can be rendered using a computer.  
         [0164]     Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.