referring now to fig1 an audio / video synchronous reproducer will be described according to the first preferred embodiment of the present invention . the audio / video synchronous reproducer comprises a file device 1 , such as a cd - rom drive , a dvd - rom drive and a hard disk drive , an av separating section 2 for reading out data from the file device 1 and separating them into video data , audio data and other data , a video processing section 3 for processing the video data separated at the av separating section 2 , and a video display device 4 such as a crt display for displaying the video data processed at the video processing section 3 . the reproducer further comprises an av synchronous control section 5 for carrying out a synchronous reproduction control of the video data and the audio data , an audio processing section 6 for processing the audio data separated at the av separating section 2 , and an audio reproducing device 7 for carrying out audio reproduction based on the audio data processed at the audio processing section 6 . in this embodiment , the file device 1 includes a plurality of file devices a , b , c , but there is no particular limitation to the number of file devices , which may also be one . the av separating section 2 comprises a file device choosing section 21 for choosing one or more of the file devices a to c to read out data therefrom , a video separating section 22 for separating only video data from the read - out data , and an audio separating section 23 for separating only audio data from the read - out data . the video processing section 3 comprises a compressed video storage 31 , a video decoder 32 , a video frame storage 33 and a video display control section 34 . the compressed video storage 31 stores the video data separated at the video separating section 22 . the video decoder 32 carries out a decompressing or expanding process when the video data stored in the compressed video storage 31 is compressed , and stores expanded video data per frame into the video frame storage 33 . the video display control section 34 transfers the expanded video data per frame to the video display device 4 , using a video time stamp given to the expanded video data as a reference time . the av synchronous control section 5 compresses a video time stamp detecting section 51 , an audio time stamp deriving section 52 , a time stamp comparing section 53 , a video skip control section 54 and a video repeat control section 55 . the video time stamp detecting section 52 obtains from the video decoder 32 a video time stamp of video data being processed . the audio time stamp deriving section 52 obtains from an audio reproduction control section 64 an amount of audio data processed up to then for audio reproduction and converts it into an audio time stamp equivalent value . the time stamp comparing section 53 compares the video time stamp from the video time stamp detecting section 51 and the audio time stamp equivalent value from the audio time stamp deriving section 52 and produces a comparison result signal . depending on the comparison result signal , the video skip control section 54 or the video repeat control section 55 controls a video frame display . the video skip control section 54 and the video repeat control section 55 cooperatively constitute a video display control means . the audio processing section 6 comprises a compressed audio storage 61 , an audio decoder 62 , an audio storage 63 and an audio reproduction control section 64 . the compressed audio storage 61 stores the audio data separated at the audio separating section 23 . the audio decoder 62 carries out an expanding process when the audio data stored in the compressed audio storage 61 is compressed , and stores expanded audio data into the audio storage 63 . the audio reproduction control section 64 transfers the expanded audio data to the audio reproducing device 7 . now , referring also to fig2 an operation of the audio / video synchronous reproducer shown in fig1 will be described in detail . the video processing section 3 , the av synchronous control section 5 and the audio processing section 6 operate independently of each other , and may be realized by specific circuits or a software control based on time - division multitask processing or the like . the file device choosing section 21 chooses one or more of the file devices a to c from the file device 1 designated by an operator or the like for video data and audio data , respectively , to read out compressed data therefrom and send the read - out compressed data to the video separating section 22 and the audio separating section 23 . the video separating section 22 separates compressed video data from the read - out compressed data and stores the compressed video data into the compressed video storage 31 ( step a 1 ). at this time , if it is immediately after the start of the reproduction , the video separating section 22 retrieves a first video time stamp and sends it to the time stamp comparing section 53 . the video display control section 34 checks whether a command of video repeat , i . e . a video repeat command signal , is received from the video repeat control section 55 ( step a 2 ). if the video repeat command signal is received , the video display control section 34 controls the video display device 4 to continue displaying a video frame being displayed for a designated time ( step a 4 ). then , the video display control section 34 checks whether a command of video skip , i . e . a video skip command signal , is received from the video skip control section 54 ( step a 3 ). if the video skip command signal is received , the video display control section 34 commands the video decoder 32 to skip a video expanding process corresponding to a designated time period ( step a 5 ). the video decoder 32 expands the compressed video data stored in the compressed video storage 31 and stores expanded video data into the video frame storage 33 ( step a 6 ). at this time , the video decoder 32 extracts a video time stamp from the video data and notifies it to the video time stamp detecting section 51 ( step a 7 ). in response to the video stamp notification , the av synchronous control section 5 starts an av synchronous process . the video display control section 34 displays the expanded video data on the video display device 4 ( step a 8 ). execution of steps a 1 to a 8 is repeated until all the video data have been processed ( step a 9 ). now , referring also to fig3 an operation of the audio processing section 6 will be described . the audio separating section 23 separates compressed audio data from the foregoing compressed data read out from the file device 1 and stores the compressed audio data into the compressed audio storage 61 ( step b 1 ). at this time , if it is immediately after the start of the reproduction , the audio separating section 23 retrieves a first audio time stamp and feeds it to the time stamp comparing section 53 . the audio decoder 62 expands the compressed audio data stored in the compressed audio storage 61 and stores expanded audio data into the audio storage 63 ( step b 2 ). the audio reproduction control section 64 controls the audio reproducing device 7 to carry out audio reproduction based on the audio data stored in the audio storage 63 ( step b 3 ). execution of steps b 1 to b 3 is repeated until all the audio data have been processed ( step b 4 ). now , referring also to fig4 an operation of the av synchronous control section 5 will be described . the video time stamp detecting section 51 obtains a video time stamp of video data being processed from the video decoder 32 ( step c 1 ). the audio time stamp deriving section 52 obtains from the audio reproduction control section 64 an amount of audio data processed up to then for audio reproduction ( step c 2 ) and converts it into an audio time stamp equivalent value ( step c 3 ). the audio time stamp equivalent value can be derived by the following conversion equation : wherein atsev represents an audio time stamp equivalent value , pada an audio data amount processed up to then for reproduction from the start of the reproduction , sf a sampling frequency , qb the number of quantization bits , and c the number of channels . the sampling frequency , the number of quantization bits and the number of channels are obtained from a format of audio reproduced at the audio reproducing device 7 . for example , assuming that , with respect to the audio data , the sampling frequency is 48 khz , the number of quantization bits is 16 , the number of channels is 2 , the unit of the data amount is byte , and the unit of a time stamp is 90 khz ( in case that a video compression technique is mpeg ), the conversion equation is given by : then , the time stamp comparing section 53 checks whether it is the first synchronous control from the start of the reproduction ( step c 4 ). if positive , the audio time stamp deriving section 52 derives a correction value a ( step c 6 ). the correction value a is given by : the correction value a is necessary when audio data is not processed for reproduction from the beginning , or when reference times of video data and audio data differ from each other . on the other hand , if negative at step c 4 , i . e . if it is not the first synchronous control from the start of the reproduction , the time stamp comparing section 53 compares a last video time stamp and a current video time stamp ( step c 5 ). if the last video time stamp is greater than the current video time stamp , the audio time stamp deriving section 52 derives a correction value b ( step c 7 ). the correction value b is given by : the correction value b is necessary for achieving av synchronization when processing data whose time stamp does not simply increase . the time stamp comparing section 53 stores the current video time stamp ( step c 8 ). this stored value is used as a last video time stamp in the next execution of step c 5 . the time stamp comparing section 53 corrects the audio time stamp equivalent value using the correction values a and b ( step c 9 ) to derive a corrected audio time stamp equivalent value . the corrected audio time stamp equivalent value is given by : then , the time stamp comparing section 53 compares the corrected audio time stamp equivalent value and the video time stamp with each other ( step c 10 ). if the video time stamp and the corrected audio time stamp equivalent value are equal to each other , nothing is done because synchronization is realized between the video and audio data . for preventing the synchronization process from being frequently carried out , it is arranged that the comparison process at step c 10 is executed with a certain time interval , for example , with a time interval corresponding to a reproducing time of several video frames . if the video time stamp is smaller than the corrected audio time stamp equivalent value , it means that the process of video data is delayed so that the video skip control section 54 commands the video decoder 32 and the video display control section 34 to skip the expanding process and the display updating process of the video data corresponding to a time delay in the process of video data ( step c 11 ). on the other hand , if the video time stamp is greater than the corrected audio time stamp equivalent value , it means that the process of video data is advanced so that the video repeat control section 55 commands the video decoder 32 and the video display control section 34 to temporarily stop the expanding process and the display updating process of the video data corresponding to an advanced time ( step c 12 ). according to the audio / video synchronous reproducer shown in fig1 the audio processing system and the video processing system can realize the exact av synchronization on the fully independent data . this is achieved by provision of the audio time stamp deriving section 52 which converts a processed audio data amount into a value equivalent to a time stamp in the video processing system . further , even if intervals between the time stamps are not constant or the time stamp does not simply increase , the reproduction can be carried out continuously without intermission . this is achieved by provision of the time stamp comparing section 53 . referring now to fig5 an audio / video synchronous reproducer according to the second preferred embodiment of the present invention will be described . in fig5 those components corresponding to the components in fig1 are assigned the same reference signs so as to omit explanation thereof . in the audio / video synchronous reproducer shown in fig5 the audio processing section 6 further includes an audio reproduction termination notifying section 65 as compared with the audio / video synchronous reproducer shown in fig1 . referring also to fig6 an operation of the audio processing section 6 will be described . first , the audio reproduction control section 64 derives an audio data reproducing size to be processed in one reproducing process ( equivalent to a data amount corresponding to a reproducing time of one video frame ) based on an audio reproducing format and a video frame rate , using the following equation ( step d 1 ): wherein adrs represents an audio data reproducing size , sf a sampling frequency , qb the number of quantization bits , c the number of channels , and fr a video frame rate . for example , assuming that , with respect to the audio data , the sampling frequency is 48 khz , the number of quantization bits is 16 , the number of channels is 2 , the unit of the data amount is byte , and the video frame rate is 30 frame / sec , the audio data reproducing size is given by : the audio reproduction control section 64 secures a plurality of audio buffers on the audio storage 63 , each having the size thus derived and set as one block ( step d 2 ). the audio decoder 62 expands the compressed audio data corresponding to a data amount to occupy all the secured audio buffers , and thus stores them in the audio storage 63 ( step d 3 ). the audio reproduction control section 64 sends the expanded audio data per block to the audio reproducing device 7 to start audio reproduction ( step d 4 ). the audio reproduction control section 64 waits for termination of the audio reproduction of one block ( step d 5 ). the audio reproduction termination notifying section 65 notifies the audio time stamp deriving section 52 of the termination of audio reproduction of one block , i . e . corresponding to one video frame ( step d 6 ). the audio reproduction control section 64 further judges whether all the audio data have been processed ( step d 7 ). if negative at step d 7 , the audio separating section 23 separates compressed audio data from compressed data read out from the file device 1 , and stores the compressed audio data into the compressed audio storage 61 ( step d 8 ). the audio decoder 62 expands the compressed audio data stored in the compressed audio storage 61 corresponding to one block and stores expanded audio data into the audio storage 63 ( step d 9 ). the audio reproduction control section 64 controls the audio reproducing device 7 to carry out audio reproduction based on the audio data stored in the audio storage 63 ( step d 10 ). execution of steps d 5 to d 10 is repeated until all the audio data have been processed ( step d 7 ). now , referring also to fig7 an operation of the av synchronous control section 5 will be described . the av synchronous control section 5 starts processing in response to the notification of the termination of audio reproduction of one block received from the audio reproduction termination notifying section 65 . the audio time stamp deriving section 52 obtains from the audio reproduction control section 64 an amount of audio data processed up to then for reproduction ( step e 1 ), and converts it into an audio time stamp equivalent value ( step e 2 ). the audio time stamp equivalent value is given by the foregoing equations ( 1 ) and ( 2 ). the audio time stamp equivalent value thus derived always becomes integer times a producing time of one video frame . therefore , it is possible to carry out the exact av synchronous process based on the audio reproducing time . the video time stamp detecting section 51 obtains from the video decoder 32 a video time stamp of video data being processed ( step e 3 ). operations at the following steps c 4 to c 12 are the same as those in the foregoing first preferred embodiment , so that explanation thereof is omitted . similarly , since an operation of the video processing section 3 is the same as that in the foregoing first preferred embodiment , explanation thereof is omitted . in the audio / video synchronous reproducer according to the second preferred embodiment , as compared with that in the foregoing first preferred embodiment , the exact av synchronization can be achieved even when the audio data amount processed for reproduction up to a given time can not be obtained or can be obtained but with poor accuracy . this is realized by provision of the audio reproduction termination notifying section which makes it possible to obtain an exact reference time being integer times a producing time of one video frame . according to the foregoing first and second preferred embodiments , since the processed audio data amount is converted into a value equivalent to a time stamp in the video processing system , the av synchronization can be achieved even with such data having different reference times for audio and video data .