BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an audio/video synchronous playback device for decoding digital stream data for the purpose of listening to and watching the decoded audio and video, which is suitable when one channel of audio data and N channels (N is an integer of two or more) of video data having different frame frequencies are simultaneously output. 
         [0003]    2. Description of the Related Art 
         [0004]    In a conventional audio/video synchronous playback device, audio data and video data are synchronized with each other as follows. Video time information extracted by a time information extraction section is compared with reference time information generated by a timer. A synchronization section performs time-axis compression/expansion with respect to a sequence of video data so that the video data sequence is synchronized with reference time. On the other hand, audio time information extracted by the time information extraction section is compared with the reference time information generated by the timer. The synchronization section performs time-axis compression/expansion with respect to a sequence of audio data so that the audio data sequence is synchronized with the reference time. As a result, audio data and video data are synchronized with each other (see Japanese Unexamined Patent Application Publication No. 2000-32397). 
       SUMMARY OF THE INVENTION 
       [0005]    In the above-described conventional configuration, when a plurality of pieces of video data having different frame frequencies are simultaneously output based on video data obtained by decoding, synchronization can be performed only in units of a video frame interval of a single frame frequency. 
         [0006]    The present invention is provided to solve the above-described conventional problem. An object of the present invention is to provide an audio/video synchronous playback device capable of performing synchronization with respect to each piece of video data having its own frame frequency when a plurality of pieces of video data having different frame frequencies are simultaneously output. 
         [0007]    To solve the above-described conventional problem, an audio/video synchronous playback device according to an aspect of the present invention includes a first decoding section for decoding a video stream to output a first video data sequence including a plurality of video frames having a first frame interval, a first time information extraction section for extracting video time information from the video stream, a video cycle interpolation section for performing an interpolation process with respect to the first video data sequence output from the first decoding section to output a second video data sequence including a plurality of video frames or video fields having a second frame or field interval, a second decoding section for decoding an audio stream to output an audio data sequence including a plurality of audio blocks, a second time information extraction section for extracting audio time information from the audio stream, a timer section for generating reference time information, a first synchronization section for comparing the video time information with the audio time information and the reference time information, and depending on a result of the comparison, repeating or skipping the first video data sequence in units of the video frame interval, thereby synchronizing the first video data sequence with the audio data sequence, and a second synchronization section for comparing the video time information with the audio time information and the reference time information, and depending on a result of the comparison, repeating or skipping the second video data sequence in units of the video frame or video field interval, thereby synchronizing the second video data sequence with the audio data sequence. 
         [0008]    With this configuration, a first video data sequence output and a second video data sequence output having different frame frequencies can be separately synchronized with one channel of audio data sequence output with their respective precisions. 
         [0009]    According to the audio/video synchronous playback device of the present invention, optimal synchronization can be achieved, depending on the frame frequencies of pieces of video data that are simultaneously output. Thereby, video outputs having any frame frequencies that are simultaneously output can be synchronized with an audio output, so that the audio output and the video outputs can be listened to and watched without feeling of unnaturalness. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a block diagram showing an audio/video synchronous playback device according to Embodiment 1 of the present invention. 
           [0011]      FIG. 2  is a diagram for describing an operation of a video cycle interpolation section of  FIG. 1 . 
           [0012]      FIG. 3  is a block diagram showing an audio/video synchronous playback device according to Embodiment 2 of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
         [0014]      FIG. 1  shows an audio/video synchronous playback device according to Embodiment 1 of the present invention. The audio/video synchronous playback device of Embodiment 1 comprises a first input section  101  for performing an input process with respect to a video stream, a second input section  102  for performing an input process with respect to an audio stream, a first decoding section  103  for decoding and converting a video stream into video data, a first time information extraction section  104  for extracting video time information from a video stream, a timer section  105  for generating reference time information, a second time information extraction section  106  for extracting audio time information from an audio stream, a second decoding section  107  for decoding and converting an audio stream into audio data, a first synchronization section  108  for performing time-axis compression/expansion with respect to video data output from the first decoding section  103  according to the video time information and the audio time information output from the first and second time information extraction sections  104  and  106  for the purpose of synchronization, a video cycle interpolation section  109  for performing an interpolation process so as to convert the video data output from the first decoding section  103  into a frame frequency, a second synchronization section  110  for performing time-axis compression/expansion with respect to cycle-interpolated video data output from the video cycle interpolation section  109  according to the video time information and the audio time information output from the first and second time information extraction sections  104  and  106  for the purpose of synchronization, a first video signal output section  111  for converting a synchronized digital video signal output from the first synchronization section  108  into an analog signal and outputting the analog signal, a second video signal output section  112  for converting a synchronized digital video signal output from the second synchronization section  110  into an analog signal and outputting the analog signal, an audio signal output section  113  for converting a digital audio signal output from the second decoding section  107  into an analog signal and outputting the analog signal, a first video output terminal  121  for outputting the analog signal of the first video signal output section  111 , a second video output terminal  122  for outputting the analog signal of the second video signal output section  112 , and an audio output terminal  123  for outputting the analog signal of the audio signal output section  113 . 
         [0015]    Hereinafter, an operation of the thus-configured audio/video synchronous playback device will be described. Initially, digitally compressed video and audio streams stored in a packaged medium, such as a BD-ROM disc or the like, are input to the first and second input sections  101  and  102 , respectively. The first and second input sections  101  and  102  perform an input process with respect to the respective streams. In the input process, for example, a structure of the stream is analyzed so that the stream is separated into truly compressed data and added data. The first decoding section  103  decodes and converts a video stream output from the first input section  101  into video data. On the other hand, the first time information extraction section  104  extracts time information about the video data. Similarly, the second decoding section  107  decodes and converts an audio stream output from the second input section  102  into audio data. On the other hand, the second time information extraction section  106  extracts time information about the audio data, and outputs the extracted audio time information to the first and second synchronization sections  108  and  110 . The audio data output from the second decoding section  107  is output through the audio signal output section  113 . 
         [0016]    The video data output from the first decoding section  103  is input to the first synchronization section  108  and the video cycle interpolation section  109 . The first synchronization section  108  compares the video time information input from the first time information extraction section  104  with the audio time information input from the second time information extraction section  106  and the reference time information input from the timer section  105 . When a difference between the video time information and the audio time information is larger than a frame cycle of the video data output from the first decoding section  103 , the first synchronization section  108  repeats or skips the video data input from the first decoding section  103  in units of a frame so that the video data is synchronized with the audio time information (synchronization). The resultant video data is output through the first video signal output section  111 . 
         [0017]    The video cycle interpolation section  109  performs an interpolation process with respect to a plurality of frames of video data output from the first decoding section  103  to generate video data including video frames or video fields having a cycle shorter than the original frame cycle, and outputs the resultant video data to the second synchronization section  110 . 
         [0018]    The process of the video cycle interpolation section  109  will be described with reference to  FIG. 2 . In  FIG. 2 , open circles represent video frames output from the first decoding section  103 , and closed circles represent video fields output from the video cycle interpolation section  109 . A video output from the first decoding section  103  is, for example, a video output having a frame frequency of 24 Hz. On the other hand, a video output from the video cycle interpolation section  109  is, for example, a video output having a field frequency of 59.94 Hz. In  FIG. 2 , it is assumed that video data corresponding to two frames (two open circles) is used to generate video data corresponding to one field (one closed circle), i.e., the interpolation process is performed using two frames of data of 24 Hz to generate one field of video data of 59.94 Hz. As a result, the output of the video cycle interpolation section  109  is a video data sequence having a lower frame frequency. 
         [0019]    The second synchronization section  110  compares the video time information input from the first information extraction section  104  with the audio time information input from the second time information extraction section  106  and the reference time information input from the timer section  105 . If a difference between the video time information and the audio time information is larger than the field cycle of the video data output from the video cycle interpolation section  109 , the second synchronization section  110  repeats or skips the video data input from the video cycle interpolation section  109  in units of a field so as to synchronize the video data with the audio time information (synchronization). The resultant video data is output through the second video signal output section  112 . 
         [0020]    With the above-described configuration, a video signal output from the first video signal output section  111  can be synchronized with an audio signal in units of 24 Hz, while a video signal output from the second video signal output section  112  can be synchronized with an audio signal in units of 59.94 Hz. Thereby, an output video signal having a low frame frequency can be synchronized with high precision, so that audio and videos can be output with less occurrence of feeling of discomfort, such as lip sync error or the like. 
         [0021]    Although it has been described in Embodiment 1 of the present invention that two channels of video outputs having different frequencies of 24 Hz and 59.94 Hz are simultaneously output, two or more channels of video outputs having any different frequencies may be used. 
         [0022]      FIG. 3  shows an audio/video synchronous playback device according to Embodiment 2 of the present invention. The audio/video synchronous playback device of Embodiment 2 is different from the audio/video synchronous playback device of Embodiment 1 (see  FIG. 1 ) in that the audio/video synchronous playback device of Embodiment 2 includes an HDMI conversion section  114  for converting synchronized video data output from the first synchronization section  108  and audio data output from the second decoding section  107  into an HDMI (High-Definition Multimedia Interface) signal, and an HDMI output terminal  131  for outputting the HDMI signal. 
         [0023]    An operation relating to conversion of audio data and video data of the audio/video synchronous playback device of  FIG. 3  will be described, and the other operations are the same as those described in Embodiment 1 and will not be described. 
         [0024]    With the configuration of  FIG. 3 , the HDMI conversion section  114  converts video data having a frame frequency of 24 Hz that has been synchronized by the first synchronization section  108  and audio data that has been obtained by the second decoding section  107  into an HDMI signal and outputs the HDMI signal to a TV monitor or the like. On the other hand, the video signal output section  112  converts video data of 59.94 Hz that has been synchronized by the second synchronization section  110  from a digital signal into an analog signal, and outputs the analog signal to a TV monitor or the like. The audio signal output section  113  converts audio data output from the second decoding section  107  from a digital signal into an analog signal, and outputs the analog signal to a TV monitor or the like. 
         [0025]    With the above-described configuration, audio data and video data output from the HDMI conversion section  114  can be synchronized with each other in units of 24 Hz, while a video signal output from the video signal output section  112  can be synchronized with an audio signal in units of 59.94 Hz. Thereby, a video data output having a low frame frequency can be synchronized with high precision, so that audio and videos can be output with less occurrence of feeling of discomfort, such as lip sync error or the like. 
         [0026]    Note that a video output having the same frame frequency as that of NTSC (National Television Standards Committee) signals may be obtained through the video output terminal  122 . Also, a video output having the same frame frequency as that of PAL (Phase Alternation by Line) signals may be obtained through the video output terminal  122   
         [0027]    As described above, the audio/video synchronous playback device of the present invention is applicable to and useful for a DVD player, a BD player or the like in which, for example, 24-Hz video data is output through an HDMI output terminal while video data having a different video cycle of 59.94 Hz is output through an S-video output terminal, a component output terminal, or a composite video output terminal.
An audio/video synchronous playback device includes a first synchronization section for repeating or skipping a first video data sequence in units of a video frame interval thereof to synchronize the first video data sequence with an audio data sequence, and a second synchronization section for repeating or skipping a second video data sequence in units of a video frame or video field interval thereof to synchronize the second video data sequence with the audio data sequence. A first video data sequence output and a second video data sequence output having different frame frequencies are separately synchronized with one channel of audio data sequence output with their respective precisions.