PATENT ABSTRACT
A stream data processing apparatus includes a demultiplexing portion configured to demultiplex multiplexed stream data, to which a PCR is added, into a plurality of pieces of stream data to which a PTS is added, a system time measuring portion configured to measure a system time according to a PCR, a synchronous control portion configured to determine continuity of a reference time according to a PCR and system time information (SYC), to determine continuity of a reproduction time according to a PTS and an STC, and to output synchronous control information according to results of these determinations, a storage portion configured to store stream data, a decoding portion configured to decode stream data stored in the storage portion, an output portion configured to output decoded data, and a decoded data output control portion configured to control a mode of an operation of handling decoded data by the output portion, according to the synchronous control information. The synchronous control information designates output of decoded data, standby to output data, or discarding of data.

PATENT DESCRIPTION
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a stream data processing apparatus and method, which demultiplex multiplexed stream data and decode stream data by an MPEG system. 
     2. Description of the Related Art 
     In a synchronous control operation of an MPEG system, system timer information (i.e., STC (System Time Clock)) obtained by a system timer operating according to reference time information (including PCR (Program Clock Reference)) added to multiplexed stream data is compared with reproduction time information (i.e., PTS (Presentation Time Stamp)) added to each piece of stream data, which is obtained by demultiplexing the multiplexed stream data. A reproducing unit provided with a stream data processing apparatus including the MPEG system operates differently depending upon the magnitude relation between the STC and the PTS. In a case where the STC is less than the PTS, the reproducing unit stands ready to reproduce data obtained by decoding the stream data. In a case where the STC is more than the PTS, the reproducing unit discards the data obtained by decoding the stream data. Also, the reproducing unit reproduces data obtained by decoding the stream data when the value represented by the STC reaches that represented by the PTS. In a case where the difference between the values respectively represented by the STC and the PTS is equal to or more than a threshold value, the reproducing unit determines that audio stream data and video stream data are asynchronously reproduced. Immediately, the reproducing unit reproduces the data obtained by decoding the stream data when the value represented by the STC reaches that represented by the PTS. Also, in a case where an overflow of a stream data buffer is detected, the audio stream data and the video stream data may be asynchronously output (see, for example, Patent Document 1). 
     Patent Document 1: JP-A-2003-101962 
     However, in a case where the continuity of values respectively represented by the PCR or the PTS is broken for some reason in the synchronous control operation, sometimes, the difference between the values respectively represented by the STC and the PTS is large. When the difference therebetween is equal to or more than the threshold value, the reproducing unit determines that the audio stream data and the video stream data are asynchronously reproduced. Consequently, the stream data are decoded and reproduced even at an undesired reproduction time. Thus, in a case where the continuity of the values respectively represented by the PCR or the PTS is broken, a desired synchronous control operation cannot be performed. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a stream data processing apparatus and a stream data processing method, which are enabled to perform a desired synchronous control operation in a case where the continuity of a time represented by the reference time information (PCR) and a time represented by the reproduction time information (PTS) is broken. 
     According to an aspect of the invention, there is provided a stream data processing apparatus, which includes a demultiplexing portion configured to demultiplex multiplexed stream data, to which reference time information is added, into a plurality of pieces of stream data to which reproduction time information is added, a system time measuring portion configured to measure a system time according to the reference time information, a synchronous control portion configured to determine continuity of a reference time according to the reference time information and system time information, to determine continuity of a reproduction time according to the reproduction time information and the system time information, and to output synchronous control information according to results of these determinations, a storage portion configured to store stream data, a decoding portion configured to decode stream data stored in the storage portion, an output portion configured to output decoded data, and a decoded data output control portion configured to control a mode of an operation of handling decoded data to be output by the output portion, according to the synchronous control information. The synchronous control information designates output of the data obtained by decoding the stream data, standby to output the data obtained by decoding the stream data, or discarding of the data obtained by decoding the stream data. 
     An embodiment of this stream data processing apparatus is configured so that in a case where a difference between a reference time represented by the reference time information and a system time represented by the system time information exceeds a predetermined threshold value, the synchronous control portion determines that the continuity of the reference time is broken, and that in a case where a first reproduction time represented by the reproduction time information and a second reproduction time represented by previous reproduction time information exceeds a second threshold value, the synchronous control portion determines that the continuity of the reproduction time is broken. 
     An embodiment of this stream data processing apparatus further comprises a time measuring unit configured to measure a time, and is adapted so that in a case where the synchronous control portion determines that the continuity of the reference time is broken, the synchronous control portion sets a system time represented by the system time information in said time measuring unit, and subsequently sets the reference time represented by the reference time information in said system time measuring portion, and is also adapted so that in a case where the synchronous control portion determines that the continuity of the reproduction time is broken, the synchronous control portion sets a time obtained by adding a difference between the first reproduction time and the second reproduction time to the system time in the time measuring unit. 
     Another embodiment of this stream data processing apparatus is adapted so that the synchronous control portion outputs, in a case where a difference between the first reproduction time and the system time is outside a predetermined range, synchronous control information corresponding to a difference between the first reproduction time and a time measured by the time measuring unit. 
     Another embodiment of the stream data processing apparatus further comprises a memory portion, and is adapted so that in a case where the synchronous control portion determines that the continuity of the reference time is broken, the synchronous control portion sets a difference between a system time represented by the system time information and the reference time represented by the reference time information in the memory portion, and subsequently sets the reference time represented by the reference time information in the system time measuring portion, and is also adapted so that in a case where the synchronous control portion determines that the continuity of the reproduction time is broken, the synchronous control portion sets a difference between the first reproduction time and the second reproduction time in the memory portion. 
     An embodiment of this stream data processing apparatus is adapted so that the synchronous control portion outputs, in a case where a difference between the first reproduction time and the system time is outside a predetermined range, synchronous control information corresponding to a difference between the first reproduction time and a time obtained by adding the difference that is stored by the memory portion. 
     Another embodiment of the stream data processing apparatus further comprises a memory portion, and is adapted so that in a case where the synchronous control portion determines that the continuity of the reference time is broken, the synchronous control portion sets the reference time represented by the reference time information, the system time represented by the system time information, and an amount of change in the system time in the memory portion, and subsequently sets the reference time represented by the reference time information in the system time measuring portion, and is also adapted so that in a case where the synchronous control portion determines that the continuity of the reproduction time is broken, the synchronous control portion causes the memory portion to store the reference time represented by the reference time information, the system time represented by the system time information, the amount of change in the system time, and a difference between the first reproduction time and the second reproduction time. 
     An embodiment of this stream data processing apparatus is adapted so that the synchronous control portion outputs, in a case where a difference between the first reproduction time and the system time is outside a predetermined range, synchronous control information corresponding to a difference between the first reproduction time and a value calculated from information stored in the memory portion. 
     According to another aspect of the invention, there is provided a stream data processing method, which comprises the steps of demultiplexing multiplexed stream data, to which reference time information is added, into a plurality of pieces of stream data to which reproduction time information is added, measuring a system time according to the reference time information, determining continuity of a reference time according to reference time information and system time information, and determining continuity of a reproduction time according to the reproduction time information and the system time information, and outputting synchronous control information according to results of the determinations, and controlling a mode of an operation of handling data, which is obtained by decoding the stream data, according to the synchronous control information. This stream data processing method is adapted so that the synchronous control information designates output of the data obtained by decoding the stream data, standby to output the data obtained by decoding the stream data, or discarding of the data obtained by decoding the stream data. 
     An embodiment of this stream data processing method is adapted so that in a case where a difference between a reference time represented by the reference time information and a system time represented by the system time information exceeds a predetermined threshold value, it is determined that the continuity of the reference time is broken, and that in a case where a first reproduction time represented by the reproduction time information and a second reproduction time represented by previous reproduction time information exceeds a second threshold value, it is determined that the continuity of the reproduction time is broken. 
     An embodiment of this stream data processing method is adapted so that in a case where the synchronous control portion determines that the continuity of the reference time is broken, a system time represented by the system time information is set in the time measuring unit, and subsequently, the reference time represented by the reference time information is set in the system time measuring portion, and is also adapted so that in a case where the synchronous control portion determines that the continuity of the reproduction time is broken, a time obtained by adding a difference between the first reproduction time and the second reproduction time to the system time is set in the time measuring unit. 
     An embodiment of this stream data processing method is adapted so that the synchronous control portion outputs, in a case where a difference between the first reproduction time and the system time is outside a predetermined range, synchronous control information corresponding to a difference between the first reproduction time and a time measured by the time measuring unit. 
     Another embodiment of the stream data processing method is adapted so that in a case where the synchronous control portion determines that the continuity of the reference time is broken, a difference between a system time represented by the system time information and the reference time represented by the reference time information is in the memory portion, and subsequently, the reference time represented by the reference time information is set in a system time measuring portion, and is also adapted so that in a case where the synchronous control portion determines that the continuity of the reproduction time is broken, a difference between the first reproduction time and the second reproduction time is set in the memory portion. 
     An embodiment of this stream data processing method is adapted so that in a case where a difference between the first reproduction time and the system time is outside a predetermined range, synchronous control information corresponding to a difference between the first reproduction time and a time obtained by adding the difference stored by the memory portion to the system is output. 
     Another embodiment of the stream data processing method is adapted so that in a case where it is determined that the continuity of the reference time is broken, the synchronous control portion sets the reference time represented by the reference time information, the system time represented by the system time information, and an amount of change in the system time are stored in a memory portion, and subsequently, the reference time represented by the reference time information is set in a system time measuring portion, and is also adapted so that in a case where it is determined that the continuity of the reproduction time is broken, the reference time represented by the reference time information, the system time represented by the system time information, the amount of change in the system time, and a difference between the first reproduction time and the second reproduction time are stored in the memory portion. 
     An embodiment of this stream data processing method is adapted so that the synchronous control portion outputs, in a case where a difference between the first reproduction time and the system time is outside a predetermined range, synchronous control information corresponding to a difference between the first reproduction time and a value calculated from information stored in the memory portion is output. 
     In accordance with the stream data processing apparatus and the stream data processing method according to the invention, a desired synchronous control operation can be performed even in a case where the continuity of a time represented by the reference time information (PCR) and a time represented by the reproduction time information (PTS) is broken. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating the configuration of a stream data processing apparatus according to a first embodiment of the invention. 
         FIG. 2  is a flowchart illustrating an operation of a synchronous control portion of the first embodiment, which is performed when receiving a PCR from a multiplexing/demultiplexing portion. 
         FIG. 3  is a flowchart illustrating an operation of the synchronous control portion of the first embodiment, which is performed when receiving a PTS from a video control portion or an audio control portion. 
         FIG. 4  is a graph illustrating a state in which the continuity of values respectively represented by the PCR and the PTS. 
         FIG. 5  is a graph illustrating a state in which the continuity of a value represented by the PCR. 
         FIG. 6  is a graph illustrating a state in which the continuity of a value represented by the PTS. 
         FIG. 7  is a block diagram illustrating the configuration of a stream data processing apparatus according to a second embodiment of the invention. 
         FIG. 8  is a flowchart illustrating an operation of a synchronous control portion of the second embodiment, which is performed when receiving a PCR from a multiplexing/demultiplexing portion. 
         FIG. 9  is a flowchart illustrating an operation of the synchronous control portion of the second embodiment, which is performed when receiving a PTS from a video control portion or an audio control portion. 
         FIG. 10  is a block diagram illustrating the configuration of a stream data processing apparatus according to a third embodiment of the invention. 
         FIG. 11  is a flowchart illustrating an operation of a synchronous control portion of the third embodiment, which is performed when receiving a PCR from a multiplexing/demultiplexing portion. 
         FIG. 12  is a flowchart illustrating an operation of the synchronous control portion of the third embodiment, which is performed when receiving a PTS from a video control portion or an audio control portion. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the invention are described with reference to the accompanying drawings. Stream data processing apparatuses according to the following embodiments decode and reproduce each of pieces of stream data obtained by demultiplexing multiplexed stream data including audio stream data and video stream data, which are multiplexed by an MPEG system. Incidentally, reference time information (PCR) is added to the multiplexed stream data. Reproduction time information (PTS) is added to the demultiplexed stream data. The invention can be applied to cases where the kind and the number of stream data used in the embodiments are changed. 
     First Embodiment 
       FIG. 1  is a block diagram illustrating the configuration of a stream data processing apparatus according to a first embodiment of the invention. As shown in  FIG. 1 , the stream data processing apparatus according to the first embodiment includes a multiplexing/demultiplexing portion  101 , a synchronous control portion  103 , a system timer  105 , a counter  107 , a video stream buffer  109 , a video decoding portion  111 , a video output portion  113 , a video control portion  115 , an audio stream buffer  117 , an audio decoding portion  119 , an audio output portion  121 , an audio control portion  123 , and a reproducing portion  125 . 
     The multiplexing/demultiplexing portion  101  demultiplexes multiplexed stream data. Video stream data and audio stream data are obtained by demultiplexing the multiplexed stream data. The multiplexing/demultiplexing portion  101  causes a video stream buffer  109  to store the video stream data. Also, the multiplexing/demultiplexing portion  101  causes an audio stream buffer  117  to store the audio stream data. Further, a PCR added to the multiplexed stream data is sent to the synchronous control portion  103 , while a PTS added to the video stream data is stored in the video stream buffer  109 . The PTS added to the audio stream data is stored in the audio stream buffer  117 . 
     The synchronous control portion  103  sets the PCR sent from the multiplexing/demultiplexing portion  101  in the system timer  105 . Incidentally, in a case where the synchronous control portion  103  detects discontinuity of the value represented by the PCR, the synchronous control portion  103  acquires system time information (STC) from the system timer  105  and sets the STC in the counter  107 . 
     Additionally, the synchronous control portion  103  compares the STC obtained from the system timer  105  with the PTS obtained from the video control portion  115 . Then, the synchronous control portion  103  sends synchronous control information to the video control portion  115 . Similarly, the synchronous control portion  103  compares the STC obtained from the system timer  105  with the PTS obtained from the audio control portion  123 . Then, the synchronous control portion  103  sends synchronous control information to the audio control portion  123 . In a case where the discontinuity of the value represented by the PTS is detected by comparing the STC with the PTS, the synchronous control portion  103  set a value, which is obtained by adding a difference between the value represented by the PTS received this time and the value represented by the PTS received the last time to the STC in the counter  107 . If the difference between the STC and the PTS is equal to or larger than a threshold value, the value represented by the PTS is compared with the value set in the counter  107 . Then, synchronous control information corresponding to a result of the comparison is sent to the video control portion  115  or to the audio control portion  123 . Details of an operation of the synchronous control portion  103  will be described later. 
     The system timer  105  measures a system time according to the PCR sent from the synchronous control portion  103 . The measured system time is output to the synchronous control portion  103  as system time information (STC). The counter  107  measures a time according to the STC sent from the synchronous control portion  103 . 
     The video stream buffer  109  stores video stream data sent from the multiplexing/demultiplexing portion  101 . The video decoding portion  111  reads and decodes video stream data from the video stream buffer  109  under the control of the video control portion  115 . The video decoding portion  111  informs the video control portion  115  of a result of decoding. Incidentally, a result of decoding includes reproduction time information (PTS) added to decoded video stream data. Data decoded by the video decoding portion  111  is sent to the video output portion  113 . Under the control of the video control portion  115 , the video output portion  113  outputs the data sent from the video decoding portion  111  to the reproducing portion  125 , alternatively stands ready to output the data to the reproducing portion  125 , alternatively, discards the data. 
     The video control portion  115  reads information, which indicates a state of storing video stream data, from the video stream buffer  109 . Further, the video control portion  115  instructs the video decoding portion  111  to read video stream data from the video stream buffer  109  and decode the read video stream data according to the information read from the video stream buffer  109 . Also, the video control portion  115  receives a signal representing a result of decoding from the video decoding portion  111 , and informs the synchronous control portion  103  of a PTS included in the signal representing the result of decoding. Furthermore, the video control portion  115  controls an operation of the video output portion  113  according to the synchronous control information sent from the synchronous control portion  103 . Details of an operation of the video output portion  113  under the control of the video control portion  115  will be described later. 
     The audio stream buffer  117  stores audio stream data sent from the multiplexing/demultiplexing portion  101 . The audio decoding portion  119  reads audio stream data from the audio stream buffer  117  and decodes the read data under the control of the audio control portion  123 . The audio decoding portion  119  informs the audio control portion  123  of a result of decoding. Incidentally, the result of decoding includes reproduction time information (OTS) added to the decoded audio stream data. The data decoded by the audio decoding portion  119  is sent to the audio output portion  121 . Under the control of the audio control portion  123 , the audio output portion  121  outputs the data sent from the audio decoding portion  119  to the reproducing portion  125 , alternatively, stands ready to output the data to the reproducing portion  125 , alternatively, discards the data. 
     The audio control portion  123  reads information, which indicates a state of storing audio stream data, from the audio stream buffer  117 . Further, the audio control portion  123  instructs the audio decoding portion  119  to read video stream data from the audio stream buffer  117  and decode the read video stream data according to the information read from the audio stream buffer  117 . Also, the audio control portion  123  receives a signal representing a result of decoding from the audio decoding portion  119 , and informs the synchronous control portion  103  of a PTS included in the signal representing the result of decoding. Furthermore, the audio control portion  123  controls an operation of the audio output portion  121  according to the synchronous control information sent from the synchronous control portion  103 . Details of an operation of the audio output portion  121  under the control of the audio control portion  123  will be described later. 
     The reproducing portion  125  reproduces video data sent from the video output portion  113  and audio data sent from the audio output portion  121 . 
     Hereinafter, an operation of the synchronous control portion  103  of the first embodiment is described in detail with reference to  FIGS. 2 and 3 .  FIG. 2  is a flowchart illustrating an operation of the synchronous control portion  103  of the first embodiment at the time of receiving a PCR from the multiplexing/demultiplexing portion  101 . As shown in  FIG. 2 , the synchronous control portion  103  receives a PCR from the multiplexing/demultiplexing portion  101  in step S 101 . Subsequently, in step S 103 , the synchronous control portion  103  compares this PCR with the STC received from the system timer  105 , and determines whether the following inequality holds: |PCR−STC|&gt;Th 1  where “Th 1 ” is a threshold value that is a positive numerical value. If it is determined in step S 103  that |PCR−STC|&gt;Th 1  (YES), the synchronous control portion  103  determines that the value represented by the PCR is discontinuous. Then, the synchronous control portion  103  acquires an STC and sets this STC in the counter  107  in step S 105 . Upon completion of processing in step S 105 , the synchronous control portion  103  sets the PCR in the system timer  105  in step S 107 . Conversely, if it is determined in step S 103  that |PCR−STC|≦Th 1  (NO), the synchronous control portion  103  proceeds to step S 107  without setting the STC in the counter  107 . 
     Thus, if the synchronous control portion  103  determines that the value represented by the PCR is discontinuous, the STC acquired by the system timer  105  is set in the counter  107 . Accordingly, a time, which is before the continuity of the value represented by the PCR is broken, along a time base can be measured. 
       FIG. 3  is a flowchart illustrating an operation of the synchronous control portion  103  of the first embodiment at the time of receiving a PTS from the video control portion  115  or from the audio control portion  123 . As shown in  FIG. 3 , the synchronous control portion  103  compares a received PCR (PTSc) with a PTS received the last time (PTSp), and determines in step S 201  whether the following inequality holds: |PTSc−PTSp|&gt;Th 2  where “Th 2 ” is a threshold value that is a positive numerical value. If it is determined in step S 201  that |PTSc−PTSp|&gt;Th 2  (YES), the synchronous control portion  103  determines that the value represented by the PTS is discontinuous. Then, in step S 203 , the synchronous control portion  103  sets a value (STCa), which is obtained by adding a value “PTSc−PTSp” to the STC obtained from the system timer  105 , in the counter  107 . Upon completion of processing in step S 203 , the synchronous control portion  103  compares the PTSc with the STC measured by the system timer  105  in step S 205 . Conversely, if it is determined in step S 203  that |PTSc−PTSp|≦Th 2  (NO), the synchronous control portion  103  advances to step S 205  without setting the STCa in the counter  107 . 
     If it is determined in step S 205  that “−Tt 2 &lt;PTSc−STC&lt;−α”, the synchronous control portion  103  sends synchronous control information, which designates the discarding of data, to the video control portion  115  or to the audio control portion  123  in step S 207 . Alternatively, in a case where “0&lt;PTSc−STC&lt;Tt 1  where Tt 1  is a positive value”, the synchronous control portion  103  sends synchronous control information, which designates the standby to output data, to the video control portion  115  or to the audio control portion  123  in step S 209 . Alternatively, in a case where “−α&lt;PTSc−STC&lt;0”, the synchronous control portion  103  sends synchronous control information, which designates output of data, to the video control portion  115  or to the audio control portion  123  in step S 211 . In a case where it is determined in step S 205  that none of these three conditions are met, that is, in a case where “Tt 1 ≦PTSc−STC” or “PTSc−STC≦−Tt 2 ”, the synchronous control portion  103  determines that audio stream data and video stream data are asynchronously reproduced. Then, in step S 213 , the synchronous control portion  103  compares the PTSc with a time (STCc) measured by the counter  107  in step S 213 . 
     In a case where it is determined in step S 213  that “−Tt 2 &lt;PTSc−STC&lt;−α”, the synchronous control portion  103  proceeds to step S 207  in which the synchronous control portion  103  sends synchronous control information designating the discarding of data to the video control portion  115  or to the audio control portion  123 . Alternatively, in a case where “0&lt;PTSc−STC&lt;Tt 1 ”, the synchronous control portion  103  proceeds to step S 209  and sends synchronous control information, which designates the standby to output data, to the video control portion  115  or to the audio control portion  123  in step S 209 . Alternatively, in a case where none of these two conditions are met, that is, in a case where “Tt 1 ≦PTSc−STC” or “PTSc−STC≦−Tt 2 ”, the synchronous control portion  103  proceeds to step S 213  and sends synchronous control information, which designates the output of data, to the video control portion  115  or to the audio control portion  123 . 
     Thus, if the synchronous control portion  103  determines in step S 201  that the value represented by the PTS is discontinuous, the STCa obtained by adding the difference between the PTS received this time (PTSc) and the PTS received the last time to the STC is set in the counter  107 . Thus, a time, which is after the continuity of the value represented by the PTS is broken, along a time base can be measured. Also, even if it is determined by the comparison processing in step S 205  that audio stream data and video stream data are asynchronously reproduced, synchronous control information designating an operation appropriate for situation of data processing performed by the video output portion  113  or the audio output portion  121  can be sent to the video control portion  115  and the audio control portion  123 . 
       FIGS. 4 ,  5 , and  6  are graphs illustrating in a case where the continuity of the value represented by the PCR and/or the value represented by the PTS is broken, the relation among the values respectively represented by the PCR and the PTS and time. In each of the figures, abscissas represent real time, while ordinates denote values respectively represented by the PCR and the PTS. 
     As illustrated in the graph shown in  FIG. 4 , the continuity of the value represented by the PCR is broken at time t 1 . The value represented by the PTS catches up with that represented by the PCR at time t 2 . In a case where the stream data processing apparatus according to the present invention is not used, the difference between the values represented by the PCR and the PTS is large in a time period between time t 1  and time t 2 . Thus, it is determined that audio stream data and video stream data are asynchronously reproduced. However, in the case of using the stream data processing apparatus according to the present embodiment, even if it is determined in step S 103  shown in  FIG. 2  that the value represented by the PCR is discontinuous at time t 1 , the STC is set in the counter  107  in step S 105 . Consequently, the counter  107  starts to measure a time, which is before the continuity of the value represented by the PCR is broken, along a time base. In the time period between time t 1  and time t 2 , it is determined in step S 205  shown in  FIG. 3  that audio stream data and video stream data are asynchronously reproduced. However, in step S 213 , the value represented by the PTS is compared with a time measured by the counter  107 . Thus, it is determined that audio stream data and video stream data are reproduced in synchronization with each other. Additionally, if the value represented by the PTS catches up with that represented by the PCR at time t 2 , it is determined in step S 205  that audio stream data and video stream data are reproduced in synchronization with each other. Thus, according to the present embodiment, even when the continuity of the value represented by the PCR is broken, a desired synchronous control operation is performed. 
     As illustrated in the graph shown in  FIG. 5 , the continuity of the value represented by the PCR is broken at time t 3 . According to the present embodiment, even when it is determined in step S 103  that audio stream data and video stream data are asynchronously reproduced, the counter  107  starts to measure a time, which is before the continuity of the value represented by the PCR is broken, along a time base. Although it is determined in step S 205  that audio stream data and video stream data are asynchronously reproduced at time t 3  or later, it is determined in step S 213  that audio stream data and video stream data are reproduced in synchronization with each other. Thus, according to the present embodiment, even when the continuity of the value represented by the PCR is broken, a desired synchronous control operation is performed. 
     As illustrated in the graph shown in  FIG. 6 , the continuity of the value represented by the PTS is broken at time t 4 . According to the present embodiment, it is determined in step S 201  shown in  FIG. 3  that the value represented by the PTS is discontinuous at time t 4 . In step S 203 , a value (STCa) obtained by adding the difference between the value represented by the PTS received this time and that represented by the PTSp received the last time to the value represented by the STC is set in the counter  107 . Thus, the counter  107  starts to measure a time, which is after the continuity of the value represented by the PTS is broken, along a time base. Although it is determined in step S 205  that audio stream data and video stream data are asynchronously reproduced at time t 4  or later, it is determined in step S 213  that audio stream data and video stream data are reproduced in synchronization with each other. Thus, according to the present embodiment, even when the continuity of the value represented by the PTS is broken, a desired synchronous control operation is performed. 
     As described above, in the stream data processing apparatus according to the present embodiment, even in a case where the continuity of the time represented by the reference time information (PCR) is broken, the counter  107  measures a time, which is before the continuity of the time represented by the reproduction time information is broken, along a time base. Thus, a desired synchronous control operation is performed. 
     Second Embodiment 
       FIG. 7  is a block diagram illustrating the configuration of a stream data processing apparatus according to the second embodiment. The stream data processing apparatus according to the second embodiment differs from the stream data processing apparatus according to the first embodiment in that a difference buffer  201  is provided instead of the counter  107 , in that even in a case where the continuity of the value represented by the PCR is broken, the synchronous control portion  203  causes the difference buffer  201  to store the difference between the values respectively represented by the PCR and the STC, and in that in a case where the continuity of the value represented by the PTS is broken, the synchronous control portion  203  causes the difference buffer  201  to store the difference between the values respectively represented by the PTS received this time and the PTS received the last time. The second embodiment is similar to the first embodiment except for these respects. In  FIG. 7 , composing elements common to the first and second embodiments are designated by same reference numerals. 
     The difference buffer  201  stores the difference between the values respectively represented by the PCR and the STC or the difference between the values respectively represented by the PTS received this time and the PTS received the last value. 
       FIG. 8  is a flowchart illustrating an operation of a synchronous control portion  203  according to the second embodiment at the time of receiving the PCR from the multiplexing/demultiplexing portion  101 . The operation illustrated by the flowchart shown in  FIG. 8  differs from the operation of the first embodiment illustrated by the flowchart shown in  FIG. 2  in that processing in step S 301  is performed instead of processing in step S 105 . In step S 301 , the synchronous control portion  203  acquires an STC from the system timer  105  and causes the difference buffer  201  to store the difference between the values respectively represented by the STC and the PCR. Thus, if the synchronous control portion  203  determines that the value represented by the PCR is discontinuous, the difference between the values represented by the STC and the PCR is referred to. Consequently, a time, which is before the continuity of the value represented by the PCR is broken, along a time base can be measured. 
       FIG. 9  is a flowchart illustrating an operation of the synchronous control portion  203  according to the second embodiment at the time of receiving a PTS from the video control portion  115  or the audio control portion  123 . The operation illustrated by the flowchart shown in  FIG. 9  differs from the operation of the first embodiment illustrated by the flowchart shown in  FIG. 3  in that processing in step S 401  is performed instead of processing in step S 203 , and that processing in step S 401  is performed instead of processing in step S 213 . In step S 401 , the synchronous control portion  203  causes the difference buffer  201  to store the difference (“PTSc−PTSp”) between the value represented by the PTS (PTSc) received this time and the value represented by the PTS (PTSp) received the last time. Also, in step S 403 , the synchronous control portion  203  compares the value represented by the PTSc with a value obtained by adding a value stored in the difference buffer to the value represented by the STCc. Thus, when the synchronous control portion  203  determines in step S 201  that the value represented by the PTS is discontinuous, the difference between the value represented by the PTS (PTSc) received this time and the value represented by the PTS (PTSP) received the last time is referred to. Consequently, a time, which is after the continuity of the value represented by the PTS is broken, along a time base can be measured. 
     Third Embodiment 
       FIG. 10  is a block diagram illustrating the configuration of a stream data processing apparatus according to a third embodiment of the invention. The stream data processing apparatus according to the third embodiment differs from the stream data processing apparatus according to the first embodiment in that a time information buffer  301  is provided instead of the counter  107 , in that in a case where the continuity of the value represented by the PCR is broken, the synchronous control portion  303  causes the time information buffer  301  to store the value represented by the PCR, the value represented by the STC, an amount of change in the STC, and the difference between the value represented by the PTS received this time and the value represented by the PTS received the last time. The third embodiment is similar to the first embodiment except for these respects. In  FIG. 10 , composing elements common to the first embodiment shown in  FIG. 1  and the third embodiment are designated by same reference numerals. 
     The time information buffer  301  stores the value represented by the PCR, the value represented by the STC, an amount of change in the STC, and the difference between the value represented by the PTS received this time and the value represented by the PTS received the last time. 
       FIG. 11  is a flowchart illustrating an operation of the synchronous control portion  303  according to the third embodiment at the time of receiving a PCR from the multiplexing/demultiplexing portion  101 . The operation illustrated in  FIG. 11  differs from the operation of the first embodiment illustrated in  FIG. 2  in that processing in step S 501  is performed instead of processing in step S 105 . In step S 501 , the synchronous control portion  303  causes the time information buffer  301  to store the value represented by the PCR, the value represented by the STC acquired from the system timer  105 , an amount of change in the value represented by the STC per predetermined time. Thus, if the synchronous control portion  303  determines in step S 103  that the value represented by the PCR is discontinuous, a time, which is before the continuity of the value represented by the PCR is broken, along a time base can be measured. 
       FIG. 12  is a flowchart illustrating an operation of the synchronous control portion  303  according to the third embodiment at the time of receiving a PTS from the video control portion  115  or the audio control portion  123 . The operation illustrated in the flowchart shown in  FIG. 12  differs from the operation of the first embodiment illustrated in the flowchart shown in  FIG. 3  in that processing in step S 603  is performed instead of processing in step S 203 , and in that processing in step S 603  is performed instead of processing in step S 213 . In step S 601 , the synchronous control portion  303  causes the time information buffer  301  to store the value represented by the PCR, the value represented by the STC, an amount of change in the STC per predetermined time, and the difference (“PTSc−PTSp”) between the value represented by the PTS (PTSc) received this time and the value represented by the PTS (PTSp) received the last time. Also, in step S 603 , the synchronous control portion  303  compares a value represented by the PTSc with a value calculated from information stored in the time information buffer  301 . Thus, if the synchronous control portion  303  determines in step S 201  that the value represented by the PTS is discontinuous, a time, which is after the continuity of the value represented by the PTS is broken, along a time base can be measured. 
     The stream data processing apparatus and the stream data processing method according to the invention can be applied to a use of performing a desired synchronous control operation even in a case where the continuity of values respectively represented by the reference time information (PCR) and the reproduction time information (PTS) is broken when decoding and outputting data obtained by demultiplexing multiplexed stream data by the MPEG system.