Abstract:
Formerly, it was difficult to exercise proper control for recording and outputting a plurality of contiguous data. To solve this problem, for example, a plurality of contiguous data are acquired from a stream in which the reference information for reproducing at an acquisition end a clock synchronized with a system clock prevailing at the time of generation is multiplexed. A plurality of timestamped data are then read from recording means. Timestamp information is removed from the read timestamped information. The resulting data without the timestamp information is handled as the read data and output with the timing dependent on the timestamp information. The timestamp information generation operation performed for a write and the output operation performed for a read with the timing dependent on the timestamp information are synchronized with an adjusted clock.

Description:
CLAIM OF PRIORITY  
       [0001]     The present application claims priority from Japanese application serial No. P2005-168978, filed on Jun. 9, 2005, the content of which is hereby incorporated by reference into this application.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a technology for recording and outputting a digital broadcast.  
         [0003]     For digital broadcasts in Japan, video data and other broadcast data encoded in compliance with the MPEG2 (Moving Picture Experts Group Phase 2) standard are multiplexed in compliance with the MPEG2-TS (Moving Picture Experts Group Phase 2—Transport Stream) standard. There is a known recorder/player for recording and playing an MPEG2-TS in whole or in part (Japanese Patent Laid-open No. 2001-110140). Further, there is a known receiver that incorporates a plurality of digital tuners to cover the increased use of digital broadcasts (Japanese Patent Laid-open No. 2001-197384).  
         [0004]     Furthermore, disclosed is a technology for extracting an arbitrary stream from multiplex data by inserting a special packet (timestamp packet) for storing a PCR (Program Clock Reference) value with a view toward playing a stream without regard to its bit rate (Japanese Patent Laid-open No. 2001-171490). Another disclosed technology records data by adding time information (timestamp) that is phase-synchronized with a digital compressed signal, and restores a packet signal time interval in accordance with the timestamp (Japanese Patent Laid-open No. 8-336131).  
       SUMMARY OF THE INVENTION  
       [0005]     An MPEG2-TS is a series of multiplexed transport packets that contain, for instance, the video data about a plurality of broadcast programs. Within the MPEG2-TS, the transport packets concerning arbitrary broadcast programs are continuously multiplexed with intervals provided. One or a plurality of transport. packets for different broadcast programs exist in the intervals. Therefore, when a specific broadcast program is to be extracted from the MPEG2-TS, recorded onto a hard disc or other recording medium, and output, it is important that the transport packet intervals prevailing before recording be reproduced at the time of output.  
         [0006]     In the conventional recorder/player disclosed by Japanese Patent Laid-open No. 2001-110140, a PCR (Program Clock Reference), which is multiplexed in an MPEG2-TS, is used as the reception arrival time for each predetermined transport packet, which constitutes the received MPEG2-TS, at the time of recording into a recording/output apparatus. In addition, a timestamp is generated and added for recording purposes by a time counter that operates in accordance with a clock generated by a clock generator. This clock is without a PLL and independent of a 27 MHz system clock that is reproduced by a PLL (Phase Lock Loop) technology. On the other hand, when the recording/output apparatus performs a playback operation, the recorded transport packet is output after comparing the time counter, which operates in accordance with the above-mentioned independent clock, with the timestamp, which is added to the transport packet as the reception arrival time. The playback operation is then performed so that the recorded transport packet intervals agree with the reception timing. However, the conventional recorder/player uses, for instance, a 27-MHz crystal oscillator for the clock to be used with the time counter. The frequency stability of a generally used crystal oscillator is often lower than 27-MHz±30 ppm. When the time counter operates in accordance with a crystal oscillator having such accuracy, the transport packet intervals recorded and played by the recording/output apparatus differ from those received. When, for instance, a multiplexed PCR is used for an output MPEG2-TS of the recording/output apparatus, the worst-case accuracy of the 27 MHz system clock played by the PLL (Phase Lock Loop) technology is 27 MHz±60 ppm.  
         [0007]     The above accuracy is lower than 27 MHz±30 ppm, which is the required system clock accuracy for a situation where an MPEG2-TS, which is defined by the MPEG standard, is recorded, output, or played.  
         [0008]     When a video/audio decoder uses the above playback system clock to perform a decoding process, an STD buffer, which is positioned before the decoder, overflows or underflows, thereby causing an imaging problem. More specifically, the image output by the decoder suffers from block noise or freezes. Even when the STD buffer does not overflow or underflow, normal color reproduction (display) does not result if the system clock deviation is not within a permissible range for the image color frequency.  
         [0009]     The apparatus disclosed by Japanese Patent Laid-open No. 2001-197384 is a digital broadcast receiver that incorporates a plurality of digital tuners and allows the digital tuners to receive different broadcast programs (different pieces of content). It is assumed that, for instance, the plurality of incorporated digital tuners are used to receive different broadcast programs (different pieces of content), and the recording/output apparatus disclosed by Japanese Patent Laid-open No. 2001-110140 is used to simultaneously record the MPEG2-TS for each broadcast program. With such an assumption, a crystal oscillator and time counter for generating an independent clock for simultaneous recording are required. In this case, too, however, the above-mentioned problem exists.  
         [0010]     A technology for extracting a stream in consideration of a timestamp is disclosed by Japanese Patent Laid-open No. 2001-171490. However, Japanese Patent Laid-open No. 2001-171490 does not state a specific method for timestamp creation or explain what timestamp should be created in what manner.  
         [0011]     A technology for restoring a packet signal time interval by using a timestamp that is phase-synchronized with a digital compressed signal is disclosed by Japanese Patent Laid-open No. 8-336131. However, it does not thoroughly describe a specific method for timestamp creation.  
         [0012]     The present invention has been made in view of the above circumstances. It is an object of the present invention to provide a recording/output apparatus and recording/output method for properly outputting recorded data.  
         [0013]     To accomplish the above object, the recording/output apparatus for recording and playing an MPEG2-TS is configured so that the recorded and output transport packet intervals agree with the reception timing. Further, the recording/output apparatus for simultaneously (not necessarily in the strict sense of the word) recording and playing a plurality of MPEG2-TSs is configured so that the recorded and played transport packet intervals agree with the reception timing.  
         [0014]     In other words, the recording/output apparatus should be configured as defined, for instance, in claim  1 .  
         [0015]     The present invention makes it possible to provide a recording/output apparatus and recording/output method for exercising control to ensure that recording and output operations are properly performed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a block diagram illustrating the configuration of a digital broadcast receiver that incorporates a recording/output apparatus according to one embodiment of the present invention.  
         [0017]      FIG. 2  is a block diagram illustrating the detailed configuration of a clock reproduction section.  
         [0018]      FIG. 3  is a block diagram illustrating the detailed configuration of a timestamp addition section.  
         [0019]      FIG. 4  is a block diagram illustrating the detailed configuration of a timestamp comparison/output section.  
         [0020]      FIG. 5  illustrates the structure of data that is handled in the digital broadcast receiver. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. Like reference numerals and symbols denote like elements.  
         [0022]      FIG. 1  illustrates a digital broadcast receiver that incorporates a recording/output apparatus according to an embodiment of the present invention. As indicated in  FIG. 1 , the digital broadcast receiver includes tuner decoding sections  101 ,  102 , selectors  103 ,  104 , separation/extraction sections (e.g., demultiplexers)  105 ,  106 , a clock reproduction section  107 , decoding sections (e.g., MPEG decoders)  108 ,  109 , a timestamp addition section  110 , a write section  111 , a recording medium (e.g., hard disc, memory, optical disc, or magnetooptical disc)  112 , a read section  113 , a timestamp comparison/output section  114 , an IEEE 1394 interface section  115 , a control section (e.g., CPU (Central Processing Unit))  116 , and a user interface section (including, for instance, a keyboard, mouse, remote controller, or other input device; a video output or display device based on a CRT (Cathode Ray Tube), LCD (Liquid Crystal Display), or PDP (Plasma Display Panel); and an audio output device including a speaker)  117 .  
         [0023]     Tuner decoding section  101  receives a digital broadcast signal from a digital broadcast source provided by a broadcast station not shown via a satellite, terrestrial, cable, or other broadcast transmission network. This tuner decoding section  101  performs a tuning process and a wave detection process on a physical or virtual channel frequency that is specified via a remote controller or other user operating control on the user interface section  117  and the control section  116 . Then, the tuner decoding section  101  outputs to selector  103  an MPEG2-TS (that is, a digital broadcast signal) that has been subjected to digital demodulation and error correction.  
         [0024]     Selector  103  performs a 3-input 1-output selection process under the control of the control section  116 , and delivers the resulting output to separation/extraction section  105 . Separation/extraction section  105  separates/extracts from an entered MPEG2-TS a transport packet of a channel (broadcast program) that is specified via a remote controller or other user operating control on the user interface section  117  and the control section  116 , and outputs the separated/extracted transport packet to the timestamp addition section  110 . This separation/extraction section  105  separates/extracts a video/audio PES (Packetized Elementary Stream) or ES (Elementary Stream) from a transport packet of a channel (broadcast program) that is specified via a remote controller or other user operating control on the user interface section  117  and the control section  116 , and outputs the separated/extracted video/audio PES or ES to decoding section  108 . Then the separation/extraction section  105  extracts a PCR (Program Clock Reference) from a transport packet of a channel (broadcast program) that is specified via a remote controller or other user operating control on the user interface section  117  and the control section  116 , and outputs the extracted PCR to the clock reproduction section  107 . Decoding section  108  receives the PES or ES of video and/or audio from separation/extraction section  105 , compares the DTS (Decoding Time Stamp) or PTS (Presentation Time Stamp) of the PES or ES with an STC count value fed from the clock reproduction section  107 , which will be described later, adjusts the decoding/display timing to achieve decoding, and outputs the decoded video and/or audio to the user interface section  117 .  
         [0025]     Tuner decoding section  102  receives a digital broadcast signal from a digital broadcast source, which is provided by a broadcast station not shown, via a satellite, terrestrial, cable, or other broadcast transmission network. This tuner decoding section  102  performs a tuning process and a wave detection process on a physical or virtual channel frequency that is specified via a remote controller or other user operating control on the user interface section  117  and the control section  116 . Then, the tuner decoding section  102  outputs to selector  103  an MPEG2-TS that has been subjected to digital demodulation and error correction. Selector  104  performs a 3-input 1-output selection process under the control of the control section  116 , and delivers the resulting output to separation/extraction section  106 . Separation/extraction section  106  separates/extracts from an entered MPEG2-TS a transport packet of a channel (that is, a broadcast program) that is specified via a remote controller or other user operating control on the user interface section  117  and the control section  116 , and outputs the separated/extracted transport packet to the timestamp addition section  110 . This separation/extraction section  106  separates/extracts a video/audio PES (Packetized Elementary Stream) or ES (Elementary Stream) from a transport packet of a channel (broadcast program) that is specified via a remote controller or other user operating control on the user interface section  117  and the control section  116 , and outputs the separated/extracted video/audio PES or ES to decoding section  109 . Then, the separation/extraction section extracts a PCR (Program Clock Reference) from a transport packet of a channel (broadcast program) that is specified via a remote controller or other user operating control on the user interface section  117  and the control section  116 , and outputs the extracted PCR to the clock reproduction section  107 .  
         [0026]     Decoding section  109  receives the PES or ES of video and/or audio from separation/extraction section  106 , compares the DTS (Decoding Time Stamp) or PTS (Presentation Time Stamp) of the PES or ES with an STC count value fed from the clock reproduction section  107 , which will be described later, adjusts the decoding/display timing to achieve decoding, and outputs the decoded video and/or audio to the user interface section  117 .  
         [0027]     The user interface section  117  displays and/or plays the decoded video and/or audio with an output device (the display device and/or audio output device).  
         [0028]     The clock reproduction section  107  uses the PCR to reproduce a receiver system clock that is synchronized (for frequency/phase matching) with the system clock of a broadcast station&#39;s encoding/multiplexing section, outputs the reproduced system clock to the timestamp addition section  110  and timestamp comparison/output section  114 , and outputs to decoding sections  108  and  109  the STC count value of an STC counter that operates in accordance with the reproduced system clock.  
         [0029]     The timestamp addition section  110  generates a timestamp by using a counter that operates in accordance with the system clock reproduced by the clock reproduction  107 , adds the timestamp to (or embeds the timestamp into) the transport packets separated/extracted by separation/extraction sections  105  and  106 , and outputs the transport packets to the write section  111 .  
         [0030]     The write section  111  performs a process for recording the transport packets, to which the timestamp is added by the timestamp addition section  110 , on the recording medium  112 . As a result, one stream having a plurality of timestamped transport packets, which contain the video data and/or audio data about a certain channel (that is, a certain broadcast program), is stored on the recording medium  112  as a single file or two or more separated data files.  
         [0031]     The timestamp is the time information about a timestamped transport packet. For example, the timestamp represents the time at which a transport packet was input from a separation/extraction section  105 ,  106  to the timestamp addition section  110 , or the time difference from a reference transport packet (e.g., the preceding or leading transport packet). This timestamp differs from a timestamp that is already included in a transport packet, such as a PTS or DTS.  
         [0032]     The read section  113  sequentially reads from the recording medium  14  a plurality of timestamped transport packets contained in a specified stream, and outputs the read transport packets to the timestamp comparison/output section  114 . The timestamp comparison/output section  114  compares the counter value of a counter that operates in accordance with the system clock reproduced by the clock reproduction section  107  with the timestamp of a timestamped transport packet read by the read section  113 . If the compared value and timestamp coincide with each other, the timestamp comparison/output section  114  deletes (removes) the timestamp from the timestamped transport packet and outputs the transport packet to the selectors  103 ,  104  and the IEEE 1394 interface section  115 .  
         [0033]     A D-VHS video deck (not shown) is connected to the IEEE 1394 interface section  115  via an IEEE 1394 (e.g., i.Link (registered trademark)) cable. The IEEE 1394 interface section  115  receives transport packets from which timestamps were deleted by the timestamp comparison/output section  114 , and outputs the transport packets to the D-VHS video deck (not shown) via the IEEE 1394 cable (not shown). Further, the IEEE 1394 interface section  115  receives transport packets that are input from the D-VHS video deck (not shown) via the IEEE 1394 cable (not shown), and outputs the transport packets to the selectors  103 ,  104 . Alternatively, a separate communication interface section may be furnished in addition to or in place of the IEEE 1394 interface section  115  for the purpose of transferring data to an external storage medium (e.g., D-VHS videotape or other magnetic tape) in compliance with another communication interface such as a LAN or wireless LAN interface.  
         [0034]     The control section  116  is connected to various sections of the digital broadcast receiver via a bus section (not shown). The control section  116  controls the operation of the entire digital broadcast receiver, and performs various processes by receiving various instruction signals from the user via the remote controller or other control on the user interface section  117  and controlling various sections connected via the bus section (not shown) in compliance with the instruction signals.  
         [0035]     A typical process involving the MPEG2-TS format has been described above. However, an operation can also be performed when the MPEG2-PS (Moving Picture Experts Group Phase 2—Program Stream) format is used. When the MPEG2-PS format is used, the clock reproduction section  107  reproduces the receiver system clock by using an SCR (System Clock Reference).  
         [0036]     The configuration and operation of the clock reproduction section  107  will now be described in detail with reference to  FIG. 2 .  
         [0037]     As indicated in  FIG. 2 , the clock reproduction section  107  includes selectors  1071 ,  1074 , a clock control section  1072 , a comparison section  1073 , an LPF (Low Pass Filter)  1075 , a VCXO (Voltage Controlled Crystal Oscillator)  1076 , and an STC counter  1077 .  
         [0038]     Selector  1071  performs a 2-input 1-output selection process under the control of the control section  116 . The PCRs separated/extracted by the separation/extraction sections  105 ,  106  are input to selector  1071 . The PCR selected by selector  1071  is output to the comparison section  1073  and STC counter  1077 . When the PCR is input, the comparison section  1073  compares the value of the PCR with the STC count value of the STC counter  1077 , which will be described later, calculates the difference between the compared values, and outputs the calculation result to selector  1074  and clock control section  1072 . The clock control section  1072  records and stores the difference value calculated by the comparison section  1073  as a clock control value or calculates an average difference value and records and stores the average difference value as a control value. In compliance with instructions from the control section  116 , the clock control section  1072  outputs the recorded value to selector  1074 . Selector  1074  performs a 2-input 1-output selection process under the control of the control section  116 . The inputs from the comparison section  1073  and clock control section  1072  are output to the LPF  1075 . The LPF  1075  receives an input signal from selector  1074 , smoothes the input signal by eliminating its high-frequency component, and outputs smoothed input signal to the VCXO  1076 . The VCXO  1076  oscillates, for instance, at a center frequency of 27 MHz, generates a clock whose oscillation frequency is controlled in accordance with the signal that was smoothed when the LPF  1075  eliminated its high-frequency component, and outputs the generated clock to the STC counter  1077 , timestamp addition section  110 , and timestamp comparison/output section  114 . The STC counter  1077  operates in accordance with the clock generated by the VCXO  1076  while using the PCR value fed from selector  1071  as an initial value. This counter  1077  outputs its count value to the comparison section  1073  and decoding sections  108 ,  109 .  
         [0039]     When selector  1074  selects an output of the comparison section  1073  in a situation where the above configuration is employed, the clock reproduction section  107  employs a PLL (Phase Lock Loop) configuration. Therefore, the PCR selected by selector  1071  can be used to reproduce a clock that is synchronized (for frequency/phase matching) with the system clock of a broadcast station&#39;s encoding/multiplexing section. Meanwhile, when selector  1074  selects an output of the clock control section  1072 , a clock can be generated in accordance with a clock control value that is recorded/stored in the clock control section  1072 . Further, when the clock control value is generated and recorded while a digital broadcast is properly received, the clock generated in accordance with the control value is infinitely close to the system clock of a broadcast station&#39;s encoding/multiplexing section in frequency.  
         [0040]     The configuration and operation of the timestamp addition section  110  will now be described in detail with reference to  FIG. 3 .  
         [0041]     As indicated in  FIG. 3 , the timestamp addition section  110  includes PCR acquisition sections  1101 ,  1102 , counters  1103 ,  1104 , and timestamp insertion sections  1105 ,  1106 .  
         [0042]     PCR acquisition section  1101  checks transport packets separated/extracted by separation/extraction section  105 , acquires a transport packet that carries a PCR, and outputs the value of the PCR to counter  1103 . Counter  1103  operates in accordance with the clock reproduced by the clock reproduction section  107  while using the PCR value acquired by PCR acquisition section  1101  as an initial value. This counter  1103  outputs its count value to timestamp insertion section  1105 . Timestamp insertion section  1105  generates a timestamp in accordance with the count value fed from counter  1103  at the time when a transport packet separated/extracted by separation/extraction section  105  is input, adds the timestamp to (or embeds the timestamp in) the transport packet, and outputs the timestamped transport packet to the write section  111 .  
         [0043]     PCR acquisition section  1102  checks transport packets separated/extracted by separation/extraction section  106 , acquires a transport packet that carries a PCR, and outputs the value of the PCR to counter  1104 . Counter  1104  operates in accordance with the clock reproduced by the clock reproduction section  107  while using the PCR value acquired by PCR acquisition section  1102  as an initial value. This counter  1104  outputs its count value to timestamp insertion section  1106 . Timestamp insertion section  1106  generates a timestamp in accordance with the count value fed from counter  1104  at the time when a transport packet separated/extracted by separation/extraction section  106  is input, adds the timestamp to (or embeds the timestamp in) the transport packet, and outputs the timestamped transport packet to the write section  111 .  
         [0044]     The configuration and operation of the timestamp comparison/output section  114  will now be described in detail with reference to  FIG. 4 .  
         [0045]     As indicated in  FIG. 4 , the timestamp comparison/output section  114  includes timestamp deletion sections  1141 ,  1142 , comparison/output sections  1143 ,  1144 , counters  1145 ,  1146 , and timestamp acquisition sections  1147 ,  1148 .  
         [0046]     Timestamp acquisition section  1147  acquires the timestamp value of a timestamped transport packet that was read by the read section  113 , and outputs the acquired timestamp value to counter  1145 . Counter  1145  operates in accordance with the clock reproduced by the clock reproduction section  107  while using the timestamp value acquired by timestamp acquisition section  1147  as an initial value. This counter  1145  outputs its count value to comparison/output section  1143 . Comparison/output section  1143  compares the counter value of counter  1145  against the timestamp of the timestamped transport packet read by the read section  113 . When the compared count value and timestamp agree with each other, comparison/output section  1143  outputs the timestamped transport packet to timestamp deletion section  1141 . Timestamp deletion section  1141  deletes (removes) the timestamp from the timestamped transport packet fed from comparison/output section  1143  and outputs the transport packet, which is now without the timestamp, to selector  103  or IEEE 1394 interface section  115 .  
         [0047]     Timestamp acquisition section  1148  acquires the timestamp value of a timestamped transport packet that was read by the read section  113 , and outputs the acquired timestamp value to counter  1146 . Counter  1146  operates in accordance with the clock reproduced by the clock reproduction section  107  while using the timestamp value acquired by timestamp acquisition section  1148  as an initial value. This counter  1146  outputs its count value to comparison/output section  1144 . Comparison/output section  1144  compares the counter value of counter  1146  with the timestamp of the timestamped transport packet read by the read section  113 . When the compared count value and timestamp agree with each other, comparison/output section  1144  outputs the timestamped transport packet to timestamp deletion section  1142 . Timestamp deletion section  1142  deletes (removes) the timestamp from the timestamped transport packet fed from comparison/output section  1144  and outputs the transport packet, which is now without the timestamp, to selector  104  or IEEE 1394 interface section  115 .  
         [0048]     The structure of data handled in the digital broadcast receiver will now be described with reference to  FIG. 5 . In the digital broadcast receiver, the MPEG2-TS to be input from tuner decoding sections  101  and  102  to separation/extraction sections  105  and  106  via selectors  103  and  104  is as indicated in  FIG. 5A . A large number of transport packets having a predetermined number of bytes (e.g., 188 bytes) are multiplexed in the MPEG2-TS for use in digital broadcasting. Each transport packet comprises a transport header (hereinafter referred to as the TS header) and a payload. In other words, the MPEG2-TS includes a series of transport packets that correspond to digital video source and other video signals. The MPEG2-TS makes it possible to multiplex and transmit a plurality of data including video and audio data. The TS header is provided with a field for storing a PID (Packet Identification) that identifies the payload in a transport packet. When a digital signal is to be played back, payloads having the same PID are first combined to extract desired data and play the extracted data. For example, when payloads having the same PID are combined with each other, a PES packet is obtained. Particular information (not shown) is attached to the MPEG2-TS to ensure that video and audio are played back with the timing predefined by a broadcast station or other broadcast source. The particular information includes a program time standard reference value that is named “PCR,” time management information for playback that is named “PTS,” and time management information for decoding that is named “DTS.” The PCR is used to set the broadcast station&#39;s standard time and effect calibration. It is embedded in the MPEG2-TS for transmission. The PTS is the information for indicating the playback timing. The DTS is the information for indicating the decoding timing. The PTS and DTS are embedded in a PES header and transmitted. In the MPEG2-TS described above, the transport packets for broadcast program (channel) A and the transport packets for broadcast program (channel) B are alternately arranged.  
         [0049]     When a separation/extraction section  105 ,  106  into which the MPEG2-TS is input selects a transport packet for broadcast program (channel) A and outputs it to the timestamp addition section  110 , the data structure is as indicated in  FIG. 5B . In other words, when an MPEG2-TS containing a plurality of transport packets is to be received, the transport packet of a certain broadcast program (channel) A is first received. The transport packet of the next broadcast program (channel) A is received after a packet interval (that is, the length of unoccupied time) for the transport packet of broadcast program (channel) B, which is removed without being extracted. Any timestamp may be attached to the transport packet of this broadcast program (channel) A as far as it represents the information that indicates the packet interval for the transport packet of program (channel) A. For example, it may represent the time at which the timestamp addition section  110  received the transport packet of broadcast program (channel) A or the time difference between the instant at which the transport packet of broadcast program (channel) A (or the transport packet of an earlier received, predetermined broadcast program (channel) A) was received and the instant at which the timestamp addition section  110  received the transport packet of the next broadcast program (channel) A.  
         [0050]      FIG. 5C  shows the data structure within the recording medium  112  that prevails when individual transport packets in a stream shown in  FIG. 5C  are timestamped and stored on the recording medium  112 . In other words, when the recording medium  112  stores a plurality of timestamped transport packets, there is no more physical interval between a certain timestamped transport packet and the next timestamped transport packet. The interval can be identified from the information indicated by the timestamp attached to a timestamped transport packet when the timestamp comparison/output section  114  reads a timestamped transport packet via the read section  113 .  
         [0051]     As is obvious from  FIGS. 5A  to  5 C, the present embodiment adds a timestamp, which has a predetermined data length, to a transport packet shown in  FIG. 5B . As a result, the timestamped transport packet is larger in data size than the transport packet without a timestamp. However, it is not always necessary to add a timestamp to each transport packet. The timestamp may be provided in any manner as far as it defines a transport packet (e.g., a special timestamp may be embedded in a predefined field or any unoccupied field of a transport packet).  
         [0052]     The digital broadcast receiver, which incorporates the recording/output apparatus described above, has a plurality of tuner decoding sections. Therefore, the digital broadcast receiver is capable of simultaneously recording two channels (broadcast programs). In such an instance, the clock reproduction section  107  can generate a clock in accordance with a PCR that is multiplexed in an MPEG2-TS for either of the digital broadcasts received by the plurality of tuner decoding sections. Consequently, it is possible to reproduce a highly accurate receiver system clock that is synchronized (for frequency/phase matching) with the system clock of a broadcast station&#39;s encoding/multiplexing section. Since the reproduced system clock is used when the timestamp addition section  110  performs a process for recording and the timestamp comparison/output section  114  performs a process for playback, the packet intervals prevailing at the time of recording can be accurately reproduced at the time of playback. Further, the reproduced system clock is also used when the decoding sections perform a decoding process. In other words, when either of the plurality of tuner decoding sections receives a digital broadcast in a situation where a plurality of processes are to be performed for recording, playback, or decoding, a highly accurate receiver system clock can be reproduced. With the reproduced system clock, it is possible to perform a plurality of recording, playback, or decoding processes. Even if all digital broadcasts are halted so that no such broadcasts can be received, a clock can be generated in accordance with a clock control value prevailing at the time of digital broadcast reception that is recorded/stored in the clock control section  1072 . When the operation described above is performed, it is possible to generate a clock whose frequency is infinitely close to that of the system clock of a broadcast station&#39;s encoding/multiplexing section, that is, a clock that meets the system clock accuracy requirements of the MPEG standard. This makes it possible to properly perform a plurality of recording/playback processes in relation to the recording/output apparatus or a plurality of decoding processes in the decoding sections  108 ,  109 .  
         [0053]     When the present embodiment is described with reference to  FIG. 1 , it is assumed that the recording medium  112  is built in the digital broadcast receiver. However, an alternative is to use a removable recording medium that complies with the iVDR (Information Versatile Disc for Removable usage) standard.