Abstract:
A digital broadcast receiving apparatus includes a channel selection control unit selecting a channel of a digital broadcast, a demultiplexing unit and a video decoder obtaining video data and data broadcast data from electrical wave of the digital broadcast of the channel selected by the channel selection control unit, a data broadcast accumulation unit accumulating the data broadcast data obtained by the acquisition unit for each channel, and a rendering unit and a video composition unit generating composite video data by reading out the data broadcast data of at least one channel that includes a channel different from a channel of the video data obtained by the acquisition unit from the data broadcast accumulation unit and combining the readout data broadcast data and the video data obtained by the acquisition unit.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This is a continuation application of PCT application No. PCT/JP2010/000761 filed on Feb. 9, 2010, designating the United States of America. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    (1) Field of the Invention 
         [0003]    The present invention relates to a digital broadcast receiving apparatus and a digital broadcast receiving method, and in particular, to video-sound watching and listening and a usage of data broadcast. 
         [0004]    (2) Description of the Related Art 
         [0005]    Digital broadcast distributes data broadcast content together with video-sound content which is content including videos and sounds. In a digital broadcast receiving apparatus, data in which the data broadcast content is rendered by browser software, and so on, for decompressing the data broadcast content and the video-sound content can be used at the same time. 
         [0006]    The data broadcast content is distributed on each broadcast channel independently. However, the data broadcast content which has little relationship with the video-sound content in the broadcast channel is often distributed. Thus, a viewer often would like use data broadcast content which is distributed on a channel different from that of video-sound content which the viewer currently watches and listens to. 
         [0007]    There is a known technique in which, even when a switch from the data broadcast content to the next data broadcast content occurs during watching and listening to video-sound content, a viewer can keep watching and listening to data broadcast content which the viewer has been watching and listening to instead of next data broadcast content (refer to Japanese Unexamined Patent Application Publication No. 2007-201766, hereinafter referred to as Patent Reference 1). 
         [0008]    Moreover, there are also known data broadcast receiving apparatus and tuner control apparatus described in Japanese Unexamined Patent Application Publication No. 2000-308026 (hereinafter referred to as Patent Reference 2) as a technique relating to an accumulation of data broadcast. 
       SUMMARY OF THE INVENTION 
       [0009]    However, the conventional digital broadcast receiving apparatus is designed so that video-sound content which a viewer watches and listens to and data broadcast content which is distributed on the same channel as the video-sound content at the same time can be used together in the same screen. Accordingly, when switching the broadcast channel of the video-sound content during use of the data broadcast content, the displaying of the data broadcast content which has been used is interrupted, and only the data broadcast content distributed on the newly selected channel can be used. Even in the data broadcast receiving apparatuses described in the Patent References 1 and 2, when the channel of the video-sound content is switched, the channel of the data broadcast content is also switched. Thus, there is a problem that the channel of the video-sound content and the channel of the data broadcast content can not be switched independently from each other. 
         [0010]    The present invention is to solve the above problem, and an object of the present invention is to provide a digital broadcast receiving apparatus which can change a data broadcast content channel, which is a channel whose data broadcast content is used, without changing a video-sound content channel, which is a channel whose video-sound content is watched and listened to, or change the video-sound content channel without changing the data broadcast content channel. 
         [0011]    To solve the above problem, the digital broadcast receiving apparatus according to an aspect of the present invention that receives electrical wave of a digital broadcast and outputs video data of the digital broadcast, the digital broadcast receiving apparatus includes: a channel selection control unit which selects a channel of the digital broadcast; an acquisition unit which obtains video data and data broadcast data from electrical wave of the digital broadcast of the channel selected by the channel selection control unit; a data broadcast accumulation unit which has a storage region for each channel and accumulates the data broadcast data obtained by the acquisition unit in the storage region of the channel selected by the channel selection control unit; and a composition unit which generates composite video data by reading out the data broadcast data of at least one channel that includes a channel different from a channel of the video data obtained by the acquisition unit from the data broadcast accumulation unit and combining the readout data broadcast data and the video data obtained by the acquisition unit. 
         [0012]    In particular, the acquisition unit includes: a front-end unit which demodulates the electrical wave of the digital broadcast of the channel selected by the channel selection control unit into digital signals; a demultiplexing unit which demultiplexes encoded video data and data broadcast data from the digital signals; and a video decoder which decodes the encoded video data, and the data broadcast accumulation unit has a storage region for each channel and accumulates the data broadcast data demultiplexed by the demultiplexing unit in the storage region of the channel selected by the channel selection control unit, and the composition unit includes: a rendering unit which generates picture data of data broadcast data of at least one channel which includes a channel different from the channel of the electrical wave of the digital broadcast demodulated by the front-end unit in accordance with the data broadcast data accumulated in the data broadcast accumulation unit; and a video composition unit which generates composite video data by combining the video data decoded by the video decoder and the picture data generated by the rendering unit. 
         [0013]    With this configuration, the data broadcast data is stored in the data broadcast accumulation unit for each channel. Thus, the data broadcast data of the desired channel can be read out from the data broadcast accumulation unit. Consequently, a user can use the pre-accumulated data broadcast data which is different from the video which the user currently watches. 
         [0014]    It is preferable that the digital broadcast receiving apparatus further includes: a CM (Commercial Message) detection unit which detects a CM of the digital broadcast of the channel specified by the channel selection control unit; and a system control unit which controls the channel selection control unit to select a channel which is different from a channel corresponding to the electrical wave which is currently demodulated by the front-end unit during a period of time when the CM detection unit detects a CM. 
         [0015]    The newest data broadcast data of the channel which is different from the channel which the user currently watches is accumulated in the data broadcast accumulation unit by controlling the channel selection control unit to select the channel which the user currently watches during the CM period. 
         [0016]    It is more preferable that the CM detection unit detects a CM in accordance with a change of supplementary information included in the encoded video data. 
         [0017]    It is more preferable that the CM detection unit detects a CM in accordance with a state that a timing of a switch between a CM and a program (or vice versa) indicates a moment at which the supplementary information included in the encoded video data changes. 
         [0018]    It is more preferable that demultiplexing unit demultiplexes encoded video data, encoded sound data, and data broadcast data from the digital signals, the digital broadcast receiving apparatus further includes a sound decoder which decodes the encoded sound data, and the CM detection unit detects a CM in accordance with a change of supplementary information included in the encoded sound data. 
         [0019]    It is more preferable that the demultiplexing unit demultiplex encoded video data, encoded sound data, and data broadcast data from the digital signals, the digital broadcast receiving apparatus further includes a sound decoder which decodes the encoded sound data, and the CM detection unit detects a CM in accordance with a state that a timing of a switch between a CM and a program (or vice versa) indicates a moment at which the supplementary information included in the encoded video data changes. 
         [0020]    According to any of these configurations, the timing of the CM start can be detected by focusing on the changing point of the video and sound. 
         [0021]    It is more preferable that the digital broadcast receiving apparatus further includes: a state management unit which manages a period of time when the front-end unit or the demultiplexing unit can be operated for purpose of accumulating the data broadcast data in the data broadcast accumulation unit; and a system control unit which controls the selection channel control unit to select at least one channel in a period of time when the front-end unit or the demultiplexing unit can be operated for purpose of accumulating the data broadcast data in the data broadcast accumulation unit. 
         [0022]    It is more preferable that the state management unit manages a period of time when electrical power of the digital broadcast receiving apparatus is turned on as a period of time when the front-end unit or the demultiplexing unit can be operated except for a purpose of accumulating the data broadcast data in the data broadcast accumulation unit, and the state management unit manages a period of time when electrical power of the digital broadcast receiving apparatus is turned off as a period of time when the front-end unit or the demultiplexing unit can be operated for purpose of accumulating the data broadcast data in the data broadcast accumulation unit. 
         [0023]    According to this configuration, the digital broadcast receiving apparatus of the present invention can detect the period of time when the channel of the data broadcast data can be selected except for the purpose that the user watches and listens to the video-sound data. 
         [0024]    The digital broadcast receiving apparatus according to another aspect of the present invention that receives electrical wave of a digital broadcast and outputs video data of the digital broadcast, the digital broadcast receiving apparatus includes: a first channel selection control unit which selects a first channel of the digital broadcast; a second channel selection control unit which selects a second channel of the digital broadcast; a first front-end unit which demodulates the electrical wave of the digital broadcast of the channel selected by the first channel selection control unit into first digital signals; a second front-end unit demodulates the electrical wave of the digital broadcast of the channel selected by the second channel selection control unit into second digital signals; a first demultiplexing unit which demultiplexes encoded video data and data broadcast data from the first digital signals; a second demultiplexing unit which demultiplexes encoded video data and data broadcast data from the second digital signals; a video decoder which decodes the encoded video data demultiplexed by the first demultiplexing unit; a data broadcast accumulation unit which has a storage region for each channel and accumulates the data broadcast data demultiplexed by the second demultiplexing unit in the storage region of the channel selected by the second channel selection control unit; a rendering unit which generates picture data of data broadcast data of at least one channel which includes a channel different from the channel of the electrical wave of the digital broadcast demodulated by the first front-end unit in accordance with the data broadcast data accumulated in the data broadcast accumulation unit; and a video composition unit which generates synthesized video data by combining the video data decoded by the video decoder and the picture data generated by the rendering unit. 
         [0025]    According to this configuration, the data broadcast data is stored in the data broadcast accumulation unit for each channel. Thus, the data broadcast data of the desired channel can be read out from the data broadcast accumulation unit. Consequently, the data broadcast data which is different from the video which the user currently watches can be sent out to the rendering unit. 
         [0026]    The digital broadcast receiving apparatus according to yet another aspect of the present invention that receives electrical wave of a digital broadcast and outputs video data of the digital broadcast, the digital broadcast receiving apparatus includes: a first channel selection control unit which selects a first channel of the digital broadcast; a second channel selection control unit which selects a second channel of the digital broadcast; a first front-end unit which demodulates the electrical wave of the digital broadcast of the channel selected by the first channel selection control unit into first digital signals; a second front-end unit which demodulates the electrical wave of the digital broadcast of the channel selected by the second channel selection control unit into second digital signals; a first demultiplexing unit which demultiplexes encoded video data and data broadcast data from the first digital signals; a second demultiplexing unit which demultiplexes encoded video data and data broadcast data from the second digital signals; a video decoder which decodes the encoded video data demultiplexed by the first demultiplexing unit or the second demultiplexing unit; a data broadcast accumulation unit which has a storage region for each channel, accumulates the data broadcast data demultiplexed by the first demultiplexing unit in the storage region of the channel selected by the first channel selection control unit, and accumulates the data broadcast data demultiplexed by the second demultiplexing unit in the storage region of the channel selected by the second channel selection control unit; a rendering unit which generates picture data of data broadcast data of at least one channel which includes a channel different from the channel of the electrical wave of the digital broadcast demodulated by the first front-end unit or the second front-end unit in accordance with the data broadcast data accumulated in the data broadcast accumulation unit; and a video composition unit which generates composite video data by combining the video data decoded by the video decoder and the picture data generated by the rendering unit. 
         [0027]    According to this configuration, the data broadcast data is stored in the data broadcast accumulation unit for each channel. Thus, the data broadcast data of the desired channel can be read out from the data broadcast accumulation unit. Consequently, the data broadcast data which is different from the video which the user currently watches can be sent out to the rendering unit. 
         [0028]    The present invention can be achieved not only as the digital broadcast receiving apparatus provided with the above characteristic processing units but also as the digital broadcast receiving method having the steps of the characteristic processing units included in the digital broadcast receiving apparatus. Moreover, the present invention can also be achieved as a program which causes a computer to execute the characteristic steps included in the digital broadcast receiving method. The above program can be distributed via a recording medium such as CD-ROM (Compact Disc-Read Only Memory) etc. and a communication network such as Internet etc. 
         [0029]    The present invention makes it possible to change the data broadcast content channel without changing a video-sound content channel or change the video-sound content channel without changing the data broadcast content channel. 
       FURTHER INFORMATION ABOUT TECHNICAL BACKGROUND TO THIS APPLICATION 
       [0030]    The disclosure of Japanese Patent Application No. 2009-048551 filed on Mar. 2, 2009 including specification, drawings and claims is incorporated herein by reference in its entirety. 
         [0031]    The disclosure of PCT application No. PCT/JP2010/000761 filed on Feb. 9, 2010, including specification, drawings and claims is incorporated herein by reference in its entirety. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the invention. In the Drawings: 
           [0033]      FIG. 1  is a block diagram illustrating a functional configuration of a digital broadcast receiving apparatus according to Embodiment 1 of the present invention; 
           [0034]      FIG. 2  is a flow chart relating to a taking of a data broadcast when receiving a digital broadcast according to Embodiment 1 of the present invention; 
           [0035]      FIG. 3  is a flow chart showing an accumulation process of the data broadcast data in detail according to Embodiments 1 and 2 of the present invention; 
           [0036]      FIG. 4  is a flow chart of a process for using the data broadcast when receiving the digital broadcast according to Embodiment 1 of the present invention; 
           [0037]      FIG. 5  is a diagram illustrating an example of a television screen according to Embodiments 1 and 2 of the present invention; 
           [0038]      FIG. 6  is a diagram illustrating an example of a television screen according to Embodiments 1 and 2 of the present invention; 
           [0039]      FIG. 7  is a diagram illustrating an example of a television screen according to Embodiments 1 and 2 of the present invention; 
           [0040]      FIG. 8  is a block diagram illustrating a functional configuration of a digital broadcast receiving apparatus according to Embodiment 2 of the present invention; 
           [0041]      FIG. 9  is a flow chart relating to a taking of a data broadcast when receiving a digital broadcast according to Embodiment 2 of the present invention; 
           [0042]      FIG. 10  is a flow chart of a process for using the data broadcast when receiving the digital broadcast according to Embodiment 2 of the present invention; and 
           [0043]      FIG. 11  is a diagram illustrating an example of a television screen according to Modification of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0044]    Embodiments of the present invention are described with reference to the drawings. Basic configuration, operation, etc. of a digital broadcast receiving apparatus are well known by a skilled person. Thus, a detailed description of them is not repeated here. 
       Embodiment 1 
       [0045]    In Embodiment 1, a digital broadcast receiving apparatus which can receive a digital broadcast of one channel at the same time is described. 
         [0046]    The digital broadcast is made up of videos and sounds and a data broadcast which are independent for each channel. The data broadcast is transmitted in carousel form. 
         [0047]    Content of the data broadcast is a hypertext form described in markup language such as BML (Broadcast Markup Language), for example. 
         [0048]    The data broadcast content is designed to be used with videos and sounds which are distributed on the same channel as the data broadcast content. 
         [0049]    At first, a functional configuration of the digital broadcast receiving apparatus according to Embodiment 1 is described. 
         [0050]    For example, the digital broadcast receiving apparatus according to Embodiment 1 is a household television or a household set-top box. The digital broadcast receiving apparatus according to Embodiment 1 may be applied to a portable television, a personal computer having a digital broadcast receiving function, a personal digital assistant (PDA), and a household video recording equipment. 
         [0051]      FIG. 1  is a block diagram illustrating a functional configuration of the digital broadcast receiving apparatus according to Embodiment 1. 
         [0052]    A digital broadcast receiving apparatus  1000  illustrated in  FIG. 1  receives a terrestrial digital broadcast or a BS (broadcasting satellite) digital broadcast. The digital broadcast receiving apparatus  1000  includes an antenna  1001 , a front-end unit  1002 , a demultiplexing unit  1003 , a video decoder  1004 , a sound decoder  1005 , a data broadcast accumulation unit  1006 , a rendering unit (browser)  1007 , a video composition unit  1008 , a channel selection control unit  1009 , a CM detection unit  1010 , a system control unit  1011 , a state management unit  1012 , an operation input unit  1013 , a video output unit  1014 , and a sound output unit  1015 . 
         [0053]    The antenna  1001  is a receiving antenna which receives electrical wave of the terrestrial digital broadcast, the BS digital broadcast, etc. 
         [0054]    The front-end unit  1002  extracts and demodulates electrical wave in a specific frequency range from the electrical wave received by the antenna  1001  and converts the electrical wave into a transport stream which is composed of transport stream packets in which plural data are multiplexed. That is to say, the front-end unit  1002  selects a predetermined channel of a broadcast wave and extracts a transport stream in electrical wave of the predetermined channel. 
         [0055]    The demultiplexing unit  1003  demultiplexes the data included in the transport stream which is outputted from the front-end unit  1002 . In particular, the demultiplexing unit  1003  demultiplexes encoded video data included in the respective transport stream packets, encoded sound data, and data broadcast data. 
         [0056]    The video decoder  1004 , which conforms to MPEG (Moving Picture Experts Group) 2, H.264, etc., decodes the encoded video data demultiplexed by the demultiplexing unit  1003  and generates the video data after the decode. 
         [0057]    The sound decoder  1005 , which conforms to MPEG2-AAC (Advanced Audio Coding) etc., decodes the encoded sound data demultiplexed by the demultiplexing unit  1003  and generates the sound data after the decode. 
         [0058]    The data broadcast accumulation unit  1006  accumulates the data broadcast data in the transport stream packet which is transmitted in carousel form. Moreover, the data broadcast accumulation unit  1006  has a region to accumulate the data broadcast data individually for each channel of the broadcast waves, and sends out the individual data broadcast data to the rendering unit  1007  by a command from the system control unit  1011  described below. 
         [0059]    The rendering unit  1007  interprets the data broadcast data sent out from the data broadcast accumulation unit  1006  in accordance with a notation in the data broadcast data and generates picture data for displaying the data broadcast data. For example, the rendering unit  1007  interprets the data broadcast data of hypertext form described in BML or the like and generates the picture data of the data broadcast data. 
         [0060]    The video composition unit  1008  combines the video data generated by the video decoder  1004  and the picture data of the data broadcast data generated by the rendering unit  1007  or selects one of these data, and outputs the combined data or the selected data to the video output unit  1014 . 
         [0061]    The channel selection control unit  1009  selects the channel of the digital broadcast. That is to say, upon receiving the command to select the channel from the system control unit  1011 , the channel selection control unit  1009  sends a command to select the channel to the front-end unit  1002 . The front-end unit  1002  can thereby extract and demodulate the electrical wave of the commanded channel and convert it into the transport stream. 
         [0062]    When CM detection unit  1010  detects the switching of the video or sound, for example, in the video data and video supplementary information included in the video data generated by the video decoder  1004  or the sound data and sound supplementary information included in the sound data generated by the sound decoder  1005 , the CM detection unit  1010  generates a timing information which indicates timings of a CM start and a CM end. The CM detection unit  1010  sends the timing information to the system control unit  1011 . For example, the CM detection unit  1010  may detect the timings of the CM start and the CM end by detecting a switching between a bilingual broadcast and a stereo broadcast, a switching between a monaural broadcast and a stereo broadcast, or the like in the sound supplementary information. Moreover, the CM detection unit  1010  may detect the timings of the CM start and the CM end by monitoring a change of a video aspect information included in the video supplementary information. 
         [0063]    The state management unit  1012  manages a period of time when the system control unit  1011  can control the front-end unit  1002  and the demultiplexing unit  1003  (a period of time when the system control unit  1011  can control the front-end unit  1002  and the demultiplexing unit  1003  for purpose of accumulating the data broadcast data in the data broadcast accumulation unit  1006 ) except for a purpose that a user watches and listens to the videos and sounds of television (except for a purpose of outputting the data to the video output unit  1014  and the sound output unit  1015 ) and sends the period of time to the system control unit  1011 . In that period of time, in the front-end unit  1002  and the demultiplexing unit  1003 , the channel can be selected for purpose other than watching and listening to the videos and sounds. For example, even during a period of time when electrical power is turned off by a user operation, the state management unit  1012  manages the state that the front-end unit  1002  and the demultiplexing unit  1003  can be controlled and sends it to the system control unit  1011 , as long as the digital broadcast receiving apparatus  1000  is made up of the respective processing units which can operate in background. The purpose of the user watching and listening to the videos and sounds may include a purpose of the user recording the videos and sounds of television. 
         [0064]    The operation input unit  1013  sends information of operation switches (not illustrated) pressed to operate the digital broadcast receiving apparatus  1000  to the system control unit  1011 . The digital broadcast receiving apparatus  1000  may be operated by receiving an operation command from infrared light outputted from an infrared remote controller or receiving an operation command from electrical signals transmitted from other control circuit other than operating the operation switches. 
         [0065]    The system control unit  1011  controls the channel selection control unit  1009  to select a channel different from that which corresponds to the electrical wave demodulated by the front-end unit  1002  currently during a period of time when the CM detection unit  1010  detects a CM. That is to say, the system control unit  1011  controls a channel selection for watching a television in accordance with the operation command from the operation input unit  1013 . Moreover, the system control unit  1011  determines the period of time when the system control unit  1011  can control the front-end unit  1002  and the demultiplexing unit  1003  in accordance with the information from the state management unit  1012  and the CM detection unit  1010  and controls the channel selection control unit  1009  for purpose of accumulating the data broadcast data in the data broadcast accumulation unit  1006 . Moreover, the system control unit  1011  controls a start-up and end of the rendering unit  1007  when watching the television and sends a command to send out the data broadcast data used in the rendering unit  1007  to the data broadcast accumulation unit  1006 . 
         [0066]    The video output unit  1014  outputs a video to a display panel or the like. The video output unit  1014  is connected to the display panel or the like via an external output terminal such as a component terminal and a HDMI (High-Definition Multimedia Interface) terminal, or a dedicated interface with the display panel. 
         [0067]    The sound output unit  1015  outputs sounds to a speaker or the like. The sound output unit  1015  outputs the sound from an analog sound output terminal, an optical digital terminal, a coaxial terminal, or a HDMI terminal and outputs the sound directly to a built-in speaker device via a built-in amplifier circuit or the like. 
         [0068]    According to the above configuration, the digital broadcast receiving apparatus  1000  receives the data broadcast of each channel at the time which is detected by the CM detection unit  1010  and the state management unit  1012  and accumulates the data broadcast in the data broadcast accumulation unit  1006 , so that the digital broadcast data which was broadcast on the other channel can be used while watching a certain digital broadcast channel. 
         [0069]    Subsequently, an operation of the digital broadcast receiving apparatus  1000  is described. 
         [0070]      FIG. 2  is a flow chart showing a processing flow of accumulating the data broadcast data in the data broadcast accumulation unit  1006 . 
         [0071]    Here, there are three digital broadcast channels which can be received, that is, channels A, B, and C. 
         [0072]    The system control unit  1011  determines whether or not the user watches the television in accordance with the information from the state management unit  1012  and the information held in the system control unit  1011  (S 2001 ). 
         [0073]    When determining that the user does not watch the television (NO in S 2001 ), the digital broadcast receiving apparatus  1000  performs an accumulation process of the data broadcast data of each channel (S 2003 ). Details of the data broadcast data accumulation process (S 2003 ) are described below with reference to a flow chart in  FIG. 3 . 
         [0074]    When determining that the user watches the television (YES in S 2001 ), the system control unit  1011  determines whether or not the CM detection unit  1010  detects a CM period (S 2002 ). 
         [0075]    When determining that the CM detection unit  1010  detects the CM period (YES in S 2002 ), the digital broadcast receiving apparatus  1000  performs the data broadcast data accumulation process (S 2003 ). 
         [0076]    When determining that the user watches the television and the CM detection unit  1010  does not detect the CM period (YES in S 2001  and NO in S 2002 ), the process of S 2001  and S 2002  is repeatedly performed. 
         [0077]      FIG. 3  is a flow chart showing the details of the data broadcast data accumulation process (S 2003  in  FIG. 2 ). 
         [0078]    The system control unit  1011  selects a channel to accumulate the data broadcast data (S 7001 ). Here, the system control unit  1011  selects preferentially the channel whose data broadcast data is not yet accumulated in the data broadcast accumulation unit  1006  and then selects a channel whose data broadcast data is the oldest in the accumulated data broadcast data. Here, the channel A is selected. 
         [0079]    Subsequently, the system control unit  1011  sends a command to select the channel A to the channel selection control unit  1009  and sends a command to start accumulating the data broadcast data of the channel A to the data broadcast accumulation unit  1006 . Upon receiving the channel selection command from the channel selection control unit  1009 , the front-end unit  1002  receives and demodulates the electrical wave from the antenna  1001  and then outputs the multiplexed transport stream to the demultiplexing unit  1003  (S 7002 ). 
         [0080]    The demultiplexing unit  1003  analyzes the multiplexed transport stream outputted from the front-end unit  1002  and sends out the transport stream packet including the data broadcast data to the data broadcast accumulation unit  1006 . The data broadcast accumulation unit  1006  accumulates the data broadcast data which corresponds to the channel A (S 7003 ). 
         [0081]    When the user watches the television or during the CM period (NO in S 2001  or YES in S 2002  in  FIG. 2 ), the data broadcast data accumulation process (S 2003 ) is repeatedly performed. Thus, after the data broadcast data of the channel A is accumulated, the system control unit  1011  selects subsequently the channel B and the channel C, which can be watched and also distribute the data broadcast, switches the channels repeatedly, and accumulates the data broadcast data. 
         [0082]    The CM period is generally several tens of seconds, so that when the system control unit  1011  determines that the data broadcast has already been taken for a certain period of time, the system control unit  1011  finishes accumulating the data broadcast data, switches the channel to watch the television broadcast which the user has been watching so that the user can continue watching the television. 
         [0083]    Subsequently, a process of using the data broadcast data accumulated in the data broadcast accumulation unit  1006  during watching the television is described. 
         [0084]      FIG. 4  is a flow chart showing a process flow when using the data broadcast data accumulated in the data broadcast accumulation unit  1006  during watching the television. 
         [0085]    Firstly, the system control unit  1011  determines whether or not the user watches the television in accordance with the information from the state management unit  1012  and the information held in the system control unit  1011  (S 3001 ). 
         [0086]    When determining that the user watches the television (YES in S 3001 ), the system control unit  1011  determines whether or not to display the data broadcast in accordance with the command from the operation input unit  1013  or the state in the system control unit  1011  (S 3002 ). When displaying the data broadcast (YES in S 3002 ), the system control unit  1011  sends a command to output the data broadcast data of the channel which the user watches to the data broadcast accumulation unit  1006 . For example, when the user instructs to display the data broadcast using the operation input unit  1013  while watching a program of channel A as shown in  FIG. 5 , the program of channel A (the video data) and the data broadcast data of channel A are displayed on the television screen as shown in  FIG. 6 . 
         [0087]    Subsequently, when the system control unit  1011  receives a command to change the data broadcast channel from the operation input unit  1013  (YES in S 3003 ), the system control unit  1011  sends a command to change an output channel of the data broadcast data to the data broadcast accumulation unit  1006 . The data broadcast accumulation unit  1006  transmits the valid data broadcast data which is already accumulated in the data broadcast accumulation unit  1006  or the data broadcast data which is being accumulated in the data broadcast accumulation unit  1006  to the rendering unit  1007  (S 3004 ). Thereby, the data broadcast is updated. For example, when a command is sent to change the output data of the data broadcast data to the channel B with a television screen displayed as shown in  FIG. 6 , the program of channel A (the video data) and the data broadcast data of channel B are displayed on the television screen as shown in  FIG. 7 . 
         [0088]    Although Embodiment 1 describes the example of fixing the channel of the program which the user watches and changing the channel of the data broadcast data, it is also applicable to change the channel of the program which the user watches and fix the channel of the data broadcast data. 
         [0089]    As described above, according to Embodiment 1, the data broadcast accumulation unit  1006  accumulates the data broadcast data of all channels in advance. Thus, it is possible to change a data broadcast content channel, which is a channel whose data broadcast content is used, without changing a video-sound content channel, which is a channel whose video-sound content is watched and listened to, or change the video-sound content channel without changing the data broadcast content channel. 
       Embodiment 2 
       [0090]    Subsequently, Embodiment 2 is described below. A digital broadcast receiving apparatus according to Embodiment 2 includes two front-end units, two demultiplexing units, and two channel selection control units. 
         [0091]      FIG. 8  is a block diagram illustrating a functional configuration of the digital broadcast receiving apparatus according to Embodiment 2. 
         [0092]    A digital broadcast receiving apparatus  4000  shown in  FIG. 8  receives a terrestrial digital broadcast or a BS digital broadcast. The digital broadcast receiving apparatus  4000  includes an antenna  4001 , a first front-end unit  4002 , a first demultiplexing unit  4003 , a video decoder  4004 , a sound decoder  4005 , a second front-end unit  4006 , a second demultiplexing unit  4007 , a data broadcast accumulation unit  4008 , a rendering unit  4009 , a video composition unit  4010 , a first channel selection control unit  4011 , a second channel selection control unit  4012 , a system control unit  4013 , an operation input unit  4014 , a video output unit  4015 , and a sound output unit  4016 . 
         [0093]    The antenna  4001  is a receiving antenna which receives electrical wave of the terrestrial digital broadcast, the BS digital broadcast, etc. 
         [0094]    The first front-end unit  4002  extracts and demodulates electrical wave in a specific frequency range from the electrical wave received by the antenna  4001  and converts the electrical wave into a transport stream which is composed of transport stream packets in which plural data are multiplexed. That is to say, the first front-end unit  4002  selects a predetermined channel of a broadcast wave and extracts a transport stream in electrical wave of the predetermined channel. 
         [0095]    The first demultiplexing unit  4003  demultiplexes the data included in the transport stream which is outputted from the first front-end unit  4002 . In particular, the first demultiplexing unit  4003  demultiplexes encoded video data included in the respective transport stream packets, encoded sound data, and data broadcast data. In Embodiment 2, the first demultiplexing unit  4003  outputs the transport stream packets composed of the video data and the sound data which are watched and listened to. 
         [0096]    The video decoder  4004 , which conforms to MPEG2, H.264, etc., decodes the encoded video data demultiplexed by the first demultiplexing unit  4003  and generates the decoded video data. 
         [0097]    The sound decoder  4005 , which conforms to MPEG2-AAC etc., decodes the encoded sound data demultiplexed by the first demultiplexing unit  4003  and generates the decoded sound data. 
         [0098]    The second front-end unit  4006  extracts and demodulates electrical wave in a specific frequency range from the electrical wave received by the antenna  4001  and converts the electrical wave into a transport stream which is composed of transport stream packets in which plural data are multiplexed. That is to say, the second front-end unit  4006  selects a predetermined channel of a broadcast wave and extracts a transport stream in electrical wave of the predetermined channel. 
         [0099]    The second demultiplexing unit  4007  demultiplexes the data included in the transport stream which is outputted from the second front-end unit  4006 . In particular, the second demultiplexing unit  4007  demultiplexes encoded video data included in the respective transport stream packets, encoded sound data, and data broadcast data. In Embodiment 2, the second demultiplexing unit  4007  outputs the transport stream packets which are composed of the data broadcast data for using the data broadcast. 
         [0100]    The data broadcast accumulation unit  4008  accumulates the data broadcast data in the transport stream packet which is transmitted in carousel form. Moreover, the data broadcast accumulation unit  4008  has a region to accumulate the data broadcast data individually for each channel of the broadcast waves, and sends out the individual data broadcast data to the rendering unit  4009  by a command from the system control unit  4013  described below. 
         [0101]    The rendering unit  4009  interprets the data broadcast data sent out from the data broadcast accumulation unit  4008  in accordance with a notation in the data broadcast data and generates picture data for displaying the data broadcast data. For example, the rendering unit  4009  interprets the data broadcast data of hypertext form described in BML or the like and generates the picture data of the data broadcast data. 
         [0102]    The video composition unit  4010  combines the video data generated by the video decoder  4004  and the picture data of the data broadcast data generated by the rendering unit  4009  or selects one of these data, and outputs the combined data or the selected data to the video output unit  4015 . 
         [0103]    The first channel selection control unit  4011  selects the channel of the digital broadcast. That is to say, upon receiving the command to select the channel from the system control unit  4013 , the first channel selection control unit  4011  sends a command to select the channel to the first front-end unit  4002 . The first front-end unit  4002  can thereby extract and demodulate the electrical wave of the commanded channel and convert it into the transport stream. 
         [0104]    The second channel selection control unit  4012  selects the channel of the digital broadcast. That is to say, upon receiving the command to select the channel from the system control unit  4013 , the second channel selection control unit  4012  sends a command to select the channel to the second front-end unit  4006 . The second front-end unit  4006  can thereby extract and demodulate the electrical wave of the commanded channel and convert it into the transport stream. 
         [0105]    The system control unit  4013  controls a channel selection for watching a television in accordance with an operation command from the operation input unit  4014 . Moreover, the system control unit  4013  controls the second channel selection control unit  4012  for purpose of accumulating the data broadcast data in the data broadcast accumulation unit  4008 . Furthermore, the system control unit  4013  controls a start-up and end of the rendering unit  4009  when watching the television and sends a command to send out the data broadcast data used in the rendering unit  4009  to the data broadcast accumulation unit  4008 . 
         [0106]    The operation input unit  4014  sends information of operation switches (not illustrated) pressed to operate the digital broadcast receiving apparatus  4000  to the system control unit  4013 . The digital broadcast receiving apparatus  4000  may be operated by receiving an operation command from infrared light outputted from an infrared remote controller or receiving an operation command from electrical signals transmitted from other control circuit other than operating the operation switches. 
         [0107]    The video output unit  4015  outputs a video to a display panel or the like. The video output unit  4015  is connected to the display panel or the like via an external output terminal such as a component terminal and a HDMI terminal, or a dedicated interface with the display panel. 
         [0108]    The sound output unit  4016  outputs sounds to a speaker or the like. The sound output unit  4016  outputs the sound from an analog sound output terminal, an optical digital terminal, a coaxial terminal, or a HDMI terminal and outputs the sound directly to a built-in speaker device via a built-in amplifier circuit or the like. 
         [0109]    According to the above configuration, the digital broadcast receiving apparatus  4000  receives the data broadcast of each channel and accumulates the data broadcast in the data broadcast accumulation unit  4008 , so that the digital broadcast data which was broadcast on the other channel can be used while watching a certain digital broadcast channel. 
         [0110]    Subsequently, an operation of the digital broadcast receiving apparatus  4000  is described. 
         [0111]      FIG. 9  is a flow chart showing a processing flow of accumulating the data broadcast data in the data broadcast accumulation unit  4008 . 
         [0112]    Here, there are three digital broadcast channels which can be received, that is, channels A, B, and C. 
         [0113]    The digital broadcast receiving apparatus  4000  performs repeatedly the process of accumulating the data broadcast data of each channel (S 5001 ). 
         [0114]      FIG. 3  is the flow chart showing the details of the data broadcast data accumulation process (S 5001  in  FIG. 9 ). 
         [0115]    The system control unit  4013  selects a channel to accumulate the data broadcast data (S 7001 ). Here, the system control unit  4013  selects preferentially the channel whose data broadcast data is not yet accumulated in the data broadcast accumulation unit  4008  and then selects a channel whose data broadcast data is the oldest in the accumulated data broadcast data. Here, the channel A is selected. 
         [0116]    Subsequently, the system control unit  4013  sends a command to select the channel A to the second channel selection control unit  4012  and sends a command to start accumulating the data broadcast data of the channel A to the data broadcast accumulation unit  4008 . Upon receiving the channel selection command from the second channel selection control unit  4012 , the second front-end unit  4006  receives the electrical wave from the antenna  4001 , demodulates it, and then outputs the multiplexed transport stream to the second demultiplexing unit  4007  (S 7002 ). 
         [0117]    The second demultiplexing unit  4007  analyzes the multiplexed transport stream outputted from the second front-end unit  4006  and sends out the transport stream packet including the data broadcast data to the data broadcast accumulation unit  4008 . The data broadcast accumulation unit  4008  accumulates the data broadcast data which corresponds to the channel A (S 7003 ). The data broadcast data accumulation process (S 5001 ) is repeatedly performed. Thus, after the data broadcast data of the channel A is accumulated, the system control unit  4013  also selects the channels B and C and accumulates the data broadcast data of the channels B and C in the same manner and controls the data broadcast accumulation from the channel A again repeatedly. 
         [0118]    Subsequently, a process of using the data broadcast data accumulated in the data broadcast accumulation unit  4008  during watching the television is described. 
         [0119]      FIG. 10  is a flow chart showing a process flow when using the data broadcast data accumulated in the data broadcast accumulation unit  4008  during watching the television. 
         [0120]    Here, the process after turning on the electrical power of the digital broadcast receiving apparatus  4000  is described. 
         [0121]    When the electrical power of the digital broadcast receiving apparatus  4000  is turned on, the system control unit  4013  sends a command to select the television broadcast channel, which is to be watched, to the first channel selection control unit  4011 . 
         [0122]    Upon receiving the channel selection command from the first channel selection control unit  4011 , the first front-end unit  4002  receives the electrical wave from the antenna  4001 , demodulates it, and then outputs the multiplexed transport stream to the first demultiplexing unit  4003   
         [0123]    The first demultiplexing unit  4003  analyzes the multiplexed transport stream outputted from the first front-end unit  4002  and sends out the transport stream packet including the encoded video data and the encoded sound data to the video decoder  4004  and the sound decoder  4005 . 
         [0124]    The video decoder  4004  decodes the encoded video data which is included in the transport stream packet outputted from the first demultiplexing unit  4003  and outputs the decoded video data. 
         [0125]    The sound decoder  4005  decodes the encoded sound data which is included in the transport stream packet outputted from the first demultiplexing unit  4003  and outputs the decoded sound data. 
         [0126]    The video composition unit  4010  combines the picture data of the data broadcast data generated by the rendering unit  4009  and the video data generated by the video decoder  4004  and outputs the combined data to the video output unit  4015  (S 6001 ). The data broadcast is not displayed when turning the electrical power on, so that the data outputted from the video composition unit  4010  is the same as the video data generated by the video decoder  4004 . 
         [0127]    The system control unit  4013  determines whether or not to display the data broadcast in accordance with the command from the operation input unit  4014  or the state in the system control unit  4013  (S 6002 ). When displaying the data broadcast (YES in S 6002 ), the system control unit  4013  sends a command to output the data broadcast data of the channel which the user watches to the data broadcast accumulation unit  4008  and starts up the rendering unit  4009 . Moreover, the system control unit  4013  sends a command to select the channel which the user watches to the second channel selection control unit  4012 . For example, when the user instructs to display the data broadcast using the operation input unit  4014  while watching the program of channel A as shown in  FIG. 5 , the program of channel A (the video data) and the data broadcast data of channel A are displayed on the television screen as shown in  FIG. 6 . 
         [0128]    Subsequently, when the system control unit  4013  receives a command to change the data broadcast channel which is currently used from the operation input unit  4014  (YES in S 6003 ), the system control unit  4013  sends a command to change a channel of an outputted data broadcast data to the data broadcast accumulation unit  4008  (S 6004 ). When the data broadcast accumulation unit  4008  accumulates the data broadcast data of the commanded channel, the data broadcast accumulation unit  4008  sends out immediately the data broadcast data to the rendering unit  4009 . When the data broadcast accumulation unit  4008  does not accumulate the data broadcast data of the commanded channel, the data broadcast accumulation unit  4008  receives the data broadcast data of the commanded channel from the second demultiplexing unit  4007  and accumulates it. The data broadcast accumulation unit  4008  transmits the valid data broadcast data which is already accumulated in the data broadcast accumulation unit  4008  or the data broadcast data which is being accumulated in the data broadcast accumulation unit  4008  to the rendering unit  4009 . Thereby, the data broadcast is updated. 
         [0129]    For example, when a command is sent to change the output data of the data broadcast data to the channel B with a television screen displayed as shown in  FIG. 6 , the program of channel A (the video data) and the data broadcast data of channel B are displayed on the television screen as shown in  FIG. 7 . 
         [0130]    Although Embodiment 2 describes the example of fixing the channel of the program which the user watches and changing the channel of the data broadcast data, it is also applicable to change the channel of the program which the user watches and fix the channel of the data broadcast data. 
         [0131]    As described above, according to Embodiment 2, the data broadcast accumulation unit  4008  accumulates the data broadcast data of all channels in advance. Thus, it is possible to change a data broadcast content channel, which is a channel whose data broadcast content is used, without changing a video-sound content channel, which is a channel whose video-sound content is watched and listened to, or change the video-sound content channel without changing the data broadcast content channel. 
         [0132]    Although the present invention is described above based on the above Embodiments 1 and 2, the present invention is not limited to those in Embodiments 1 and 2. 
         [0133]    For example, not only switching the data broadcast channel during watching the television can be achieved, but accessibility to the data broadcast can also be enhanced by displaying the data broadcast data of each channel accumulated in the data broadcast accumulation unit side-by-side on one screen.  FIG. 11  illustrates an example of displaying the data broadcast data of the three channels, the channels A to C, side-by-side on one screen. 
         [0134]    Moreover, it is also applicable that when accumulating the data broadcast data in the data broadcast accumulation unit, the data broadcast data of the channel which is instructed by the user in advance is preferentially accumulated instead of accumulating preferentially the data broadcast data of the channel corresponding to the data broadcast data which is the oldest in the updated data broadcast data. 
         [0135]    Moreover, in Embodiment 2, it is also applicable that the data broadcast accumulation unit  4008  has a region to accumulate the data broadcast data of one channel, sends a command to select the channel to the second channel selection control unit  4012  every time when the channel of the data broadcast is switched, and sends out the data broadcast data which is accumulated at that time to the rendering unit  4009  each time. According to such a configuration, although it requires some time to display the data broadcast data, a capacity of the data broadcast accumulation unit  4008  can be made smaller. 
         [0136]    Moreover, in Embodiment 2, it is described that the first front-end unit  4002  and the first demultiplexing unit  4003  are used for watching and listening to the video and the sound, and the second front-end unit  4006  and the second demultiplexing unit  4007  are used for receiving the data broadcast, however, the present invention is not limited to this configuration. For example, a crossbar switch configuration is applied to a connection of the first demultiplexing unit  4003  and the second demultiplexing unit  4007  with the video decoder  4004  and the sound decoder  4005  and with the data broadcast accumulation unit  4008 . According to such a configuration, the second front-end unit  4006  and the second demultiplexing unit  4007  can be used for watching and listening to the video and the sound, and the first front-end unit  4002  and the first demultiplexing unit  4003  can be used for receiving the data broadcast. 
         [0137]    Moreover, in Embodiment 2, the input system of the data broadcast transport stream packet from the demultiplexing unit to the data broadcast accumulation unit  4008  may be increased in number. That is to say, the first demultiplexing unit  4003  and the second demultiplexing unit  4007  may be connected to the data broadcast accumulation unit  4008 , respectively. According to such a configuration, the plural systems of the front-end units and the demultiplexing units in the digital broadcast receiving apparatus are not used, the plural front-end units and the plural demultiplexing units are operated in parallel to receive the data broadcast, so that the time to take all the data broadcast data which are broadcast can be reduced. 
         [0138]    Moreover, the system of the demultiplexing unit may be increased in number in a digital broadcast receiving apparatus corresponding to both a satellite wave digital broadcast and a terrestrial digital broadcast, for example. That is to say, the first demultiplexing unit  4003  and the second demultiplexing unit  4007  may be connected to the video decoder  4004 , the sound decoder  4005 , and the data broadcast accumulation unit  4008 , respectively. According to such a configuration, data broadcast of the satellite wave digital broadcast may be accumulated in the data broadcast accumulation unit  4008  during receiving the terrestrial digital broadcast or data broadcast of the terrestrial digital broadcast may be accumulated in the data broadcast accumulation unit  4008  during receiving the satellite wave digital broadcast. 
         [0139]    Moreover, each apparatus described above may be constructed as a computer system which is made up of, in particular, a microprocessor, a ROM, a RAM, a hard disk drive, a display unit, a keyboard, a mouse, etc. A computer program is stored in the RAM or the hard disk drive. Each apparatus achieves its function when the microprocessor operates in accordance with the computer program. Here, the computer program is made up of a combination of plural operation codes indicating a command to a computer to achieve a predetermined function. 
         [0140]    Furthermore, a part or all of the constituent elements of each apparatus described above may be made up of one system LSI (Large Scale Integration). The system LSI is a super multifunctional LSI manufactured by integrating plural structural units on one chip, and in particular, it is a computer system including a microprocessor, a ROM, a RAM, etc. A computer program is stored in the RAM. The system LSI achieves its function as the microprocessor operates in accordance with the computer program. 
         [0141]    Furthermore, a part or all of the constituent elements of each apparatus described above may be made up of an IC card which can be attached to and detached from each apparatus or a stand-alone module. The IC card or the module is a computer system which is made up of a microprocessor, a ROM, a RAM, etc. The IC card or the module may include the above super multifunctional LSI. The IC card or the module achieves its function as the microprocessor operates in accordance with the computer program. The IC card or the module may be tamper-resistant. 
         [0142]    Moreover, the present invention may be the methods described above. Moreover, the present invention may be a computer program which achieves the methods by a computer and may be digital signals made up of the computer program. 
         [0143]    Furthermore, the present invention may be a computer-readable recording medium such as a flexible disk, a hard disk, a CD-ROM, an MO, a DVD, a DVD-ROM, a DVD-RAM, a BD (Blu-ray Disc (registered trademark)), a semiconductor memory, or the like in which the computer program or the digital signals are recorded. Moreover, the present invention may be the above digital signals which are recorded in these recording media. 
         [0144]    Moreover, the present invention may transmit the above computer program or digital signals via an electrical communication circuit, a wireless or wired communication circuit, a network such as Internet, a data broadcast, etc. 
         [0145]    Moreover, the present invention may be a computer system provided with a microprocessor and a memory in which the memory may store the above computer program and the microprocessor may operate in accordance with the above computer program. 
         [0146]    Moreover, the present invention may be carried out by another independent computer system by transferring the above program or the digital signals recorded in the recording medium or transferring the program or the digital signals via the above network or the like. 
         [0147]    Furthermore, the present invention may be any combination of the above embodiments and modifications. 
         [0148]    Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention. 
       INDUSTRIAL APPLICABILITY 
       [0149]    The present invention may be applied to a digital broadcast receiving apparatus for receiving a terrestrial digital broadcast and a satellite wave digital broadcast. In particular, the present invention may be applied to a digital broadcast receiving apparatus such as a household television, a video recorder, a set-top box, an in-car television, a portable television, a car navigation system, a personal computer, a handheld terminal, a mobile phone equipment, etc.