JP2008011430A - Method for retransmitting contents, method for receiving contents, and apparatus for receiving contents - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to decode a content immediately after generating a receiving request in a retransmission system. <P>SOLUTION: The method for retransmitting contents includes: a step to generate a receiving request; a broadcast receiving step to receive a content stream broadcast-transmitted from a content retransmitting apparatus in response to the receiving request; an individual receiving step to receive cache data which have individually transmitted from the content retransmitting apparatus in response to the receiving request and include a position where the content stream can be started to decode; and a synthesizing step to synthesize the cache data received by the individual receiving step and the content stream received by the broadcast receiving step. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a content retransmission method, a content reception method, and a content reception device suitable for a retransmission system that receives and retransmits a digital broadcast.

  In recent years, digital broadcasting that transmits and receives digitally has been started. In digital broadcasting, MPEG (Moving Picture Expert Group) 2 system is adopted. The MPEG system reduces the redundancy in the time direction by taking the difference between frames of the moving image signal, and further reduces the redundancy in the frequency direction by performing orthogonal transform processing such as discrete cosine transform (DCT). Highly efficient compression is possible.

  By the way, the code string compressed in accordance with the MPEG standard has a structure called GOP (Group of Picture). A GOP is composed of several image frames. The GOP includes an intra-frame-coded I picture, a unidirectional predictive encoded P picture, and a bidirectional predictive encoded B picture.

  P and B pictures are encoded by referring to the previous and subsequent frames, and must be decoded using the previous and subsequent frames at the time of decoding. On the other hand, since the I picture is encoded using only the information in the frame, it can be decoded only by the information in the frame at the time of decoding. Therefore, one I picture is always provided in the GOP, and the encoding is completed in the GOP. Therefore, at the time of decoding, it cannot be completely decoded unless it is from the head data of the GOP.

  By the way, in recent years, digital broadcast program distribution using the Internet protocol (IP) has been studied. IP re-transmission, in which a digital broadcast is once received by a re-transmission apparatus and transmitted via the Internet using an IP packet, is about to be implemented. In the IP retransmission, the received digital broadcast is converted into an IP packet and retransmitted to the Internet by multicast.

  Even in such IP retransmission, complete decoding is impossible if there is no data from the beginning of the GOP. Therefore, in the digital television receiver, depending on the decoding start timing, decoding may be started with a delay of 1 GOP at the maximum from the start of reception.

  In Patent Document 1, in order to reduce the channel change time, the incoming data stream is cached according to the channel change command, the program specifying information (PSI) included in the incoming data stream is searched, and the PSI is determined. A technique for decoding a cache data stream is disclosed.

However, also in this patent document 1, the decoding process may be started with a delay of 1 GOP at the maximum from the start of reception.
JP 2005-522953 A

  Thus, conventionally, when receiving a digital broadcast, the decoding process may be delayed by a maximum of 1 GOP from the start of reception. For this reason, there has been a problem that it takes a relatively long time from the start of reception until the program is displayed in the television receiver.

  An object of the present invention is to provide a content retransmission method, a content reception method, and a content reception device that can display a program by decoding immediately after the start of reception.

  The content receiving method according to the present invention includes a step of generating a reception request, a broadcast receiving step of receiving a content stream broadcast from the content retransmission apparatus in response to the reception request, and a response to the reception request. Cache data individually transmitted from the content retransmitting apparatus, the cache receiving data including the decoding start possible position of the content stream, and the cache data received by the individual receiving step. A synthesizing step for synthesizing the content stream received by the information receiving step.

  According to the present invention, it is possible to display a program by decoding immediately after the start of reception.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a retransmission system for realizing a content retransmission method and a content reception method according to the first embodiment of the present invention.

  In this embodiment, as shown in FIG. 1, the re-transmission system enables re-transmission by using the IP network 20 for data transmission between the re-transmission side and the reception side of the broadcast content. Yes.

  The retransmission side is constituted by a digital broadcasting device 10 as a content retransmission device. On the other hand, the receiving side is constituted by a set top box 40 as a content receiving device. In FIG. 1, only one content receiving device is shown on the receiving side, but the receiving side is configured by a plurality of set-top boxes 40 that can be connected to the IP network 20 and installed in each home.

  The digital broadcast device 10 includes a tuner 11, a multicast server 12, and a cache server 13. The tuner 11 receives the broadcast and sends the broadcast data to the multicast server 12 and the cache server 13. The multicast server 12 transmits broadcast data to the IP network 20 by multicast. In other words, the digital broadcast device 10 can receive a digital broadcast and retransmit it to the IP network. Further, the cache server 13 transmits part of the broadcast data to the IP network 20 by unicast.

  The IP network 20 is a network capable of communication using an IP protocol such as the Internet. Data from the digital broadcast apparatus 10 that performs retransmission is transferred to the router 30 via the IP network 20. Data from the router 30 is transferred to the digital broadcasting device 10 via the IP network 20.

  The set-top box 40 on the receiving side can generate a reception request (CH reception request) to the router 30. The router 30 relays communication packets between the IP network 20 and the set-top box 40 on the receiving side. The router 30 has a function of selectively transferring the multicast data transmitted by the multicast server 12 to the set top box 40 that has issued the CH reception request.

  The set-top box 40 is arranged in each home as a terminal for receiving retransmission broadcasts, for example, and receives and plays back the retransmitted digital broadcasts.

  Next, a specific configuration of the digital broadcasting apparatus 10 will be described with reference to FIGS. FIG. 2 is an explanatory view showing a TTS packet, and FIG. 3 is an explanatory view for explaining the operation of the multicast server 12 in FIG. FIG. 4 is a block diagram showing a specific configuration of the cache server 13 in FIG. FIG. 5 is an explanatory diagram for explaining the operation of the cache server 13 in FIG.

  A digital broadcast signal is input to the tuner 11. In digital broadcasting, the MPEG2 system is adopted. MPEG2 is designed to transmit transmission data in units of packets in order to facilitate time division multiplexing of a plurality of images, sounds, data, and the like. One packet is composed of the same type of data, and an identification signal indicating the type of data is added to each packet. In the MPEG2 standard, a signal is transmitted by a transport stream (TS) having a transport packet (TS packet) having a length of 188 bytes as a transmission unit. Each stream such as video data and audio data is transmitted by an elementary stream (ES).

  The tuner 11 receives a digital broadcast and extracts a data stream from the broadcast signal. The tuner 11 converts each TS packet constituting the data stream into a TTS (see FIG. 2) to which a 32-bit time stamp is added. This time stamp is generated by counting a predetermined clock by a counter (not shown), and a unique value is assigned to each TS within the period range of the counter. The data stream (TTS data) converted to TTS (see FIG. 3) is sent to the cache server 13 and the multicast server 12.

  The multicast server 12 packetizes the TTS every predetermined number and transmits the packets in multicast. As shown in FIG. 3, the multicast data is packetized into RTP packets defined by RFC1889, and further RTP packets are packetized into UDP / IP packets defined by RFC768 and RFC791. The RTP packet includes the sequence number of the RTP packet. The IP packet includes a source address and a multicast address.

  Multicast transmitted IP packets are distributed via the IP network 20. In this way, digital broadcast IP retransmission can be performed.

  In the present embodiment, the digital broadcast device 10 has a cache server 13. The cache server 13 stores the received TTS as cache data. Further, the cache server 13 individually transmits the cache data based on a request from the set-top box 40 on the receiving side.

  In FIG. 4, the cache server 13 includes a control unit 15, a reception unit 16, a data cache unit 17, and a communication unit 18. The control unit 15 controls each unit of the cache server 13. The receiving unit 16 receives TTS data from the tuner 11 and sends it to the data cache unit 17. The data cache unit 17 sequentially stores TTS data as cache data. Further, the data cache unit 17 sends the stored cache data to the communication unit 18 under the control of the control unit 15.

  When the communication unit 18 receives a cache data transmission request from the receiving side via the IP network 20, the communication unit 18 transmits the cache data transmission request to the control unit 15. When receiving the cache data transmission request, the control unit 15 instructs the data cache unit 17 and the communication unit 18 to transmit the cache data to the cache data transmission request source. Thereby, the communication unit 18 packetizes the data in the data cache unit 17 and transmits it to the IP network 20 by unicast. The data cache unit 17 stores a predetermined amount of the latest data in advance, and erases old data when the storage amount exceeds a predetermined amount.

  As shown in FIG. 5, the data cache unit 17 sequentially stores input data streams, and stores, for example, the latest data stream of 1 GOP or more as cache data. Thereby, the cache data always includes the data of the head portion of the GOP. The communication unit 18 of the multicast server 12 transmits, for example, 1 GOP worth of cache data stored in the data cache unit 17 as unicast data.

  The communication unit 18 obtains unicast data by packetizing cache data into RTP packets in order from the top, and further packetizing the RTP packets into UDP / IP packets in substantially the same manner as multicast data from the multicast server 12. In this case, the communication unit 18 sets the IP address of the set-top box 40 on the receiving side that has issued the cache data transmission request instead of the multicast address as the transmission destination of the IP packet.

  If the delay time difference between the transmission processing of the cache server 13 and the transmission processing of the multicast server 12 is ignored, the unicast data transmitted by the communication unit 18 includes the head portion of the GOP to which the multicast data belongs at the time when the cache data transmission request occurs. 1 GOP worth of data is included.

  Next, a specific configuration of the television receiver will be described with reference to FIG. FIG. 6 is a block diagram showing a specific configuration of the set top box 40 in FIG.

  The set top box 40 is provided with a control unit 49. The control unit 49 controls each part in the set top box 40 (not shown). A packet from the router 30 is given to the communication unit 41. The communication unit 41 is controlled by the control unit 49 and transmits a CH reception request to the router 30. The communication unit 41 receives a broadcast content packet from the router 30. Of the received packets, the communication unit 41 outputs multicast packets to the multicast buffer 42 and outputs unicast packets to the unicast buffer 43.

  In the present embodiment, the communication unit 41 is controlled by the control unit 49 and transmits a cache data transmission request when a channel selection request is made. In this case, the communication unit 41 designates the destination cache server by the IP address. Note that the control unit 49 acquires and stores the IP address of the cache server in advance, and the communication unit 41 uses the IP address specified by the control unit 49. The transmitted cache data transmission request is given to the cache server 13 of the digital broadcast apparatus 10 via the router 30 and the IP network 20. When the communication unit 41 receives the cache data from the router 30, the communication unit 41 outputs a notification indicating the reception to the control unit 49. When detecting the reception of the cache data by the communication unit 41, the control unit 49 searches and analyzes a PAT (Program Association Table) and a PMT (Program Map Table) from the received cache data. The control unit 49 sets the ES to be selected in the demultiplexing unit 45 based on the analysis result. In addition, the control unit 49 instructs the TS combining unit 44 to combine the multicast packet and the unicast packet and to transmit the combined packet data to the demultiplexing unit 45 (TS transmission).

  In response to the TS transmission start instruction, the TS synthesizing unit 44 reads out the unicast data (cache data) stored in the unicast buffer 43 and searches for the head of the GOP. The TS synthesizing unit 44 skips data until it detects the GOP head packet. The TS synthesizing unit 44 detects the head of the GOP, reads the cache data after the GOP head portion in order from the unicast buffer 43, and sends it to the demultiplexing unit 45 in the MPEG2-TS format. The reading of the cache data by the TS combining unit 44 and the transmission to the demultiplexing unit 45 are repeated until all the cache data in the unicast buffer 43 is read.

  When detecting that the reading of the cache data is completed, the TS combining unit 44 switches the data reading source from the unicast buffer 43 to the multicast buffer 42. That is, the TS combining unit 44 performs reading so that cache data and multicast data are continuous. First, the TS combining unit 44 searches for a connection position of multicast data.

  For example, the TS synthesizing unit 44 sequentially reads TS packets from the multicast buffer 42, and the read TS packet is the same TS packet as the cache data TS packet (hereinafter referred to as the final TS packet) read last from the unicast buffer 43. Determine whether it is a packet. The TS synthesizing unit 44 can determine whether the TS packets match or not by comparing the TTS time stamps. The TS combining unit 44 skips multicast data until the TS packet from the multicast buffer 42 matches the final TS packet. When the TS combining unit 44 detects that the TS packet read from the multicast buffer 42 matches the final TS packet, the TS packet immediately after the matched TS packet (hereinafter referred to as a concatenated head TS packet) is used as the concatenated head position. And

  The TS synthesizing unit 44 concatenates the concatenated head TS packet to the final TS packet, and subsequently reads TS packets sequentially from the multicast buffer 42 and sends them to the demultiplexing unit 45. Thus, TS packets after the TS packet including the head portion of the GOP corresponding to the timing of the CH reception request are successively and sequentially output from the TS combining unit 44.

  The demultiplexing unit 45 demultiplexes the transport stream, extracts only the packet corresponding to the PID designated by the control unit 49 for each type, and outputs the extracted packet. That is, the demultiplexing unit 45 provides the video decoder 46 and the audio decoder 47 with video and audio packets corresponding to the PID designated by the user, respectively.

  The video decoder 46 and the audio decoder 47 decode the input video or audio data, respectively, to obtain a video signal and an audio signal. The video signal is supplied to a display device (not shown), and the audio signal is supplied to a device such as a speaker (not shown). In this way, the retransmitted broadcast content can be viewed.

  Next, the operation of the embodiment configured as described above will be described with reference to FIGS. FIG. 7 is an explanatory diagram for explaining TS synthesis on the receiving side, and FIG. 8 is a timing chart for explaining the operation of the entire retransmission system.

  The standby state in FIG. 8 indicates a state in which a digital broadcast signal is not received on the receiving side. Even in this state, IP retransmission of the digital broadcast is performed up to the router 30 that distributes the broadcast. That is, the tuner 11 of the digital broadcast 10 receives the digital broadcast and adds a 32-bit time stamp to each TS packet of the data stream. The tuner 11 sends the generated TTS data to the cache server 13 and the multicast server 12.

  The multicast server 12 packetizes the TTS data for every predetermined number and transmits it in multicast. This multicast data is transmitted to the router 30 via the IP network 20. The double line in FIG. 8 indicates this multicast transmission. As shown in FIG. 8, this multicast transmission is repeated even in the standby state.

  On the other hand, the cache server 13 stores the received TTS as cache data. The contents in the data cache unit 17 in the cache server 13 are sequentially updated, and the latest data for 1 GOP or more is always stored.

  Here, it is assumed that the set-top box 40, which is a predetermined receiving terminal on the receiving side, starts receiving digital broadcasting. The control unit 49 in the set-top box 40 generates a CH reception request for performing channel selection based on a user operation to the router 30. When the router 30 receives the CH reception request, the router 30 selectively transmits corresponding CH multicast data to the set-top box 40 that has issued the CH reception request.

  The control unit 49 also transmits a cache data request transmission together with the CH reception request. This cache data request transmission is supplied from the router 30 to the cache server 13 via the IP network 20.

  When receiving the cache data request transmission via the communication unit 18, the control unit 15 of the cache server 13 controls the data cache unit 17 and the communication unit 18 to issue the cache data request transmission to the stored cache data. Unicast transmission to the set top box 40.

  The set top box 40 receives multicast data and unicast data transferred from the router 30 via the communication unit 41. The communication unit 41 gives multicast data to the multicast buffer 42 for storage, and gives unicast data to the unicast buffer 43 for storage. The multicast buffer 42 updates multicast data that is sequentially input while additionally storing it.

  When the communication unit 41 receives the cache data from the router 30, the communication unit 41 outputs a notification indicating the reception to the control unit 49.

  When detecting the reception of the cache data by the communication unit 41, the control unit 49 searches and analyzes the PAT and PMT from the received cache data. Based on the analysis result, the control unit 49 sets a PID corresponding to the ES to be selected in the demultiplexing unit 45. In addition, the control unit 49 instructs the TS combining unit 44 to combine the multicast packet and the unicast packet and to transmit the combined packet data to the demultiplexing unit 45 (TS transmission).

  As shown in FIG. 7, it is assumed that a reception request is generated in the middle of a predetermined GOP of TS data transferred from the digital broadcast apparatus 10 to the router 30. The cache server 13 of the digital broadcast apparatus 10 transmits the cache data for about 1 GOP that is held at the timing of transmission of the cache data request generated along with this reception request. As a result, as shown in FIG. 7, the unicast buffer 43 transfers and stores TTS data from about 1 GOP before the timing of the reception request. The cache data includes data at the head of the GOP.

  The TS synthesis unit 44 detects the GOP head packet from the cache data stored in the unicast buffer 43, and sequentially reads TS packets after the GOP head packet. That is, the packet of the C1 portion is read without reading the packet of the A1 portion in FIG. When the TS combining unit 44 reads all TS packets after the GOP head packet in the unicast buffer 43, it next reads TS packets from the multicast buffer 42 (see FIG. 8).

  In this case, the TS synthesis unit 44 searches for a TS packet that matches the last TS packet read last from the unicast buffer 43. Then, the TS combining unit 44 performs reading from the packet after the packet that matches the final TS packet (concatenated head TS packet). That is, without reading the TS packet of the A2 portion, the packet of the C2 portion after the concatenated head TS packet is read. In this way, the TS synthesis unit 44 obtains a series of TS packets including a TS packet from the GOP head as shown in FIG.

  Thus, the demultiplexing unit 45 is given the TS stream from the GOP head. The demultiplexing unit 45 demultiplexes the transport stream, extracts only the packets corresponding to the PID designated by the control unit 49 for each type, and outputs them. That is, the demultiplexing unit 45 provides the video decoder 46 or the audio decoder 47 with video and audio packets corresponding to the PID designated by the control unit 49, respectively. The video decoder 46 and the audio decoder 47 decode the input video or audio data, respectively, to obtain a video signal and an audio signal.

  As described above, in the present embodiment, the digital broadcasting device holds the latest cache data, and when a cache data transmission request is generated, the cache data is transmitted to the receiving terminal that issued the cache data transmission request by unicast. It is like that. That is, when a reception request is generated, cache data including the head data of the GOP including the timing of this reception request is supplied to the receiving terminal. As a result, each receiving terminal captures cache data at the start of a reception request, combines the cache data and multicast data, obtains the top data of the GOP included in the reception request, and decodes from the GOP head Is possible. Thereby, immediately after the start of the reception request, it is possible to decode and reproduce and display data from the GOP head.

  FIG. 9 is a flowchart showing the second embodiment of the present invention.

  In the first embodiment, the digital broadcasting device 10 accumulates cache data for one GOP or more in the cache server so that the leading data of the GOP is reliably stored. On the receiving side, the head of the GOP is detected from the cache data stored in the unicast buffer 43, thereby enabling decoding immediately after reception. On the other hand, in the present embodiment, the cache data from the GOP head can be stored and transmitted so that the GOP head detection process on the receiving side can be omitted.

  This embodiment differs only in the control method of the data cache unit 17 in the cache server 13, and can be realized by the same hardware configuration as that of the first embodiment.

  FIG. 9 is a flowchart showing a control method of the data cache unit 17.

  When the TTS data is received, the control unit 15 in the cache server 13 dynamically controls the data stored in the data cache unit 17 so that the cache data is in a prescribed format. For example, the control unit 15 stores data for a predetermined period from the beginning of the GOP as cache data.

  That is, when the control unit 15 receives new data from the new cache data reception standby state in step S1 of FIG. 9, the control unit 15 determines a cache data head candidate in step S2. In step S3, the control unit 15 determines whether the new data satisfies the condition for the leading candidate. If the new data satisfies the condition of the leading candidate, the control unit 15 causes the data cache unit 17 to store the corresponding packet as a leading candidate (step S4). There may be a plurality of head candidates. For example, it is possible to set the head candidate condition to be the head of the GOP.

  Next, the control unit 15 determines the cache head from the stored cache head candidates (step S5). That is, the control unit 15 determines whether or not each head candidate satisfies the cache head condition in the newest order. Next, the control unit 15 determines a head candidate that first satisfies the cache head condition as an actual cache head, and stores the cache head in the data cache unit 17 (steps S6 and S7).

  For example, the control unit 15 determines that the leading condition is satisfied when the leading GOP is detected. In this case, the head candidate is stored as an immediate cache head.

  Next, the control unit 15 determines a cache update condition in step S8. The control unit 15 determines that the cache is updated when the cache update condition is satisfied. For example, the control unit 15 determines that the cache update condition is satisfied when the GOP head is detected. In this case, it is considered that the immediate cache update condition is satisfied at the detection timing of the leading candidate.

  When the cache update condition is satisfied, the control unit 15 shifts the processing from step S9 to step S10 and executes the cache update. In this case, the control unit 15 deletes data older than the beginning of the cache data as an update operation.

  FIG. 10 is an explanatory diagram for explaining cache data stored in the data cache unit 17 by such control of the data cache. As described above, the control unit 15 determines whether or not the newly input TTS data is the cache head depending on whether or not it is the GOP head. As a result, as shown in FIG. 10, the cache data stored in the data cache unit 17 becomes data for a predetermined period from the beginning of the GOP.

  In the above description, since all of the head candidate condition, the cache head condition, and the cache update condition are the GOP head, the cache head is immediately updated when the GOP head is detected. On the other hand, the control unit 15 may change the setting of these conditions. Thereby, the control part 15 can memorize | store data of various formats as cache data. For example, when the control unit 15 sets the cache update condition to be 100 msec after GOP detection, it is possible to store at least 100 msec of data as cache data.

  FIG. 11 is a timing chart for explaining the operation of the retransmission system employed in the second embodiment. FIG. 12 is an explanatory diagram for explaining TS synthesis on the receiving side.

  The example of FIG. 11 is different from the timing chart of FIG. 8 in that the top of the GOP head is omitted when reading from the unicast buffer 43 (see FIG. 6) on the receiving side.

  As shown in FIG. 8, the unicast buffer 43 stores cache data for a predetermined period from the beginning of the GOP. Therefore, the TS synthesizing unit 44 may read out the cache data stored in the unicast buffer 43 in order from the top data after the reception request. Therefore, the GOP head search process (see FIG. 8) in the TS synthesizing unit 44 and the unicast buffer 43 can be omitted.

  Other operations are the same as those in the first embodiment.

  Thus, also in this embodiment, the same effect as that of the first embodiment can be obtained.

  FIG. 13 is a block diagram showing a third embodiment of the present invention. In FIG. 13, the same components as those of FIG.

  This embodiment is an example applied to a retransmission system having a scramble function. The present embodiment is different from the embodiment of FIG. 4 in that a digital broadcasting apparatus having a cache server 50 instead of the cache server 13 is adopted on the retransmission side.

  The cache server 50 is different from the cache server 13 in that a descrambling unit 51 and a re-scramble unit 52 are added. The digital broadcast signal input to the tuner 11 (see FIG. 1) is scrambled by a broadcast station (not shown). In the scrambled stream, the head of the GOP cannot be detected. Therefore, in the present embodiment, descrambling processing is performed to control writing and reading of the data cache unit 17.

  That is, the descrambling unit 51 performs descrambling on the TTS data from the receiving unit 16 and decodes it. The descrambling unit 51 obtains a descrambling key by decrypting key information in a predetermined conditional access method such as ECM (Entitlement Control Message) in the ARIB standard.

  The descrambling unit 51 outputs the TTS data after the descrambling process to the data cache unit 17. Thus, the writing and reading control of the data cache unit 17 is performed on the descrambled TTS data. Thus, the control unit 15 can detect the head of the GOP and can set data for a predetermined period from the head of the GOP as cache data.

  The re-scramble unit 52 scrambles the TTS data from the data cache unit 17 using a scramble key and outputs the scrambled data to the communication unit 18. The re-scramble unit 52 uses the descrambling key used in the descrambling unit 51.

  Thus, in this embodiment, even when a digital broadcast signal is scrambled, data at a predetermined position in the GOP can be stored as cache data.

  In the case where only the head of the GOP is included as the cache data and it is not necessary to define the position of the head of the GOP in the cache data, even if the broadcast signal is scrambled, the present embodiment There is no need for descrambling and re-scramble processing.

  FIG. 14 is a block diagram showing a fourth embodiment of the present invention. In FIG. 14, the same components as those of FIG.

  This embodiment is an example applied to a retransmission system having a scramble function. This embodiment is different from the embodiment of FIG. 1 in that a set top box 55 is adopted on the receiving side. The set top box 55 is different from the set top box 40 in that a demultiplexing / descramble unit 56 is used instead of the demultiplexing unit 45.

  The digital broadcast signal input to the tuner 11 (see FIG. 1) is scrambled by a broadcast station (not shown). It is necessary to acquire an ECM for decoding a stream that has been scrambled. Furthermore, in order to acquire ECM, it is necessary to acquire PMT. The ECM is updated at a predetermined cycle. Unless the updated ECM is acquired, it is not possible to descramble the data after the first data of the GOP.

  Therefore, in the present embodiment, the demultiplexing / descrambling unit 56 acquires the PAT, PMT, and ECM from the multicast buffer 42 or the unicast buffer 43 prior to processing for the output from the TS combining unit 44. It has become.

  The demultiplexing / descrambling unit 56 decrypts the acquired ECM and acquires a descrambling key. That is, the control unit 49 performs ECM retrieval together with PAT and PMT retrieval, further decrypts the acquired ECM using a predetermined method, and obtains a descrambling key from the decryption result. The demultiplexing / descrambling unit 56 performs descrambling on the output of the TS combining unit 44 using the descrambling key for the selected ES simultaneously with the ES selection processing. Thereby, the demultiplexing / descrambling unit 56 can sequentially execute descrambling from the first TS for transmission from the TS synthesis unit 44.

  The demultiplexing / descrambling unit 56 acquires PAT, PMT, and ECM by the first output of the TS combining unit 44 and performs the descrambling process by the second output from the TS combining unit 44. Good. Further, the demultiplexing / descrambling unit 56 may directly access the multicast buffer 42 or the unicast buffer 43 and acquire the PAT and ECM.

  FIG. 15 is an explanatory diagram for explaining a fifth embodiment of the present invention. FIG. 15 is an explanatory diagram for explaining the operation of the cache server 50.

  This embodiment can be realized by a hardware configuration similar to that of FIG. This embodiment is an example applied to a retransmission system having a scramble function.

  As described above, in order to perform descrambling on the receiving side, an updated ECM and a PMT for acquiring this ECM are required. When the ECM is updated, the ECM before and after the update is included in the stream over 2 GOPs. Therefore, when the ECM is updated, the descrambling process can be performed from the GOP head by acquiring the ECM and PAT immediately before the head of each GOP on the receiving side.

  Therefore, in the present embodiment, the control unit 15 (see FIG. 13) controls the data cache unit 17 so as to include PAT, PMT, and ECM immediately before the GOP head as cache data.

  That is, as shown in FIG. 15, the cache data is in the order of the PAT TTS packet, the PMT TTS packet, the TTS packet, the ECM TTS packet, and the GOP head TTS packet from the head.

  Such cache data control can be realized by the processing flow shown in FIG. That is, in FIG. 9, it is assumed that the condition of the head candidate is satisfied by detecting the PAT. Further, it is assumed that the condition at the head of the cache is satisfied by detecting PAT and PMT in order. Further, it is assumed that the cache update condition is satisfied by detecting the GOP. As a result, as shown in FIG. 15, the cache data becomes data that appears in the order of PAT-PMT-GOP from the top.

  On the receiving side, in the example of FIG. 14, before descramble processing the output of the TS synthesizer 44, it is necessary to output, for example, two outputs from the TS synthesizer 44 in order to acquire and decode the ECM. there were. On the other hand, in the present embodiment, since the PAT and ECM are input to the demultiplexing / descramble unit 56 as the cache data before the head data of the GOP, there is no need to perform the ECM decoding process in advance. The TS synthesis unit 44 only needs to output the synthesized data once.

  FIG. 16 is an explanatory diagram for explaining a modification of the fifth embodiment. FIG. 16 shows the operation of the cache server 50.

  In the embodiment of FIG. 15, the control unit 15 (see FIG. 13) controls the data cache unit 17 to include the PAT and ECM immediately before the GOP head as the cache data. Only the PAT, PMT, and ECM immediately before the GOP head need be included in the cache data. Therefore, in the example of FIG. 16, the control unit 15 extracts only the PAT, PMT, and ECM immediately before the beginning of the GOP, and rearranges them in the order of PAT, PMT, and ECM to obtain cache data.

  Note that the control unit 15 erases the TTS except the PAT, PMT, and ECM from the cache data. As the time stamps of PAT, PMT, and ECM, values obtained by back calculation using the time stamps of subsequent data are used.

  According to this example, the top of cache data transmitted at the time of transmission is in the order of PAT, PMT, ECM, and GOP head. Therefore, even in this case, on the receiving side, it is possible to decode the retransmitted data by the same operation as in the fifth embodiment.

  FIG. 17 is a timing chart for explaining the sixth embodiment of the present invention. FIG. 17 shows the operation of the retransmission system employed in the sixth embodiment. In FIG. 17, the description of the same procedure as in FIG. 11 is omitted. In the present embodiment, the cache server 13 or 50 in FIG. 4 or FIG. 13 can be adopted as the cache server on the retransmission side, and the set top box 55 in FIG. 14 is used as the set top box on the reception side. Can be adopted.

  The example of FIG. 17 is for transmitting channel selection data for descrambling processing before transmission of cache data in the digital broadcasting apparatus. The control unit 15 extracts PAT, PMT, and ECM in the cache data from the data cache unit 17 as channel selection data. When cache data request transmission occurs from the receiving side, the control unit 15 transmits channel selection data PAT, PMT, and ECM prior to cache data transmission.

  The control unit 49 on the receiving side gives the received channel selection data to the demultiplexing / descrambling unit 56 for data analysis, performs ES selection, and sets a descrambling key. Next, the control unit 15 on the retransmission side transmits cache data including the GOP head. The control unit 49 on the receiving side causes the TS combining unit 44 to combine the cache data stored in the unicast buffer 43 and the multicast data stored in the multicast buffer 42. The demultiplexing / descrambling unit 56 performs descrambling processing on the output of the TS synthesis unit 44 using the set descrambling key.

  On the receiving side, it is not necessary to perform PAT and PMT searches, ES selection associated therewith, and descramble key settings for the stored cache data.

  Thus, in the present embodiment, the extracted PAT, PMT, and ECM are transmitted separately from the transmission of the cache data in the digital broadcasting device. The receiving side performs descrambling using the received PAT, PMT, and ECM. Thus, also in this embodiment, the same effects as those in the above embodiments can be obtained.

  FIG. 18 is an explanatory diagram for explaining a seventh embodiment of the present invention. FIG. 18 is a diagram for explaining TS synthesis on the receiving side. The present embodiment can be realized by a hardware configuration similar to that of each of the above embodiments.

  In each of the above embodiments, the final data of the TTS data in the cache data is configured to be included in the TTS data in the multicast data on the receiving side. However, for example, when a transmission delay of multicast data occurs, there is a possibility that data at the time of switching from cache data to multicast data becomes discontinuous.

  Therefore, in the present embodiment, in consideration of the transmission delay of multicast data, the cache data continues to be stored even after the reception request, and the cache data having a sufficiently long time is transmitted to the receiving side. Yes. That is, on the transmission side, after the cache data is transmitted, the cache data that is sequentially accumulated is continuously transmitted as a continuation.

  FIG. 18 shows that multicast data is received with a delay of the transmission delay time with respect to the reception request. On the other hand, in the unicast buffer, not only the memory at the beginning of transmission but also the cache data for the continuation is stored. By securing a sufficient duration for the transmission delay time, the time stamp is continuous between the TTS data in the unicast buffer and the TTS data in the multicast buffer without causing data discontinuity. Can be synthesized as follows.

  Thus, in the present embodiment, reception can be performed without interruption even if the start of multicast packet transfer is delayed. As a result, immediately after the start of reception, data including the head of the GOP can be reliably decoded.

1 is a block diagram showing a retransmission system for realizing a content retransmission method and a content reception method according to a first embodiment of the present invention. Explanatory drawing which shows a TTS packet. Explanatory drawing for demonstrating operation | movement of the multicast server 12 in FIG. The block diagram which shows the specific structure of the cache server 13 in FIG. Explanatory drawing for demonstrating operation | movement of the cache server 13 in FIG. The block diagram which shows the concrete structure of the set top box 40 in FIG. Explanatory drawing for demonstrating TS synthetic | combination in the receiving side. The timing chart for demonstrating operation | movement of the whole retransmission system. The flowchart which shows the 2nd Embodiment of this invention. Explanatory drawing for demonstrating the cache data memorize | stored in the data cache part 17. FIG. The timing chart for demonstrating operation | movement of the retransmission system employ | adopted in 2nd Embodiment. Explanatory drawing for demonstrating TS synthetic | combination in the receiving side. The block diagram which shows the 3rd Embodiment of this invention. The block diagram which shows the 4th Embodiment of this invention. Explanatory drawing for demonstrating the 5th Embodiment of this invention. Explanatory drawing for demonstrating the modification of 5th Embodiment. The timing chart for demonstrating the 6th Embodiment of this invention. Explanatory drawing for demonstrating the 7th Embodiment of this invention.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 10 ... Digital broadcasting apparatus, 11 ... Tuner, 12 ... Multicast server, 13 ... Cache server, 20 ... IP network, 30 ... Router, 40 ... Set top box.

Claims (5)

Receiving a content stream;
A quiche step of sequentially storing and updating the received content stream to hold data including a decoding start possible position of the content stream as cache data;
A retransmission step for broadcasting the received content stream;
An individual transmission step of individually transmitting the cache data held by the cache step to the content reception device that has generated the reception request when a reception request is generated from a predetermined content reception device; Resend method. Descrambling the received content stream before storing the cached data by the caching step;
The content re-transmission method according to claim 1, further comprising: re-descrambling the cache data before transmitting the cache data in the individual transmission step. Generating a receive request;
A broadcast receiving step of receiving a content stream broadcast from the content retransmission apparatus in response to the reception request;
An individual reception step of receiving cache data individually transmitted from a content retransmission apparatus in response to the reception request, the cache data including a decoding start possible position of the content stream;
A content receiving method comprising: a combining step of combining the cache data received in the individual receiving step and the content stream received in the broadcast receiving step.   4. The content receiving method according to claim 3, further comprising a step of descrambling the content stream synthesized by the synthesizing step. Control means for generating a reception request;
Receiving means for receiving a stream from the content retransmission apparatus;
A broadcast stream storage means for storing the received content stream when the content stream broadcast from the content retransmission apparatus in response to the reception request is received by the reception means;
When cache data that is individually transmitted from the content retransmission apparatus in response to the reception request and includes the decoding start possible position of the content stream is received by the reception unit, the received cache Individual stream storage means for storing data;
A content receiving apparatus comprising: combining means for combining the cache data stored by the individual stream storage means and the content stream stored by the broadcast stream storage means.

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