JP3881900B2 - Data stream recording apparatus, data stream recording method and program - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a data stream recording apparatus, a data stream recording method, and a program.
[0002]
[Prior art]
Digital broadcasting that broadcasts content such as images and sounds in the form of a data stream composed of continuous packets including data representing the content is used.
[0003]
Digitally broadcast content can be stored in a storage device as data in digital format, and data deterioration is unlikely to occur during storage.
For this reason, a technique for protecting rights such as copyrights relating to digitally broadcast content is used. Specifically, there is a method of encrypting and storing data representing content.
[0004]
[Problems to be solved by the invention]
However, if the encryption method is not strong enough to attack, the encrypted data can be easily decrypted by a person who does not know the decryption key, and the data cannot be sufficiently protected. .
[0005]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a data stream recording apparatus and a data stream recording method for sufficiently protecting data.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a data stream recording apparatus according to the first aspect of the present invention provides:
Thinning means for acquiring a data stream and distributing a plurality of packets constituting the acquired data stream to a plurality of groups according to a predetermined rule;
First storage means having a first storage area that substantially prevents access from other than the thinning means;
Second storage means having a second storage area,
The thinning-out means stores a part of the packets belonging to the group in the first storage area, and the acquired data stream is replaced with a packet for a dummy packet. Converted into a replaced data stream and stored in the second storage area,
The dummy packet includes identification information that identifies a thinning target packet replaced by the dummy packet.
It is characterized by that.
[0007]
The thinning means may generate aggregate data representing a combination of packets belonging to the partial group and store the aggregated data in the first storage area.
In this case, the identification information may include information representing a logical position occupied by the packet replaced by the dummy packet including the identification information in the aggregated data.
[0008]
The identification information may include information representing a logical position occupied in the first storage area by a packet replaced by a dummy packet including the identification information.
[0009]
The packet constituting the data stream acquired by the thinning-out means and the dummy packet are composed of, for example, a TS (Transport Stream) packet. In this case, the identification information is included, for example, in the payload portion of the TS packet. Just do it.
[0010]
The thinning-out means may comprise combining means for reading out the packets distributed to the plurality of groups from the first and second storage areas and restoring the data stream based on the read-out packets.
[0011]
The thinning unit may include a processor. In this case, the processor may access the first storage area by executing a predetermined program.
[0012]
The first storage unit and the thinning-out unit may be connected to each other via a bus that enables data transmission when the processor executes a predetermined program.
[0013]
The thinning-out means may encrypt the packet distributed to the partial group and / or another group and store the encrypted packet in the first and / or second storage area.
[0014]
A data stream recording method according to the second aspect of the present invention includes:
Acquire a data stream, distribute a plurality of packets constituting the acquired data stream into a plurality of groups according to a predetermined rule,
Storing packets belonging to some groups in a first storage area that substantially prevents access from other than a predetermined access device;
A data stream recording method for converting the acquired data stream into a replaced data stream in which packets assigned to the partial group are replaced with dummy packets and storing the converted data stream in a second storage area. ,
The dummy packet includes identification information that identifies a thinning target packet replaced by the dummy packet.
It is characterized by that.
[0015]
Packets belonging to the partial group may be stored in the first storage area as aggregated data representing a combination of the packets.
In this case, the identification information may include information representing a logical position occupied by the packet replaced by the dummy packet including the identification information in the aggregated data.
[0016]
A program according to the third aspect of the present invention is:
Computer
Thinning means for acquiring a data stream and distributing a plurality of packets constituting the acquired data stream to a plurality of groups according to a predetermined rule;
First storage means having a first storage area that substantially prevents access from other than the thinning means;
A program for functioning as a second storage means having a second storage area,
The thinning unit stores a part of the packets belonging to the group in the first storage area, and the acquired data stream is replaced with a dummy packet for the packet distributed to the part of the group Converted into a replaced data stream and stored in the second storage area,
The dummy packet includes identification information that identifies a thinning target packet replaced by the dummy packet.
It is characterized by that.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a digital broadcast recorder according to an embodiment of the present invention. As shown in the figure, this digital broadcast recorder includes a motherboard 1, a motherboard storage 2, and a receiving unit 3. The motherboard storage 2 is connected to the motherboard 1, and the receiving unit 3 is connected to the motherboard 1 via the connection bus B.
[0018]
The motherboard 1 includes, for example, a processor composed of a CPU (Central Processing Unit), a memory composed of a RAM (Random Access Memory), and a bus controller. The connection bus B is a PCI (Peripheral Component).
Interface) bus.
The memory of the motherboard 1 has a storage area that becomes a work area of the processor of the motherboard 1. The bus controller of the motherboard 1 includes a control circuit for controlling data exchange between the processor of the motherboard 1 and a device external to the motherboard 1 via the connection bus B.
[0019]
The mother board 1 reads out the broadcast recording / reproducing program stored in the motherboard storage 2 and performs the processing described later according to this broadcast recording / reproducing program.
The process controlled by the broadcast recording / reproducing program functionally includes a plurality of processing blocks. Specifically, a demultiplexer 1A, a stream decimation block 1B, a stream synthesis block 1C, a storage recording block 1D, an MPEG (Moving Picture Expert Group) decoding block 1E, and a storage reading block 1F, which will be described later with reference to FIGS. , Each processing block is included.
[0020]
The motherboard storage 2 is composed of a hard disk device or the like, and stores the above-described broadcast recording / reproducing program in advance. Then, in accordance with an access from the mother board 1, data supplied by the mother board 1 is stored, or data stored by itself is read out and supplied to the mother board 1.
[0021]
The receiving unit 3 includes a digital broadcast receiving unit 31, a PCI bus bridge 32, a content storage internal memory 33, and an IDE (Intelligent Drive Electronics) bus bridge 34.
[0022]
The digital broadcast receiving unit 31 includes a demodulation circuit and is connected to the PCI bus bridge 32 via an internal bus. The digital broadcast receiving unit 31 restores TS (Transport Stream) packets constituting the data stream by inputting and demodulating a modulated wave representing the data stream digitally broadcast from the outside. Then, the restored TS packet is supplied to the mother board 1 via the PCI bus bridge 32 and the connection bus B.
The data stream represented by the modulated wave received by the digital broadcast receiving unit 31 represents content composed of images and sounds, and is composed of a plurality of continuous TS packets as shown in FIG.
[0023]
A TS packet is a packet representing an image or sound constituting content, and has a data structure shown in FIG. That is, the TS packet includes a TS packet header and a payload portion (adaptation / payload portion) following the TS packet header.
[0024]
The payload portion is a portion including data representing content. As shown in FIG. 3, each payload part includes data that constitutes the same frame image (or the same sound) in the order in which TS packets including these payload parts are arranged. By connecting each other, a PES (Packetized Elementary Stream) packet can be formed.
[0025]
When the data stream represents MPEG2 format image data (or image data having substantially the same data structure as the MPEG2 format image data), the PES packet is an I picture, B that is data representing an image constituting a moving image. One or more of three types of pictures or P pictures are included. Of these, the B picture and the P picture represent differences from the I picture.
[0026]
As shown in FIG. 3, the PES packet includes a PES header including information for identifying the PES packet and a picture layer including any one of an I picture, a B picture, and a P picture.
[0027]
The PES packet including the I picture includes a sequence header code having a predetermined value. The PES packet including the I picture includes the video sequence layer, the GOP (in addition to the PES header and the picture layer). Group Of Picture) layer.
[0028]
As shown in FIG. 2, the TS packet header includes a synchronization byte, TS error data, payload unit start indicator, transport priority data, PID (Program IDentifier), transport scramble control data, and adaptation field control data in order from the top. And continuity indicators.
[0029]
Among these, the payload unit start indicator indicates whether or not the payload portion of the TS packet including the payload unit start indicator itself includes the top data of the PES packet. Specifically, for example, when the value of the payload unit start indicator is “1”, it indicates that the payload portion of the TS packet including the payload unit start indicator itself includes the head data of the PES packet, When it is “0”, it indicates that the payload part does not include the head data of the PES packet.
[0030]
Therefore, one PES packet is, for example, a TS packet including a payload unit start indicator having a value of “1” in the data stream, and immediately before a next TS packet including a payload unit start indicator having a value of “1”. It is generated by concatenating the payload portions of successive TS packets up to TS packets.
[0031]
The PID is data for identifying which content (for example, which image or sound represents) the payload part of the TS packet including the PID itself represents.
[0032]
The PCI bus bridge 32 is configured by a bus controller or the like, is connected to the motherboard 1 via the connection bus B, and is connected to the IDE bus bridge 34 and the digital broadcast receiver 31 via an internal bus. Yes.
The PCI bus bridge 32 mediates access to the content storage internal memory 33 which is performed by the mother board 1 according to the control of the broadcast recording / reproducing program. It also mediates the supply of data from the digital broadcast receiver 31 to the content storage internal memory 33.
[0033]
The content storage internal memory 33 includes a nonvolatile memory such as a compact flash memory and an interface circuit for transmitting data via the IDE bus.
[0034]
The IDE bus bridge 34 is composed of a bus controller or the like, and is connected to the PCI bus bridge 32 via an internal bus, while being connected to the content storage internal memory 33 via the IDE bus. The IDE bus bridge 34 mediates access to the content storage internal memory 33 that the motherboard 1 performs according to the control of the broadcast recording / playback program.
The PCI bus bridge 32 and the IDE bus bridge 34 substantially prevent this access even if the motherboard 1 accesses the content storage internal memory 33 without following the control of the broadcast recording / reproducing program.
[0035]
(Operation)
Next, the operation of this digital broadcast recorder will be described.
FIG. 4 is a diagram showing a flow of processing for recording content.
FIG. 6 is a diagram showing a flow of processing for reproducing the recorded content.
[0036]
(Recording content)
When a modulated wave representing a data stream is supplied to the digital broadcast receiver 31 of the receiving unit 3, the digital broadcast receiver 31 restores the data stream by demodulating the modulated wave, and the restored data stream Are supplied to the mother board 1 via the PCI bus bridge and the connection bus B.
[0037]
On the other hand, the mother board 1 reads out and executes a broadcast recording / reproducing program from the mother board storage 2 in response to a recording instruction supplied from the outside in accordance with the operation of the operator.
[0038]
When the motherboard 1 executing the broadcast recording / playback program is supplied with the data stream (that is, when TS packets are sequentially supplied), the motherboard 1 specifies the PID included in the supplied TS packets according to the control of the demultiplexer 1A. Then, it is determined whether or not the specified PID indicates content to be accumulated. The content to be accumulated may be designated by data supplied from the outside according to the operation of the operator, for example.
[0039]
If the mother board 1 determines that the PID does not indicate the content to be accumulated, the motherboard 1 discards the TS packet including the PID. If determined that the PID indicates, the motherboard 1 converts the TS packet including the PID as shown in FIG. The data is delivered to each processing block of the stream synthesis block 1C and the stream decimation block 1B.
[0040]
When the TS packet is delivered from the demultiplexer 1A to the stream synthesizing block 1C (that is, when this digital broadcast recorder receives a digital broadcast), the motherboard 1 specifically processes this TS packet according to the control of the stream synthesizing block 1C. The TS packet is delivered to the MPEG decode block 1E without being added.
[0041]
When the TS packet is delivered to the MPEG decoding block 1E, the mother board 1 decodes the image and sound represented by the TS packet according to the control of the MPEG decoding block 1E, and a video signal such as a composite signal as shown in FIG. And output as content data consisting of audio signals.
[0042]
On the other hand, the mother board 1 thins out TS packets sequentially delivered from the demultiplexer 1A to the stream thinning block 1B so as to conform to a certain rule according to the control of the stream thinning block 1B. That is, according to this rule, TS packets are divided into two groups, TS packets belonging to one group (hereinafter referred to as thinning target packets) are written in the content storage internal memory 33 of the receiving unit 3 and belong to the other group A TS packet (hereinafter referred to as a non-decimation target packet) is delivered to the storage recording block 1D. The specific contents of the rules are arbitrary.
[0043]
It is assumed that the mother board 1 writes the thinning target packets to be written into the content storage internal memory 33 in the form of a packet set file composed of serially connected thinning target packets as shown in FIG. Arrangement order of each thinning-out target packet in the packet set file is arbitrary. For example, it may be arranged in the order of arrangement in the original data stream.
Each thinning target packet is assigned, for example, a packet number indicating the number of the thinning target packet from the beginning in the packet set file. FIG. 5 schematically shows a thinning-out target packet to which packet numbers “k−1”, “k”, and “k + 1” (k is an arbitrary integer equal to or greater than 2) are assigned.
[0044]
The motherboard 1 accesses the content storage internal memory 33 via the PCI bus bridge 32 and the IDE bus bridge 34 to write the packet set file (that is, a set of packets to be thinned out) to the content storage internal memory 33. To do. That is, when the motherboard 1 accesses the content storage internal memory 33 and the packet set file is supplied to the receiving unit 3, the PCI bus bridge 32 of the receiving unit 3 transfers the packet set file to the IDE bus bridge 34. The IDE bus bridge 34 accesses the content storage internal memory 33, and stores this packet aggregate file in the storage area of the content storage internal memory 33.
[0045]
On the other hand, the mother board 1 that performs the processing of the stream thinning block 1B delivers the non-thinning target packet delivered to the storage recording block 1D to the storage recording block 1D in the form of a replaced data stream as shown in FIG.
As shown in the figure, the replaced data stream is composed of a data stream having a data structure corresponding to the original data stream received by the receiving unit 3 in which the thinning target packet is replaced with a dummy packet.
[0046]
As shown in FIG. 5, the payload portion of the dummy packet includes identification data for identifying the thinning target packet replaced by the dummy packet. For example, as shown in FIG. 5, the identification data may consist of the above-mentioned packet number, or may consist of an address indicating the position of the thinning-out target packet in the packet set file. FIG. 5 schematically shows the replaced data stream in which the thinning-out target packet assigned the packet number “k” is replaced with a dummy packet.
[0047]
In addition, the contents of the payload portion of the dummy packet are different from the contents of the payload portion of the thinning target packet replaced by the dummy packet. It is desirable that there is substantially no correlation between the content of the payload portion of the dummy packet and the content of the payload portion of the thinning target packet at the position of the dummy packet.
[0048]
When the replaced data stream is delivered to the storage recording block 1D, the motherboard 1 accesses the motherboard storage 2 according to the control of the storage recording block 1D, and stores this replaced data stream in the storage area of the motherboard storage 2. To do.
[0049]
(Replay recorded content)
When playing back the recorded content, the motherboard 1 reads out and executes the broadcast recording / playback program from the motherboard storage 2 in response to a content playback instruction supplied from the outside in accordance with the operation of the operator.
[0050]
Then, the motherboard 1 reads from the motherboard storage 2 a replaced data stream (a set of non-thinning target packets) representing the content to be played back.
[0051]
Specifically, for example, the mother board 1 delivers information indicating the replaced data stream (for example, a file name, an address of a stored storage area, and the like) from the stream synthesis block 1C to the storage read block 1F. Then, the motherboard storage 2 is accessed according to the control of the storage read block 1F, the replaced data stream indicated by this information is read from the motherboard storage 2, and delivered to the stream synthesis block 1C.
[0052]
On the other hand, the motherboard 1 accesses the content storage internal memory 33 via the PCI bus bridge 32 and the IDE bus bridge 34, and reads a packet set file (that is, a set of thinning target packets) representing the content to be played back. The read packet set file is supplied to the IDE bus bridge 34, and the IDE bus bridge 34 transfers the packet set file to the PCI bus bridge 32. The PCI bus bridge 32 passes the packet set file through the connection bus B. To the motherboard 1.
The packet set file to be read may be specified based on the content of identification data included in any dummy packet in the replaced data stream representing the content to be played back, for example.
[0053]
As shown in FIG. 6, the mother board 1 delivers the packet set file read from the receiving unit 3 to the stream synthesis block 1C.
[0054]
Next, under the control of the stream synthesis block 1C, the mother board 1 restores the replaced data stream delivered to the stream synthesis block 1C to the original data stream. Then, as shown in FIG. 6, the restored data stream is delivered to the MPEG decoding block 1E.
[0055]
Specifically, the mother board 1 replaces a dummy packet included in the replaced data stream delivered to the stream synthesis block 1C with a thinning target packet included in the packet set file, so that the original data stream is replaced. Perform restoration. The mother board 1 specifies which packet to be thinned out to replace each dummy packet based on identification data included in the dummy packet.
[0056]
When the original data stream is delivered to the MPEG decode block 1E, the mother board 1 decodes the image and sound represented by this data stream according to the control of the MPEG decode block 1E, and outputs it as content data as shown in FIG. .
[0057]
The digital broadcast recorder that performs the operation described above stores a part of TS packets that match a certain rule in the content storage internal memory 33. Then, even if the I picture head packet is read out without following the control of the broadcast recording / reproducing program, the access is substantially blocked. Therefore, even if, for example, the motherboard storage 2 is disconnected and an external computer or the like is used to play back content based on the stored contents of the motherboard storage 2, data included in some TS packets cannot be obtained. Therefore, the content cannot be played back correctly. As a result, the content can be protected.
Then, it is possible to easily identify which thinning target packet to replace the dummy packet in the replaced data stream by verifying the identification data included in the dummy packet. For this reason, it is possible to easily restore the data stream without requiring a separate table indicating the position of the thinning target packet in the original data stream.
[0058]
The configuration of this digital broadcast recorder is not limited to the above.
For example, the data structure of the TS packet may not be as described above, and may have an arbitrary data structure. The dummy packet does not necessarily include the identification data in the payload portion, and may be included in any other position in the dummy packet. Further, the image data included in the TS packet does not necessarily have to be MPEG2 format data, and may be MPEG4 or other arbitrary format data.
The receiving unit 3 may include a plurality of content storage internal memories 33, and the data stream may be distributed into three or more groups.
[0059]
Further, the identification data included in the dummy packet may include an address indicating a position occupied by the thinning-out target packet replaced by the dummy packet in the storage area of the content storage internal memory 33. In this case, the thinning-out target packet stored in the content storage internal memory 33 does not necessarily have to take the form of the packet aggregate file described above.
[0060]
In addition, the digital broadcast recorder may include a video circuit that controls display of an image represented by the content data generated by the motherboard 1 and a display device such as a liquid crystal panel that displays an image according to this control. Further, an amplifier circuit, a speaker, and the like for reproducing the sound represented by the content data may be provided. A video circuit and an amplifier circuit may be mounted on the motherboard 1.
[0061]
Further, the connection bus B is not necessarily limited to the PCI bus, and may be a bus conforming to an arbitrary standard. Therefore, the connection bus B may be composed of, for example, a bus conforming to PC Card Standard or may be composed of an ISA (Industry Standard Architecture) bus. However, when the connection bus B is not a PCI bus, the reception unit 3 is provided with a bus controller or the like that mediates data exchange conforming to the standard to which the connection bus B conforms instead of the PCI bus bridge 32.
[0062]
The bus connecting the content storage internal memory 33 and the IDE bus bridge 34 is not necessarily limited to the IDE bus, and may be a bus conforming to an arbitrary standard. Therefore, this bus may comprise a memory dedicated bus, for example. However, when this bus is not an IDE bus, the receiving unit 3 is provided with a bus controller or the like that mediates data exchange conforming to the standard to which this bus conforms instead of the IDE bus bridge 34, and for content storage It is assumed that the interface circuit provided in the internal memory 33 also mediates data exchange conforming to the standard to which this bus complies.
[0063]
Further, when recording content, the mother board 1 encrypts the non-decimation target packet and then stores it in the motherboard storage 2. When reproducing the recorded content, the mother board 1 reads and decrypts the encrypted non-decimation target packet. The data stream may be restored after conversion.
Similarly, when content is recorded, the thinning-out target packet is encrypted and then written into the content storage internal memory 33. When the recorded content is reproduced, the encrypted thinning-out target packet is read and decrypted before data is recorded. Stream restoration may be performed.
[0064]
Although the embodiment of the present invention has been described above, the data stream device according to the present invention can be realized using a normal computer system, not a dedicated system.
For example, by installing the program from a medium (CD-ROM, MO, FD, etc.) storing a program for causing the personal computer to execute the operations of the mother board 1, the mother board storage 2, and the receiving unit 3 described above, A digital broadcast recorder that executes the above process can be configured.
[0065]
Further, for example, the program may be posted on a bulletin board (BBS) of a communication line and distributed via the communication line. Also, a carrier wave is modulated by a signal representing the program, and the obtained modulated wave is An apparatus that transmits and receives the modulated wave may demodulate the modulated wave to restore the program.
Then, the above-described processing can be executed by starting the program and executing it in the same manner as other application programs under the control of the OS.
[0066]
When the OS shares a part of the process, or when the OS constitutes a part of one component of the present invention, a program excluding that part is stored in the recording medium. May be. Also in this case, in the present invention, it is assumed that the recording medium stores a program for executing each function or step executed by the computer.
[0067]
【The invention's effect】
As described above, according to the present invention, a data stream recording apparatus and a data stream recording method for sufficiently protecting data are realized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a digital broadcast recorder according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a data structure of a data stream and a TS packet.
FIG. 3 is a diagram illustrating a data structure of a PES packet.
FIG. 4 is a diagram showing a flow of processing for recording content.
FIG. 5 is a diagram illustrating a data structure of a packet aggregate file, a replaced data stream, and a dummy packet.
FIG. 6 is a diagram showing a flow of processing for reproducing recorded content.
[Explanation of symbols]
1 Motherboard 2 Motherboard Storage 3 Receiving Unit 31 Digital Broadcasting Reception Unit 32 PCI Bus Bridge 33 Content Storage Internal Memory 34 IDE Bus Bridge B Connection Bus

Claims (11)

Thinning means for acquiring a data stream and distributing a plurality of packets constituting the acquired data stream to a plurality of groups according to a predetermined rule;
First storage means having a first storage area that substantially prevents access from other than the thinning means;
Second storage means having a second storage area,
The thinning-out means stores a part of the packets belonging to the group in the first storage area, and the acquired data stream is replaced with a packet for a dummy packet. Converted into a replaced data stream and stored in the second storage area,
The dummy packet includes identification information that identifies a thinning target packet replaced by the dummy packet.
A data stream recording apparatus. The thinning means generates aggregate data representing a combination of packets belonging to the partial group and stores them in the first storage area,
The identification information includes information indicating a logical position occupied by the packet replaced by the dummy packet including the identification information in the set data.
The data stream recording apparatus according to claim 1, wherein: The identification information includes information indicating a logical position occupied in the first storage area by a packet replaced by a dummy packet including the identification information.
The data stream recording apparatus according to claim 1, wherein: The packet constituting the data stream acquired by the thinning unit and the dummy packet are TS (Transport Stream) packets, and the identification information is included in the payload portion of the TS packet.
4. The data stream recording apparatus according to claim 1, 2, or 3. The thinning unit includes a combining unit that reads out the packets distributed to the plurality of groups from the first and second storage areas and restores the data stream based on the read packets.
The data stream recording apparatus according to claim 1, wherein the data stream recording apparatus is a data stream recording apparatus. The thinning means includes a processor, and the processor accesses the first storage area by executing a predetermined program.
The data stream recording apparatus according to claim 1, wherein the data stream recording apparatus is a data stream recording apparatus. The first storage unit and the thinning unit are connected to each other via a bus that enables data transmission by the processor executing a predetermined program.
The data stream recording apparatus according to claim 6. The thinning-out means encrypts the packet distributed to the partial group and / or another group and stores the encrypted packet in the first and / or second storage area.
The data stream recording apparatus according to claim 1, wherein the data stream recording apparatus is a data stream recording apparatus. Acquire a data stream, distribute a plurality of packets constituting the acquired data stream into a plurality of groups according to a predetermined rule,
Storing packets belonging to some groups in a first storage area that substantially prevents access from other than a predetermined access device;
A data stream recording method for converting the acquired data stream into a replaced data stream in which packets assigned to the partial group are replaced with dummy packets and storing the converted data stream in a second storage area. ,
The dummy packet includes identification information that identifies a thinning target packet replaced by the dummy packet.
A data stream recording method. Packets belonging to the partial group are stored in the first storage area as aggregated data representing a combination of the packets,
The identification information includes information indicating a logical position occupied by the packet replaced by the dummy packet including the identification information in the set data.
The data stream recording method according to claim 9. Computer
Thinning means for acquiring a data stream and distributing a plurality of packets constituting the acquired data stream to a plurality of groups according to a predetermined rule;
First storage means having a first storage area that substantially prevents access from other than the thinning means;
A program for functioning as a second storage means having a second storage area,
The thinning-out means stores a part of the packets belonging to the group in the first storage area, and the acquired data stream is replaced with a packet for a dummy packet. Converted into a replaced data stream and stored in the second storage area,
The dummy packet includes identification information that identifies a thinning target packet replaced by the dummy packet.
A program characterized by that.

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