JP2001244984A - Data accumulation circuit, data accumulation device and data accumulation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a data accumulation circuit which can decrease the capacity of a recording medium in particular about a data accumulation device which accumulates the image or voice data in an MPEG form and also to provide a data accumulation method. SOLUTION: A null packet deleting device 2 outputs a transport stream A2 obtained by deleting a null packet from a transport stream A1 to an accumulation part 4. A packet output controller 5 performs the output control of each of packets accumulated in the part 4 in accordance with the arrival recording time C2 of each packet counted by an arrival time counter 3 and recorded at the part 4 and also with its own counted time. Then a null packet inserting device 6 restores the deleted null packet according to the output control of the controller 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data storage device for storing video or audio data in MPEG format, and more particularly to a data storage circuit, a data storage device, and a data storage device capable of reducing the capacity of a recording medium. Regarding the accumulation method.

[0002]

2. Description of the Related Art In recent years, MPEG (Moving Picture Experts Group) which has been put into practical use as a moving picture coding system has been developed.
A moving picture coding standard called MPEG1 (International Telecommunication Union; ITU-
T Recommendation H. 261) and MPEG2 (ITU-T Recommendation H.262), which has higher image quality and higher speed than MPEG1. Among them, MPEG2 has attracted special attention as a media-integrated video coding standard aiming at interoperability in the fields of communication, storage, broadcasting, and computer.
SDTV (current television) quality such as SC system is 4 ~
Realized with about 9 megabits of information and HDTV
(High-definition television) Quality is realized with an information amount of about 15 to 30 megabits per second. This MPEG2 has two formats: a program stream system and a transport stream system.
Two methods are specified. Among them, the transport stream method is a method used in a communication channel having a fixed transmission bit rate, and a transport stream (hereinafter sometimes referred to as TS) which is the transmission data is 1
It is composed of a plurality of 88-byte fixed-length TS packets.

As a general-purpose high-speed serial interface for connecting a personal computer with its peripheral devices and AV (audio / visual) devices, an IE has been developed.
The EE1394 standard (hereinafter referred to as the 1394 standard) is known. Since the 1394 standard can guarantee a transfer band, it is rapidly applied to applications requiring real-time data transmission such as video and audio. A transport stream with a fixed bit rate of MPEG2 is defined in the transmission data format. Therefore, a device that stores video or audio data and that outputs the video or audio data according to the 1394 standard outputs the stored video or audio data as a transport stream at a fixed bit rate (for example, 10 Mbits / sec). There is a need. Hereinafter, a conventional data storage device that generates and stores a transport stream having a fixed bit rate by inserting a TS packet for adjusting a transmission bit rate (hereinafter, referred to as a null packet) will be described.

FIG. 5 shows a conventional data storage device 200 for outputting video or audio data in accordance with the 1394 standard.
FIG. 3 is a block diagram showing the configuration of FIG. In FIG. 1, reference numeral 1 denotes an input digital video signal and an audio signal which are MPEG2.
And encodes the compressed and encoded data as a transport stream A1 with a transfer clock B
1, the TS encoder 10 outputs the transport stream A1 based on the transfer clock B1 input from the TS encoder 1, and stores the transport stream A1. When the transport stream A1 is reproduced, the transport stream A1 outputs the transport stream A1. Transfer clock B4
And a storage unit 7 for outputting the transport stream A4 based on the transfer clock B4 input from the storage unit 10, and outputting the input transport stream A4 as an output signal of the 1394 standard. . The TS encoder 1 and the storage unit 10 generate the transfer clocks B1 and B4 from the input reference clock.
B4 is output only during transfer of each of the transport streams A1 and A4. The storage unit 10 may be a storage device such as a hard disk or a DVD (Digital Video).
Disc) or the like and a storage device unit including a recording device and a read / write control unit.

FIG. 6 is a block diagram showing a configuration of the TS encoder 1 shown in FIG. In this figure, reference numeral 21 denotes a video encoder which compresses and encodes an input video signal at a variable bit rate according to MPEG2, and 22 denotes a video buffer which temporarily holds video encoded data which has been compression-coded by the video encoder 21. , 23 are audio encoders for compressing and encoding an input audio signal by MPEG2, 24 is an audio buffer for temporarily holding audio encoded data compressed and encoded by the audio encoder 23, and 25 is a PSI (Program Specific Specific). I
A PSI packet generator that generates a TS packet (hereinafter, referred to as a PSI packet) containing information defined by MEPG2 called “nformation”, and a null packet generator 26 that generates a null packet.

Reference numeral 27 denotes a virtual buffer T-ST defined in TTC (Telecommunications Telecommunications Commission) standard H.222.0.
By performing the simulation of D, it is determined which encoded data to be output as TS packets, out of the encoded video data held in the video buffer 22 or the encoded audio data held in the audio buffer 24. Processor, and the decision result and MPEG
In accordance with TS standard 2, any one of TS packets of video encoded data or audio encoded data or PSI packets is
A control signal indicating whether to output as 1 is output. Reference numeral 28 denotes a multiplexer which selects an output packet based on a control signal input from the processor 27 to form a transport stream A1, and outputs the transport stream A1 together with a transfer clock B1 generated from a reference clock. It should be noted that when there is no corresponding output packet, the multiplexer 28 sets the null packet generator 2
The null packet generated by 6 is output as transport stream A1.

As described above, in the conventional data storage device 200, the transport stream A1 output from the TS encoder 1 has a fixed bit rate by outputting null packets even when there are no output packets, It is stored in the storage unit 10. Therefore, the transport stream A4 output from the storage unit 10 also has a fixed bit rate, and the output interface circuit 7
4 can be converted to an output signal of the 1394 standard.

[0008]

However, in the above-described conventional data storage device 200, a large-capacity recording medium (hard disk, DVD, etc.) is required in the storage unit 10 in order to store the transport stream A1. There is a problem. The present invention has been made in view of such circumstances, and has as its object to provide a data storage circuit, a data storage device, and a data storage method that can reduce the capacity of a recording medium.

[0009]

According to a first aspect of the present invention, there is provided a data storage circuit for outputting a stream composed of a plurality of packets to a storage means. A null packet deleting unit for deleting a null packet and outputting the null packet to the storage unit is provided. According to a second aspect of the present invention, in the first aspect of the present invention, a null packet restoring unit for restoring a null packet deleted by the null packet deleting unit in a stream output from the storage unit. It is characterized by having.

According to a third aspect of the present invention, in the data storage circuit for outputting a stream composed of a plurality of packets to the storage means, a null packet which deletes null packets from the stream and outputs the null packet to the storage means. Packet deleting means, and performing output control of packets stored in the storing means based on the arrival time of each packet to the storing means, so that the null packet deleting means is added to the stream output from the storing means. And null packet restoring means for restoring the null packet deleted by (1).

According to a fourth aspect of the present invention, in the third aspect of the present invention, the null packet restoring means includes an arrival time measuring means for measuring an arrival time of each packet arriving at the storage means; Packet output control means for controlling output of the packets stored in the storage means based on the arrival time of each packet measured by the arrival time measurement means and the self-measurement time; and a stream output from the storage means. And null packet insertion means for inserting a null packet based on output control performed by the packet output control means.

According to a fifth aspect of the present invention, in the data storage circuit for outputting a stream composed of a plurality of packets to the storage means, a null packet which deletes null packets from the stream and outputs the null packet to the storage means. Packet deleting means for generating a dummy packet indicating the number of consecutive null packets deleted by the null packet deleting means and the deletion position, and outputting from the storage means based on the dummy packet; The stream to be deleted is provided with null packet restoring means for restoring null packets deleted by the null packet deleting means.

According to a sixth aspect of the present invention, in the fifth aspect of the invention, the null packet restoring means generates a dummy packet for giving the number of consecutive null packets, and Null packet converting means for outputting to the storage means instead of the null packet deleted by the deleting means; and when the dummy packet is output as a stream output from the storage means, Instead, a dummy packet converting means for generating null packets corresponding to the number of consecutive null packets added to the dummy packet is provided.

According to a seventh aspect of the present invention, a null packet deleting unit for deleting a null packet from a stream composed of a plurality of packets, and a stream from which the null packet has been deleted by the null packet deleting unit. By performing output control of the packets stored in the storage means based on the storage means for storing and the arrival time of each packet to the storage means, the null packet is deleted in the stream output from the storage means. Null packet restoring means for restoring null packets deleted by the means.

[0015] According to the present invention, a null packet deleting unit for deleting a null packet from a stream composed of a plurality of packets, and a stream from which the null packet has been deleted by the null packet deleting unit. A storage unit for storing, and a dummy packet indicating the number of consecutive null packets deleted by the null packet deletion unit and the deletion position, and generating a dummy packet based on the dummy packet. Null packet restoration means for restoring a null packet deleted by the null packet deletion means in the output stream.

According to a ninth aspect of the present invention, a first step of removing null packets from a stream composed of a plurality of packets, and storing the stream from which null packets have been removed by the first step. A second step of controlling the output of the packets stored in the storage means based on the arrival time of each packet to the storage means, and an output performed by the third step. And a fourth step of restoring the null packet deleted in the first step to the stream output from the storage means based on the control.

According to a tenth aspect of the present invention, a first step of removing null packets from a stream composed of a plurality of packets, and storing the stream from which null packets have been removed by the first step. A third step of generating a dummy packet indicating the number of consecutive null packets deleted in the first step and the position of the deletion, and And a fourth step of restoring the null packet deleted in the first step to the stream output from the storage means based on the first step.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the data storage device 110 according to the first embodiment of the present invention. In this figure, a data storage device 110 is composed of a data storage circuit 100 and a storage unit 4,
Is different from the conventional data storage device 200 shown in FIG.
A null packet remover 2 for removing a null packet from the transport stream A1 output from the S encoder 1 and a transport stream A2 output from the null packet remover 2 are stored. The packet arrival time C1 is measured and output as the arrival time of the storage unit 4 whose output is controlled and the leading byte data of each packet constituting the transport stream A2 input to the storage unit 4 to the storage unit 4. The arrival time measurement device 3 and the packet arrival time C1 measured by the arrival time measurement device 3 are stored in the storage unit 4 based on each packet arrival recording time C2 recorded in the storage unit 4 and the self-measurement time. A packet output controller 5 for outputting an output permission signal D1 for controlling the output of each packet,
Based on the output permission signal D1 output from the packet output controller 5, a transport stream A3 composed of packets output from the storage unit 4 is output as a transport stream A4. In the case of output, a null packet inserter 6 that inserts a null packet and outputs a transport stream A4 is provided. The arrival time measuring device 3, the storage unit 4, the packet output controller 5, A reference clock is input to the null packet inserter 6. The transfer clocks B2, B3, and B4 output from the null packet deleter 2, the storage unit 4, and the null packet inserter 6, respectively,
It is output only during transfer of each transport stream A2, A3, A4. The configurations and operations of the TS encoder 1 and the output interface circuit 7 are the same as those provided in the conventional data storage device 200 shown in FIG.

Next, referring to FIG. 1, the above-described data storage device 110 deletes null packets from the transport stream A1, stores the null packets in the storage unit 4, and restores the deleted null packets. The operation to be performed will be described. First, a null stream is transmitted from the transport stream A1.
An operation of deleting a packet and storing the packet in the storage unit 4 will be described. First, when the transport stream A1 is input together with the transfer clock B1 from the TS encoder 1, the null packet eliminator 2 uses the input transport stream A1 and transfer clock B1 as the transport stream A2 and transfer clock B2. Output.
However, when the null packet eliminator 2 detects a null packet as a packet constituting the transport stream A1, it does not output the transfer clock B2 in a section corresponding to the null packet transfer section. When the transfer clock B2 is not output, that is, when the transfer of the transport stream A2 is stopped, the null packet is deleted. The detection of a null packet by the null packet eliminator 2 is based on the PID (packet identifier) included in the header of each packet being a value assigned to the null packet, for example, “1” in hexadecimal.
FFF ".

Next, the storage unit 4 inputs and stores the transport stream A2 based on the transfer clock B2 input from the null packet eliminator 2. At this time,
The storage unit 4 records the packet arrival time C1 measured by the arrival time measuring device 3 using the reference clock as a packet arrival time file in association with the packet. Note that the arrival time measuring device 3 outputs a count value obtained by operating a provided counter with a reference clock as a packet arrival time C1.

Next, the operation of restoring the null packet deleted by the null packet deleter 2 when the transport stream A2 stored in the storage section 4 is reproduced will be described. First, the accumulation unit 4 reads the packet arrival time file recorded at the time of accumulation, and outputs each packet arrival recording time C2 to the packet output controller 5 from the beginning in the order of arrival time. Packet output controller 5
Sets the initial value of the counter provided with the first packet arrival recording time C2 output from the storage unit 4, sets the count value obtained by operating the counter with the reference clock as the self-measurement time, An output permission signal D1 for one packet is output as a permission state. Thereafter, when the self-measurement time matches the input packet arrival recording time C2, the packet output controller 5 outputs the output permission signal D1 for one packet as a permission state. Next, each time the output permission signal D1 is input for one packet from the packet output controller 5, the storage unit 4 stores the stored packets one by one in the order of arrival time, in the transport stream A.
3 and output together with the transfer clock B3.

Next, when the output permission signal D1 input from the packet output controller 5 is in a permission state, the null packet inserter 6 converts the transport stream A3 and the transfer clock B3 input from the storage section 4 into the null state. Output as transport stream A4 and transfer clock B4. On the other hand, when the output permission signal D1 input from the packet output controller 5 is in the non-permission state, a null packet is generated, and the transport stream A4 and the transfer clock B4 are generated together with the transfer clock generated from the reference clock.
Output as

Thus, the null packet eliminator 2
Each null packet deleted from the transport stream A1 is restored to the deleted corresponding position in the transport stream A4. As a result, the transport stream A1 output from the TS encoder 1 and the transfer clock B1 are combined with the transport stream A4 output from the null packet inserter 6.
And restored as the transfer clock B4 and input to the output interface circuit 7.

In the first embodiment, the transport stream A2 from which null packets have been deleted by the null packet deleter 2 is stored in the storage unit 4. In comparison, the capacity of the recording medium provided in the storage unit 4 can be reduced. Further, an arrival time measuring device 3, a packet output controller 5 and a null packet inserting device 6 are provided, and the packet output controller 5 measures each packet arrival record measured by the arrival time measuring device 3 and recorded in the storage section 4. Based on the time C2 and the self-measurement time, the output of each packet stored in the storage unit 4 is controlled, and based on the output control of the packet output controller 5, the null / packet inserter 6 deletes the deleted null. Since the packet is restored, the transport stream A1 and the transfer clock B1 output from the TS encoder 1 are restored as the transport stream A4 and the transfer clock B4 output from the null packet inserter 6. You.

Next, FIG. 2 is a block diagram showing a configuration of a data storage device 111 according to a second embodiment of the present invention. In this figure, a data storage device 111 includes a data storage circuit 101 and a storage unit 10, and the configuration different from the conventional data storage device 200 shown in FIG.
A null packet is deleted from the transport stream A1 output from the encoder 1, and the null packet is deleted.
A null packet converter 11 that generates a dummy packet that gives the continuous number of packets as the number of consecutive null packets and outputs it as a transport stream A12 instead of the deleted null packet, and a dummy packet that is input from the storage unit 10. Packet converter 12 that generates null packets for the number of consecutive null packets added to the dummy packets included in the transport stream A13 and outputs the same as the transport stream A4 instead of the dummy packets And a reference clock is input to the dummy packet converter 12. The transfer clock B output from each of the null packet converter 11 and the dummy packet converter 12
12, B4 are transport streams A12, A
4 is output only during transfer. Note that the null packet converter 11 has a buffer for temporarily holding packets in order to output dummy packets. The configurations and operations of the TS encoder 1, the storage unit 10, and the output interface circuit 7 are the same as those included in the conventional data storage device 200 shown in FIG.

Next, the operation of the null packet converter 11 shown in FIG. 2 will be described with reference to the flowchart shown in FIG. First, when the transport stream A1 is input based on the input transfer clock B1, the null packet converter 11 determines whether or not each packet of the transport stream A1 is a null packet. The determination is made in the same manner as the null packet eliminator 2 of the embodiment (step S1). If the result of this determination is that the packet is a null packet (the determination result of step S1 is "YES"), the null packet is deleted (step S2). Next, the null packet converter 11
If the packet held in the buffer is held (when the determination result in step S3 is "YES"), the transport stream A12 is used as the transport stream A12 instead of the null packet obtained by deleting the packet held in the buffer. Also, the input transfer clock B1 is
12, and are output together (step S4). On the other hand, if the determination result in step S3 is "NO", the null packet converter 11 does not output the transfer clock B12.

Next, the determination result of step S1 is "NO".
If the input current packet is not a null packet, it is determined whether or not the previous packet input immediately before the current packet is a null packet (step S5). If the result of this determination is that the packet is a null packet (the determination result of step S5 is "YES"), the input current packet is held in the buffer (step S6). Next, a dummy packet shown in FIG. 3 is generated (step S7), and the input transfer clock B1 is used as the transport stream B12 instead of the current packet held in the buffer, and the input transfer clock B1 is used as the transfer clock B.
12, and are output together (step S4). This figure 3
Is a 4-byte TS header E1 to which a PID not used by the TS encoder 1 is assigned, a 2-byte continuous null packet number E2 indicating the number of continuously deleted null packets, and a 182-byte dummy packet. And stuffing data E3.

Next, the determination result of step S5 is "NO".
If the previous packet is not a null packet, and if there is a packet held in the buffer, the packet held in the buffer is input again as the transport stream A12 instead of the current packet. Transfer clock B1 as a transfer clock B12
Output both, and hold the current packet in the buffer. on the other hand,
If there are no packets held in the buffer, the current packet is output as the transport stream A12, and the input transfer clock B1 is output as the transfer clock B12 (step S4).

The dummy packet generated in this manner and output as the transport stream A12 indicates the number of consecutive null packets deleted by the null packet converter 11 and the position where the transport stream A1 is deleted. .

Next, the dummy packet converter 12 shown in FIG.
Will be described. The dummy packet converter 12 converts the transport stream A1 input from the storage unit 10
3 and the transfer clock B13
3 and the transfer clock B4. When the dummy packet shown in FIG. 3 is input, null packets corresponding to the number of consecutive null packets added to the dummy packet are generated, and the input dummy packet is output. Instead of the packet, it outputs the transport clock A4 and the transfer clock B4 together with the transfer clock generated from the reference clock.

Therefore, each null packet deleted by the null packet converter 11 is added to the transport stream A4 in the transport stream A4.
1 is restored to the position corresponding to the deletion position of the transport stream A, which is output from the TS encoder 1.
1 and the transfer clock B1 are the dummy packet converter 1
2 and are restored as the transport stream A4 and the transfer clock B4, which are input to the output interface circuit 7.

In the second embodiment described above, the transport stream A12 from which null packets have been deleted by the null packet converter 11 is stored in the storage unit 10, so that the same as in the first embodiment. Furthermore, compared to the conventional data storage device 200, the capacity of the recording medium provided in the storage unit 10 can be reduced. Further, a dummy packet converter 12 is provided, and based on the dummy packet generated by the null packet converter 11,
The dummy packet converter 12 is the null packet converter 1
Since the null packet deleted by step 1 is restored, there is no need to perform output control on the storage unit 10 as in the first embodiment, and with a simpler configuration,
The transport stream A1 output from the TS encoder 1 and the transfer clock B1 are combined with the transport stream A4 output from the dummy packet converter 12.
Is restored as the transfer clock B4.

In the above embodiment, the transport stream A4 is output as an output signal of the 1394 standard by the output interface circuit 7, but the transmission format of the output signal is limited to the 1394 standard. is not.

[0034]

As described above, according to the present invention,
A null packet is deleted from the stream composed of a plurality of packets, the stream from which the null packet has been deleted is stored in the storage unit, and the null packet is stored in the storage unit based on the arrival time of each packet to the storage unit. The output of the stored packet is controlled, and the null packet deleted in the stream output from the storage unit is restored based on the output control. Therefore, the capacity of the recording medium provided in the storage unit can be reduced. Can be.

Further, null packets are deleted from the stream composed of a plurality of packets, the stream from which the null packets have been deleted is stored in the storage means, and the number of consecutive null packets of the deleted null packets is determined. A dummy packet indicating the deletion position is generated, and based on the dummy packet, a stream output from the storage unit includes:
By recovering null packets that have been dropped,
In addition to being able to reduce the capacity of the recording medium provided in the storage means, it is possible to restore a null packet with a simpler configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a data storage device 110 according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a data storage device 111 according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a dummy packet generated by a dummy packet converter 12 shown in FIG.

FIG. 4 is a flowchart for explaining the operation of the null packet converter 11 shown in FIG.

FIG. 5 is a block diagram showing a configuration of a conventional data storage device 200.

FIG. 6 is a block diagram showing a configuration of the TS encoder 1.

[Explanation of symbols]

 Reference Signs List 1 TS encoder 2 Null packet deleter 3 Arrival time measuring device 4 Storage unit 5 Packet output controller 6 Null packet inserter 7 Output interface circuit 100 Data storage circuit 110 Data storage device

Claims (10)

[Claims] 1. A data storage circuit for outputting a stream composed of a plurality of packets to a storage means thereof, comprising a null packet deletion means for deleting null packets from the stream and outputting the null packet to the storage means. A data storage circuit characterized by the following. 2. The stream according to claim 1, further comprising a null packet restoring unit for restoring the null packet deleted by the null packet deleting unit in the stream output from the storage unit. Data storage circuit. 3. A data storage circuit for outputting a stream composed of a plurality of packets to a storage means thereof, comprising: a null packet deleting means for deleting a null packet from the stream and outputting the null packet to the storage means; By controlling the output of the packets stored in the storage means based on the arrival time of each packet to the means, a null packet deleted by the null packet deletion means is added to the stream output from the storage means. And a null packet restoring means for restoring the data. 4. An arrival time measuring means for measuring an arrival time of each packet arriving at the storage means, an arrival time of each packet measured by the arrival time measuring means, and a self-measurement. Packet output control means for controlling the output of the packets stored in the storage means based on the time; and a null stream based on the output control performed by the packet output control means for the stream output from the storage means. The data storage circuit according to claim 3, further comprising: a null packet inserting unit that inserts a packet. 5. A data storage circuit for outputting a stream composed of a plurality of packets to a storage means thereof, comprising: a null packet deleting means for deleting a null packet from the stream and outputting the null packet to the storage means; Null deleted by packet deletion means
A dummy packet indicating the number of consecutive null packets of the packet and the deletion position is generated, and a null packet deleted by the null packet deletion unit is added to a stream output from the storage unit based on the dummy packet. A data storage circuit, comprising: null packet recovery means for recovering a packet. 6. The null packet restoring means generates a dummy packet for giving the number of consecutive null packets, and sends the dummy packet to the storage means instead of the null packet deleted by the null packet deleting means. Null packet converting means for outputting, and when the dummy packet is output as a stream output from the storage means, the number of consecutive null packets given to the dummy packet instead of the dummy packet The data storage circuit according to claim 5, further comprising: dummy packet conversion means for generating a minute null packet. 7. A null packet deleting unit for deleting a null packet from a stream composed of a plurality of packets, an accumulation unit for accumulating a stream from which the null packet has been deleted by the null packet deleting unit, By controlling the output of the packets stored in the storage unit based on the arrival time of each packet to the storage unit, the null output deleted by the null packet deletion unit is added to the stream output from the storage unit. A data storage device comprising: null packet restoring means for restoring a packet. 8. A null packet deleting unit for deleting a null packet from a stream composed of a plurality of packets, an accumulation unit for accumulating a stream from which the null packet has been deleted by the null packet deleting unit, Nulls deleted by the null packet deletion means
A dummy packet indicating the number of consecutive null packets of the packet and the deletion position is generated, and a null packet deleted by the null packet deletion unit is added to a stream output from the storage unit based on the dummy packet. A data storage device comprising: null packet restoring means for restoring a packet. 9. A first step of removing null packets from a stream composed of a plurality of packets, and a second step of storing the stream from which null packets have been removed by the first step in storage means. And a third step of performing output control of the packets stored in the storage means based on the arrival time of each packet to the storage means, based on the output control performed in the third step,
A fourth method for restoring the null packet deleted in the first step to the stream output from the storage means.
And a data storage method. 10. A first step of removing null packets from a stream composed of a plurality of packets, and a second step of storing the stream from which null packets have been removed by the first step in storage means. A third step of generating a dummy packet indicating the number of consecutive null packets deleted in the first step and the position of the null packet, and from the storage means based on the dummy packet. A fourth step of restoring a null packet deleted in the first step in the output stream.