JP2002175208A - System for delivering digital image/voice-data, video server, and method of controlling buffer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate unnecessary disk access to effectively use a disk access band and to reduce the time required for heading. SOLUTION: Disk numbers and sector numbers on a disk device where address and read data exist are held in buffer structures in correspondence to buffer areas, the unused release-finished buffer structure 1-6 thereof is controlled by first-in first-out system of free list 1-7, a reference counter is increased and then the corresponding buffer structure is returned when a required data exists on the buffer area, the forefront buffer structure is returned when not, based on a reading-finished buffer table 1-5, an entry to the corresponding buffer structure is registered when the data is read into a new buffer area, the reference counter is reduced, the used buffer structure is returned to the free list 1-7 when the reference counter is zero, and an entry to the corresponding buffer structure is registered into the buffer control table 1-5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a system for distributing digital video / audio data such as video-on-demand,
The present invention relates to a method for controlling a server, a storage medium, and a buffer.

[0002]

2. Description of the Related Art In a system for distributing digital video / audio data stored in a hard disk such as video-on-demand, it is necessary to read data from the hard disk in accordance with the data distribution speed and continue to transmit data to the client. If the transmission is delayed, the video and audio are disturbed, and if the transmission is too fast, the buffer overflows. A bottleneck in performance in such a system is reading data from a disk. Therefore, the access timing is scheduled so that the disk can be accessed as efficiently as possible. However, since the timing does not always coincide with the data transmission timing, the data is buffered on the memory and the difference is absorbed. Patent No. 2
In 742390, when a user pauses on a common stream that is shared by multiple viewers,
It describes how to back up in a future stream that is being used for another playback.

[0003]

However, in the conventional method, only the data in the buffer after completely used is reused, so that the data being used by another task cannot be reused. Was. For this reason, there has been a case where the opportunity to reduce the load by avoiding the disk access or to shorten the start time from the reproduction request to the start of the reproduction is wasted. An object of the present invention is to eliminate unnecessary disk access by reusing data remaining in the buffer even when another task is in use, to further utilize the disk access bandwidth and reduce the cueing time. It is an object of the present invention to provide a digital video / audio data distribution system, a video server, and a buffer control method that realize reduction.

[0004]

According to a first aspect of the present invention, there is provided a system for distributing digital video / audio data stored in a disk device, wherein a buffer area in the disk device is subdivided. A buffer structure for holding a disk number and a sector number on the disk device where addresses and read data are present in one-to-one correspondence with each of the divided and subdivided partial areas; A free list that manages the released buffer structures that do not exist in a first-in first-out manner, and one buffer structure or free list in the free list that has valid data in the free list that is not used in the free list but is used by the task and data is read. Used for fast retrieval of one buffer structure already used, and used by tasks In the case of, a read buffer management table holding a reference counter indicating the number of tasks shared and used, and a reference counter when necessary data is in the buffer area based on the read buffer management table. Buffer acquisition means for returning the corresponding buffer structure after increasing the number, and returning the first buffer structure of the free list when the necessary data is not in the buffer, and reading the data into a new buffer area. Buffer read setting means for registering an entry to the relevant buffer structure in the read buffer management table in the case where the reference counter of the relevant entry on the read buffer management table is 0. Comprises buffer releasing means for returning a used buffer structure to the free list. Characterized by including the features.

According to a second aspect of the present invention, in the system according to the first aspect, a read buffer management table capable of retrieving the plurality of buffer structures while maintaining the order of the plurality of buffer structures, and the plurality of buffer structures And a buffer release unit that can return the plurality of buffer structures collectively to the free list. An invention according to claim 3, further comprising a disk device for storing digital video / audio data, wherein the video server transmits data stored in the buffer to the client in response to a data distribution request from the client. A buffer structure for holding a disk number and a sector number on the disk device in which an address and read data are present in one-to-one correspondence with each of the divided sub-regions; A free list that manages unused buffer structures that are not being used in a first-in first-out manner, and one of the free lists that has valid data in the free list or a free list that does not exist in the free list and is being used by the task To search one buffer structure for which data has already been read A read buffer management table that holds a reference counter indicating the number of tasks that are used and shared and used when the task is being used, and necessary data is stored in the buffer area based on the read buffer management table. Buffer acquisition means for returning the corresponding buffer structure after incrementing the reference counter if it is on the top, and returning the first buffer structure of the free list if the required data is not on the buffer; and Buffer read setting means for registering an entry to the buffer structure in the read buffer management table when data is read into the buffer area of the buffer, and decrementing a reference counter of the entry on the read buffer management table. If the reference counter is 0, return the used buffer structure to the free list Characterized by comprising a Ffa release means.

According to a fourth aspect of the present invention, in the video server according to the third aspect, a read buffer management table capable of retrieving the plurality of buffer structures together while maintaining the order, and the plurality of buffer structures And a buffer release unit that can return the plurality of buffer structures collectively to the free list. The invention according to claim 5 is applied to a video server having a disk device, which transmits data to the client via a network in response to a data distribution request from the client, and executes a program for executing the video server in a predetermined operation. In a held computer-readable storage medium, a buffer area in the disk device is subdivided, and a disk number and a sector on the disk device in which an address and read data exist in one-to-one correspondence with each of the subdivided partial regions. Holding the numbers in a buffer structure, managing unused buffer structures among the held buffer structures in a first-in first-out free list, and valid in the free list for this management. One free list in the free list with data It is used for high-speed retrieval of one buffer structure that is not present in the buffer structure or free list but is in use by the task and for which data has been read. If the required data is in the buffer area based on the read buffer management table that holds the reference counter indicating the number of tasks that are in use, the reference counter is increased and the corresponding buffer structure is returned. If not, return the buffer structure at the head of the free list, and, when data is read into a new buffer area, register an entry for the buffer structure in the read buffer management table. And decreasing the reference counter of the corresponding entry on the read buffer management table, There 0
In the case of (1), a step of returning a used buffer structure to the free list is executed.

The invention according to claim 6 is applied to a system for distributing digital video / audio data stored in a disk device, and transmits data in a buffer to the client in response to a data distribution request from the client. In the above buffer control method, the buffer area in the disk device is subdivided, and the disk number and sector number on the disk device where the address and the read data exist in one-to-one correspondence with the subdivided partial areas are defined. The buffer structure is held in the buffer structure, and the released buffer structure that is not used among the held buffer structures is managed by a first-in first-out free list. Not in one buffer structure or free list of Used for high-speed retrieval of one buffer structure that is in use and for which data has been read, and a read counter that holds a reference counter indicating the number of tasks shared and used when being used by tasks If the required data is on the buffer area based on the buffer management table, the reference counter is incremented and the corresponding buffer structure is returned.If the required data is not on the buffer, the first buffer in the free list is returned. When the structure is returned and data is read into the new buffer area, an entry to the corresponding buffer structure is registered in the read buffer management table, and the reference counter of the corresponding entry on the read buffer management table is set. Reducing the used buffer structure to the free list when the reference counter is 0. To.

According to a seventh aspect of the present invention, in the buffer control method according to the sixth aspect, the plurality of buffer structures are combined, and the buffer structure is searched and returned while maintaining the order of the combined buffer structures. The feature is to return to the free list.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a digital video / audio data distribution system, a video server, and a buffer control method according to the present invention will be described with reference to the drawings. FIG. 2 is a block diagram showing a video-on-demand system which is an example of a digital video / audio data distribution system according to the present invention. In FIG. 2, client 2
-11 from the network 2-10
To the video server 2-1. The network 2-10 can take various forms such as Ethernet, ATM, CATV, and the like. The video reproduction request transmitted to the video server 2-1 is received by the communication control device 2-9 and sent to the request receiving function 2-4. The communication control device 2-9 is a device for transmitting and receiving data corresponding to various network forms. A plurality of the communication control devices 2-9 support a plurality of networks, and transmission and reception are performed by separate devices. And various configurations. The request receiving function 2-4 generates one control task 2-5 in response to the video reproduction request. The control task 2-5 has a one-to-one correspondence with the reproduction request, and reads the data from the disk device 2-3 to the network 2
Responsible for a series of processing up to transmission to -10.

The control task 2-5 includes a disk device 2-3.
From the buffer 2-8. Since the disk device 2-3 has a large access overhead such as the seek time of the head, it is inefficient if data of a certain size is not read at once. Therefore, the data is handled by being divided into certain fixed sizes. This unit is called a segment. One segment is arranged in a continuous area on one disk device 2-3. The next segment is arranged on another disk device 2-3. In this manner, the disk access load is distributed by cyclically arranging the disk devices 2-3. The arrangement of each segment from which sector of which disk device 2-3 is recorded in the disk arrangement information 2-2. Here, each disk device 2-3 is not only a single disk, but also an RA.
There may be a configuration in which an ID or the like is used to make the disk look virtually a single disk. Since a plurality of video reproduction requests may be generated at the same time, it is necessary to perform exclusive control so that disk access by each control task 2-5 does not simultaneously occur to the same disk device 2-3. This is performed by the scheduler 2-6. Scheduler 2-6
Guarantees exclusive disk access and continuous disk access so that data transmission is not interrupted for each registered control task 2-5, and instructs access timing. Here, the details of the scheduler 2-6 are omitted.

It is necessary to perform exclusive control between the control tasks 2-5 for the buffer 2-8 area as well. This is performed by the buffer management function 2-7, which is a part corresponding to each claim of the present invention. The control task 2-5 realizes exclusion by using only the partial area of the buffer 2-8 acquired from the buffer management function 2-7. In the present embodiment, it is assumed that the media data to be transmitted has a constant bit rate. Therefore, the playback time of each segment is always constant in one content. This time is called a segment time. The control task 2-5 continues to send the segment data in the buffer 2-8 to the communication control device 2-9 at a constant rate throughout the segment time. Communication control device 2
-9 transmits data to the client 2-11 which has requested video reproduction via the network 2-10. FIG. 3 shows how to use the buffer 2-8. Two buffer partial areas (buffer units) of a size that can fit one segment
While the transmission is being performed in one buffer unit, the next segment is read from the disk device 2-3 in another buffer unit. This method is called double buffering. The scheduler 2-6 guarantees reading of the data from the disk device 2-3 by the transmission start time of a certain segment. When there is a disk access instruction from the scheduler 2-6, the control task 2-5 acquires a buffer unit from the buffer management function 2-7, and reads the segment data there. When the transmission start time of the segment comes, the data is transmitted at a constant rate over the segment time.

When the data bit rate changes, either the segment size or the segment time must change. There are the following two methods for uniformly handling data of various bit rates on one system. (1) The segment size is fixed. The higher the bit rate, the shorter the segment time. (2) The segment time is fixed. The higher the bit rate, the larger the segment size. FIG. 4 shows the case of FIG. 3 where double bit rate data is handled with the constant segment size of (1). The segment time is halved and the disk access interval is halved. FIG. 5 shows the case of FIG. 3 where double bit rate data is handled in the constant segment time of (2). Because the segment size is doubled,
The number of buffer units used at a time is also doubled.
Although the disk access interval does not change, the time required for one disk access is doubled. The configuration of the buffer management function according to the embodiment of the present invention will be described with reference to FIG. Since (2) the configuration in which the segment time is constant includes the configuration in which (1) the segment size is constant, here, (2) the case in which the segment time is constant will be described. I do.

The buffer 1-4 is subdivided into a size corresponding to the segment size. Each of them is called a buffer unit. Each buffer unit has one-to-one corresponding buffer structures 1-6 and 1-8. The buffer structures 1-6 and 1-8 hold the addresses of the corresponding buffer units. Buffer structures not currently used are referred to as released buffer structures 1-6 and free lists 1-7.
Has been put into The contents of the buffer unit corresponding to the released buffer structure 1-6 are not rewritten.
Free list 1-7 is a first-in first-out list (queue)
By using this to manage, the most recently used data is stored for the longest time. The buffer structure is retrieved from the free list 1-7, and the control task 1
When passed to -1, the buffer unit indicated by the in-use buffer structure 1-8 can be used. In the present invention, a buffer unit that has been read and that is not rewritten, and a buffer structure 1-8 corresponding to the buffer unit can be shared by a plurality of control tasks 1-1. In order to reuse the read data, the read buffer management table 1-5 is used, and the disk number and sector number of the disk device in which the currently read segment exists in the buffer structures 1-6 and 1-8. Add a field to hold. The buffer structures 1-6 and 1-8 are all connected to the free list 1-7 at the time of system startup.
An initial value is set in the sector number field. This initial value indicates that valid data is not included in the corresponding buffer unit. The buffer structure 1-6 used once and returned to the free list 1-7 is set with a disk number and a sector number, and indicates which data is included in the corresponding buffer unit. This data is not destroyed as long as the buffer structure 1-6 is in the free list 1-7. The read buffer management table 1-5 is used for quickly searching for a buffer structure 1-6 holding data to be sought, and is realized by a hash or the like using a disk number and a sector number as keys. In the present invention, the used buffer structure 1-8 for which data has been read can also be managed and searched for in the read buffer management table 1-5. While the buffer unit may be rewritten, the buffer structure 1-8 is not managed on the read buffer management table 1-5. If the data of the target segment remains in the buffer 1-4, the corresponding buffer structure 1 is read using the read buffer management table 1-5.
-6 and 1-8 can be acquired regardless of whether they are released or in use.

In the read buffer management table 1-5, 1
An entry can also point to a plurality of buffer structures 1-6, 1-8. When a plurality of buffer units are used for one segment, when reusing data, it is necessary to know in what order data was previously read in buffer units. Therefore, the read buffer management table 1-
The entry 5 is recorded in such a manner that the use order of the buffer structures 1-6 and 1-8 is preserved. The transfer of the buffer structure 1-8 to and from the control task 1-1 is also performed while preserving the order of use. In the present invention, the buffer structure 1-8 can be shared among the plurality of control tasks 1-1, but refer to the entry of the read buffer management table 1-5 to record the number of used tasks. Provide a counter field. If the reference counter is 0, it means that the buffer structure 1-6 indicated by the entry has been released and exists in the free list 1-5. When receiving the disk access instruction from the scheduler, the control task 1-1 searches the disk arrangement information 1-2 to obtain the disk number and the sector number in which the segment to be read next is written. Next, the control task 1-1 calls a buffer acquisition process 1-9 to the buffer management function 1-3.

FIG. 7 shows the contents of the buffer acquisition processing 1-9.
Shown in The input of the process is a disk number, a sector number and the number of acquisition buffer units. Buffer management table 1-5 read from input disk number and sector number
Search for. Although there is a possibility that a plurality of entries are searched, any one entry may be used. If an entry exists in the table (S2, S3), the pointers of all buffer structures 1-6, 1-8 indicated by the entry are obtained. If the reference counter of the corresponding entry is 0 (S4), since those buffer structures 1-6 exist in the free list 1-7, they are removed from the free list 1-7 (S5). Since the number of tasks using the acquisition buffer structures 1-6 and 1-8 is increased by one, the value of the reference counter of the corresponding entry is increased by 1 (S6). Read buffer management table 1-5
Is failed (S2), the necessary number of buffer structures 1-6 are removed from the head of the free list 1-7. For each of the acquired buffer structures 1-6, it is necessary to delete the entry pointing to itself from the read buffer management table 1-5, so the data of the disk number and sector number fields of the acquired buffer structure 1-6 From the read buffer management table 1-5. If there is a buffer structure 1-6 pointing to other than the entry in the entry, the data of the buffer unit is no longer valid, so the initial values are set to the disk number and sector number of the buffer structure 1-6. And change it to indicate that it is invalid data. Thereafter, the entry is deleted from the read buffer management table 1-5 (S9 to S12). If the disk number and sector number fields are initial values, there is no entry pointing to the buffer structure 1-6, so that search / deletion is unnecessary. Free list 1-7
, The disk is read from the same disk number and sector number as the input values, and the values are set in the fields of all the buffer structures 1-6 (S10). The pointer of the last buffer structure 1-6 and the logical value indicating whether or not the data has been read are returned.

The control task 1-1 performs a buffer acquisition process 1-
When returning from step 9, it is checked whether the data has been read. If the data has been read, the disk access is omitted. As a result, the omitted disk access opportunity can be allocated to another task such as data writing or data restoration, and the disk access band can be used more effectively. If the data has been read, the buffer unit may be shared with another task, so that the data must not be written in the buffer unit. When the control task 1-1 acquires a buffer unit in which data has not been read by the buffer acquisition process 1-9, it is necessary to read data from the disk into this area and use it. After the data is read and it is determined that the contents will not be rewritten thereafter, this buffer unit can be shared with other tasks. In this case, the control task 1-1 calls the buffer read setting process 1-11 to the buffer management function 1-3. The buffer structure 1-8 specified in the buffer read setting process 1-11 can be used for another task after the process is executed. Buffer read setting processing 1
FIG. 8 shows the processing contents of No. 11. The input of the process is the pointer of all the buffer structures 1-8 that have been acquired (T
1). If there is no entry pointing to the input buffer structure 1-8 in the read buffer management table 1-5 (T2), each structure is pointed to using the disk number and sector number value of the buffer structure 1-8 as a key. The entry is registered in the read buffer management table 1-5. At this time, the order of use of each buffer structure 1-8 is preserved. Next, the value of the reference counter of the corresponding entry is set to 1 (T3), and the process ends (T4).

When the control task 1-1 has finished transmitting all the data of the segment and the buffer unit is no longer needed, the buffer management function 1-3 is instructed to perform buffer release processing 1-10.
Call. FIG. 9 shows the processing contents of the buffer release processing 1-10. The input of the process is a pointer to all buffer structures 1-8 to be released (U1). If there is no entry pointing to the input buffer structure 1-8 in the read buffer management table 1-5 (U2), there is no reusable data in that buffer unit, so the buffer structure 1
After initial values are set to the disk number and sector number of −8, all the buffer structures 1-6 are connected to the end of the free list 1-7 (U4), and the process is terminated (U7). If an entry exists in the read buffer management table 1-5 (U2), first, the value of the reference counter of the entry is decremented by 1 (U3). When the value of the reference counter becomes 0 (U5), since there is no other shared task,
The entire buffer structures 1-6 are linked to the end of the free list 1-7 (U6), and the processing is terminated (U7). In addition,
Buffer acquisition processing 1-9, buffer read setting processing 1
-11, it is necessary to perform exclusive control so that the buffer release processing 1-10 is not executed simultaneously by a plurality of control tasks 1-1.

There is a high possibility that the cueing time from the video playback request to the actual start of playback can be reduced when the first segment has been read, compared to when it has not been read. FIG.
As shown in (1), when there is no read data, it is necessary to first read the disk of the first segment and then start reproduction. Also, disk access is not immediately possible due to scheduling concerns. In the example of FIG. 6, the control task 1-1 concentrates on disk access, and the disk can be accessed only after 4 unit time, and the reproduction is started after 6 unit time with a read grace time of 1 unit time.
Here, the read grace time is a grace time in consideration of a case where the disk access completion is delayed. When there is read data, the reproduction can be started immediately if the reading of the next segment can be scheduled by the read grace time minus the segment time. That is, by reusing the read data, the expected value of the cueing time is reduced. The above is an example of only the task of reading a disc. However, the buffer unit in which data has been read and used by the task of writing a disc can be reused by the disc reading task. It is very effective in follow-up playback.

In the present invention, the problem is solved by equipping a computer or a server with the above-mentioned functions by hardware or software, and the present invention has a hardware configuration or a software configuration. It does not matter. Here, in the case of the software configuration, as shown in FIG.
OS running on the computer or the like based on the instructions of the program installed on the computer or the like from 0
(Operating system), MW (middleware) such as database management software, network software, etc., may execute a part of each process for realizing the present embodiment. The storage medium can store programs such as a magnetic disk, a floppy (registered trademark) disk, a hard disk, an optical disk (CD-ROM, CD-R, DVD, etc.), a magneto-optical disk (MO, etc.), a semiconductor memory, etc. In addition, as long as it is a tangible storage medium that can be read by a computer or the like, the storage form may be any form. Further, the storage medium in the present invention is not limited to a medium independent of a computer, but also includes a storage medium in which a program transmitted via a LAN, the Internet, or the like is downloaded and stored or temporarily stored.

Further, the number of storage media is not limited to one, and the case where the processing in this embodiment is executed from a plurality of media is also included in the storage media of the present invention, and any media configuration may be used. Note that the computer, server, and the like in the present invention are based on a program stored in a storage medium.
The computer executes each process in the present embodiment, and may have any configuration such as a single computer, an apparatus including a server, and a system in which a plurality of apparatuses are connected to a network. In the computer and the like according to the present invention, devices and devices that can realize the functions of the present invention by a program, including an arithmetic processing unit and a microcomputer included in an information processing device, are collectively referred to.

[0021]

As described above, according to the present invention, unnecessary disk access is eliminated, the effective use of the disk access band, and the reduction of the cueing time are realized. It is possible to provide a distribution system, a video server, and a buffer control method.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram of a distribution system to which the present invention is applied.

FIG. 3 is an explanatory diagram of a method of using a buffer.

FIG. 4 is an explanatory diagram of a method of using a buffer unit in a constant segment size method.

FIG. 5 is an explanatory diagram of a method of using a buffer unit in a constant segment time system.

FIG. 6 is an explanatory diagram of a cueing time reduction by reusing data.

FIG. 7 is a flowchart of a buffer acquisition process according to an embodiment of the present invention.

FIG. 8 is a flowchart of a buffer read setting process according to an embodiment of the present invention.

FIG. 9 is a flowchart of a buffer release process according to an embodiment of the present invention.

FIG. 10 is a block diagram showing a storage medium of the present invention.

[Explanation of symbols]

 1-1 Control task 1-2 Disk allocation information 1-3 Buffer management function 1-4 Buffer 1-5 Read buffer management table 1-6 Released buffer structure 1-7 Free list 1-8 Buffer structure in use 1-9 Buffer Acquisition Process 1-10 Buffer Release Process 2-1 Video Server 2-2 Disk Location Information 2-3 Disk Device 2-4 Request Accepting Function 2-5 Control Task 2-6 Scheduler 2-7 Buffer Management Function 2 -8 buffer 2-9 communication control device 2-10 network 2-11 client

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B060 AA06 AC18 5B082 AA13 FA02 5C052 AA03 AB03 AB04 AC01 AC08 CC06 DD04 5C064 BA01 BA07 BB10 BC16 BC18 BC20 BC23 BC27 BD02 BD07 BD08 BD09

Claims (7)

[Claims] 1. A system for distributing digital video / audio data stored in a disk device, wherein a buffer area in the disk device is subdivided, and addresses and read-outs are provided in one-to-one correspondence with the subdivided partial regions. A buffer structure for holding a disk number and a sector number on the disk device where data exists, a free list for managing a released buffer structure that is not used among the buffer structures in a first-in first-out manner, Of a buffer structure in a free list having valid data or a buffer structure which does not exist in the free list but is in use by a task and has been read in data. A reference counter that indicates the number of tasks that are shared and used when in use And a read buffer management table for holding the buffer structure. When necessary data is in the buffer area based on the read buffer management table, a reference counter is incremented and the corresponding buffer structure is returned. Buffer acquisition means for returning the buffer structure at the head of the free list when the buffer structure is not above, and when data is read into a new buffer area, an entry for the buffer structure is stored in the read buffer management table. Buffer read setting means for registering, and buffer release means for reducing a reference counter of the corresponding entry on the read buffer management table and returning a used buffer structure to the free list when the reference counter is 0. A digital video / audio data distribution system, comprising: 2. A read buffer management table capable of retrieving the plurality of buffer structures collectively while preserving the order, and a buffer acquisition unit capable of retrieving the plurality of buffer structures collectively and preserving the order. 2. The digital video / audio data distribution system according to claim 1, further comprising: a buffer releasing unit configured to collectively return the plurality of buffer structures to the free list. 3. A video server having a disk device for storing digital video / audio data and transmitting data in a buffer to the client in response to a data distribution request from the client, wherein a buffer area in the disk device is subdivided. A buffer structure for holding a disk number and a sector number on the disk device in which addresses and read data exist in one-to-one correspondence with each of the divided and subdivided partial areas; A free list that manages buffer structures that have not been released in a first-in first-out manner, and one of the buffer structures or free lists in the free list that has valid data in the free list does not exist in the free list and is used by the task and data is read. Used for fast retrieval of one buffer structure that has already been used. A read buffer management table holding a reference counter indicating the number of tasks shared and used when the task is being used; and necessary data are stored in the buffer area based on the read buffer management table. Buffer acquisition means for returning the corresponding buffer structure after increasing the reference counter in some cases, and returning the first buffer structure of the free list when the required data is not on the buffer; and A buffer read setting means for registering an entry to a corresponding buffer structure in the read buffer management table when data is read into an area; and decreasing a reference counter of the corresponding entry on the read buffer management table by referring to the read buffer management table. A buffer for returning a used buffer structure to the free list if the counter is 0 Video server, characterized by comprising a releasing means. 4. A read buffer management table capable of retrieving the plurality of buffer structures collectively while preserving the order, and a buffer acquisition unit capable of retrieving the plurality of buffer structures preserving the order while preserving the order. 4. The video server according to claim 3, further comprising: a buffer releasing unit configured to collectively return the plurality of buffer structures to the free list. 5. A computer which is applied to a video server having a disk device and which transmits data to the client via a network in response to a data distribution request from the client, and which has a program for executing the video server in a predetermined operation. In a readable storage medium, a buffer area in the disk device is subdivided, and an address and a disk number and a sector number on the disk device in which read data exist in one-to-one correspondence with each of the divided subregions are buffered. Holding in a structure, managing unused buffer structures that are not used among the held buffer structures in a first-in first-out free list, and holding valid data in the free list for the management. One buffer structure in the free list A task that is used for high-speed retrieval of one buffer structure that is not in the body or in the free list but is in use by a task and for which data has been read, and is shared and used when it is in use by a task If the required data is in the buffer area based on the read buffer management table that holds the reference counter indicating the number of data, the reference counter is increased and the corresponding buffer structure is returned, and the required data is stored in the buffer. If not, returning a buffer structure at the head of the free list; and, when data is read into a new buffer area, registering an entry for the buffer structure in the read buffer management table. Decrement the reference counter of the corresponding entry on the read buffer management table, Returning a used buffer structure to the free list. 6. The buffer control method applied to a system for distributing digital video / audio data stored in a disk device and transmitting data in a buffer to the client in response to a data distribution request from the client. In the above, the buffer area in the disk device is subdivided, and the disk number and the sector number on the disk device in which the address and the read data exist in one-to-one correspondence with each of the subdivided partial areas are stored in a buffer structure. An unused buffer structure that is not used among the held buffer structures is managed by a first-in first-out free list, and one buffer structure in the free list having valid data in the free list for this management. Or data that is not on the free list but is in use by the task Based on a read buffer management table that is used for high-speed retrieval of one buffer structure that has been read, and that holds a reference counter indicating the number of tasks that are shared and used when being used by a task. If the required data is in the buffer area, the reference counter is incremented and the corresponding buffer structure is returned.If the required data is not in the buffer, the head buffer structure of the free list is returned. When data is read into a new buffer area, an entry to the buffer structure is registered in the read buffer management table, the reference counter of the corresponding entry on the read buffer management table is reduced, and the reference counter is reduced. Returning a used buffer structure to the free list when is zero. Method. 7. The buffer control method according to claim 6, wherein a plurality of the buffer structures are collected, searched while maintaining the order of the collected buffer structures, returned, and returned to the free list. .