FR2767622A1 - Video word storage method - Google Patents

Abstract

The read method can be terminated on a desired frame and use of the time windows allows the read command to continue even when different binary rates are used.

Description

METHOD FOR STORING VIDEO DATA
BACKGROUND OF THE INVENTION
Field of the invention
The present invention relates to a method of storing video data for a video server which stores and plays back data recorded on discs, such as audio or video data, having a real-time property and more particularly a method of storing video data whereby data of different bit rates can be efficiently read.

Description of associated art
In a video server, video data is stored in the form of compressed codes on disks of the video server and is read from the recording media in response to a request from a client connected to the video server, then distributed to the client. .

 An example of one of the conventional video servers is described for example in Japanese patent application No. Heisei 8-88834 and is shown in Figure 5. Referring to Figure 5, the video server or video system on request, includes a storage device 501, a data reading device 502, a memory writing device 5031 to 503n, buffer memories 5041 to 504n, memory reading devices 5051 to 505n, terminal units 5061 to 506n and a control device 507. The storage device 501 comprises a plurality of storage media 5011 to 501m such as, for example, magnetic disks.

 The video data stored in the storage device 501 is read by the data reading device 502 and temporarily stored in the buffer memories 5041 to 504n via the memory writing device 5031 to 503n. The data stored in the buffer memories 5041 to 504n are read by the memory reading device 5051 to 505n and are sent to the terminal units 5061 to 506n, by which they are respectively decompressed, re-read and displayed. The controller 507 controls the storage device 501 and the data playback device 502 in response to the distribution request signals applied as input from the terminal units 5061 to 506n, so that the video data stored in the storage device 501 are read by the data reading device 502 and written to the buffer memories 5041 to 504n.

In the conventional video on demand system described above, the video data is divided for each predetermined length and periodically stored in the storage device 501. One way in which the video data is stored, where the number of storage media 5011 to 501m constituting the storage device 501 is four, is illustrated in FIG. 6. The video data are divided into blocks of video data VD-110,
VD-002, -, VD-k and stored periodically in order of a time series in the storage medium 5011 to 5014.

 The video data stored in the storage device 501 is read by the data reading device 502 and finally replayed and displayed by one of the terminal units 5061 to 506n. FIG. 7 illustrates a relation between the time of reading from the storage device 501 and the time of display of replay by the terminal units 5061. The video data VD-001 stored in the storage medium 5011 are read and stored in the buffer memory 5041 in one reading time of DTread video data. The terminal unit 5061 re-plays the video data in a replay time of DTplay video data. If it is now assumed that the DTread video data playback time is equal to a quarter of the DTplay video data replay time, then four blocks of video data can be read from the storage media 5011 within the time to replay video data from a block.

 It is here examined the replay of video data using the terminal unit 5061. The video data block VD-001 stored in the video medium 5011 is read by the data reading device 502 and transferred to the memory writing device. 5031. The memory writing device 5031 stores the data in the buffer memory 5041. After the data is stored, it is read by the memory reading device 5051 and read and displayed by the terminal unit 5061. Before the playback display by the terminal unit 5061 ends, the data reading device 502 reads the following video data VD-002 from the storage medium 5012 and stores the data in the buffer memory 5041 via the device write to memory 5031. Since the required following video data is required to be stored in a buffer before the previous video data replay display If the DTread video data playback time is shorter than the DTplay video playback time, the data playback device 502 can play a plurality of video data from the same recording medium.

FIG. 8 illustrates an example in which four video data are read within a replay time of DTplay video data. A unit obtained by plotting the video data for each time of replaying DTplay video data for a certain time is called a frame and a unit obtained by dividing a frame by a time for playing DTread video data is called time window. Video data includes four types of VD1 data,
VD2, VD3 and VD4 and the data reading device 502 reads video data blocks VD1-001, VD2-001,
VD3-001 and VD4-001 in order, from the storage medium 5011 and stores them respectively in the buffers 5041 to 5044. When the blocks of video data are received, the terminal units 5061 to 5064 decompress them, replay them and display them.

Before the replay display of the terminal units 5061 to 5064 ends, the following blocks of video data are read from the storage medium 5012 and the images based on the video data are played back and displayed continuously.

 When four recording media, each of which four time windows can be fixed for one frame, are used in this way, different images can be output so as to total 4 x 4 = 16 terminal units.

 However, in the conventional video server described above, since a time window is allocated to a terminal for replaying video information, when video data of different bit rates are read simultaneously, time windows are determined uniformly so as to satisfy the higher bit rates, as seen in Figure 9. When a time window determination method as just described is used, since the time windows are constructed in accordance with a bit rate as high as that of the video data B illustrated in FIG. 9, an useless time appears in a time window for video data of low bit rate such as video data A. If for example, all the video data intended to be delivered have a low bit rate like that of video data A, so half the playback capacity and disk processing is spent unnecessarily.

 On the other hand, another method is available in which the command to read video data is carried out so that a total sum of playing time of different video data DTread can be included in a frame, as shown in FIG. 10 In this case, while the playback capacity of the recording medium can be used with higher efficiency, when video data of high bit rate is involved, a large amount of data must be read at a time. a recording medium, similar to the method described above. Consequently, the second method presents a problem in that, when video data of low bit rates, for example, the video data blocks A, B, C, D, E, F, G and H, are allocated uniformly to a time window as shown in FIG. 11, although the reading and processing capacity is sufficiently large, the playback of video data Z having a high bit rate is deactivated. Here, Fig. 11 illustrates a way in which, although each frame has sufficient space, a block of Z-1 video data cannot be received in a frame.

 On the other hand, Japanese patent application No.

Heisei 8-163072 describes a different method in which, also when video data has a high bit rate, the video data is divided into blocks of a fixed size and the blocks are stored in order on the recording media. According to the method just described, the number of blocks to be read at a time is set in accordance with a bit rate required by a terminal, so that video data of different bit rates can be supplied to the terminal.

 However, the method presents a problem in that, since blocks of video data are allocated in a twisted manner to the video media, if video data of different bit rates are replayed, then the command to read the recording media becomes out of order.

 On the other hand, when a plurality of video data having an equal bit rate is replayed, since the video medium from which the data is read is successively replaced by a following recording medium during a transition to a next frame of in such a way that, in a first frame, video data is read in a block from the video medium -1, but in a second frame, video data is read in a block from the video medium 2, as shown in the figure 8.

 However, with the method described in Japanese patent application No. Heisei 8-163072, when video data having a bit rate as high as double must be played back, when transitioning to a next frame, the recording medium from which the data to be read is successively replaced by a second recording medium following in such a way that, as seen in FIG. 12, in a first frame, two blocks are read from the recording medium -1 and the recording medium -2 and in a second frame, two blocks are read from the recording medium -3 and the recording medium -4.

Consequently, when, for example, video data blocks of video data A, B, C and D, having a lower bit rate are allocated in a group, as shown in FIG. 13 and it is desired to allocate video data Z with a bit rate as high as double the lower bit rate, the read command becomes out of adjustment. In the example of Figure 18, since the video data Z has a double bit rate, it is required to read two blocks of video data per frame. In a first frame, the video data blocks A-1, B-1, C-1, D-1 and Z-1, Z-2, are suitably allocated to the time windows.

However, in a second frame, the video data blocks A-2, B-2, C-2, D-2 and Z-3, can be read properly, but the reading of a video data block Z-4 is not finished in the second frame in which it was intended to be read. In other words, even if video data is appropriately allocated first, since the time window movements are different among video data of different bit rates, the method described above presents a problem to be solved in that, at As time goes by, it becomes impossible to finish playback in a scheduled frame.

SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of storing video data by which, in replaying video data in which time windows are used, even when video data having different bit rates is to be replayed, the video data can be played back without disrupting the playback control of recording media, and the possibilities of reading the recording media can be used effectively.

 To achieve the aim described above, according to the present invention, a method of storing video data is proposed, comprising the steps consisting in dividing the video data in advance into basic blocks having a determined size with reference to a bit rate base, periodically allocate the basic blocks in order of a time series to a plurality of video files and periodically store the partial video files in a plurality of recording media by considering each of the partial video files as video data.

 In the video data storage method, when video data having a bit rate as high as an integer number of times the basic bit rate is to be stored, the video data is divided for each amount of fixed data, which is equal the amount of basic bit rate video data when the basic bit rate video data is replayed for a fixed period of time, i.e. divided into units of a basic block and is stored discreetly as s 'there was a group of a plurality of video data of the basic bit rate. As a result, even when replaying of video data having different bit rates is performed simultaneously, the video data can be steadily replayed without causing any problem in controlling playback of the storage media and furthermore the possibilities of reading the media. storage can be used effectively.

 Consequently, with the video data storage method, when video data with a bit rate as high as an integer number of times the basic bit rate has to be replayed, since playback from storage media can be managed in a manner quite similar to the reading of video data of the basic bit rate from the storage media, the command to read the storage media is not disturbed. As a result, there is no need to provide an extreme margin for a time window and the read capacities of the recording media can be used efficiently as much as possible.

 The above objects, features and advantages of the present invention, as well as others, will become more apparent from the following description and the appended claims, taken in conjunction with the appended drawings, in which like parts or elements are indicated by the same reference symbols.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart illustrating a method of storing video data to which the present invention is applied
Figure 2 is a schematic view illustrating a manner in which video data is divided into partial video files in the method of storing video data illustrated in Figure 1
Figure 3 is a schematic view illustrating a way in which video data is stored on different disks in the video data storage method illustrated in Figure 1
Figure 4 is a schematic view illustrating the operation of time windows with which the video data illustrated in Figure 3 is played from the discs
Figure 5 is a block diagram showing a construction of a conventional video server
Figure 6 is a schematic view illustrating a manner in which video data is discreetly stored on a plurality of disks in the video server shown in Figure 5
FIG. 7 is a time diagram illustrating a relationship between times of reading from recording media of the video server of FIG. 5 and times of display of replay by terminal units
FIG. 8 is a timing diagram illustrating the playback of four video data in a reproduction display time
Fig. 9 is a schematic view illustrating an object to be resolved when video data having different bit rates is read from discs using a conventional technique
Fig. 10 is a schematic view illustrating a method of playing video data having different bit rates from discs using another conventional technique
Figure 11 is a schematic view illustrating a second object to be resolved when video data having different bit rates is played from discs using the conventional technique used in the method illustrated in Figure 10
Fig. 12 is a schematic view illustrating a method of reading video data having different bit rates, using another conventional technique; and
FIG. 13 is a schematic view illustrating a third object to be resolved when video data having different bit rates are read from discs, using the conventional technique used in the method illustrated in FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENT
Before describing a preferred embodiment, several terms used in the present application are described. In a video server to which a method of storing video data according to the present invention is applied, a basic bit rate is determined in advance. The basic bit rate is a bit rate that refers to the bit rates used to store video data. If for example, the basic bit rate is set to 3 Mb / s, then the bit rates of video data that can be stored are multiples of the basic bit rate, such as 3 Mb / s, 6 Mb / s, 9 Mb / s and so on. A basic bit rate video data unit which is a quantity of data by which the video data is replayed for a certain fixed period of time, is called a basic block. If, for example, video data is divided every 0.5 seconds, then the basic block has a data amount of around 190 Kbytes.

 FIG. 1 illustrates the broad outlines of the operation of the video server to which the video data storage method according to the present invention is applied. Referring to Figure 1, the video data is first divided into basic blocks and the basic blocks are arranged in order of a time series to form n partial video files so that the basic blocks can have a period of n (step 1). Here, n is an integer equal to or greater than 1 and represents a multiple of the bit rate of the video data to be stored. When, for example, the basic bit rate is 3 Mb / s, if video data of 9 Mb / s is to be stored, then n = 3. An example of dividing video data where n = 3 is illustrated in the figure 2. Then, the partial video files obtained by the division described above are periodically stored in recording media, considering each of them as a video file (step 2). Figure 3 illustrates an example of a case where the partial video files are stored in four recording media. The partial video file -0 illustrated in FIG. 2 is periodically stored in the recording medium -1, the recording medium -2, ... in FIG. 3, as if it were a file single video. The partial video file -1 is also periodically stored in the recording medium -2, the recording medium -3, ... in a similar manner. In this example, while the storage of the partial video files can start from any recording medium, to ensure a significant effect of the present invention, the recording media from which the storage is to start is preferably made different among different partial video files. However, when the number of partial video files is greater than the number of storage media, storage can be started from the same video media.

 Allocation and storage can be done in parallel with each other. In particular, it is not necessary that all video data is stored in recording media after it has been allocated to partial video files, but after data for each basic block is received, it can be successively stored in the recording media. When, for example, video data is divided into the partial video file -0, the partial video file -1 and the partial video file -2, the storage location of each video data for a basic block among the storage media recording can be calculated, considering a remainder when the block number of each basic block is divided by n (= 3) as the number of the partial video file to which the basic block belongs, based on the block number and the number of the partial video file.

A method of playing video data stored in a manner as described above is now described with reference to Figure 4. Video data having a bit rate (for example, 9 Mb / s) as high as three times the basic bit rate are read as follows. Here, partial video files are indicated by VD1, VD2 and VD3. In the first 0.5 seconds, a total of three blocks VD1-1, VD2-1 and VD3-1 of partial video files
VD1, VD2 and VD3 are read from the recording medium -1, the recording medium -2 and the recording medium -3 and the three blocks are connected together in a buffer memory. During the next 0.5 seconds, a total of three blocks VD12, VD2-2 and VD3-2 of the partial video files VD1, VD2 and VD3 are played from the recording medium -2, the recording medium -3 and the recording medium -4 and the three blocks are connected together in the buffer memory. A sequence of operations such as the one just described is repeated, thus allowing the replay of 9 Mb / s video data. When only the read operation is considered, since it is equivalent to the operation of playback of three video files of the basic bit rate, no time window operation is out of adjustment.

 It should be noted that the data stored according to the video data storage method of the present invention can be replayed using a known data replay device as described above with reference to FIG. 5.

 Although preferred embodiments of the present invention have been described using specific terms, this description is for explanatory purposes only and it should be understood that variations can be made without departing from the spirit or the scope of the following claims.

Claims (4)

 1. A method for storing video data, characterized in that it comprises the steps consisting in:  divide the video data in advance into basic blocks having a determined size with reference to a basic bit rate  periodically allocating the basic blocks in order of a time series to a plurality of video files; and  periodically store the partial video files in a plurality of recording media by considering each of the partial video files as video data.  2. A method of storing video data according to claim 1, characterized in that the set of basic blocks are periodically allocated to the plurality of partial video files, then periodically stored in the plurality of recording media.  3. Method for storing video data according to claim 1, characterized in that, for each of the basic blocks, the periodic allocation to the plurality of partial video files and the periodic storage in the plurality of recording media are carried out .  4. A method of storing video data according to any one of claims 1 to 3, characterized in that each of the basic blocks has an amount of data equal to that which exists when video data of the basic bit rate is replayed during a certain duration.