JP2007036666A - Contents distribution system, client, and client program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contents distribution system which is possible to change a reproduction bit rate at the predetermined position of the contents. <P>SOLUTION: A server 10 has bit rates which are different each other for the same contents, and has stream data STi (i=1 to 3) divided into a plurality of parts. A client 20 reproduces the stream data STi distributed from the server 10 while receiving them. At the time, the client 20 discriminates whether the data amount of the next part is already stored in buffer regions 27A or 27B or not in every completion of reproduction of the parts. If it is stored, the client calculates a data amount which is possible to be stored in the buffer regions 27A and 27B during a reproduction time of the next part, and selects stream data STi to request to the server 10 based on the calculation result. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a content distribution system, a client, and a client program. More specifically, the present invention relates to a content distribution system, a client, and a client program for streaming content from a server to a client.

  The streaming content distribution system includes a server having a plurality of stream data related to content such as a moving image, and a client that reproduces the content while receiving the distribution of the stream data from the server.

  In such a streaming-type content distribution system, it is necessary to prevent playback from being interrupted by the client even if the network traffic state changes.

  In order to solve this problem, Japanese Patent Laid-Open No. 2004-215074 (Patent Document 1) prepares a plurality of stream data with different bit rates in advance in a server, and sets an appropriate reproduction bit rate according to the traffic state of the network. A multi-bit rate method capable of distributing stream data is disclosed. Japanese Patent Laying-Open No. 2003-259333 (Patent Document 2) discloses a content distribution system in which a server can change a compression rate and a frame rate of a content according to a network situation. According to these methods, it is possible to prevent the reproduction from being interrupted by the client during the stream distribution.

However, in these methods, there is a possibility that data stored in the client is depleted and reproduction is interrupted when the reproduction bit rate, compression rate, and frame rate are changed. Furthermore, in these methods, the bit rate is changed depending on the state of the network without depending on the content of the content being reproduced. That is, regardless of the scene of the moving image being reproduced, the image quality is changed by changing the bit rate. As a result, image quality changes suddenly, giving the user a discomfort to view the content.
Japanese Patent Laid-Open No. 2004-215074 JP 2003-259333 A

An object of the present invention is to provide a content distribution system for preventing interruption of reproduction during stream distribution.
Another object of the present invention is to provide a content distribution system capable of changing a reproduction bit rate at a predetermined position of content.

Means for Solving the Problems and Effects of the Invention

  The content distribution system according to the present invention includes a server and a client connected to the server. The server includes stream data storage means and distribution means. The stream data storage unit stores a plurality of stream data. Each of the plurality of stream data is divided into a plurality of parts arranged in succession with different reproduction bit rates for the same content. The distribution means performs stream distribution of the parts of the stream data in order of arrangement in response to the request from the client. The client includes buffer means, playback means, determination means, data amount calculation means, selection means, and request means. The buffer means sequentially stores the streamed parts. The reproduction means sequentially reproduces the parts stored in the buffer means. The determining means determines whether or not an unreproduced part is accumulated in the buffer means when the reproduction of the part is completed. When the unreproduced part is accumulated as a result of the determination, the data amount calculation means calculates the amount of data that can be accumulated in the buffer means with the reproduction time of the unreproduced part. The selection means selects the stream data and distribution start part requested from the server based on the calculation result. The requesting unit requests the stream distribution of the selected stream data from the distribution start part.

  In this content distribution system, the client accumulates unreproduced parts in advance, selects stream data based on the amount of data that can be accumulated during the reproduction time of the unreproduced part, and reproduces the unreproduced part. During this time, the selected stream data is acquired sequentially. Therefore, it is possible to prevent the data to be reproduced from being exhausted and to prevent the content reproduction from being interrupted. Furthermore, since the stream data is sequentially received and reproduced in parts, the reproduction bit rate can be changed in parts. That is, the reproduction bit rate change position can be set to a predetermined position (partition position between parts). If each part is separated by a playback position that has little effect on viewing even if the image quality or sound quality changes, for example, in the case of a movie, if the playback bit rate changes In addition, it is possible to suppress a sense of incongruity due to changes in image quality and sound quality.

  Preferably, the data amount calculating unit includes a distribution bit rate specifying unit. The distribution bit rate specifying means specifies the distribution bit rate of the stream data distributed from the server when the reproduction of the part is completed. The data amount calculation means calculates the data amount based on the identified delivery bit rate and the playback time of the unplayed part.

  In this case, the distribution bit rate at the time when the reproduction of the part is completed is specified, and the data amount is calculated. Therefore, the value calculated by the data amount calculation means can be brought close to the data amount actually stored, and the prediction accuracy of the data amount to be stored can be improved.

  Preferably, the client includes a stream information storage unit. The stream information accumulating unit accumulates stream information related to the data amount and reproduction time of each part of the stream data and other stream data parts corresponding to each part. The selecting means selects the stream data and the distribution start part based on the calculation result and the stream information.

In this case, the stream data and the distribution start part can be selected by comparing the data amount calculated by the data amount calculation means with the data amount of each part based on the stream information.

  Preferably, as a result of the determination by the determination unit, when an unreproduced part is not accumulated in the buffer unit, the selection unit selects the stream data having the lowest reproduction bit rate from among the plurality of stream data.

  In this case, even if unreproduced parts are not stored in the buffer means, by obtaining stream data having the lowest reproduction bit rate, it is possible to prevent interruption of reproduction to some extent.

  The client program according to the present invention is a client that can be connected to a server that stores a plurality of stream data divided into a plurality of parts arranged in succession, each having a different reproduction bit rate for the same content. A program to be executed by a computer. The client program sequentially accumulates the parts streamed from the server, sequentially reproduces the accumulated parts, and determines whether or not an unreproduced part is accumulated when the reproduction of the part is completed. And a step of calculating the amount of data that can be stored in the playback time of the unplayed part when the unplayed part is accumulated as a result of the determination, and the stream data requested to the server based on the calculation result And a step of selecting a distribution start part and a step of requesting the selected stream data to be stream-distributed from the distribution start part.

  This client program stores unplayed parts in advance, selects stream data based on the amount of data that can be stored during the playback time of the unplayed part, and selects it while playing the unplayed part. Get stream data sequentially. Therefore, it is possible to prevent the data to be reproduced from being exhausted and to prevent the content reproduction from being interrupted. Furthermore, since the stream data is sequentially received and reproduced in parts, the reproduction bit rate can be changed in parts. That is, the reproduction bit rate change position can be set to a predetermined position (partition position between parts).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

1. Configuration Referring to FIG. 1, the content distribution system includes a server (computer) 10 and a plurality of clients (computers) 20. The server 10 and the client 20 are connected via the Internet 30, but may be connected via a LAN (Local Area Network), a WAN (Wide Area Network), or other computer networks.

  The server 10 accumulates a plurality of stream data relating to contents such as moving images and music, and in response to a request from the client 20, the stream data is streamed. In short, this system is a streaming type content distribution system.

[Server configuration]
With reference to FIG. 1, the server 10 includes a hard disk drive (HDD) 11, a CPU 12, and a memory 13. These are connected to each other by a bus 17.

  The HDD 11 stores a plurality of stream data ST1 to ST3. The stream data ST1 to ST3 are stream data related to the same content, and have different reproduction bit rates. The structure of the stream data ST1 to ST3 will be described later. The HDD 11 also stores a plurality of stream data related to content different from the stream data ST1 to ST3.

  The HDD 11 further stores a stream information database 15 and a server application (program) 16. The stream information database 15 registers information related to the plurality of stream data described above. The stream information database 15 will be described later.

  The server application (program) 16 performs streaming delivery of stream data corresponding to the request from the client 20. The CPU 12 reads the server application 16 into the memory 13 and executes the operation of the server application 16 described above.

[Structure of stream data]
FIG. 2 shows the data structure of the stream data ST1 to ST3. The horizontal axis shows the playback time. Moreover, the area of each stream data ST1-ST3 shows data amount.

  The stream data ST1 to ST3 have different reproduction bit rates BR1 to BR3. The reproduction bit rate BR1 of the stream data ST1 is the lowest, the reproduction bit rate BR2 of the stream data ST2 is higher than the reproduction bit rate BR1, and the reproduction bit rate BR3 of the stream data ST3 is the highest. Therefore, the data amount of the stream data ST3 is the largest, and the data amount of the stream data ST1 is the smallest.

  Although the data amounts of the stream data ST1 to ST3 are different from each other, their reproduction times are the same (time t0 to time t8). This is because they are created based on the same content.

  Each stream data ST1 to ST3 is divided into a plurality of parts (P0 to P7) arranged continuously. At this time, each part Pj (part number j = 0 to 7) is divided at a reproduction position (time t1 to t7) that has little influence on viewing even if the image quality and sound quality change. For example, in the case of a moving image, the scene setting is divided at a position where the scene setting is changed. Therefore, the reproduction times (D0 to D7) of the parts P0 to P7 are different from each other.

  Since the stream data ST1 to ST3 are divided at the same playback position (t1 to t7), the same part Pj of each stream data has the same playback time Dj. For example, the part P0 of the stream data ST1, the part P0 of the stream data ST2, and the part P0 of the stream data ST3 have the same reproduction time D0.

[Stream information database]
Referring to FIG. 3, stream information database 15 includes data block 151 in which information regarding each stream data STi (rate number i = 1 to 3) is registered.

  Each data block 151 has an identifier STi (for example, ST1) of stream data and reproduction bit rate information BRi (for example, BR1). The data block 151 further has a part list. In the part list, information related to the part Pj of each stream data STi is registered. Specifically, the part list has records for the number of parts included in the stream data STi. Each record has a field for registering a part identifier (for example, P0, P1, etc.), a field for registering a reproduction time Dj, and a field for registering the data amount SZ (i, j) of the corresponding part Pj.

  Referring to the data block 151 of the stream data ST1 to ST3, the part identifiers having the same number in each data block 151 correspond to each other. For example, part P1 of stream data ST1 corresponds to part P1 of stream data ST2 and ST3. As described above, the playback time of each part identifier is the same, but the data amount is different.

  As described above, the stream information database 15 includes information on the stream data, information on the reproduction time and data amount of each part in each stream data, and information on other stream data parts corresponding to each stream data part. including.

[Client Configuration]
Referring to FIG. 1 again, the client 20 includes an HDD 21, a CPU 22, a memory 23, and a display 24. These are connected to each other by a bus 26.

  The HDD 21 stores a client application (program) 25. The client application 25 requests the stream data STi from the server 10 and reproduces content based on the part Pj of the received stream data STi. The client application 25 further selects the stream data STi requested from the server 10 during reproduction. Details will be described later.

The HDD 21 further includes buffer areas 27A and 27B (collectively referred to as a buffer area 27). The buffer area 27 sequentially accumulates stream data STi stream-distributed from the server 10. The buffer areas 27A and 27B accumulate stream data STi having different reproduction bit rates BRi.
The HDD 21 stores the stream information database 15 transmitted from the server 10.

  The CPU 22 reads the client application 25 into the memory 23 and executes the operation of the client 20 described below.

2. Operation 2.1. Overview In the content distribution system according to the present embodiment, the client 20 reproduces the stream data STi distributed from the server 10 while receiving it. At this time, every time the reproduction of each part Pj is completed, the client 20 determines whether or not the data amount SZ (i, j + 1) of the next part Pj + 1 is already accumulated in the buffer area 27. If so, the amount of data that can be stored in the buffer area 27 during the playback time of the next part Pj + 1 is calculated, and the stream data STi requested from the server is selected based on the calculation result.

FIG. 4 shows changes in the distribution bit rate BRcur and the data amount DL (t) accumulated in the buffer area 27 at time t when the client 20 is playing back while receiving the stream data STi from the server 10. It is a graph to show. The delivery bit rate BRcur is a bit rate (bit / sec) at the time of delivery of data stream-delivered from the server 10 to the client 20. The upper graph in FIG. 4 shows the fluctuation of the distribution bit rate BRcur, and the vertical axis is the bit rate (bit / sec). The lower graph in FIG. 4 shows the data amount DL (t) accumulated in the buffer area 27, and the vertical axis represents the data amount (bytes). D _{ST1 to} D _ST3 in the graph indicate the amount of data necessary for reproducing each stream data _{ST1 to ST3} . In each graph, the horizontal axis is time (sec).

Referring to FIG. 4, client 20 first requests server 10 for stream data STi (eg, ST3). The client 20 receives the stream data ST3 from the server 10 and accumulates it in the buffer area 27. When the accumulated data amount reaches a predetermined data amount DL (t0), the client 20 starts reproduction. From time t0 to time t2, the distribution bit rate BRcur is higher than the reproduction bit rate BR3. For this reason, the amount of data received is larger than the amount of data to be reproduced. That is, the slope of DL (t) in FIG. 4 is larger than the slope of _DST3 . Therefore, data is sequentially stored in the buffer area 27.

  The client 20 selects the stream data STi requested from the server at the time t1 when the reproduction of the part P0 ends (data request process: FIG. 6). In the data request process, it is determined whether or not the total data amount SZ (3, 1) of the next part (part P1) has already been accumulated in the buffer area 27, and if already accumulated, during the reproduction time D1 of part P1. Based on the amount of data that can be stored in the buffer area 27, it is determined whether or not to change the reproduction bit rate BR3 (stream data ST3). At time t1, it is determined that the data amount SZ (3, 1) has already been accumulated in the buffer area 27 and is maintained at the reproduction bit rate BR3, and reproduction is continued as it is.

At time t21, the delivery bit rate BRcur decreases and becomes lower than the reproduction bit rate BR3. Therefore, the data amount DL (t) accumulated in the buffer area 27 decreases after time t21. That is, the slope of DL (t) in FIG. 4 is smaller than the slope of _DST3 .
The client 20 performs the data request process at time t3, and the data amount SZ (3, 3) of the next part P3 has already been accumulated, but if the reproduction is continued as it is, the data accumulated during the reproduction of the part P4 Is depleted (DL (t) in FIG. 4 is lower than _DST3 ). At this time, the client 20 determines that the reproduction is not interrupted after the part P4 if the data to be reproduced is switched to the stream data ST2 (bit rate BR2), and requests the server 10 to distribute the stream data ST2 from the part P4. By this operation, the client 20 reproduces the stream data ST2 after time t4 (part P4).

  At time t51, the distribution bit rate BRcur rises again and becomes higher than the reproduction bit rate BR3. The client 20 determines that the data SZ (2, 6) of the part P6 of the stream data ST2 has already been accumulated at time t6, and further the stream data ST3 (reproduction bit rate BR3) during the reproduction time D6 of the part P6. It is determined that the data SZ (3, 7) of the part P7 of FIG. As a result, at time t6, the client 20 requests the server 10 to distribute the stream data ST3 from the part P7. The client 20 acquires the data SZ (3, 7) of the part P7 of the stream data ST3 during the reproduction time D6, and reproduces the data after time t7.

As described above, when the reproduction of the part Pj is completed, the client 20 accumulates the part Pj + 1 to be reproduced next in principle. Further, based on the amount of data that can be stored during the playback time Dj + 1 of the part Pj + 1, the playback bit rate BRi (stream data STi) of the data of the next part Pj + 2 is selected, and the part Pj + 2 of the selected stream data STi To get. Therefore, it is possible to prevent the content reproduction from being interrupted.
Furthermore, when switching the reproduction bit rate BRi, the client 20 switches in units of part Pj. Since each part Pj is divided in advance at a position where there is little discomfort even if the image quality and sound quality are changed, it is possible to suppress the influence on viewing by changing the image quality and sound quality as much as possible. In addition, since the client 20 determines a change in the reproduction bit rate BRi (stream data STi), the load on the server is reduced. Hereinafter, the operation of the content distribution system will be described in detail using a flowchart.

2.2. Overall Operation Referring to FIG. 5, first, the client 20 requests the stream information database 15 of desired content (S1). The server 10 monitors the request from the client 20 (S2), and when receiving the request (YES in S2), transmits the corresponding stream information database 15 (S3).

  The client 20 receives the stream information database 15 and displays information on the reproduction bit rates BR1 to BR3 of the stream data ST1 to ST3 on the display 24. The user of the client 20 refers to the display 24 and selects a reproduction bit rate (for example, BR3). Based on the user operation, the client 20 requests the server 10 to distribute the stream data ST3 of the selected reproduction bit rate BR3 from the part P0 (S4). Specifically, the client 20 refers to the stream information database 15 and transmits a distribution request command including the stream data identifier = ST3 corresponding to the bit rate information BR3 and the part identifier = P0 to the server 10.

  The server 10 monitors the distribution request from the client 20 (S5), and when receiving the distribution request command (YES in S5), the server 10 performs stream distribution of the stream data ST3 from the part P0 based on the distribution request command (S6).

  The client 20 monitors whether or not data is received from the server 10 (S7). When the data is received (YES in step S7), the received data is sequentially stored in the buffer area 27 (S8). At this time, the client 20 designates one of the buffer areas 27A and 27B (for example, 27A) as a reception buffer, and accumulates data in the buffer area 27A designated as the reception buffer. Hereinafter, the buffer area 27 designated as the reception buffer is also simply referred to as a reception buffer.

  The client 20 determines whether or not the data amount DL (t) accumulated in the reception buffer exceeds the data amount SZ (3, 0) of the part P0 (S9), and when it exceeds (YES in S9), the part 20 Playback of P0 is started (S10). At this time, the client 20 designates the buffer area 27A having the data amount DL (t) as a reproduction buffer, reads data from the designated reproduction buffer, and starts reproduction of the part P0. In this case, one buffer area 27A functions as a reception buffer and a reproduction buffer. Hereinafter, the buffer area 17 designated as the reproduction buffer is also simply referred to as a reproduction buffer.

  After reproduction, every time the reproduction of each part Pj is completed, the client 20 selects the stream data STi to be requested from the server 10 and requests distribution of the selected stream data STi (S11: data request processing). In response to the request from the client 20, the server 10 distributes the stream data STi (S12). The server 10 ends the operation when the delivery of the last part P7 of the stream data STi is completed (YES in S14).

  The client 20 continues to reproduce the stream data STi received from the server 10 (S13: reproduction process), and ends the operation when all the stream data STi is reproduced.

  The data request process in step S11 and the reproduction process in step S13 are performed every time reproduction of each part Pj is completed. Hereinafter, data request processing and reproduction processing will be described.

2.3. Data request processing The data request processing is executed every time reproduction of each part Pj is completed. In the data request process, first, stream data STi to be requested and a part (distribution start part) Pj for starting distribution are selected (FIG. 6: stream data selection process). Subsequently, a request is made to distribute the selected stream data STi from the distribution start part Pj (FIG. 7: request processing).

2.3.1. Stream Data Selection Processing When the client 20 completes the reproduction of the part Pj, the client 20 determines whether or not all data of the next part Pj has already been accumulated. If so, it is determined whether or not to change the reproduction bit rate BRi based on the amount of received data that can be accumulated in the reception buffer during the reproduction time Dj of the next part Pj, and the requested stream data STi is selected. . Details will be described below.

  Referring to FIG. 6, when reproduction of part Pj (for example, j = 0) is completed (YES in S21) and part Pj is not final part P7 (NO in S22), client 20 determines the current distribution bit. The rate BRcur is specified (S23). Specifically, the current distribution bit rate BRcur (bit / sec) is calculated based on the following equation (1).

BRcur = (DL (tj + 1) −DL (tj)) × 8 / Dj (1)
When j = 0, BRcur = (DL (t1) −DL (t0) / D0. In short, the playback time Dj (sec) of the part Pj that has been played back and the buffer accumulated during the playback time The distribution bit rate BRcur is calculated based on the received data amount DL (tj + 1) −DL (tj) (bytes), and is used when determining whether or not to change the reproduction bit rate. .

  Next, the client 20 increments the part number j (S24, j = 1), and determines whether or not the part Pj (part P1) to be reproduced next is stored in the buffer area 27 ( S25). Specifically, the client 20 determines whether or not the following formula (2) is satisfied.

DL _unused (tj) ≧ SZ (i, j) (2)
Here, DL _unused (tj) indicates the unreproduced data amount of the stream data STi stored in the buffer area 27 at time tj. For example, in the determination in step S25 at time t1, it is determined whether DL _unused (t1) ≧ SZ (i, 1) is satisfied. The client 20 specifies the data amount SZ (i, j) of each part Pj based on the stream information database 15.

  As a result of the determination, if the expression (2) is not satisfied (NO in S25), the client 20 does not accumulate the total data amount of the part Pj scheduled to be reproduced next, and accumulates only a part of the data of the part Pj. is doing. Therefore, the client 20 does not reproduce the partial data of the part Pj stored in the reception buffer, but instead selects the stream data ST1 having the lowest reproduction bit rate BR1 as data to be reproduced, and sets the distribution start part as Pj. (S35). This is because the stream data ST1 has the smallest data amount SZ (1, j) of each part Pj, and therefore, even if it is reproduced while receiving data from the server 10, it is possible to prevent interruption of reproduction as much as possible.

  On the other hand, as a result of the determination in step S25, if the expression (2) is satisfied (YES in S25), the client 20 has already accumulated the data amount SZ (i, j) of the part Pj to be reproduced next in the reception buffer. Yes. Therefore, the data of the next part Pj + 1 can be sequentially stored during the reproduction time Dj of the part Pj. Therefore, the client 20 considers which stream data STi of the stream data ST1 to ST3 is requested for the part Pj + 1 (S20).

  First, the client 20 determines whether or not all the data of the part Pj + 1 of the stream data STi can be accumulated when the reproduction of the part Pj of the stream data STi that has already been accumulated is completed (S26). At this time, the client 20 determines whether or not the following expression (3) is satisfied.

DL _unused (tj) + (BRcur × Dj / 8) ≧ SZ (i, j) + SZ (i, j + 1) (3)
Here, the client 20 specifies the playback time Dj of each part Pj based on the stream information database 15.
When Expression (3) is not satisfied (NO in S26), the client 20 cannot accumulate all data of the next part Pj + 1 when the reproduction of the part Pj is completed. Therefore, the client 20 studies to reduce the reproduction bit rate BRi (S27 to S29). On the other hand, when Expression (3) is satisfied (YES in S26), all data of the next part Pj + 1 can be accumulated when the reproduction of the part Pj is completed. That is, playback can be continued at least at the current playback bit rate BRi. Therefore, in this case, it is examined whether or not the reproduction bit rate BRi can be further increased (S30 to S33). Hereinafter, the case where the reproduction bit rate BRi is lowered (S27 to S29) and the case where it is raised (S30 to S33) will be described with specific examples.

[Study to reduce playback bit rate (S27 to S29)]
In the case where the reproduction is executed while receiving the stream data ST3 and the data request process is executed at the time t3 in FIG. 4, the client 20 determines in step S26 that the expression (3) is not satisfied. (NO in S26). That is, it is determined that the total data amount SZ (3,4) of part P4 cannot be accumulated at the end of reproduction of part P3.
At this time, the client 20 considers reducing the reproduction bit rate BRi. Specifically, the stream data STi that can acquire the data amount SZ (i, 4) of the part P4 during the reproduction time D3 is selected.

  The client 20 decrements to rate number i = i−1 (that is, rate number i = 2) (S27). Since the decremented rate number 2 is not the minimum value = 1 (NO in S28), the client 20 determines whether or not the part Pj + 1 (that is, part 4) of the stream data ST2 satisfies the following expression (4) ( S29).

BRcur × Dj / 8 ≧ SZ (i, j + 1) (4)
When BRcur × D3 / 8 ≧ SZ (2, 4) and Expression (4) is satisfied (YES in S29), the data amount SZ (2, 4) of the part P4 of the stream data ST2 can be acquired within the reproduction time D3. Therefore, the stream data ST2 is selected as the stream data requested to the server 10, and the distribution start part is set to P4 (S34). On the other hand, if the expression (4) is not satisfied (NO in S29), the process returns to step S27, the rate number i is further decremented, the determinations in steps S28 and S29 are executed, and the requested stream data STi is selected (S34). . As a result of decrementing the rate number i, when it is determined in step S28 that the rate number i = 1 (YES in S28), the client 20 selects the stream data ST1 and sets the distribution start part to P4 (S34).

[Study to increase playback bit rate (S30 to S33)]
In the case where the reproduction is performed while receiving the stream data ST2, and when the data request process is executed at time t6 in FIG. 4, the client 20 determines in step S26 that the expression (3) is satisfied (in S26). YES) That is, it is determined that the total data amount SZ (2, 7) of the part P7 of the stream data ST2 can be accumulated at the time t7 when the reproduction of the part P6 is completed.
At this time, the client 20 examines whether or not the stream data STi having the bit rate BRi higher than the current value can be requested.

  The client 20 increments the rate number i = i + 1 (that is, the rate number i = 3) (S30). Subsequently, the client 20 determines whether or not the part Pj + 1 (that is, the part P7) of the stream data ST3 satisfies Expression (4) (S31).

  When BRcur × D6 / 8 ≧ SZ (3, 7) is satisfied and Expression (4) is satisfied (YES in S31), stream data ST3 having a higher bit rate than the present can be acquired. Here, it is determined whether or not the rate number i is the maximum (= 3) (S33). Since the rate number i is the maximum (YES in S33), the client 20 selects the stream data ST3 and distributes it. The start part is set as part P7 (S34).

If the rate number i is not the maximum (NO in S33) as a result of the determination in step S33, the process returns to step S30 to examine whether or not the reproduction bit rate BRi can be further increased, and steps S31 to S33. Execute. When the expression (4) is not satisfied in step S31 (NO in S31), the data amount SZ (i, j + 1) of the part Pj + 1 of the stream data STi cannot be accumulated during the reproduction time Dj, so the rate number i is decremented. Return to the next lower rate number i (S32), select the stream data STi of the returned rate number i, and set part Pj + 1 as the distribution start part (step S34).
Through the above stream selection processing, the stream data STi (reproduction bit rate BRi) that can acquire all the data SZ (i, j + 1) of the part Pj + 1 during the reproduction time Dj of the part Pj to be reproduced next is selected. Therefore, the data to be reproduced is not exhausted in the middle, and the reproduction can be prevented from being interrupted.

2.3.2. Request Process Referring to FIG. 7, after executing the stream data selection process shown in FIG. 6 (S111), the client 20 determines whether or not the selected stream data STi is the same as the currently received stream data STi. Judgment is made (S51). If they are the same (YES in S51), since the client 20 has already received the stream data STi, it continues to receive it as it is. In short, in this case, the distribution request command is not transmitted to the server 10.

  On the other hand, when the selected stream data STi (eg, ST2) is different from the currently received stream data STi (eg, ST3) (NO in S51), the client 20 sends the selected stream data ST2 to the server 10. The distribution is requested from the distribution start part Pj + 1 (S54). Specifically, the client 20 transmits a new distribution request command including the stream data identifier = ST2 and the part identifier = Pj + 1 based on the stream information database 15.

  Before transmitting a new distribution request, the client 20 switches the buffer area (for example, 27A) currently designated as the reception buffer among the buffer areas 27A and 27B (S52). The buffer area 27B is used as a reception buffer. Further, the data stored in the buffer area 27B newly designated as the reception buffer is deleted (S53).

  When receiving a new distribution request command, the server 10 stops the distribution of the stream data ST3 that has been distributed so far, and distributes the selected stream data ST2 from the distribution start part Pj + 1 (S55).

  The client 20 receives the stream data ST2 distributed from the server 10 and accumulates it in the reception buffer (buffer area 27B) designated in step S52.

As described above, when new stream data ST2 different from the stream data ST3 received so far is received, the stream data ST2 is accumulated in a buffer area 27B different from the buffer area 27A in which the stream data ST3 is accumulated. .
If stream data STi having different bit rates BRi are stored in the same buffer area, the reproduction process becomes complicated. Thus, stream data STi having different bit rates BRi is accumulated in different buffer areas 27A and 27B, and the reception process is facilitated by separating the reception buffer from the reproduction buffer. Hereinafter, the reproduction process will be described.

2.4. Reproduction Process The reproduction process is performed every time reproduction of each part Pj is completed. Referring to FIG. 8, client 20 determines whether or not reproduction of part Pj of stream data STi (eg, ST3) being reproduced has been completed (S61). When the reproduction is completed (YES in S61), it is determined whether or not the part Pj that has been reproduced is the final part P7 (S62). If it is part P7 (YES in S62), since all the content has been reproduced, the reproduction is stopped (S68), and the reproduction process is terminated.

  If the part Pj that has been reproduced is not the part P7 (NO in S62), the reproduction is continued. At this time, when the reproduction of the part Pj of the stream data ST3 is completed, the client 20 determines whether or not the reception buffer and the reproduction buffer are the same (S63). That is, it is determined whether one buffer area (27A or 27B) functions as a reproduction buffer and a reception buffer.

  When the reproduction buffer and the reception buffer are not the same (NO in S63), the client 20 acquires data of different stream data STi (eg, ST2) during the reproduction time Dj of the part Pj of the stream data ST3. Therefore, the part Pj to be reproduced next is accumulated in a buffer area (for example, 27B) different from the conventional reproduction buffer (for example, buffer area 27A). Therefore, the reproduction buffer is switched (S65), and a different buffer area 27B is designated as the reproduction buffer. Further, since the part Pj to be reproduced next has a reproduction bit rate BR2 different from the reproduction bit rate BR3 so far, the reproduction bit rate is changed from BR3 to BR2 (S66), and reproduction is started (S67).

  On the other hand, when reproduction of the part Pj is completed, if the reproduction buffer and the reception buffer are the same (YES in S63), the part number j is incremented (S69), and the data amount SZ of the part Pj of the stream data ST3 to be reproduced next It is determined whether (3, j) is accumulated (S64).

  Here, the case where the data amount SZ (3, j) is not accumulated (NO in S64) corresponds to the case where the expression (2) is not satisfied in step S25 in FIG. 6, and the lowest bit rate BR1. This is a case where the part Pj of the stream data ST1 is reproduced simultaneously with reception. In this case, since the reproduction is performed at the same time as reception, the reception buffer and the reproduction buffer need to be in the same buffer area 27. Therefore, the reproduction buffer is switched (S65), and the reception buffer and the reproduction buffer switched in step S52 during the request processing shown in FIG. Subsequently, the reproduction bit rate BRi is set to BR1 (S66), and reproduction is started (S67). Thereby, the stream data ST1 can be reproduced simultaneously with reception.

As a result of the determination in step S64, when the data amount SZ (3, j) of the part Pj (stream data ST3) to be reproduced next is accumulated (YES in S64), the part Pj to be reproduced next is Since the reproduction bit rate BR3 is the same as the reproduced data, reproduction is started at the same reproduction bit rate BR3 as before (S67).
As described above, if it is determined whether or not the reception buffer and the reproduction buffer are the same, and whether or not the part Pj to be reproduced next is stored in the reproduction buffer, the part to be reproduced next The reproduction bit rate BRi of Pj can be determined.

  In the content distribution system described above, the distribution bit rate BRcur is specified based on Expression (1), but the distribution bit rate BRcur may be specified by other methods. For example, the fluctuation of the distribution bit rate during each reproduction time Dj is measured, and based on the measured value, the fluctuation of the distribution bit rate BRcur during reproduction of the part Pj to be reproduced next is predicted to identify the bit rate BRcur. May be.

  Further, in the stream data selection process (FIG. 6), the judgment criterion in step S31 may be strict. For example, in step S31, the following equation (5) may be used instead of equation (4).

BRcur × Dj / 8 ≧ SZ (i, j + 1) + SZ (i, j + 2) (5)
In this case, although the reproduction bit rate BRi is difficult to increase, the frequency of changing the selection of the stream data STi is reduced, so that the frequency of changing the image quality and sound quality of the content can be suppressed.

  While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

It is a functional block diagram which shows the structure of the content delivery system by embodiment of this invention. It is a figure which shows the detail of the structure of the stream data accumulate | stored in the server shown in FIG. It is a figure which shows the detail of the data structure of the stream information database accumulate | stored in the server and client shown in FIG. It is a figure which shows the relationship between the delivery bit rate in the content delivery system shown in FIG. 1, and the data amount accumulate | stored in a client. It is a flowchart which shows operation | movement of the content delivery system shown in FIG. It is a flowchart which shows the detail of a stream data selection process among the operation | movement of step S11 in FIG. FIG. 6 is a flowchart showing the operation of a request process performed after the stream data selection process of FIG. 6 among the operations of step S11 in FIG. It is a flowchart which shows operation | movement of step S13 in FIG.

Explanation of symbols

10 Server 11, 21 Hard disk drive 15 Stream information database 16 Server application 20 Client 23 Memory 25 Client application 27, 27A, 27B Buffer area

Claims (9)

A content distribution system comprising a server and a client connected to the server,
The server
Stream data accumulating means for accumulating a plurality of stream data divided into a plurality of parts, each having a different reproduction bit rate and the same content, with respect to the same content;
A delivery means for streaming the parts of the stream data in order of arrangement in response to the request of the client;
The client
Buffer means for sequentially storing the streamed parts;
Playback means for sequentially playing back the parts stored in the buffer means;
Determining means for determining whether or not an unreproduced part is accumulated in the buffer means when the reproduction of the part is completed;
As a result of the determination, when the unreproduced part is accumulated, a data amount calculating means for calculating the amount of data that can be accumulated in the buffer means with the reproduction time of the unreproduced part;
Based on the calculation result, selection means for selecting stream data to be requested to the server and a delivery start part;
A content distribution system comprising: request means for requesting the stream distribution of the selected stream data from the distribution start part. The content distribution system according to claim 1,
The data amount calculating means includes
A delivery bit rate specifying means for specifying a delivery bit rate of the stream data delivered from the server when the reproduction of the part is completed;
The content distribution system, wherein the data amount is calculated based on the identified distribution bit rate and the reproduction time of the unreproduced part. The content distribution system according to claim 1 or 2,
The client
Stream information storage means for storing stream information related to the data amount and playback time of each part of the stream data, and parts of other stream data corresponding to each part,
The content distribution system, wherein the selection unit selects the stream data and a distribution start part based on the calculation result and the stream information. The content distribution system according to any one of claims 1 to 3,
As a result of the determination, when the unreproduced part is not accumulated in the buffer means, the selection means selects the stream data having the lowest reproduction bit rate from among the plurality of stream data. Content distribution system. Each of which is a client that can be connected to a server that stores a plurality of stream data divided into a plurality of parts arranged in succession with different playback bit rates for the same content,
Buffer means for sequentially storing the parts streamed from the server;
Playback means for sequentially playing back the parts stored in the buffer means;
Determining means for determining whether or not an unreproduced part is accumulated in the buffer means when the reproduction of the part is completed;
As a result of the determination, when the unreproduced part is accumulated, a data amount calculating means for calculating the amount of data that can be accumulated in the buffer means with the reproduction time of the unreproduced part;
Based on the calculation result, selection means for selecting stream data to be requested to the server and a delivery start part;
A client comprising: request means for requesting the selected stream data to be streamed from the delivery start part. 6. The client according to claim 5, wherein
The data amount calculating means includes
A delivery bit rate specifying means for specifying a delivery bit rate of the stream data delivered from the server when the reproduction of the part is completed;
The client, wherein the data amount is calculated based on the identified delivery bit rate and the playback time of the unplayed part. The client according to claim 5 or 6, wherein
Stream information storage means capable of storing stream information relating to the data amount and playback time of each part of the stream data, and other parts of the stream data corresponding to each part;
The client is characterized in that the selection means selects the stream data and the distribution start part based on the calculation result and the stream information. A client according to any one of claims 5 to 7,
As a result of the determination, when the unreproduced part is not accumulated in the buffer means, the selection means selects the stream data having the lowest reproduction bit rate from among the plurality of stream data. Client. A client program that is executed by a client computer that can be connected to a server that accumulates a plurality of stream data divided into a plurality of parts arranged in succession with different playback bit rates for the same content. There,
Sequentially storing the parts streamed from the server;
Sequentially playing back the accumulated parts;
Determining whether or not unplayed parts are accumulated when playback of the part is completed;
As a result of the determination, when the unreproduced part is accumulated, calculating the amount of data that can be accumulated in the reproduction time of the unreproduced part;
Selecting stream data and a delivery start part to be requested from the server based on the calculation result;
A client program that causes a client computer to execute a step of requesting the stream distribution of the selected stream data from the distribution start part.

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