JP2017157958A - Client device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize a bit rate of a required segment in accordance with a situation of a client device or attributes of a content.SOLUTION: A client device is configured to request and acquire over a network a segment while designating a bit rate for each segment to a content having multiple bit rates and divided into multiple segments. The client device comprises: an update section which updates a reference for determining the bit rate of the requested segment from an index of throughput in the client device on the basis of a situation of the client device and at least one of attributes of the content; and a determination section which determines a bit rate in accordance with the reference updated by the update section.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a client apparatus and method.

  2. Description of the Related Art In recent years, a distribution form that dynamically changes a distribution bit rate typified by DASH (dynamic adaptive streaming over hyper transfer protocol) type distribution has been widely adopted in online video distribution services. According to this method, by preparing data of different quality (bit rate) for a certain content in advance and dividing it into segment units, it is possible to request content with the optimum and highest quality according to the network situation. It becomes like this. Specifically, the content bit rate is compared with the latest measured throughput index, and a segment file with a bit rate in a range not exceeding the throughput is requested. For example, Non-Patent Document 1 divides the playback time of a segment by the time actually required to receive the segment, and if the value is equal to or greater than a preset threshold, the requested bit rate is set as one. A technique for raising the level and lowering it in the opposite case is disclosed.

MMSys'11-Proceedings of the 2011 ACM Multimedia Systems Conference, 2011, p. 169-174

  However, in the method described in Non-Patent Document 1, since the logic for comparing the content bit rate and the throughput is fixed, it is not possible to consider the actual environment in which the receiving apparatus is placed. In other words, the logic that is used is the same regardless of whether or not there is actually a sudden change in throughput or a situation in which the change in throughput is stable. An example of the former situation is a situation where the terminal moves and frequent handovers are performed. In handover, the change in the interface of the base station and the stop of data communication during the terminal registration period occur instantaneously, so that the throughput can fluctuate rapidly.

  For this reason, for example, if the required bit rate increases rapidly in a situation where the throughput is likely to fluctuate, there is a high probability that an unexpected buffer underflow will occur. Conversely, even if the throughput is difficult to fluctuate, the requested bit rate does not increase quickly, which can lead to a decrease in quality experienced by the user. Thus, the conventional method as described in Non-Patent Document 1 may be insufficient in performance.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a technique capable of optimizing the bit rate of a requested segment in accordance with the status of the client device and the attribute of the content.

  One embodiment of the present invention relates to a client device. The client device is a client device that requests a content divided into a plurality of segments by specifying a bit rate for each segment and obtains the content via a network. In accordance with the update unit for updating the bit rate of the requested segment from the throughput index in the client based on at least one of the status of the client device and the attribute of the content, and the criterion updated by the update unit A determination unit that determines a bit rate.

  It should be noted that any combination of the above-described constituent elements, or those obtained by replacing the constituent elements and expressions of the present invention with each other between apparatuses, methods, systems, computer programs, recording media storing computer programs, and the like are also included in the present invention. It is effective as an embodiment of

  According to the present invention, the bit rate of the requested segment can be optimized according to the status of the client device and the content attribute.

It is a block diagram which shows the function and structure of a delivery system provided with the client apparatus which concerns on embodiment. It is explanatory drawing of the content hold | maintained at the DASH server of FIG. FIG. 2 is a data structure diagram illustrating an example of a handover information holding unit in FIG. 1. FIG. 2 is a data structure diagram illustrating an example of a throughput holding unit in FIG. 1. It is a time chart which shows a series of processes in the delivery system of FIG. 6 is a flowchart showing a flow of third bit rate determination processing in FIG. 5.

  Hereinafter, the same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated description is appropriately omitted. In addition, in the drawings, some of the members that are not important for explanation are omitted.

  FIG. 1 is a block diagram illustrating functions and configurations of a distribution system 100 including a client device 106 according to the embodiment. Each block shown here can be realized by hardware such as a computer (CPU) (Central Processing Unit) and other elements and mechanical devices, and software can be realized by a computer program or the like. The functional block realized by those cooperation is drawn. Therefore, it is understood by those skilled in the art who have touched this specification that these functional blocks can be realized in various forms by a combination of hardware and software.

  The distribution system 100 includes a DASH server 102 and a client device 106 connected to the DASH server 102 via a network 104 such as the Internet. The DASH server 102 holds contents such as movies, animations, and other moving images, and distributes them in a streaming format in response to a request from the client device 106. The client device 106 may be a mobile phone, a tablet terminal, a smartphone, a desktop PC (Personal Computer), a notebook PC, or the like. In this embodiment, the client device 106 is connected to the network 104 via a base station or a wireless access point. It is assumed that the mobile terminal is connected wirelessly.

  FIG. 2 is an explanatory diagram of content held in the DASH server 102. The DASH server 102 holds one content at a plurality of bit rates (encoding speeds). The multiple bit rates include, but are not limited to, 300 kbps, 1.2 Mbps, and 5 Mbps. In the DASH server 102, one content is divided into N segments (N is a natural number of 2 or more). Each segment corresponds to a predetermined playback length or data amount. In the present embodiment, the segment corresponds to a playback length of 3 seconds, 5 seconds, or 10 seconds. However, it is not limited to these. Each segment has a segment file corresponding to each of a plurality of bit rates.

  FIG. 2 shows content divided into N segments with a playback length of 3 seconds. That is, the total playback length of this content is 3 · N seconds. For each segment, the amount of data in the segment file increases as the bit rate increases. As shown in FIG. 2, the DASH server 102 is prepared with data having different bit rates for each segment, and can specify different bit rates for each segment. For example, a segment file 202 of 300 kbps for segment 1, a segment file 204 of 1.2 Mbps for segment 2, and a segment file 206 of 5 Mbps for segment 3 may be designated and distributed to the client device 106. The bit rate designation is included in the segment request from the client device 106.

  Returning to FIG. 1, the client apparatus 106 acquires content via the network 104. The client device 106 sequentially reproduces the already buffered data while buffering the received data. Here, the accumulation of data does not catch up with the reproduction of data, and there is no “remaining amount” of data, that is, the amount of data downloaded to the client device 106 and stored in the buffer but not yet provided for reproduction. This is called buffer underflow. When the buffer underflow occurs, the user experience may be deteriorated, such as playback being interrupted.

  In order to suppress or eliminate buffer underflow, the client device 106 calculates a content reception speed, that is, an index of throughput (throughput itself and other parameters indicating the throughput) each time a segment is received. If the calculated index satisfies the criterion, the client device 106 changes the bit rate specified for the next requested segment. In the present embodiment, the client device 106 dynamically updates this standard according to the communication environment, buffer status, and content attributes. Accordingly, it is possible to realize a distribution system in which buffer underflow caused by a sudden change in throughput is less likely to occur than when a fixed reference is used. In particular, it is possible to suppress a buffer underflow caused by a variation in throughput with a period similar to the segment reproduction length. Alternatively, when there is not much variation in throughput, it becomes possible to reproduce higher quality content at an earlier stage, and the user experience is improved.

  The client device 106 includes an HTTP access client 108, a media engine 110, a control engine 112, a display 114, a handover detection unit 116, a user operation reception unit 118, a handover information holding unit 120, and an MPD holding unit 122. A throughput holding unit 124.

  The HTTP access client 108 is a client for HTTP access, and functions as an interface with the network 104. The HTTP access client 108 receives data sent to the client device 106 via the network 104 and provides it to other members, acquires data to be transmitted from the other members, and transmits it to the network 104.

  The media engine 110 performs processing such as decryption for reproducing the content received by the client device 106 and causes the display 114 to display the content. Media engine 110 includes a buffer 136 for holding segment files of received content. The segment file transmitted from the DASH server 102 is received by the HTTP access client 108 via the network 104, transmitted from the HTTP access client 108 to the media engine 110, and stored in the buffer 136 in the media engine 110. Further, the media engine 110 reads out the segment file to be reproduced from the buffer 136, processes it, and displays it on the display 114.

  The handover detection unit 116 detects a handover in the wireless connection between the client device 106 and the network 104 and registers the detection result in the handover information holding unit 120. The handover detection unit 116 periodically calls an API (Application Programming Interface), for example, at predetermined intervals ΔT, and acquires the base station ID of the currently connected base station. The handover detection unit 116 registers the acquired base station ID and the time when the base station ID is acquired in the handover information holding unit 120 in association with each other. Further, the handover detection unit 116 refers to the handover information holding unit 120, compares the base station ID registered this time with the base station ID immediately before it, and determines that a handover has occurred if they are different. When it is determined that a handover has occurred, the handover detection unit 116 registers in the handover information holding unit 120 that a handover has occurred.

  The handover detection interval ΔT may or may not correspond to the segment playback length. Further, the handover detection unit 116 may detect a handover every time a segment is received instead of using the interval ΔT.

  FIG. 3 is a data structure diagram illustrating an example of the handover information holding unit 120. The handover information holding unit 120 holds the time when the base station ID is acquired, the base station ID, and information indicating the presence / absence of handover in association with each other. For the entry at time “13:02:26”, the base station ID is “xxx” and the base station ID immediately before (time “13:02:25”) is also “xxx”. It is determined that no handover has occurred, and “N” is registered in the presence / absence of handover of the entry. For the entry at time “13:02:27”, the base station ID is “yyy”, and the base station ID immediately before (time “13:02:26”) is “xxx”, which is different. The unit 116 determines that a handover has occurred, and registers “Y” in the presence / absence of handover of the entry.

  Returning to FIG. 1, the user operation accepting unit 118 is connected to an input device such as a touch panel (not shown), and accepts designation of content to be reproduced from the user. The user operation accepting unit 118 accepts a user operation related to content reproduction, for example, an instruction to start or stop content reproduction.

  The control engine 112 controls reception of content from the DASH server 102. The control engine 112 requests an MPD (Media Presentation Description) file, which is a metafile of the content to be played, from the DASH server 102, obtains it from the DASH server 102, and registers it in the MPD holding unit 122. The MPD file includes information about content, for example, information about the playback length of a segment, a bit rate that can be specified for each segment, information about DRM (Digital Rights Management), and information about an encoding method. The MPD file may conform to, for example, MPEG-DASH (ISO / IEC 2309-1).

  The control engine 112 analyzes the MPD file held in the MPD holding unit 122 and determines a bit rate to be designated for the next requested segment based on the analysis result. A criterion for determining the bit rate of the next requested segment from the throughput index in the client device 106 is referred to as a determination criterion. The control engine 112 updates the decision criteria each time a segment is received. The control engine 112 includes a segment request unit 126, an index calculation unit 128, a variation coefficient calculation unit 130, a threshold update unit 132, and a bit rate determination unit 134.

  The segment request unit 126 specifies the bit rate determined by the bit rate determination unit 134 and requests the DASH server 102 via the network 104 for the next segment. The segment request unit 126 generates a segment request signal including the ID of the next segment to be requested and the bit rate specified for the segment, and transmits the segment request signal to the DASH server 102 via the HTTP access client 108 and the network 104. The DASH server 102 transmits a segment file having a bit rate specified by the received segment request signal to the client device 106. The buffer 136 holds the segment file transmitted from the DASH server 102.

The index calculation unit 128 calculates an index that quantifies the current throughput. The throughput index may be anything as long as the magnitude of the throughput is expressed by a numerical value, and may be, for example, the throughput itself or a value related to the throughput. In the present embodiment, the index calculation unit 128 calculates, as a throughput index, the ratio between the reception time that is the time required to receive the segment acquired immediately before and the playback length of the segment. Since the segment playback length reflects the data amount of the segment file, this index is a good index indicating the size of the throughput. More specifically, each time a segment file is received, the index calculation unit 128 calculates an index from the reception time and playback length of the segment file. When the number of segments is N (N is a natural number greater than or equal to 2) and the (m + 1) -th segment is requested after the m-th segment (m is a natural number smaller than N) is received, the index calculation unit 128 an indication mu _m for the m-th segment mu _{m =} (playback length of the m-th segment) / (reception time of the m-th segment) ... (equation 1)
Calculate according to

The bit rate determination unit 134 determines the bit rate to be designated for the next requested segment in accordance with the determination criteria updated by the threshold update unit 132. Bitrate setter 134 determines a bitrate on the basis of the magnitude relation between the threshold is updated by the index mu _m and the threshold value updating section 132 calculated by the index calculation unit 128.

Specifically, the bit rate determination unit 134 determines that the rate increase criterion is satisfied, that is, μ _m > μu _{m + 1.}
In this case, the bit rate required for the (m + 1) th segment is determined to be higher than the bit rate of the mth segment. μu _{m + 1} is a rate-up threshold for the (m + 1) -th segment, and is calculated by the threshold update unit 132. The bit rate determination unit 134 determines that the rate down criterion is satisfied, that is, μ _m <μd _{m + 1.}
In this case, the bit rate required for the (m + 1) th segment is determined to be lower than the bit rate of the mth segment. μd _{m + 1} is a rate down threshold for the (m + 1) th segment, and is calculated by the threshold update unit 132.

The initial values (μu ₂ , μd ₂ ) of μu _{m + 1} and μd _{m + 1} are determined as follows.
μu ₂ : Maximum value of the ratio between adjacent rates (BR 2 / BR 1, BR 3 / BR 2,...) when the bit rates available for content described in the MPD file are BR 1, BR 2, BR 3,. In an example where the available bit rates are 300 kbps, 1.2 Mbps, and 5 Mbps, 1.2 / 0.3 = 4 and 5 / 1.2 = 4.2, so μu ₂ is 4.2.
μd ₂ : a preset constant, for example, about 0.8.

  Each time the segment file is received, the threshold update unit 132 updates the determination criterion based on at least one of the status of the client device 106 and the content attribute. The threshold update unit 132 updates the determination criterion so that the bit rate is less likely to increase as (1) the variation in throughput is larger or (2) the frequency of handover is higher.

More specifically, the threshold update unit 132 updates the rate up threshold and the rate down threshold in the bit rate determination unit 134 as follows. The threshold update unit 132 sets the rate-up threshold μu _{m + 1} and the rate-down threshold μd _{m + 1} for the (m + 1) -th segment for m greater than ₁ as μu _{m + 1} = (1−α) · μu _m + α · μu. ₂ · k (Formula 2)
μd _{m + 1} = (1−β) · μd _m + β · μd ₂ · k (Formula 3)
Calculate according to μu _m and μd _m are a rate-up threshold value and a rate-down threshold value for the m-th segment, respectively. α and β are weighting coefficients, and in particular, learning rates indicating the reflection ratios of the latest values. k is a coefficient of variation that is updated for each segment based on an index σ _th that represents the degree of variation in throughput and an index σ _ho that represents the degree of handover frequency.

The variation coefficient calculation unit 130 calculates the variation coefficient k each time a segment file is received and supplies the variation coefficient k to the threshold value update unit 132. The coefficient of variation k is a two-dimensional function k = f (σ _th , σ _ho ) (0.5 ≦ k ≦ 2) that monotonically increases with respect to two variables of the index σ _th and the index σ _ho.
It is. The variation coefficient calculation unit 130 calculates the index σ _th and the index σ _ho as follows, and calculates k by substituting them into the above formula. The value range of k is set as an example because the threshold value does not diverge.

  The coefficient of variation calculation unit 130 calculates the throughput from the size of the segment file received immediately before and the time required to finish receiving all the segment files after requesting the segment. The variation coefficient calculation unit 130 registers the calculated throughput and the time when the throughput is calculated in the throughput holding unit 124 in association with each other.

  FIG. 4 is a data structure diagram illustrating an example of the throughput holding unit 124. The throughput holding unit 124 holds the time when the throughput is calculated and the calculated throughput value in association with each other.

として算出される。変動係数算出部１３０は、各セグメントの受信を完了した時点で指標σ_ｔｈを算出する。 Returning to FIG. 1, the variation coefficient calculation unit 130 calculates an index σ _th representing the degree of variation in throughput within a certain time T including the throughput calculated for the segment file received immediately before. When n (n is a natural number greater than 2 and less than N) throughput observed within a certain time T is Th ₁ , Th ₂ ,..., Th _n and the average is Th, σ _th is a standard of n throughputs. deviation

Is calculated as The variation coefficient calculation unit 130 calculates the index σ _th when reception of each segment is completed.

The variation coefficient calculation unit 130 calculates an index σ _ho indicating the degree of occurrence of handover within a certain time T as the cumulative number of occurrences of handover within the certain time T. The coefficient of variation calculation unit 130 refers to the handover information holding unit 120 and calculates how many times a handover has occurred from a time T before the current time to the current time. The variation coefficient calculation unit 130 sets the calculated value (number of times) as an index σ _ho .

The operation of the distribution system 100 configured as above will be described.
FIG. 5 is a time chart showing a series of processes in the distribution system 100. The client device 106 requests the DASH server 102 for the MPD file of the content to be played back (S502). The DASH server 102 transmits the MPD file generated in advance to the client device 106 (S504). The client device 106 performs a first bit rate determination process based on the content of the acquired MPD file (S506). The first bit rate determination process is a process for determining a bit rate to be designated for the first segment when requesting the first segment of the content. In the present embodiment, since the determination criterion of the bit rate designated for the first segment is predetermined (for example, the lowest rate among the available bit rates), the client device 106 uses the determination criterion according to the determination criterion. Determine the bitrate you want to specify for the segment. The determination criterion in the first bit rate determination process does not depend on the throughput index or the degree of variation of the throughput.

  The client device 106 requests the first segment (segment 1) from the DASH server 102 by designating the bit rate determined in step S506 (S508). In response to the request in step S508, the DASH server 102 transmits the segment 1 segment file corresponding to the designated bit rate to the client device 106 (S510).

The client device 106, the second bit rate determining process performed based on the index mu ₁ throughput for segment 1 (S512). The second bit rate determination process is a process for determining a bit rate to be specified for the second segment based on the index μ ₁ of the first segment when requesting the second segment of the content. The client device 106 calculates the throughput of the segment 1 from the size of the segment file received for the segment 1 and the time required to finish receiving all the segment files after requesting the segment 1, and holds the throughput. Registered in the unit 124. Further, the client device 106 calculates the index μ _{1 according} to the above equation 1, determines whether the rate up criterion is satisfied, that is, whether μ ₁ > μu ₂ is satisfied, and whether the rate down criterion is satisfied, that is, It is determined whether μ ₁ <μd ₂ is satisfied. If the rate increase criterion is satisfied, the client device 106 determines a bit rate higher than the bit rate specified for the first segment as the bit rate specified for the second segment. If the rate down criterion is satisfied, the client device 106 determines a bit rate that is lower than the bit rate specified for the first segment as the bit rate specified for the second segment. The determination criterion in the second bit rate determination process depends on the throughput index, but does not depend on the degree of variation in throughput.

  The client device 106 requests the second segment (segment 2) from the DASH server 102 by designating the bit rate determined in step S512 (S514). In response to the request in step S514, the DASH server 102 transmits the segment 2 segment file corresponding to the designated bit rate to the client device 106 (S516).

The client device 106, the third bit rate determining process performed on the basis of the index sigma _ho representing the degree of index mu ₂ and indicators sigma _th handover representing the degree of variation in the throughput frequency of the throughput for segment 2 (S518 ). The third bit rate determination process, when requesting third and subsequent segments of the content, specifies previous segment (m-th segment, m ≧ 2) based on indices mu _m for the (m + 1) th segment This is a process for determining the bit rate.

FIG. 6 is a flowchart showing the flow of the third bit rate determination process. The client device 106 calculates the throughput of the segment m from the size of the segment file of the received segment m and the time required to finish receiving all the segment files after requesting the segment m, and holds the throughput. Registered in the unit 124. Further, client device 106 calculates an index mu _m throughput according to Equation 1 above (S602). The client apparatus 106 calculates an index σ _th of fluctuation in throughput (S604). The client device 106 calculates an index σ _ho of the handover frequency (S606). The client device 106 calculates the coefficient of variation k from the index σ _th calculated in step S604 and the index σ _ho calculated in step S606, and the rate-up threshold value μu _{m + 1} according to the above formulas 2 and 3, The rate down threshold value μd _{m + 1} is updated (S608). The client device 106, or the updated rate up criteria are met, i.e. to determine μ _m> μu _{m + 1} is satisfied, whether the updated rate down criteria are met, namely μ _{m <μd m + 1} is satisfied Is determined (S610). When the rate increase criterion is satisfied, the client device 106 determines a bit rate higher than the bit rate specified for the mth segment as the bit rate specified for the (m + 1) th segment (S612). When the rate down criterion is satisfied, the client device 106 determines a bit rate lower than the bit rate specified for the mth segment as the bit rate specified for the (m + 1) th segment (S612). The decision criterion in the third bit rate decision process depends on the throughput index and the degree of fluctuation of the throughput.

  Returning to FIG. 5, the client device 106 requests the third segment (segment 3) from the DASH server 102 by designating the bit rate determined in step S518 (S520). In response to the request in step S520, the DASH server 102 transmits the segment 3 segment file corresponding to the designated bit rate to the client device 106 (S522). Thereafter, the client device 106 performs a third bit rate determination process for the fourth segment requested next (S524). Thereafter, the segment distribution and the third bit rate determination process are repeated until all the segments are distributed.

  In the embodiment described above, examples of the holding unit are a hard disk and a semiconductor memory. Further, based on the description of the present specification, each unit is configured by a CPU (not shown), a module of an installed application program, a module of a system program, a semiconductor memory that temporarily stores the content of data read from the hard disk, or the like. It will be appreciated by those skilled in the art who have touched this specification that this can be achieved.

  According to the client device 106 according to the present embodiment, in a situation where the throughput is likely to fluctuate, the threshold value is updated so that the bit rate is unlikely to increase, so that occurrence of unexpected buffer underflow can be suppressed or eliminated. Conversely, the threshold is updated so that the bit rate is likely to increase in situations where the throughput is not likely to fluctuate, so that high-quality content can be quickly provided to the user, and the quality experienced by the user can be improved. Can be increased.

  The configuration and operation of the client device 106 according to the embodiment has been described above. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to each component and combination of processes, and such modifications are within the scope of the present invention.

  In the embodiment, the case where the bit rate is determined on the client side has been described. However, the present invention is not limited to this, and the server side receives the report of the throughput from the client and determines the bit rate. Thoughts may be applied.

  In the embodiment, the case has been described in which the index calculation unit 128 calculates the ratio between the reception time, which is the time required to receive the segment acquired immediately before, and the playback length of the segment as a throughput index. Not limited to. For example, the index calculation unit may calculate, as an index, the ratio between the sum of the reception times of the two previous segments and the immediately preceding segment and the total of their playback lengths. In this way, an index calculated for a segment acquired in the past may be used.

  In the embodiment, the case has been described in which the threshold update unit 132 updates the determination criterion so that the bit rate is less likely to increase as (1) the variation in throughput increases or (2) the frequency of handover increases. However, it is not limited to this. For example, the threshold update unit updates the determination criterion so that the bit rate is less likely to increase as (3) the remaining amount of the buffer 136 is smaller, or (4) the larger the amount of segment data requested after the next. May be. The data amount of the segment requested after the next is represented by, for example, the playback length of the segment or the size information of the segment distributed in the future.

For example, the longer the playback length of a segment, the weaker it is to sudden fluctuations in throughput.
It is good.

  Alternatively, the threshold update unit may update the determination criterion based on the user operation statistical information received by the user operation reception unit 118. The statistical information is, for example, the number of reproduction stops within a certain period and the reproduction stop time within a certain period. Alternatively, the threshold update unit 132 may update the determination criterion based on encoded content information (for example, CBR, VBR, ABR) and DRM information. Regarding the statistical information of the user operation, the bit rate to be requested may vary depending on the user operation. For example, if the user performs a large amount of seek, the initial delay until each reproduction becomes longer, so it is more convenient to lower the bit rate. Such a situation can be dealt with when the decision criterion is updated based on the statistical information of the user operation.

  Alternatively, since playback stoppage occurs due to buffer underflow, the threshold update unit updates the determination criteria so that the bit rate is less likely to increase as the number of such stoppages increases or the period increases. Also good.

In the embodiment, the case where the standard deviation of the throughput is adopted as the index σ _th representing the degree of fluctuation of the throughput has been described, but the present invention is not limited to this, and any index may be used as long as it represents the degree of fluctuation of the throughput. . For example, the standard deviation of the index mu _m may be employed, it may be the standard deviation of the reception time of the past segment is employed.

  In the embodiment, the case where the threshold update unit 132 updates the threshold used when requesting the next segment every time a segment file is received has been described. However, the present invention is not limited to this. For example, when focusing on handover, it may fluctuate with a finer granularity than the general playback length. Therefore, the threshold update unit may update the threshold with a time granularity finer than the reproduction length. For example, the threshold update unit may update the threshold multiple times during reception of the segment file. Alternatively, the threshold update unit may update the threshold at intervals of 1 second or 2 seconds for a segment having a playback length of 5 seconds. Alternatively, the threshold update unit 132 may update the threshold every time a handover is detected.

  100 distribution system, 102 DASH server, 104 network, 106 client device.

Claims (13)

A client device that has a plurality of bit rates and requests a content divided into a plurality of segments by specifying a bit rate for each segment, and obtains the content via a network.
An update unit that updates a criterion for determining a bit rate of a requested segment from an index of throughput in the client device based on at least one of the status of the client device and an attribute of content;
And a determining unit that determines a bit rate according to the reference updated by the updating unit.   The client device according to claim 1, wherein the updating unit updates the reference so that the bit rate is less likely to increase as the variation in throughput increases.   The client device according to claim 1, wherein the updating unit updates the reference so that the bit rate is less likely to increase as the frequency of handovers increases.   The client device according to claim 1, wherein the updating unit updates the reference every time a segment is acquired.   5. The client device according to claim 1, further comprising a requesting unit that requests the next segment via the network by designating the bit rate determined by the determining unit. A buffer for holding the obtained segment file;
The client device according to claim 1, wherein the updating unit updates the reference so that the bit rate is less likely to increase as the remaining amount of the buffer is smaller. A buffer for holding the obtained segment file;
The client device according to claim 1, wherein the updating unit updates the reference based on the number or period of reproduction stop caused by the remaining amount of the buffer. A reception unit that receives a user operation related to reproduction of the acquired content;
The client device according to claim 1, wherein the update unit updates a reference based on statistical information of a user operation received by the reception unit.   The client device according to claim 1, wherein the updating unit updates the reference so that the bit rate is less likely to increase as the requested data amount of the segment increases. A calculation unit that calculates a ratio of a time required for receiving a segment acquired in the past and a reproduction length or a data amount of the segment as a throughput index;
The determination unit determines a bit rate based on a magnitude relationship between the index calculated by the calculation unit and a threshold value,
The client device according to claim 1, wherein the update unit updates a threshold value in the determination unit. When the number of segments is N (N is a natural number greater than or equal to 3) and the (m + 1) th segment is requested after the mth segment (m is a natural number greater than 1 and less than N) is received,
The calculation unit (playback length of the m-th segment) Indicators mu _m to mu _{m =} / (time required for reception of m-th segment)
Calculate according to
The update unit sets the first threshold value μu _{m + 1} and the second threshold value μd _{m + 1} to μu _{m + 1} = (1−α) · μu _m + α · μu ₂ · k.
μd _{m + 1} = (1−β) · μd _m + β · μd ₂ · k
Where α and β are weighting factors, and k is a value that is updated for each segment based on at least one of the client device status and content attributes,
The determination unit
μ _m > μu _{m + 1}
, The requested bit rate for the (m + 1) th segment is determined to be higher than the bit rate of the mth segment,
μ _m <μd _{m + 1}
11. The client device according to claim 1, wherein the bit rate requested for the (m + 1) -th segment is determined to be lower than the bit rate of the m-th segment. A method having a plurality of bit rates for content divided into a plurality of segments, specifying a bit rate for each segment, making a request, and acquiring the content via a network,
Updating a criterion for determining a required bit rate of a segment from an index of throughput in the receiving device based on at least one of the status of the receiving device and an attribute of the content;
Determining a bit rate according to the updated criteria. A function for specifying and requesting a bit rate for each segment for content having a plurality of bit rates and being divided into a plurality of segments, and acquiring it via a network;
A function for updating a criterion for determining a required bit rate of a segment from an index of throughput in the receiving device based on at least one of the status of the receiving device and an attribute of the content;
A computer program for causing a computer to realize a function of determining a bit rate according to the updated standard.

Images