Distribution device, distribution method, and distribution program

Abstract

To provide a distribution system which can suppress reduction in quality of experience due to degradation of quality in an important scene, during streaming a video.SOLUTION: A distribution server 10 includes: a segment storage unit 121 which stores multiple streams with different qualities, and dummy streams with meta information higher in quality than the highest quality and storing entities lower in quality than the quality indicated by the meta information, by segment; an importance storage unit 122 which stores importance of each segment; a request receiving unit 111 which receives a request to distribute a segment from a receiving terminal 20; a receiving terminal allowance determination unit 112 which determines that the terminal has a margin in quality for reception when a dummy stream is requested; a segment selection unit 113 which selects, when a determination is made that the terminal has a margin, an undistributed segment in preference to segments of high importance; and a segment distribution unit 114 which distributes the selected segment together with the segment for which the distribution request has been received.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an apparatus, a method, and a program for streaming video. [Background technology]

[0002] The current mainstream method of streaming video distribution on the Internet is to use general-purpose web servers to deliver streaming content using the HTTP protocol. HTTP protocol streaming delivery methods, especially adaptive streaming methods, include proprietary technologies from IT vendors and the international standard MPEG-DASH (ISO / IEC23009-1).

[0003] The basic concept of both technologies is the same: a web server prepares a stream of video content encoded at one or more qualities (image size, bit rate, etc.) divided into files of several to several tens of seconds each as segments, and a manifest file describing the video content's attributes and URLs. The receiving terminal selects a quality from the manifest file, taking into account the screen size of its own terminal and the state of the network bandwidth of the transmission path, and receives the segments one after another, splicing them into a single video content for playback (see, for example, Non-Patent Document 1).

[0004] There are no standards for quality selection methods, and methods that control quality based on network conditions or the remaining buffer capacity of the receiving terminal are widely used (see, for example, Non-Patent Document 2). Another proposed method involves determining the current transmission rate each time the receiving terminal receives a segment, obtaining statistical information related to the expected future transmission rate as a function of the current transmission rate, deriving a target transmission rate from the statistical information, and receiving subsequent segments according to the target transmission rate (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2016-506644 [Patent Document 2] Special Publication No. 2015-501090 [Non-patent literature]

[0006] [Non-Patent Document 1] "Next-generation video distribution technology 'MPEG-DASH': Technical overview and trends in standardization and related technologies," Journal of the Institute of Image Information and Television Engineers, Vol. 67, No. 2, pp. 109-115 (2013) [Non-patent document 2] “Neural Adaptive Video Streaming with Pensieve”, SIGCOMM, pp. 197-210 (Aug. 2017) Summary of the Invention [Problem to be solved by the invention]

[0007] However, adaptive streaming can lead to a degradation in the quality of experience, such as a drop in quality during important scenes in video content, depending on the network conditions. In response to this, a method has been proposed in which priority information is assigned to multiple quality segments containing the same scene, and quality is determined based on this priority (see, for example, Patent Document 2), but this method is not based on the priority between different segments (importance of the scene). Also, even in this case, depending on the network conditions at the time of distribution, it is often not possible to distribute the segment of the determined quality.

[0008] The present invention aims to provide a distribution device, a distribution method, and a distribution program that can suppress degradation of the quality of experience caused by quality degradation in important scenes during streaming playback of moving images. [Means for solving the problem]

[0009] The distribution device of the present invention comprises a segment storage unit that stores, for each video content, a plurality of streams of different quality from each other, and a dummy stream that is assigned meta information of higher quality than the stream with the highest quality among the plurality of streams and contains an entity of lower quality than the quality indicated by the meta information, each on a segment basis; an importance storage unit that stores, for each of the video content, the importance of each segment; a request receiving unit that receives from a receiving terminal a request for distribution of a segment of a quality that the receiving terminal can receive; a receiving terminal margin determination unit that determines, when distribution of a segment of the dummy stream is requested, that there is a margin of quality that the receiving terminal can receive; a segment selection unit that, when it is determined that there is a margin of quality that the receiving terminal can receive, selects one of the undistributed segments, giving priority to segments with a higher importance; and a segment distribution unit that distributes the segment selected by the segment selection unit along with the segment for which the distribution request was received.

[0010] The segment selection unit may select a segment that constitutes a stream of the highest quality from among the plurality of streams.

[0011] The segment selection unit may select, from the plurality of streams, segments that constitute a stream having a quality according to the importance.

[0012] The quality indicated by the meta information may be a bit rate for each segment.

[0013] In the dummy stream, the actual bit rate may be the highest among the plurality of streams, and the bit rate indicated by the meta information may be an integer multiple of the actual bit rate.

[0014] The importance of the segment located at the beginning of each of the plurality of chapters constituting the video content may be set to be higher than a predetermined level.

[0015] The distribution method of the present invention stores, for each video content, multiple streams of different quality, and a dummy stream that is assigned meta information of higher quality than the highest quality stream among the multiple streams and contains an entity of lower quality than the quality indicated by the meta information, each on a segment basis, and the distribution device stores the importance of each segment for each video content.The distribution method executes the following steps: a request receiving step for receiving from a receiving terminal a distribution request for a segment of a quality that the receiving terminal can receive; a receiving terminal margin determination step for determining, when distribution of a segment of the dummy stream is requested, that there is a margin for the quality that the receiving terminal can receive; a segment selection step for selecting one of the undelivered segments, giving priority to segments with a higher importance, when it is determined that there is a margin for the quality that the receiving terminal can receive; and a segment distribution step for distributing the segment selected by the segment selection unit along with the segment for which the distribution request was received.

[0016] A distribution program according to the present invention causes a computer to function as the distribution device. [Effects of the Invention]

[0017] According to the present invention, degradation of the quality of experience due to quality degradation in important scenes is suppressed during streaming playback of moving images. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing a system configuration for realizing adaptive streaming, which is a premise of an embodiment. [Figure 2] FIG. 2 is a diagram illustrating a functional configuration of a distribution server that constitutes the content distribution system according to the embodiment. [Figure 3] 1 is a diagram illustrating a comparison of multiple streams of video content according to an embodiment; [Figure 4] FIG. 2 is a diagram illustrating an example of a manifest file of video content in the embodiment. [Figure 5]FIG. 2 is a diagram illustrating an example of a basic configuration of a segment according to an embodiment. [Figure 6] FIG. 10 is a diagram illustrating an example of importance information according to an embodiment. [Figure 7] 10 is a flowchart illustrating an example of a process for realizing a distribution method according to an embodiment. [Figure 8] FIG. 2 is a diagram illustrating an example of a buffer provided in a receiving terminal according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] An example of an embodiment of the present invention will be described below. FIG. 1 is a diagram showing a system configuration for realizing adaptive streaming, which is a premise of this embodiment.

[0020] The video data is encoded separately at multiple qualities by an encoder, and time-divided segments of several seconds are generated for each quality. In the example shown, segments 1 to 4 of a low-quality video stream, segments 1' to 4' of a medium-quality video stream, and segments 1" to 4" of a high-quality video stream are generated. The manifest file also registers attribute information such as the URL of each segment, the bit rate for each quality level, and the image size. The generated segments and manifest file are served to a web server.

[0021] The receiving terminal receives the manifest file from the web server and determines the bit rate and segment configuration from the manifest file (1). Next, the receiving terminal selects the quality for each segment based on the screen size of the terminal and the network reception bandwidth status, and receives the segments via the HTTP protocol (2). Next, the receiving terminal connects the received segments in order according to the manifest file, and plays them in the order 1", 2', 3, 4", for example (3). In this way, the receiving terminal can receive and continue playing a series of video content by repeating the processes (2) and (3).

[0022] In contrast, the content distribution system of this embodiment prepares content consisting of streams of multiple qualities, each of which is made up of multiple segments associated with information indicating the importance of a scene. When a receiving terminal requests a segment from a distribution device, if the distribution device determines that the receiving terminal has sufficient network bandwidth and buffer space, it distributes undelivered segments of high importance along with the segments requested by the receiving terminal. This allows segments of scenes with high importance to be distributed preferentially without reducing the viewing stability of the current and subsequent scenes with high importance. In this embodiment, a case will be described in which the bit rate is mainly used as an example of the quality of video content.

[0023] FIG. 2 is a diagram showing the functional configuration of the distribution server 10 that constitutes the content distribution system 1 in this embodiment. The distribution server 10 (distribution device) is a server that is connected to the receiving terminal 20 via the Internet and distributes segments specified by the receiving terminal 20, and may be a general web server.

[0024] The distribution server 10 is an information processing device (computer) that includes a control unit 11, a storage unit 12, various input / output devices, a communication interface (I / F) 13, and the like.

[0025] The control unit 11 is a part that controls the entire distribution server 10, and realizes each function in this embodiment by appropriately reading and executing various programs stored in the storage unit 12. The control unit 11 may be a CPU. Specifically, the control unit 11 includes a request receiving unit 111, a receiving terminal availability determining unit 112, a segment selecting unit 113, and a segment delivering unit 114. Details of each of these functional units will be described later.

[0026] The memory unit 12 is a storage area for various programs and various data that cause the hardware group to function as the distribution server 10, and may be a ROM, RAM, flash memory, hard disk drive (HDD), etc., and may be composed of multiple devices. Specifically, the memory unit 12 includes an area for storing a program (distribution program) for causing the control unit 11 to execute each function of this embodiment, as well as a segment memory unit 121, an importance memory unit 122, and a distributed list memory unit 123.

[0027] The segment storage unit 121 stores segments that make up the video content to be distributed, and a manifest file. The importance storage unit 122 stores importance information for each segment of each video content. The distributed list storage unit 123 stores a list of segments that have been distributed to the receiving terminal 20 .

[0028] Here, the video content distributed from the distribution server 10 is a stream of multiple bit rates consisting of multiple segments. Of these, the maximum bit rate stream is a dummy stream in which meta information indicating the bit rate is written at a larger value than the actual bit rate.

[0029] FIG. 3 is a diagram illustrating a comparison between multiple streams of video content in this embodiment. In this example, there are four types of meta-information describing bit rates: 1Mbps, 2Mbps, 5Mbps, and 10Mbps. Of these, the 10Mbps stream has a 10Mbps description in the meta-information describing the bit rate, but the actual video data is a dummy stream identical to the 5Mbps stream.

[0030] In the dummy stream, the actual bit rate may be, for example, the highest of the multiple streams provided, and the bit rate indicated by the meta information may be an integer multiple (for example, twice) of the actual bit rate. However, the setting of meta information in the dummy stream is not limited to this.

[0031] FIG. 4 is a diagram showing an example of a manifest file of video content in this embodiment. Here, an excerpt is shown using the MPD (Media Presentation Description) defined in MPEG-DASH as an example.

[0032] "Representation" shows the information of each stream. "Bandwidth" is meta information showing the bit rate, and "media" shows a template for deriving the segment file name. The segment file name is determined by replacing "$Number$" in this template with the segment number.

[0033] The bottom stream (id="dummy") is a dummy stream, and although its "bandwidth" is 10Mbps (10000000), its "media" is the same value (file name) as 5Mbps, indicating that the entity is the same.

[0034] It is possible to determine which streams are dummy streams, for example, by setting the "id" of "Representation" to a special value (for example, "dummy"). Also, special meta information that can only be interpreted by the distribution server 10 and is ignored by receiving terminals may be defined and added separately.

[0035] A receiving terminal 20 that receives such an MPD cannot determine that the content includes a dummy stream, and therefore, if there is sufficient network bandwidth, will request a dummy stream whose meta information indicates a high bit rate. In this case, even if the distribution server 10 distributes the requested dummy stream as is, the receiving terminal 20 can receive and play it normally.

[0036] FIG. 5 is a diagram showing an example of the basic configuration of a segment in this embodiment. Here, the basic structure of a segment in ISO-BMFF (ISO Base Media File Format) format, which is commonly used in MPEG-DASH, is shown as an example.

[0037] A segment consists of an mdat, which contains the actual media data such as video and audio, and a moof, which contains metadata such as the playback start time and playback duration of the subsequent mdat. A moof and an mdat are a pair, and one segment may contain multiple moof and mdat combinations.

[0038] The storage unit 12 also stores information indicating the importance of scenes in each segment for each piece of content. FIG. 6 is a diagram showing an example of importance information in this embodiment.

[0039] The importance of a scene may be a value predetermined by the content creator, for example. Alternatively, it may be a value automatically determined according to a predetermined rule, such as automatically being assigned according to the volume of cheers in a sports program. The importance may have multiple levels, but in the example shown in the figure, there are only two levels, 0 and 1. In this embodiment, the importance information does not necessarily have to be included in a manifest file such as an MPD, because it does not need to be notified to the receiving terminal 20. Therefore, the importance information is associated with the content and notified separately to the distribution server 10, or is automatically determined by the distribution server 10 and stored in the storage unit 12.

[0040] In this way, the distribution server 10 stores multiple streams of video content in segments in the storage unit 12, and manages the importance information for each segment by listing it for each piece of content, for example. The storage unit 12 also stores a list of segment numbers (identifiers) for each receiving terminal 20 that have been distributed to the receiving terminal 20. Based on the information stored in the storage unit 12, the control unit 11 of the distribution server 10 operates as the following functional units.

[0041] The request receiving unit 111 receives from the receiving terminal 20 a request for delivery of a segment of receivable quality, that is, the highest bit rate that is determined to be capable of continuous playback, according to the network status and buffer status of the receiving terminal 20.

[0042] When a request is made to deliver a segment of a dummy stream, the receiving terminal margin determination unit 112 determines that the receiving terminal 20 has margin for the quality it can receive, i.e., that it has margin for receiving a stream of higher quality (higher bit rate) than the highest quality stream.

[0043] If it is determined that there is a margin in the quality that can be received by the receiving terminal 20, the segment selection unit 113 selects one of the undelivered segments, giving priority to segments with a high assigned importance. At this time, the segment selection unit 113 may select the segments that make up the stream with the highest quality from among the multiple streams.

[0044] Alternatively, the segment selection unit 113 may select segments that constitute a stream of quality according to the importance from among a plurality of streams. For example, the higher the importance, the higher the quality of the stream that is selected.

[0045] Furthermore, for example, by setting the importance of the segments located at the beginning of each of the multiple chapters that make up the video content to be higher than a predetermined value or to a specific value, the segment selection unit 113 can deliver in advance segments that may be played back in response to a chapter skip operation. The quality of the segment selected at this time does not necessarily have to be the highest; for example, multiple segments of a certain quality or higher may be delivered at the same time.

[0046] The segment distribution unit 114 distributes to the receiving terminal 20 the segment selected by the segment selection unit 113 together with the segment for which the distribution request has been received.

[0047] FIG. 7 is a flowchart showing an example of processing for implementing the distribution method according to this embodiment. In this example, in order to maintain the quality of important scenes in video content, the distribution server 10 distributes the highest quality segment corresponding to the scene in advance when the receiving terminal 20 has the capacity.

[0048] In step S1, the request receiving unit 111 receives a request for a segment from the receiving terminal 20.

[0049] In step S2, the receiving terminal margin determination unit 112 determines whether there is margin in the network bandwidth, buffer capacity, etc. of the receiving terminal 20 and whether more data can be distributed, depending on whether the requested segment is a dummy stream. In the example of the MPD in Fig. 4, the receiving terminal margin determination unit 112 determines that there is margin when a stream with "Representation id="dummy"" is requested. If the determination is YES, the process proceeds to step S3, and if the determination is NO, the process proceeds to step S5.

[0050] In step S3, the segment selection unit 113 determines whether there is a segment that has a segment number greater than that of the requested segment, has a predetermined level of importance, and is not stored in the delivered segment list. If the determination is YES, the process proceeds to step S4, and if the determination is NO, the process proceeds to step S5.

[0051] In step S4, the segment selection unit 113 selects the segment with the highest quality (highest bit rate) that has an undelivered segment number and is of high importance. The segment to be selected may be the one with the highest importance among undelivered segments, or may be selected according to a predetermined condition, such as the most recent segment with a predetermined importance or higher, or the most important segment among undelivered segments within a predetermined period.

[0052] In step S5, the segment distribution unit 114 distributes to the receiving terminal 20 the segment selected in step S4 together with the segment requested by the receiving terminal 20.

[0053] In step S6, the segment distribution unit 114 distributes only the requested segments to the receiving terminal 20 because the receiving terminal 20 does not have room to receive additional segments.

[0054] In step S7, the segment distribution unit 114 stores the segment numbers distributed to the receiving terminal 20 in the distributed list storage unit 123.

[0055] In step S8, the control unit 11 determines whether to end the distribution based on notification such as the current playback time on the receiving terminal 20 reaching the end time of the content or the stop button being pressed. If the determination is YES, the process ends, and if the determination is NO, the process returns to step S1.

[0056] Next, the functions of the receiving terminal 20 will be described. The receiving terminal 20 of this embodiment is a video playback device that performs streaming playback in the order of segment numbers using a buffer that manages received segments in association with information on playback start times and playback durations.

[0057] Many viewing players (receiving devices) that run on HTML5 use the MSE (Media Source Extensions) standard defined by the standards organization W3C (World Wide Web Consortium). Using MSE, HTML5 video elements (video tags) can reference a buffer as a source. Received segments can be inserted into the buffer using Javascript (registered trademark), making it possible to view a variety of adaptive streaming formats using HTML5 video elements and Javascript.

[0058] Here, the buffer model of MSE will be explained. The buffer (SourceBuffer) manages the received segments in association with information on the playback start time and playback duration (length). FIG. 8 is a diagram showing an example of a buffer provided in the receiving terminal 20 in this embodiment.

[0059] In this example, segments with a playback start time of 0 and a playback duration of 5 seconds, a playback start time of 5 and a playback duration of 5 seconds, and a playback start time of 15 and a playback duration of 5 seconds (shaded areas) are inserted. In this case, the buffered attribute, which is management information for the buffering range of SourceBuffer, is 0 to 10 seconds and 15 to 20 seconds.

[0060] There is no set order in which the receiving terminal 20 acquires segments, but in general, segments are acquired in order starting from the segment closest to the current playback time and not stored in the SourceBuffer. In addition, various methods can be appropriately adopted for selecting the bit rate of the segment to be received from multiple qualities (bit rates), such as a method based on the network bandwidth measured by the receiving terminal 20, or a method based on the buffer capacity of the receiving terminal 20.

[0061] According to this embodiment, the distribution server 10 prepares a dummy stream in which quality values ​​such as bit rate described in the meta information are set to higher quality than the actual quality, and when the receiving terminal 20 requests distribution of the dummy stream, the distribution server 10 determines that the receiving terminal 20 has capacity. This allows the distribution server 10 to distribute the subsequent segments of high importance in advance along with the requested dummy stream when there is spare capacity in the receiving terminal 20. Therefore, the distribution server 10 can suppress degradation of the quality of experience due to quality degradation in important scenes during streaming playback of moving images. As a result, users can view important scenes in high quality, and the peak-end effect is expected to improve the quality of their experience.

[0062] When the receiving terminal 20 has capacity, the distribution server 10 selects a segment that constitutes the highest quality stream from among multiple streams, thereby minimizing quality degradation in streaming playback and improving the user's quality of experience.

[0063] Furthermore, the distribution server 10 can select segments from a plurality of streams that constitute a stream with a quality that corresponds to the importance. This allows the distribution server 10 to appropriately determine the quality of the segment to be distributed in accordance with the preset importance.

[0064] For example, the distribution server 10 can set the importance of the segments located at the beginning of each of the multiple chapters that make up the video content to a level higher than a predetermined level, thereby prioritizing the distribution of the start positions of the chapters, thereby speeding up chapter-by-chapter skip operations.

[0065] By using the quality indicated by the meta information as the bit rate for each segment, the distribution server 10 can quantitatively grasp the margin of the receiving terminal 20 and simultaneously select appropriate segments that can be distributed.

[0066] Specifically, the distribution server 10 may set the actual bit rate of the dummy stream to the highest among the multiple streams, and the bit rate indicated by the meta information to an integer multiple of the actual bit rate. For example, if the meta information of a dummy stream is set to twice the maximum bit rate, it can be assumed that when this dummy stream is requested, the receiving terminal 20 will have room to receive two segments at the maximum bit rate. Therefore, by delivering the requested segment as well as any highly important segments that have not yet been delivered at the maximum bit rate, the distribution server 10 can prioritize the delivery of segments containing highly important scenes without reducing viewing stability.

[0067] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. Furthermore, the effects described in the above-described embodiments are merely a list of the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments.

[0068] In the above embodiment, an example was given in which an integral multiple of the actual bit rate is set in the meta information of the dummy stream, but the setting of the meta information is not limited to this. For example, a video with a bit rate of 10 Mbps, which is higher than the maximum bit rate (for example, 5 Mbps), may be prepared, and the meta information of the dummy stream may be set to 15 Mbps.

[0069] In addition, the distribution server 10 can simultaneously distribute multiple videos at a medium bit rate (e.g., 2 Mbps) using the free space in the dummy stream, i.e., the difference between the set value of the meta information and the actual value (e.g., 10 Mbps - 5 Mbps). This allows, for example, the response time when skipping a chapter to be improved by distributing a large number of segments at the beginning of the chapter in advance. When a segment with a bit rate lower than the maximum bit rate is delivered in this way, the receiving terminal 20 may request a new segment with a higher quality than the segment that has already been received, if there is room in the buffer capacity that has already been received.

[0070] In this embodiment, the configuration and operation of the distribution server 10 have been mainly described, but the present invention is not limited to this and may be configured as a method or program for distributing video content, including each component.

[0071] Furthermore, the functions of distribution server 10 may be realized by recording a program for realizing the functions of distribution server 10 on a computer-readable recording medium, and reading and executing the program recorded on this recording medium into a computer system.

[0072] The term "computer system" here includes hardware such as the OS and peripheral devices. Additionally, "computer-readable recording media" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems.

[0073] Furthermore, the term "computer-readable recording medium" may include a medium that dynamically stores a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, or a medium that stores a program for a fixed period of time, such as a volatile memory within a computer system that serves as a server or client in such a case. Furthermore, the program may be one that realizes part of the above-mentioned functions, or may be one that can realize the above-mentioned functions in combination with a program already recorded in the computer system. [Explanation of symbols]

[0074] 1 Content distribution system 10 Distribution server (distribution device) 11 Control section 12 Storage section 20 Receiving terminal 111 Request Receiving Unit 112 Receiving terminal margin determination unit 113 Segment selection section 114 Segment Distribution Department 121 Segment memory section 122 Importance storage section 123 Distribution list storage unit

Claims

1. a segment storage unit that stores, for each video content, a plurality of streams having mutually different qualities, and a dummy stream that is assigned meta information of higher quality than the stream with the highest quality among the plurality of streams and stores an entity of lower quality than the quality indicated by the meta information, each in segments; an importance storage unit that stores the importance of each segment for each of the video content; a request receiving unit that receives, from a receiving terminal, a request for delivery of a segment of a quality that the receiving terminal can receive; a receiving terminal margin determination unit that determines, when distribution of a segment of the dummy stream is requested, that there is margin for quality that the receiving terminal can receive; a segment selection unit that selects one of the undelivered segments, giving priority to a segment with a high degree of importance, when it is determined that the quality that the receiving terminal can receive has a margin; a segment distribution unit that distributes the segment selected by the segment selection unit along with the segment for which the distribution request has been received.

2. The distribution device according to claim 1 , wherein the segment selection unit selects a segment that constitutes a stream of the highest quality from among the plurality of streams.

3. The distribution device according to claim 1 , wherein the segment selection unit selects, from the plurality of streams, segments that constitute a stream having a quality corresponding to the importance.

4. 4. The distribution device according to claim 1, wherein the quality indicated by the meta information is a bit rate for each segment.

5. 5. The distribution device according to claim 4, wherein the actual bit rate of the dummy stream is the highest among the plurality of streams, and the bit rate indicated by the meta information is an integer multiple of the actual bit rate.

6. 6. The distribution device according to claim 1, wherein the importance of a segment located at the beginning of each of a plurality of chapters constituting the video content is set to be higher than a predetermined level.

7. For each video content, a plurality of streams having mutually different qualities and a dummy stream to which meta information of higher quality than the stream with the highest quality among the plurality of streams is assigned and in which an entity of lower quality than the quality indicated by the meta information is stored are stored in units of segments, a distribution device that stores the importance of each segment for each of the video content, a request receiving step of receiving, from a receiving terminal, a delivery request for a segment of a quality that the receiving terminal can receive; a receiving terminal margin determination step of determining, when distribution of the dummy stream segment is requested, that there is margin for quality that the receiving terminal can receive; a segment selection step of selecting one of the undelivered segments, giving priority to the segment with a high importance, when it is determined that the quality that the receiving terminal can receive has a margin; a segment distribution step of distributing the segment selected in the segment selection step together with the segment for which the distribution request has been received.

8. A distribution program for causing a computer to function as the distribution device according to any one of claims 1 to 6.

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