Distribution server, receiving device, video distribution system, and program

Abstract

To reduce the costs of an encoding process and mitigate a quality change of video playback as a reception condition changes.SOLUTION: An encoding rate information notification unit 12 of a distribution server 10 includes a quality-by-quality totalization unit 122, for totaling the number A of receiving devices receiving a segment for each quality of the segment, a quality-by-quality totalization prediction unit 124, for predicting the number B of receiving devices receiving the segment for each quality corresponding to a candidate encoding rate, which is a candidate for a change in encoding rate value, an encoding rate determining unit 125, for determining a new encoding rate on the basis of the difference between A and B, and an encoding stop determining unit 126, for stopping encoding the video content at the first encoding rate to the encoder 13 when the difference between the first encoding rate and the second encoding rate, which is lower than the first encoding rate, is less than or equal to a threshold value, among the encoding rates determined by the encoding rate determining unit 125.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a distribution server, a receiving device, a video distribution system, and a program. [Background technology]

[0002] Standards such as MPEG-DASH (MPEG-Dynamic Adaptive Streaming over HTTP), HLS (HTTP Live Streaming), and HDS (HTTP Dynamic Streaming) have been established for streaming video distribution over the Internet using adaptive streaming. Adaptive streaming can reduce interruptions in video playback caused by deterioration of line quality.

[0003] These share the same basic mechanism, and a distribution server that distributes video content prepares multiple streams with different encoding rates (corresponding to quality) divided into files of several to several tens of seconds each (segments), as well as a manifest file that describes the attributes and URLs of these video contents. Each receiving device grasps the bit rate and segment configuration from the manifest file, and autonomously selects a video file with an encoding rate that can be played on a segment-by-segment basis depending on the quality of the reception conditions accompanying changes in the quality of the Internet line, etc. Then, the devices connect the video files together into a single video content according to the manifest file and play it back (for example, see Non-Patent Document 1).

[0004] In conventional adaptive streaming, a distribution server generates video streams with encoding rates of high, medium, and low quality. The upper limit of the quality that can be received is naturally determined by the potential performance (line capacity) of the Internet reception environment installed by the receiver. For example, a household with an optical fiber contract can receive high-quality video, but if a communication environment with low line capacity such as a metal line or mobile line is used, they will have no choice but to receive medium or low-quality video. Therefore, when the line quality of the Internet is ignored, the number of receiving devices that receive high-quality, medium-quality, and low-quality video is determined by the line capacity of the receiver's equipment, etc.

[0005] In reality, quality degradation factors (reception conditions) such as Internet congestion change from moment to moment. In adaptive streaming, the receiving device autonomously selects the quality that can be reproduced appropriately according to the reception conditions, so interruptions in video playback are unlikely to occur. However, for example, if the quality suddenly changes from high quality to medium quality or low quality (or in the worst case, the playback is interrupted), the user will experience quality degradation, and the more frequently this occurs, the more uncomfortable it will feel.

[0006] As a method for avoiding sudden quality deterioration, for example, by generating many video streams with qualities between high and medium quality, or between medium and low quality, in advance, the amount of change in quality can be reduced even if the quality selected by the receiving device changes. However, the more quality types there are, the more the amount of encoding processing increases, which leads to an increase in the number of machines in the case of hardware processing, and an increase in the amount of calculations in the case of software processing, which leads to an increase in costs.

[0007] Therefore, Patent Document 1 proposes a video distribution system that can smooth out changes in video playback quality caused by changes in reception conditions without increasing the costs of encoding, making it difficult for users to experience quality degradation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2017-175597 A [Non-patent literature]

[0009] [Non-Patent Document 1] Mitsuharu Hirabayashi, "Next-generation video distribution technology "MPEG-DASH" technical overview and standardization and related technology trends", Journal of the Institute of Image Information and Television Engineers, 2013, Vol.67, No.2, pp.109-115 Summary of the Invention [Problem to be solved by the invention]

[0010] The distribution server 10 disclosed in Patent Document 1 describes that, for example, when the initial values ​​of the encoding rates corresponding to high quality, medium quality, and low quality are 20 Mbps, 10 Mbps, and 240 kbps, the candidate encoding rates are set to 20 Mbps to 15 Mbps in increments of 0.5 Mbps for high quality, 10 Mbps to 5 Mbps in increments of 0.5 Mbps for medium quality, and 240 kbps or 120 kbps for low quality. That is, it is described that the amount of change for each quality can be freely determined for each quality, and the quality difference between the qualities is not taken into consideration. For this reason, for example, when the lower limit of high quality is set close to the upper limit of medium quality, the difference between the encoding rates of high quality and medium quality determined by the encoding rate determination unit 125 may become small, and as a result, no difference in image quality deterioration appears regardless of which quality is selected. In this case, there is no point in setting high quality and medium quality in the first place, and the cost of encoding processing is wasted in order to perform encoding processing for each quality.

[0011] The object of the present invention, made in consideration of the above circumstances, is to provide a distribution server, receiving device, video distribution system, and program that can reduce the change in quality of video playback that accompanies changes in reception conditions, and can reduce the cost of encoding processing by reducing the number of quality types when the encoding rate becomes asymptotic between qualities. [Means for solving the problem]

[0012] In order to solve the above problems, a distribution server according to the present invention is a distribution server that distributes video content to a plurality of receiving devices, and includes an encoding rate information notification unit that adaptively determines a plurality of encoding rates corresponding to a plurality of qualities of the video content based on reception conditions of the plurality of receiving devices, a manifest generation unit that generates a manifest file based on the encoding rates, an encoder that encodes the video content based on the encoding rates, and a segment generation unit that divides data encoded by the encoder to generate segments, and the encoding rate information notification unit includes a quality-based counting unit that counts the number of receiving devices receiving a segment for each quality of the segment, and a manifest generation unit that generates a manifest file based on the reception conditions of the plurality of receiving devices. the encoding rate determination unit determines a new encoding rate from the plurality of candidate encoding rates based on a difference N between the number of receiving devices counted by the quality count unit and the number of receiving devices predicted by the quality count prediction unit; and, when a difference between a first encoding rate and a second encoding rate lower than the first encoding rate among the encoding rates determined by the encoding rate determination unit becomes equal to or smaller than a threshold, causes the encoder to stop encoding video content at the first encoding rate.

[0013] Furthermore, in the distribution server of the present invention, when resuming encoding of video content that was stopped, the encoding rate determination unit determines the encoding rate at the time of resumption to be equal to or higher than the second encoding rate at the time of resumption and equal to or lower than the first encoding rate at the time of stopping.

[0014] Furthermore, in the distribution server according to the present invention, the encoding rate determination unit determines, as the new encoding rate, the candidate encoding rate when N is minimum or when N is equal to or smaller than a threshold value.

[0015] In addition, in order to solve the above problems, a receiving device of the present invention is a plurality of receiving devices that receive video content from a distribution server, and includes a terminal information sending unit that sends the reception status of the video content to the distribution server, a manifest acquisition unit that acquires a manifest file from the distribution server, a segment acquisition unit that acquires segments from the distribution server into which a video stream encoded at an encoding rate determined based on the reception status is divided, a decoder that decodes the segments, and a superimposing unit that superimposes information indicating a concentration of access on the video decoded by the decoder when information of video content of a predetermined quality is deleted from the manifest file.

[0016] In order to solve the above problem, a video distribution system according to the present invention includes the above distribution server and a plurality of receiving devices.

[0017] In order to solve the above problem, a program according to the present invention is characterized in that it causes a computer to function as the distribution server or the receiving device. Effect of the Invention

[0018] According to the present invention, it is possible to reduce the change in quality of video playback due to changes in reception conditions, and to reduce the cost of encoding processing by reducing the number of quality types when the encoding rate becomes asymptotic between qualities. [Brief description of the drawings]

[0019] [Figure 1] 1 is a conceptual diagram of a video distribution system according to an embodiment of the present invention. [Diagram 2] 1 is a block diagram showing an example of the configuration of a receiving device according to an embodiment of the present invention; [Diagram 3] FIG. 3 is a block diagram showing a modified example of the receiving device shown in FIG. [Figure 4] 1 is a block diagram showing an example of the configuration of a distribution server according to a first embodiment of the present invention. [Diagram 5] 2 is a block diagram showing an example of the configuration of an encoding rate information notifying unit in a distribution server according to the first embodiment of the present invention. FIG. [Figure 6] 4A to 4C are diagrams illustrating the stopping and restarting of encoding of a high-quality moving image in a distribution server according to the first embodiment of the present invention. [Figure 7] FIG. 11 is a block diagram showing an example of the configuration of a distribution server according to a second embodiment of the present invention. [Figure 8] 13] FIG. 13 is a block diagram showing an example of the configuration of an encoding rate information notifying unit in a distribution server according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0021] (Video distribution system) 1 shows a conceptual diagram of a video distribution system according to an embodiment of the present invention. The video distribution system 1 includes a distribution server 10 and a plurality of receiving devices 20 (20-1, 20-2, . . . , 20-n). The distribution server 10 and the plurality of receiving devices 20 are connected via the Internet 30.

[0022] In response to a video distribution request from the receiving device 20, the distribution server 10 generates a video stream by adaptive streaming and distributes it to the receiving device 20 via the Internet 30. The distribution server 10 prepares a plurality of segments with different qualities (encoding rates) and a manifest file that describes the attributes and URLs of the video content. In this embodiment, it is described that two types of segments, high quality and low quality, are prepared, but any type of segment can be prepared.

[0023] The receiving device 20 obtains the manifest file from the distribution server 10 and analyzes the contents. Then, based on the information described in the manifest file, the receiving device 20 makes a distribution request to the distribution server 10. When the receiving device 20 receives segments from the distribution server 10, the receiving device 20 splices the segments into one video content and plays it back.

[0024] (Receiving device) First, the configuration of the receiving device 20 will be described. Fig. 2 shows an example of the configuration of the receiving device 20 according to an embodiment of the present invention. The receiving device 20 shown in Fig. 2 includes a manifest acquisition unit 21, a segment acquisition unit 22, a buffer 23, a decoder 24, a playback unit 25, a reception status measurement unit 26, and a terminal information transmission unit 27. Note that the arrows in the figure indicate the main data flows, and data may be exchanged in both directions.

[0025] When an application is started or a program is selected, the manifest acquisition unit 21 generates a manifest request and transmits it to the distribution server 10. Then, as a response to the request, the manifest file (MPD file) of the desired program is acquired from the distribution server 10. Then, based on the manifest file, a segment URL list is generated in which segment start times and segment URLs are associated with each other, and the segment URL list is output to the segment acquisition unit 22.

[0026] The reception status measurement unit 26 periodically measures the communication speed (receiving speed of segments) and the amount of storage in the buffer 23 as the reception status of the video content, and outputs the results to the segment acquisition unit 22 and the terminal information transmission unit 27. The communication speed can be found, for example, from the change in the amount of storage in the buffer 23 per second.

[0027] The segment acquisition unit 22 extracts the URL of the segment associated with the segment start time from the segment URL list input from the manifest acquisition unit 21. Then, based on the reception status (communication speed and buffer accumulation amount) input from the reception status measurement unit 26, it selects one of two types of segments, high quality and low quality, and generates a segment request including the URL of the selected segment and transmits it to the distribution server 10. Before the reception status is input from the reception status measurement unit 26, a predetermined quality is selected. For example, a receiving device 20 connected to an optical line selects high quality, and a receiving device 20 connected to a metal line or a mobile line selects low quality.

[0028] The segment acquisition unit 22 may select one of a plurality of types of segments by a conventional mechanism of adaptive streaming. When the segment acquisition unit 22 acquires a corresponding segment from the distribution server 10 as a response to the request, the segment acquisition unit 22 accumulates the segment in the buffer 23.

[0029] The buffer 23 is a memory for temporarily storing the segments input from the segment acquisition unit 22 .

[0030] The decoder 24 reads out the segment requested by the playback unit 25 from the buffer 23. Then, the decoder 24 decodes the read segment in accordance with the media format (video, audio, text, etc.) to generate a video and outputs it to the playback unit 25.

[0031] When a playback command including playback start time information is input, the playback unit 25 plays the video based on the playback start time, and when a stop command is input, the playback unit 25 stops the playback.

[0032] The terminal information transmitting unit 27 periodically transmits to the distribution server 10 the reception status (communication speed and buffer accumulation amount) input from the reception status measuring unit 26 and terminal information including identification information for identifying the receiving device.

[0033] Next, a modified example of the receiving device 20 will be described with reference to Fig. 3. The receiving device 20' shown in Fig. 3 includes a manifest acquisition unit 21, a segment acquisition unit 22, a buffer 23, a decoder 24, a playback unit 25, a reception status measurement unit 26, a terminal information transmission unit 27, and a superimposing unit 28. The receiving device 20' differs from the receiving device 20 in that it further includes the superimposing unit 28. As the other configurations are the same as those of the receiving device 20, the same reference numbers are used and the description is omitted as appropriate.

[0034] The manifest acquisition unit 21 has a function of detecting that information on video content of a predetermined quality has been deleted from information on high-quality and low-quality video content. When the manifest acquisition unit 21 detects that information on video content of a predetermined quality has been deleted, the manifest acquisition unit 21 notifies the superimposing unit 28 of a superimposing instruction.

[0035] When the superimposing unit 28 is notified of a superimposing instruction from the manifest acquiring unit 21, the superimposing unit 28 superimposes information indicating the concentration of access (i.e., information indicating the occurrence of network congestion) on the video decoded by the decoder 24. For example, the superimposing unit 28 displays the text "Access to the video is currently congested" by superimposing it on the video.

[0036] (Distribution server) Next, the configuration of the distribution server 10 will be described. Fig. 4 shows an example of the configuration of the distribution server 10. The distribution server 10 shown in Fig. 4 includes a terminal information receiving unit 11, an encoding rate information notifying unit 12, an encoder 13, a manifest generating unit 14, a segment generating unit 15, a manifest transmitting unit 16, a data generating unit 17, and a segment transmitting unit 18. The encoder 13 may be a device provided outside the distribution server 10. Note that the arrows in the figure indicate the main data flow, and data may be exchanged in both directions. Also, a buffer that temporarily stores data such as a manifest file and segments is omitted from the illustration.

[0037] The terminal information receiving unit 11 receives terminal information transmitted from the receiving device 20 at a pre-specified time interval, and outputs the reception status included in the terminal information to the encoding rate information notifying unit 12 .

[0038] The encoding rate information notification unit 12 adaptively determines encoding rates corresponding to multiple qualities of video content every time the reception status is input from the terminal information receiving unit 11, and outputs the determined encoding rates to the encoder 13 and the manifest generating unit 14. In this embodiment, the encoding rate information notification unit 12 determines the encoding rate of high-quality video content (hereinafter referred to as "high-quality video") and the encoding rate of low-quality video content (hereinafter referred to as "low-quality video"). In addition, when the encoding rate of the high-quality video approaches the encoding rate of the low-quality video, the encoding rate information notification unit 12 also outputs encoding stop information for instructing the stop of encoding the high-quality video to the encoder 13 and the manifest generating unit 14. Details of the encoding rate information notification unit 12 will be described later.

[0039] The encoder 13 generates a video stream by encoding the video at the encoding rate notified by the encoding rate information notifying unit 12, and outputs the video stream to the segment generating unit 15. When encoding stop information is input from the encoding rate information notifying unit 12, the encoder 13 stops encoding the high-quality video. When the encoding stop information is released (becomes inactive), the encoder 13 resumes encoding the high-quality video.

[0040] The manifest generation unit 14 generates a manifest file based on the encoding rate input from the encoding rate information notification unit 12, and outputs it to the manifest transmission unit 16 and the data generation unit 17. The encoding rate described in the manifest file is changed at any time based on the encoding rate notified from the encoding rate information notification unit 12. When encoding stop information is input from the encoding rate information notification unit 12, the manifest generation unit 14 deletes the description of the high-quality video from the manifest file. When the encoding stop information is released (becomes inactive), the manifest generation unit 14 resumes describing the high-quality video.

[0041] When the manifest transmission unit 16 receives a manifest request from the receiving device 20 , the manifest transmission unit 16 transmits the manifest file input from the manifest generation unit 14 to the receiving device 20 .

[0042] The segment generation unit 15 divides the moving image stream input from the encoder 13 to generate segments in a predetermined format, and outputs them to the data generation unit 17 .

[0043] Based on the manifest file input from the manifest generation unit 14, the data generation unit 17 converts the segments input from the segment generation unit 15 into a predetermined adaptive streaming file format, and outputs the converted data to the segment transmission unit 18.

[0044] When the segment transmission unit 18 receives a segment request from the receiving device 20 , it transmits the segment input from the data generation unit 17 to the receiving device 20 .

[0045] (Encoding rate information notification section) Next, the processing contents of the encoding rate information notification unit 12 will be described with reference to Fig. 5. Fig. 5 is a block diagram showing an example of the configuration of the encoding rate information notification unit 12. The encoding rate information notification unit 12 shown in Fig. 5 includes a reception status acquisition unit 121, a quality-based tally unit 122, a reception status analysis unit 123, a quality-based tally prediction unit 124, an encoding rate determination unit 125, and an encoding stop judgment unit 126. Note that the arrows in the figure indicate the main data flows, and data may be exchanged in both directions.

[0046] The reception status acquisition unit 121 acquires the reception status (communication speed and buffer accumulation amount) of the multiple reception devices 20 from the terminal information reception unit 11 , and outputs it to the quality-based aggregation unit 122 and the reception status analysis unit 123 .

[0047] Each time the reception status is input from the reception status acquisition unit 121, the quality counting unit 122 determines what quality of segment each reception device 20 is requesting, and counts the number H now and the number L of receiving devices 20 receiving low-quality segments. now The total number of receiving devices for each quality is calculated as H now ,L now to the quality-based counting prediction unit 124 and the encoding rate determination unit 125. Alternatively, the quality-based counting unit 122 determines the quality of the segment requested from the segment request received from the receiving device 20, and outputs the quality-based receiving device number H now ,L now may be aggregated.

[0048] The reception status analysis unit 123 judges whether the reception status of each receiving device 20 is good or bad each time the reception status is input from the reception status acquisition unit 121, and outputs the judgment result to the quality-based aggregation prediction unit 124. For example, if the buffer accumulation amount is greater than a predetermined number of bytes, it judges the reception status to be good, and if the buffer accumulation amount is equal to or less than the predetermined number of bytes, it judges the reception status to be bad. In addition, if the reception status is good, it judges how much higher the encoding rate of the segment that can be received, and if the reception status is bad, it judges how much lower the encoding rate of the segment that can be received.

[0049] For example, if the receiving device 20, which was initially receiving high-quality 5 Mbps segments, begins to experience a decrease in buffer storage due to deterioration in line quality, it is predicted that the device will switch quality and request low-quality 1 Mbps segments to prevent video interruption. However, if the encoding rate corresponding to high quality is changed from 5 Mbps to 3 Mbps, it is predicted that the device will request high-quality 3 Mbps segments instead of requesting low-quality 1 Mbps segments.

[0050] Therefore, the quality-based aggregation prediction unit 124 determines a plurality of candidate encoding rates that are candidates for the change value of each encoding rate corresponding to high quality and low quality. Then, the quality-based aggregation prediction unit 124 determines the number of receiving devices for each quality H now ,L now Based on the judgment result input from the reception status analysis unit 123, the predicted number of receiving devices that will receive the segment for each quality corresponding to the candidate encoding rate (predicted number of receiving devices for each quality) H after ,L after and outputs it to the encoding rate determination unit 125. This process is repeated while changing the value of the candidate encoding rate. In other words, assuming that the encoding rate values ​​corresponding to high quality and low quality are changed, the number H after and the number L of receiving devices 20 expected to receive low quality segments. after Request.

[0051] The quality-based aggregation prediction unit 124 may arbitrarily select the order of trial of the candidate encoding rates. For example, when the ratio of the receiving devices 20 with good reception conditions is equal to or greater than a threshold, the candidate encoding rates with higher encoding rates than the current encoding rate may be trialed in an order in which the difference from the current encoding rate gradually increases. When the ratio of the receiving devices 20 with poor reception conditions is equal to or greater than a threshold, the candidate encoding rates with lower encoding rates than the current encoding rate may be trialed in an order in which the difference from the current encoding rate gradually increases. The amount of change in the candidate encoding rate may be the same for both high quality and low quality, or the amount of change may differ for each quality, or the encoding rate for low quality may not be changed.

[0052] The encoding rate determination unit 125 determines the difference between the number of receiving devices 20 counted by the quality-based counting unit 122 and the number of receiving devices predicted by the quality-based counting prediction unit 124, that is, the total number of receiving devices 20 predicted to change the quality of the segments they receive when the encoding rate is changed to a candidate encoding rate (predicted number of quality changes) N. N is expressed by equation (1). Then, based on the predicted number of quality changes N, a new encoding rate is determined from multiple candidate encoding rates, and output to the encoder 13 and the manifest generation unit 14.

[0053]

number

[0054] An example of determining a new encoding rate from the candidate encoding rates will be described below. In a first encoding rate determination example, the encoding rate determination unit 125 determines the candidate encoding rate at which the predicted quality change number N is minimum as the new encoding rate.

[0055] In the second encoding rate determination example, the quality-based aggregation prediction unit 124 obtains the predicted quality change number N from the encoding rate determination unit 125, and when the predicted quality change number N becomes equal to or less than a threshold, stops processing at that point, and the encoding rate determination unit 125 determines the candidate encoding rate when the predicted quality change number N becomes equal to or less than the threshold as the new encoding rate.

[0056] Furthermore, if the predicted quality change number N does not decrease even when the candidate encoding rate is lowered and the change in the predicted quality change number N becomes equal to or less than the threshold, it is considered that an abnormality has occurred in the line. Therefore, in the third encoding rate determination example, the quality-based aggregation prediction unit 124 acquires the predicted quality change number N from the encoding rate determination unit 125, and when the change in the predicted quality change number N becomes equal to or less than the threshold, it stops processing at that point, and the encoding rate determination unit 125 determines the candidate encoding rate immediately before the change in the predicted quality change number N becomes equal to or less than the threshold as the new encoding rate.

[0057] Moreover, it is considered that the number of receiving devices 20 that switch to a lower quality increases when the value of the candidate encoding rate is increased. Therefore, in the fourth encoding rate determination example, the quality-based aggregation prediction unit 124 acquires the predicted quality change number N from the encoding rate determination unit 125, and when the amount of change in the predicted quality change number N becomes equal to or greater than a threshold, stops processing at that point, and the encoding rate determination unit 125 determines the candidate encoding rate immediately before the amount of change in the predicted quality change number N becomes equal to or greater than the threshold as the new encoding rate.

[0058] Here, consider an example in which the encoding rate of high-quality video is gradually decreased and the encoding rate of low-quality video is maintained unchanged. When the encoding rate of high-quality video is decreased, for example, from 5 Mbps in increments of 0.5 Mbps, it is assumed that the encoding rate may eventually reach 1.5 Mbps or 1 Mbps if line congestion worsens. When the encoding rate of low-quality video is 1 Mbps, the difference with the encoding rate of high-quality video becomes small, and the subjective image quality does not change. In other words, the subjective image quality does not change regardless of whether the receiving side selects high-quality video or low-quality video. In this case, it is useless to encode the high-quality video, so it is reasonable to encode only the low-quality video. Therefore, the encoding rate information notification unit 12 performs the following process.

[0059] When the difference between a first encoding rate and a second encoding rate lower than the first encoding rate among the encoding rates determined by the encoding rate determination unit 125 becomes equal to or less than a threshold, the encoding stop determination unit 126 causes the encoder 13 to stop encoding the video content at the first encoding rate. In other words, when the difference between the two encoding rates determined by the encoding rate determination unit 125 becomes equal to or less than a threshold, the encoder 13 stops encoding the video content with the higher encoding rate.

[0060] When resuming the encoding of the stopped video content, the encoding rate determination unit 125 determines the encoding rate at the time of resumption to be equal to or higher than the second encoding rate at the time of resumption and equal to or lower than the first encoding rate at the time of stop. This makes it possible to make the quality of the video playback change gradually even when the encoding of the video content is resumed.

[0061] For example, as shown in FIG. 5, the encoding stop determination unit 126 includes an encoding rate difference calculation unit 127, a determination unit 128, and an encoding stop notification unit 129.

[0062] The encoding rate difference calculation unit 127 obtains the encoding rate from the encoding rate determination unit 125, calculates the difference between the two encoding rates, and outputs the difference to the judgment unit 128. In this embodiment, since there are only two types of encoding rates determined by the encoding rate determination unit 125, the encoding rate difference calculation unit 127 calculates the difference between the encoding rate of the high-quality video and the encoding rate of the low-quality video.

[0063] When the difference between the encoding rates calculated by the encoding rate difference calculation unit 127 becomes equal to or smaller than a threshold value, the determination unit 128 determines to stop encoding of the high-quality video, and outputs the determination result to the encoding stop notification unit 129.

[0064] When the decision unit 128 decides to stop encoding of the high-quality moving image, the encoding stop notification unit 129 outputs encoding stop information for instructing the encoding rate determination unit 125 to stop encoding of the high-quality moving image.

[0065] When the encoding stop information is input from the encoding stop notifying unit 129, the encoding rate determining unit 125 outputs the encoding stop information to the encoder 13 and the manifest generating unit 14. The encoding rate determining unit 125 determines the encoding rate at the time of resuming encoding of the high-quality video to be equal to or higher than the encoding rate of the low-quality video at the time of resuming and equal to or lower than the encoding rate of the high-quality video at the time of stopping encoding.

[0066] FIG. 6 is a diagram showing the stopping and restarting of encoding of high-quality video. In the figure, H indicates the encoding rate (bit rate [bps]) of high-quality video, L indicates the encoding rate (bit rate [bps]) of low-quality video, and the horizontal axis indicates time [s]. When network congestion worsens over time, the encoder 13 gradually lowers the encoding rate of high-quality video content. As shown in FIG. 6(a), when the difference between the encoding rates of high-quality video and low-quality video becomes equal to or less than the first threshold (time t1), the encoder 13 stops encoding the high-quality video and encodes only the low-quality video. When the network congestion is recovered and the difference between the encoding rates calculated by the encoding rate difference calculation unit 127 becomes equal to or more than the second threshold (time t2), the encoder 13 resumes encoding of the high-quality video and gradually increases the encoding rate. The first threshold and the second threshold may be the same value. The encoding rate of the high-quality video at time t2 may be the same as the encoding rate of the high-quality video at time t1 as shown in FIG. 6(a), or it may be the same as the encoding rate of the low-quality video at time t2, or it may be a value between these.

[0067] As shown in FIG. 6(b), when congestion worsens (time t3) during the period when only low-quality video is encoded (after time t1), the encoding rate information notification unit 12 may gradually lower the encoding rate of low-quality video while stopping encoding of high-quality video. After that, the encoding rate of low-quality video may be set to a predetermined value from time t4 to time t5, and gradually increased from time t5. Furthermore, when the congestion is alleviated and the encoding rate of low-quality video becomes approximately the same as that at time t1 (time t6), encoding of high-quality video may be resumed. The encoding rate of high-quality video at time t6 may be the same as the encoding rate of high-quality video at time t1 as shown in FIG. 6(b), may be the same as the encoding rate of low-quality video at time t6, or may be a value between them.

[0068] The distribution server 10 does not perform the encoding of the high-quality video during the period when encoding of the high-quality video is stopped (the period from time t1 to time t2 in FIG. 6(a) and the period from time t1 to time t4 in FIG. 6(b)), so that the cost related to the encoding process can be reduced. Similarly, when there are three or more encoding rates determined by the encoding rate determination unit 125, the encoding of the video content with the higher encoding rate is stopped when the difference between two of the encoding rates becomes equal to or less than a threshold, so that the cost related to the encoding process can be reduced. In this way, in the present invention, the cost of the encoder 13 can be reduced while maintaining the quality of experience as much as possible while utilizing the mechanism of adaptive streaming as it is.

[0069] (Distribution Server According to the Second Embodiment) Next, a distribution server according to the second embodiment will be described. The distribution server 10 according to the first embodiment determines the encoding rate based on the terminal information, but may determine the encoding rate based on other information in addition to the terminal information. Therefore, in the second embodiment, a distribution server that determines the encoding rate based on the terminal information and emergency information will be described.

[0070] Fig. 7 shows an example of the configuration of a distribution server 40 according to the second embodiment of the present invention. The distribution server 40 shown in Fig. 7 includes a terminal information receiving unit 11, an emergency information receiving unit 41, an encoding rate information notifying unit 42, an encoder 13, a manifest generating unit 14, a segment generating unit 15, a manifest transmitting unit 16, a data generating unit 17, and a segment transmitting unit 18. The distribution server 40 differs from the distribution server 10 according to the first embodiment in that it further includes an emergency information receiving unit 41 and includes an encoding rate information notifying unit 42 instead of the encoding rate information notifying unit 12. The other configurations are the same as those of the distribution server 10, so the same reference numbers are used and the description will be omitted.

[0071] When the emergency information receiving unit 41 receives the emergency information, it outputs the emergency information to the encoding rate information notifying unit 42. The emergency information is, for example, a signal issued upon detection of a chime sound in a television broadcast of an emergency earthquake warning, or an emergency earthquake warning issued by the Japan Meteorological Agency.

[0072] The encoding rate information notification unit 42, like the encoding rate information notification unit 12 of the distribution server 10, adaptively determines encoding rates corresponding to multiple qualities of the video content each time reception status is input from the terminal information receiving unit 11, and outputs the determined encoding rates to the encoder 13 and the manifest generation unit 14. However, when emergency information is input, the encoding rate is reduced for a certain period of time.

[0073] FIG. 8 is a block diagram showing a configuration example of the encoding rate information notification unit 42. The encoding rate information notification unit 42 shown in FIG. 8 includes a reception status acquisition unit 121, a quality-based aggregation unit 122, a reception status analysis unit 123, a quality-based aggregation prediction unit 124, an encoding rate determination unit 125, and an encoding rate adjustment unit 421. Note that the arrows in the figure indicate main data flows, and data may be exchanged in both directions. The encoding rate information notification unit 42 differs from the encoding rate information notification unit 12 of the distribution server 10 according to the first embodiment in that it further includes an encoding rate adjustment unit 421. The other configurations are the same as those of the encoding rate information notification unit 12, and therefore the same reference numbers are used and description thereof is omitted.

[0074] When emergency information is input, the encoding rate adjustment unit 421 reduces the encoding rate determined by the encoding rate determination unit 125 for a certain period of time. The time for the reduction can be set arbitrarily (for example, 30 seconds), and after this time has elapsed, the encoding rate is restored to the original state.

[0075] The encoding rate adjustment unit 421 may lower the frame rate together with the encoding rate. For example, when the frame rate is set to 1 frame / sec, which is 1 / 30 of 30 frames / sec, the encoding rate may also be set to 1 / 30, or may be set arbitrarily between 1 / 1 and 1 / 30 to improve image quality within a frame (particularly the image quality of map information and text information).

[0076] The distribution server 10 according to the first embodiment can maintain the quality of experience as described above, but if the quality of the video playback drops when streaming a television broadcast of an Earthquake Early Warning based on an announcement by the Japan Meteorological Agency, the visibility of the map information and text information superimposed on the screen drops. In such a case, the distribution server 40 according to the second embodiment reduces the frame rate of the video, so that the video quality of each frame is maintained and the map information and text information of the Earthquake Early Warning can be played back with less degradation.

[0077] (program) A computer capable of executing program instructions may be used to function as the above-mentioned receiving devices 20, 20' and distribution servers 10, 40. Here, the computer may be a general-purpose computer, a special-purpose computer, a workstation, a PC (Personal Computer), an electronic notepad, etc. The program instructions may be program code, code segments, etc. for performing the necessary tasks.

[0078] The computer includes a processor, a storage unit, an input unit, an output unit, and a communication interface. The processor reads out a program from the storage unit and executes it to control each of the above components and perform various arithmetic processing. The processor is a CPU (Central Processing Unit), an MPU (Micro Processing Unit), a GPU (Graphics Processing Unit), a DSP (Digital Signal Processor), a SoC (System on a Chip), or the like, and may be composed of multiple processors of the same type or different types. The input unit is an input interface that receives a user's input operation and acquires information based on the user's operation, and is a pointing device, a keyboard, a mouse, or the like. The output unit is an output interface that outputs information, and is a display, a speaker, or the like. The communication interface is an interface for communicating with an external device.

[0079] The program may be recorded on a computer-readable recording medium. By using such a recording medium, the program can be installed on the computer. Here, the recording medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a CD-ROM, a DVD-ROM, or a USB (Universal Serial Bus) memory. In addition, the program may be in a form that is downloaded from an external device via a network.

[0080] Although the above-mentioned embodiment has been described as a representative example, it is obvious to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the above-mentioned embodiment, and various modifications and changes are possible without departing from the scope of the claims. For example, it is possible to combine multiple building blocks shown in the configuration diagram of the embodiment into one, or to divide one building block. [Explanation of symbols]

[0081] 1. Video distribution system 10,40 Distribution Server 11 Terminal information receiving unit 12,42 Encoding rate information notification section 13 Encoders 14 Manifest Generation Unit 15 Segment Generation Unit 16 Manifest Transmission Unit 17 Data Generation Section 18 Segment transmitter 20,20' Receiver 21 Manifest Acquisition Department 22 Segment Acquisition Section 23 Buffer 24 Decoder 25 Playback Department 26 Reception status measurement section 27 Terminal information transmission unit 28 Superimpose Section 30 Internet 41 Emergency Information Receiving Unit 121 Reception status acquisition unit 122 Quality Counting Section 123 Reception Status Analysis Department 124 Quality Aggregation and Forecasting Department 125 Encoding rate determination unit 126 Encoding stop decision unit 127 Encoding rate difference calculation unit 128 Judgment Department 129 Encoding stop notification section 421 Encoding rate adjustment unit

Claims

1. A distribution server that distributes video content to a plurality of receiving devices, an encoding rate information notifying unit that adaptively determines a plurality of encoding rates corresponding to a plurality of qualities of video content based on the reception conditions of the plurality of receiving devices; a manifest generation unit that generates a manifest file based on the encoding rate; an encoder for encoding video content based on the encoding rate; a segment generation unit that divides the data encoded by the encoder to generate segments; The encoding rate information notifying unit is a quality counting unit that counts the number of receiving devices receiving the segment for each quality of the segment; a quality-based aggregation prediction unit that determines a plurality of candidate encoding rates that are candidates for a change value of the encoding rate based on the reception status, and predicts the number of receiving devices that will receive the segments for each quality corresponding to each candidate encoding rate; an encoding rate determination unit that determines a new encoding rate from the plurality of candidate encoding rates based on a difference N between the number of receiving devices counted by the quality-based count unit and the number of receiving devices predicted by the quality-based count prediction unit; an encoding stop determination unit that, when a difference between a first encoding rate and a second encoding rate lower than the first encoding rate among the encoding rates determined by the encoding rate determination unit becomes equal to or smaller than a threshold value, causes the encoder to stop encoding of the video content at the first encoding rate; A distribution server comprising:

2. 2. The distribution server according to claim 1, wherein, when encoding of video content that has been stopped is resumed, the encoding rate determination unit determines the encoding rate at the time of restart to be equal to or higher than the second encoding rate at the time of restart and equal to or lower than the first encoding rate at the time of stop.

3. 3. The distribution server according to claim 1, wherein the encoding rate determination unit determines, as the new encoding rate, the candidate encoding rate when the number N is smallest or when the number N is equal to or smaller than a threshold value.

4. A plurality of receiving devices that receive video content from a distribution server, a terminal information transmission unit that transmits a reception status of the video content to the distribution server; A manifest acquisition unit that acquires a manifest file from the distribution server; a segment acquisition unit that acquires, from the distribution server, segments obtained by dividing a video stream that has been encoded at an encoding rate determined based on the reception status; a decoder for decoding the segments; a superimposing unit that, when information on video content of a predetermined quality is deleted from the manifest file, superimposes information indicating concentration of accesses onto the video decoded by the decoder; A receiving device comprising:

5. A distribution server according to any one of claims 1 to 3; A plurality of receiving devices according to claim 4; A video distribution system comprising:

6. A program for causing a computer to function as the distribution server according to any one of claims 1 to 3.

7. A program for causing a computer to function as the receiving device according to claim 4.

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