JP6149562B2 - Stream delivery system, stream creation device, stream delivery method, and stream creation method - Google Patents

Description

  The present invention relates to a stream delivery system, a stream creation device, a stream delivery method, and a stream creation method.

  In recent years, video distribution via the Internet has become widespread. For example, MPEG-DASH (Dynamic Adaptive Streaming over HTTP) is known as a standard for distributing video without interruption even when the network bandwidth changes. For example, an MPEG-DASH compliant stream distribution system prepares in advance a stream in which one content is encoded at a plurality of bit rates. The stream distribution system selects and distributes a stream having an appropriate bit rate in accordance with a change in the network bandwidth. Thereby, the delay of stream delivery is reduced. As a result, the phenomenon in which the distributed video is interrupted is reduced.

  Note that in a stream distribution system that selects and distributes an appropriate stream from a plurality of streams having different bit rates, there is a possibility that the image may be disturbed when the bit rate of the stream to be distributed is switched. For example, when the bit rate is different between streams before and after switching, the reference image of the first B picture of the stream after switching is different between encoding and decoding, so that the decoded image may be deteriorated. A B picture is, for example, a picture encoded by bidirectional prediction.

  As a method for suppressing image quality deterioration at the time of stream switching, a method of creating a stream so as to become a closed GOP (Group of Picture) at a stream switching point is known (see, for example, Patent Documents 1 and 2). . Further, a method has been proposed in which the first B picture of the stream after switching is replaced with an exchange picture obtained by blending the last reference image of the stream before switching and the first reference image of the stream after switching (for example, (See Patent Document 3).

JP 2004-56234 A JP 2011-40879 A JP 2009-147930 A

  In the closed GOP, since the B picture before the first I picture is only backward prediction, the compression efficiency is lower than that of an open GOP that can use forward prediction or bidirectional prediction. For this reason, there is a possibility that the image quality of the closed GOP is deteriorated as compared with the open GOP. In the closed GOP, since the reference relationship is divided before and after the stream switching, the continuity of image quality is lost at the switching point. For this reason, in the closed GOP, the change in image quality at the stream switching point may be larger than in the open GOP in which bidirectional prediction can be used.

  In the method of replacing the first B picture of the stream after switching with the replacement picture obtained by blending the last reference image of the stream before switching and the first reference image of the stream after switching, an input image (content image) is used. ) May be delivered. For example, the exchange picture is created from the preceding and following reference images regardless of the content of the B picture (input image) to be replaced. For this reason, when the motion is large, an exchange picture different from the input image may be created.

  In one aspect, the stream distribution system, the stream generation device, the stream distribution method, and the stream generation method disclosed herein are intended to suppress a change in image quality at the time of stream switching.

  According to one aspect, the stream distribution system selects a first stream to be distributed from a plurality of first streams having different bit rates created for each stream obtained by dividing a content stream in the time direction; A first holding unit for holding a plurality of replacement streams created for each bit rate switching point of the first stream, and a picture of the first stream before switching to the first stream selected by the first selection unit A replacement stream including a replacement picture encoded by bi-prediction is selected from a plurality of replacement streams using a direction reference image and a picture of the first stream selected by the first selection unit as a backward reference image. Replacing a part of the first stream selected by the second selector and the first selector with the replacement stream selected by the second selector; And a replacement unit for creating a stream of credit.

  According to another aspect, the stream creation device receives a plurality of first streams having different bit rates created for each stream obtained by dividing the content stream in the time direction, and at each switching point of the bit rate of the first stream. For each combination of first streams before and after the switching point, a creation unit that creates a replacement stream including a replacement picture obtained by encoding the pictures of the first stream before and after the switching point as a reference image for bidirectional prediction is provided. .

  According to another aspect, in the stream distribution method, the first stream to be distributed is selected from a plurality of first streams having different bit rates created for each stream obtained by dividing the content stream in the time direction. A plurality of replacement streams created at each bit rate switching point of the first stream are stored, the picture of the first stream before switching to the selected first stream is set as a forward reference image, and the picture of the selected first stream Is selected from a plurality of replacement streams, and a part of the selected first stream is replaced with the selected replacement stream. Create a stream for delivery.

  According to another aspect, the stream creation method receives a plurality of first streams having different bit rates created for each stream obtained by dividing a content stream in a time direction, and at each switching point of the bit rate of the first stream. For each combination of first streams before and after the switching point, a replacement stream including a replacement picture obtained by encoding the pictures of the first stream before and after the switching point as a reference image for bidirectional prediction is created.

  The stream delivery system, stream creation device, stream delivery method, and stream creation method disclosed herein can suppress changes in image quality when switching streams.

It is a figure which shows one Embodiment of a stream delivery system and a stream production apparatus. It is a figure which shows an example of the division | segmentation stream and substitution stream which are produced with the stream production | generation apparatus shown in FIG. It is a figure which shows an example of the reference relationship of the picture of a division | segmentation stream. It is a figure which shows an example of the reference relationship of the picture of a replacement stream. It is a figure which shows an example of the data arrangement | positioning of a replacement stream. It is a figure which shows an example of the stream delivery by the stream delivery system shown in FIG. It is a figure which shows an example of the picture replacement at the time of stream delivery. It is a figure which shows an example of operation | movement of the stream production | generation apparatus shown in FIG. It is a figure which shows an example of operation | movement of the stream delivery system shown in FIG. It is a figure which shows another embodiment of a stream delivery system.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 shows an embodiment of a stream distribution system and a stream creation device. The dashed arrows in FIG. 1 indicate the flow of signals and the like. The stream distribution system DSYS and the stream creation device DGEN of this embodiment distribute content such as video via the Internet, for example. For example, the stream distribution system DSYS and the stream creation device DGEN support video distribution standards such as MPEG-DASH (Dynamic Adaptive Streaming over HTTP).

  For example, the stream creation device DGEN receives the content stream STIN and creates a first stream STD (hereinafter also referred to as a divided stream STD) and a replacement stream RST used in the stream distribution system DSYS. The stream STIN is, for example, H.264. H.264 / MPEG-4 Part 10 Advanced Video Coding (hereinafter also referred to as H.264). Note that the stream STIN is H.264. It may be encoded by an encoding method other than H.264.

  For example, the stream creation device DGEN includes a division unit DIV and a replacement stream creation unit RSGEN.

  The dividing unit DIV creates a plurality of divided streams STD having different bit rates for each stream obtained by dividing the content stream STIN in the time direction. For example, the dividing unit DIV divides the stream STIN in the time direction with a switching point when changing the bit rate as a boundary. Furthermore, the dividing unit DIV converts each stream divided in the time direction into all the bit rates (10 Mbps, 6 Mbps, and 2 Mbps in the example of FIG. 2) that may be selected at the time of distribution. Thereby, a plurality of divided streams STD are created.

  Note that the divided stream STD is encoded with, for example, an open GOP that can be referenced across multiple GOPs (Group of Picture). The GOP is a data unit having a plurality of pictures, and has at least one I picture. The I picture is, for example, a picture that uses only intra-frame prediction.

  Further, the divided stream STD is output to, for example, the replacement stream creation unit RSGEN and the stream distribution system DSYS. The divided stream STD may be transferred to the stream distribution system DSYS via a network or the like, or may be transferred to the stream distribution system DSYS via a storage medium or the like.

  The replacement stream creation unit RSGEN is an example of a creation unit that creates a replacement stream RST. For example, the replacement stream creation unit RSGEN receives the divided stream STD from the division unit DIV. Then, the replacement stream creation unit RSGEN creates a replacement stream RST for each combination of the divided streams STD before and after the switching point at each switching point of the bit rate of the divided stream STD. For example, the replacement stream RST includes a replacement picture obtained by encoding a picture of the divided stream STD before and after the switching point as a reference image for bidirectional prediction.

  That is, the replacement stream creating unit RSGEN includes, for each combination of the divided streams STD before and after the switching point, a replacement stream RST including a replacement picture obtained by encoding a picture of the divided stream STD before and after the switching point as a reference image for bidirectional prediction. Create Therefore, as many replacement streams RST as the number of combinations of the divided streams STD before and after the switching point are created. For example, when the bit rate of the divided stream STD is n, the number of replacement streams RST at each switching point is n × (n−1). Hereinafter, the switching point of the bit rate of the divided stream STD is also referred to as a switching point of the divided stream STD.

  The replacement stream RST is output to the stream distribution system DSYS, for example. The replacement stream RST may be transferred to the stream distribution system DSYS via a network or the like, or may be transferred to the stream distribution system DSYS via a storage medium or the like.

  The stream distribution system DSYS receives, for example, a divided stream STD encoded with a plurality of bit rates for one content, a replacement stream RST, and band information BINF indicating a network band. Then, the stream distribution system DSYS uses the divided stream STD and the replacement stream RST to distribute a stream STO having an appropriate bit rate according to the network bandwidth. As a result, for example, the content stream STIN received by the stream creation device DGEN is distributed as a stream STO having a bit rate corresponding to the bandwidth of the network.

  For example, the stream distribution system DSYS includes a divided stream storage unit MEMD, a replacement stream storage unit MEMR, a divided stream selection unit SELD, a replacement stream selection unit SELR, a replacement unit REP, and a distribution unit OPT. The divided stream storage unit MEMD stores, for example, the divided stream STD created by the division unit DIV of the stream creation device DGEN. Also, the divided stream storage unit MEMD outputs the divided stream STD selected by the divided stream selection unit SELD to the replacement unit REP.

  The replacement stream storage unit MEMR is an example of a first holding unit that holds a plurality of replacement streams RST created for each bit rate switching point of the divided stream STD. For example, the replacement stream storage unit MEMR stores the replacement stream RST created by the replacement stream creation unit RSGEN of the stream creation device DGEN. Also, the replacement stream accumulation unit MEMR outputs the replacement stream RST selected by the replacement stream selection unit SELR to the replacement unit REP.

  The divided stream selection unit SELD is an example of a first selection unit that selects a divided stream STD to be distributed from a plurality of divided streams STD having different bit rates created for each stream obtained by dividing the content stream STIN in the time direction. . For example, the divided stream selection unit SELD receives band information BINF indicating a network band. Then, the divided stream selection unit SELD selects, for each switching point of the divided stream STD, the divided stream STD to be distributed after the switching point based on the band indicated by the band information BINF.

  The selection result of the divided stream selection unit SELD is notified to the divided stream storage unit MEMD and the replacement stream selection unit SELR. Note that if the bit rate of the divided stream STD does not change before and after the switching point of the divided stream STD, the divided stream selection unit SELD indicates that it is not necessary to replace a part of the divided stream STD with the replacement stream RST. Notify

  The replacement stream selection unit SELR is an example of a second selection unit that selects, from a plurality of replacement streams RST, a replacement stream RST that replaces a part of the divided stream STD selected by the divided stream selection unit SELD. For example, the replacement stream selection unit SELR selects the replacement stream RST based on the selection result received from the split stream selection unit SELD.

  The replacement picture of the replacement stream RST selected by the replacement stream selection unit SELR is, for example, a picture of the divided stream STD before switching as a forward reference image and a picture of the divided stream STD after switching as a backward reference image. Encoded with bi-directional prediction. That is, the replacement stream RST selected by the replacement stream selection unit SELR has a replacement picture encoded using a picture of the divided stream STD before switching and a picture of the divided stream STD after switching as a reference image for bidirectional prediction. ing.

  For example, the divided stream STD selected by the divided stream selection unit SELD corresponds to the divided stream STD after switching. Therefore, the divided stream STD before switching corresponds to the divided stream STD before switching to the divided stream STD selected by the divided stream selection unit SELD. The selection result of the replacement stream selection unit SELR is notified to the replacement stream storage unit MEMR, for example.

  As described above, the replacement stream selection unit SELR receives the combination information of the divided streams STD before and after the switching from the divided stream selection unit SELD. Then, the replacement stream selection unit SELR selects a replacement stream RST that replaces a part of the divided stream STD after switching (part to be replaced) based on the combination information of the divided streams STD before and after switching. Also, the replacement stream selection unit SELR outputs information on the selected replacement stream RST to the replacement stream storage unit MEMR.

  Here, the part to be replaced is a picture preceding the first I picture of the divided stream STD. For example, when the GOP has an IBBP structure, the part to be replaced is the first and second B picture. The B picture is a picture that can use, for example, intra-frame prediction or bidirectional inter-frame prediction (temporal direction prediction). Hereinafter, the replacement picture of the replacement stream RST is also referred to as a B picture without being distinguished from other B pictures.

  The replacement unit REP is an example of a replacement unit that creates a stream STO for distribution. For example, the replacement unit REP replaces a part of the divided stream STD selected by the divided stream selection unit SELD with the replacement stream RST selected by the replacement stream selection unit SELR. As a result, a distribution stream STO corresponding to the network bandwidth is created.

  That is, the replacement unit REP replaces a part of the divided stream STD received from the divided stream storage unit MEMD (for example, the B picture before the first I picture) with the replacement stream RST received from the replacement stream storage unit MEMR. A stream STO for distribution is created. Then, replacement section REP outputs stream STO created by replacing a part of divided stream STD with replacement stream RST to distribution section OPT.

  When the bit rate of the divided stream STD does not change before and after the switching point of the divided stream STD, the replacement unit REP outputs the divided stream STD received from the divided stream storage unit MEMD to the distribution unit OPT as a distribution stream STO. To do. In this case, for example, the replacement unit REP does not perform replacement processing on the segment stream STD.

  Distribution unit OPT distributes stream STO received from replacement unit REP. As described above, the stream distribution system DSYS selects and distributes a stream STO having an appropriate bit rate in accordance with a change in the network bandwidth.

  Note that the configuration of the stream distribution system DSYS is not limited to this example. For example, the divided stream storage unit MEMD may be included in the divided stream selection unit SELD or may be included in the replacement unit REP. Further, the replacement stream storage unit MEMR may be included in the replacement stream selection unit SELR or may be included in the replacement unit REP.

  FIG. 2 shows an example of the divided stream STD and the replacement stream RST created by the stream creation device DGEN shown in FIG. FIG. 2 illustrates an example of the divided stream STD and the replacement stream RST when the bit rate of the stream STO that may be distributed is three of 10 Mbps, 6 Mbps, and 2 Mbps. In the example of FIG. 2, the number of switching points SWP when changing the bit rate of the stream to be distributed is three.

  For example, the dividing unit DIV divides one content stream STIN to be distributed into four in the time direction, and converts each divided stream into three bit rates of 10 Mbps, 6 Mbps, and 2 Mbps. As a result, a 10 Mbps split stream STDa (STDa1-STDa4), a 6 Mbps split stream STDb (STDb1-STDa4), and a 2 Mbps split stream STDc (STDc1-STDc4) are created.

  Also, the replacement stream creation unit RSGEN creates six replacement streams RST including B pictures (replacement pictures B) encoded by bidirectional prediction for each switching point SWP (SWP1-SWP3) of the divided stream STD. . For example, the replacement stream RSTab (RSTab2-RSTab4) is used when switching from the divided stream STDa to the divided stream STDb. Also, the replacement stream RSTac (RSTac2-RSTac4) is used when switching from the divided stream STDa to the divided stream STDc.

  The replacement stream RSTba (RSTba2-RSTba4) is used when switching from the divided stream STDb to the divided stream STDa. The replacement stream RSTbc (RSTbc2-RSTbc4) is used when switching from the divided stream STDb to the divided stream STDc. The replacement stream RSTca (RSTca2-RSTca4) is used when switching from the divided stream STDc to the divided stream STDa. Also, the replacement stream RSTcb (RSTcb2-RSTcb4) is used when switching from the divided stream STDc to the divided stream STDb.

  FIG. 2 shows a replacement stream RST when the GOP has an IBBP structure. Accordingly, each replacement stream RST has two B pictures (replacement picture B). For example, the first two characters at the end of a code such as a B picture Bab correspond to the next character after the code STD of the divided stream STD including the forward reference image. Also, the last two characters at the end of the code such as the B picture Bab correspond to the character next to the code STD of the divided stream STD including the backward reference image.

  Also, the number at the end of the code of each replacement stream RST (RSTac2 etc.) corresponds to the number at the end of the code of the split stream STD (STDa2 etc.) to be replaced. For example, the B picture Bab of the replacement stream RSTab2 is a B picture encoded by bi-directional prediction using the picture of the divided stream STDa1 as a forward reference image and the picture of the divided stream STDb2 as a backward reference image. Also, for example, the B picture Bca of the replacement stream RSTca4 is a B picture encoded by bi-directional prediction using the picture of the divided stream STDc3 as a forward reference picture and the picture of the divided stream STDa4 as a backward reference picture. is there.

  The GOP is not limited to the IBBP structure. For example, the GOP may have an IBP structure. When the GOP has an IBP structure, each replacement stream RST has one B picture, for example.

  FIG. 3 shows an example of the reference relationship of pictures of the divided stream STD. FIG. 3 shows an example of a picture reference relationship when the GOP has an IBBP structure. A comparative example is shown in parentheses in FIG. In the comparative example, the boundary of the divided stream STD is encoded with a closed GOP. On the other hand, in this embodiment, the boundary of the divided stream STD is encoded with an open GOP. The arrangement order of the pictures in FIG. 3 corresponds to the display order of the images.

  The symbol I in the figure indicates an I picture that uses only intra-frame prediction. Hereinafter, I picture I is also referred to as I picture. Also, a symbol Pa in the figure indicates a P picture that can use intra-frame prediction and forward inter-frame prediction (temporal direction prediction). A symbol Baa in the figure indicates a B picture that can use intra-frame prediction or bidirectional inter-frame prediction (temporal direction prediction). A symbol B_a in the figure indicates a B picture in which inter-frame prediction (temporal direction prediction) is limited only in the backward direction.

  In the 10 Mbps split stream STDa, for example, the first two B pictures Baa (the B picture Baa indicated by the bold line in the figure) of the split stream STDa2 are used with the last P picture Pa of the split stream STDa1 as a forward reference image. Yes. The first two B pictures Baa of the divided stream STDa2 use, for example, the first I picture of the divided stream STDa2 as a backward reference image.

  Note that the B picture Baa after the I picture of the divided stream STDa2 (in the figure, the B picture Baa on the right side of the I picture) uses, for example, the first I picture of the divided stream STDa2 as a forward reference image. As described above, in the divided stream STD after the switching point SWP, the picture after the first I picture does not refer to the picture of the divided stream STD before the switching point SWP. Also, the picture of the divided stream STD before the switching point SWP does not refer to the picture of the divided stream STD after the switching point SWP. For example, the last B picture Baa of the divided stream STDa1 uses the last P picture Pa of the divided stream STDa1 as a backward reference image.

  The reference relationship of the pictures of the divided stream STD (for example, 6 Mbps divided stream STDb) of other bit rates is the same as that of the divided stream STDa.

  In the comparative example in which the boundary of the divided stream STD is encoded with closed GOP, for example, the first two B pictures B_a (the B picture B_a indicated by the bold line in the drawing) of the divided stream STDa2 are the pictures of the divided stream STDa1. Do not refer to. For example, the first two B pictures B_a of the divided stream STDa2 use the first I picture of the divided stream STDa2 as a backward reference image. That is, the first two B pictures B_a of the divided stream STDa2 are encoded without using forward prediction.

  Here, the difference in the quality of the decoded image tends to increase between an I picture that uses only intra-frame prediction and a P picture that can use intra-frame prediction and temporal direction prediction. For example, in the closed GOP, the first two B pictures B_a of the divided stream STDa2 do not refer to the P picture Pa of the divided stream STDa1. For this reason, the image quality of the first two B pictures B_a of the divided stream STDa2 is the image quality of a B picture (for example, the first two B pictures Baa of the open GOP divided stream STDa2) encoded by bidirectional prediction. Compared to the image quality of I picture. For this reason, in the comparative example, there is a possibility that a change in image quality at the boundary (for example, the switching point SWP1) of the divided stream STD becomes large.

  On the other hand, in this embodiment, the boundary of the divided stream STD is encoded with an open GOP. For example, in this embodiment, the first two B pictures Baa of the divided stream STDa2 refer to the P picture Pa of the divided stream STDa1 and the I picture of the divided stream STDa2. For this reason, the image quality of the first two B pictures Baa of the divided stream STDa2 is higher than the image quality of the P picture Pa and the image quality of the B picture B_a encoded by backward prediction using only the I picture as a reference image. It approaches the image quality averaged with the picture quality. As a result, the image quality at the boundary (for example, the switching point SWP1) of the divided stream STDa smoothly changes from the last P picture Pa of the divided stream STDa1 to the first I picture of the divided stream STDa2. That is, in this embodiment, it is possible to suppress a change in image quality at the boundary of the divided stream STD.

  FIG. 4 shows an example of the reference relationship of pictures in the replacement stream RST. FIG. 4 shows an example of the reference relationship between the pictures of the replacement streams RSTab2 and RSTac2 shown in FIG. The meaning of the code of each picture is the same as in FIG. 2 or FIG. For example, the symbols Baa, Bbb, Bcc, Bab, and Bac in the figure indicate B pictures that can use intra-frame prediction and bidirectional inter-frame prediction (temporal direction prediction).

  In the replacement stream RSTab2 used when switching from the divided stream STDa1 to the divided stream STDb2, the two B pictures Bab use the last P picture Pa of the divided stream STDa1 as a forward reference image. The two B pictures Bab of the replacement stream RSTab2 use the first I picture of the divided stream STDb2 as a backward reference image.

  In the replacement stream RSTac2 used when switching from the divided stream STDa1 to the divided stream STDc2, the two B pictures Bac use the last P picture Pa of the divided stream STDa1 as a forward reference image. Then, the two B pictures Bac of the replacement stream RSTac2 use the first I picture of the divided stream STDc2 as a backward reference image.

  The reference relationship of the pictures of the other replacement stream RST is the same as that of the divided stream STDa. For example, for the B picture of each replacement stream RST shown in FIG. 2, the last P picture of the divided stream STD corresponding to the first two characters at the end of the B picture code (Bab, etc.) is the forward reference image. It is said. Further, the B picture of each replacement stream RST uses the first I picture of the divided stream STD corresponding to the last two characters at the end of the B picture code (Bab or the like) as a backward reference image.

  As described above, the B picture of the replacement stream RST is encoded using the pictures of the two divided streams STD having different bit rates as reference images for bi-directional prediction. Accordingly, the replacement stream creation unit RSGEN shown in FIG. 1 encodes the B picture of the replacement stream RST after decoding the divided stream STD received from the division unit DIV, for example.

  FIG. 5 shows an example of the data arrangement of the replacement stream RST. FIG. 5 shows an example of the data arrangement of the replacement stream RST when five bit rate divided streams STD are created. For example, the replacement stream RST used when switching from the divided stream STD having a bit rate different from that of the divided stream STDe to the divided stream STDe is selected from the replacement streams RSTAe, RSTbe, RSTce, and RSTde.

  The hatched portion in the figure indicates B picture data, and the black portion indicates multiplexed data and audio data. A shaded portion indicates stuffing data. The multiplexed data is, for example, header data, caption data, private data regardless of usage, and the like. Hereinafter, data that is neither multiplexed data nor audio data (picture data and stuffing data) is also referred to as video data.

  For example, the replacement stream RST includes B picture (replacement picture) data, multiplexed data, audio data, and stuffing data. In each replacement stream RST, stuffing data is inserted so that the information amount (data amount) of the video data portion is the same as the information amount (data amount) of the video data portion to be replaced. For example, the top B picture streams of the divided stream STDe, the replacement stream RSTae, RSTbe, RSTce, and RSTde are created so that the information amount of the video data portion is the same. In addition, for example, the second B picture streams of the divided stream STDe, the replacement stream RSTae, RSTbe, RSTce, and RSTde are created so that the information amount of the video data portion is the same.

  That is, the replacement stream creation unit RSGEN determines the information amount of the video data portion of the first B picture stream of the replacement stream RSTae, RSTbe, RSTce, RSTde, and the information of the video data portion of the first B picture stream of the divided stream STDe. Adjust to the same amount. Similarly, the replacement stream creation unit RSGEN determines the information amount of the video data portion of the second B picture stream of the replacement streams RSTae, RSTbe, RSTce, and RSTde, and the video data of the second B picture stream of the divided stream STDe. Adjust to be the same as the amount of information in the part.

  In this way, the replacement stream creation unit RSGEN makes the information amount of the replacement stream RST the same as the information amount of the part to be replaced in the divided stream STD after the switching point SWP. Also, the multiplexed data and audio data of each replacement stream RST are arranged so as to have the same positional relationship as the multiplexed data and audio data of the B picture stream to be replaced. Thereby, in this embodiment, the stream STO can be created by replacing the stream of the first and second B picture of the divided stream STDe with the replacement stream RST without executing the remultiplexing process.

  Note that the data arrangement of the replacement stream RST is not limited to this example. For example, the replacement stream RST may be created by omitting multiplexed data and audio data. That is, the replacement stream RST may include only video data (picture data and stuffing data). In this case, for example, the replacement unit REP illustrated in FIG. 1 replaces the video data of the divided stream STD with the video data of the replacement stream RST without changing the positions of the multiplexed data and audio data of the divided stream STD.

  Alternatively, the replacement stream RST may include only B picture (replacement picture) data among multiplexed data, audio data, and B picture (replacement picture) data. In this case, for example, the replacement unit REP replaces the video data of the divided stream STD with the picture data of the replacement stream RST without changing the positions of the multiplexed data and audio data of the divided stream STD. Note that, for example, the replacement unit REP inserts stuffing data in a portion where the information amount of video data of the divided stream STD is larger than the information amount of picture data of the replacement stream RST.

  When the replacement stream RST in which the multiplexed data and the audio data are omitted is used, the capacity of the replacement stream storage unit MEMR can be reduced compared to the case where the replacement stream RST including the multiplexed data and the audio data is used. Note that when the replacement stream RST including the multiplexed data and the audio data is used, the replacement process can be simplified as compared with the case where the replacement stream RST in which the multiplexed data and the audio data are omitted is used.

  Further, the information amount of the video data portion of the replacement stream RST may be an information amount different from the replacement target portion of the divided stream STD. In this case, for example, when the replacement unit REP replaces the first B-picture stream and the second B-picture stream of the divided stream STDe with the replacement stream RST, the replacement unit REP executes re-multiplexing processing to create a stream STO.

  FIG. 6 shows an example of stream delivery by the stream delivery system DSYS shown in FIG. In the example of FIG. 6, the divided stream STD and replacement stream RST created based on the content to be distributed are the divided stream STD and replacement stream RST shown in FIG. A segment stream STD and a replacement stream RST in parentheses of the stream STO indicate the segment stream STD and the replacement stream RST selected to distribute the stream STO.

  For example, the stream distribution system DSYS receives band information BINF indicating that the network band is a sufficient band for distributing a stream STO of 10 Mbps before starting distribution. Thus, the stream distribution system DSYS first distributes the 10 Mbps divided stream STDa1 as the stream STOa1.

  At time t10 (time corresponding to the switching point SWP1 shown in FIG. 2), the stream distribution system DSYS switches the stream STO to be distributed to the stream STOb2 of 6 Mbps according to the decrease in the network bandwidth. Thereby, for example, at time t10, the bit rate of the stream STO is switched from 10 Mbps to 6 Mbps. The stream STOb2 is a stream in which, for example, the top two B pictures of the 6 Mbps split stream STDb2 are replaced with the replacement stream RSTab2.

  At time t20 (time corresponding to the switching point SWP2 shown in FIG. 2), the stream distribution system DSYS switches the stream STO to be distributed to the stream STOc3 of 2 Mbps in accordance with the further decrease in the network bandwidth. Thereby, for example, at time t20, the bit rate of the stream STO is switched from 6 Mbps to 2 Mbps. The stream STOc3 is a stream in which, for example, the top two B pictures of the 2 Mbps divided stream STDc3 are replaced with the replacement stream RSTbc3.

  At time t30 (time corresponding to the switching point SWP3 shown in FIG. 2), the stream distribution system DSYS switches the stream STO to be distributed to the stream STOb 4 of 6 Mbps according to the increase in the network bandwidth. Thereby, for example, at time t30, the bit rate of the stream STO is switched from 2 Mbps to 6 Mbps. The stream STOb4 is, for example, a stream in which the top two B pictures of the 6 Mbps divided stream STDb4 are replaced with the replacement stream RSTcb4.

  As described above, the stream distribution system DSYS selects the bit rate of the stream STO to be distributed from three bit rates of 10 Mbps, 6 Mbps, and 2 Mbps according to the change in the network bandwidth. Thereby, in this embodiment, a stream STO having an appropriate bit rate according to the network bandwidth can be distributed. Further, when the bit rate of the stream STO to be distributed is switched, the stream distribution system DSYS replaces the top two B pictures of the divided stream STD after the switching with the replacement stream RST. Thereby, in this embodiment, a change in image quality at the time of stream switching can be suppressed.

  FIG. 7 shows an example of picture replacement during stream distribution. FIG. 7 shows an example of picture replacement when the bit rate of the stream STO is switched from 10 Mbps to 6 Mbps. The arrangement order of the pictures in FIG. 7 corresponds to the display order of the images.

  In the 6 Mbps divided stream STDb2 before picture replacement, the first two B pictures Bbb (the B picture Bbb indicated by a thick line in the figure) are encoded using the picture of the divided stream STDb1 as a forward reference image. Therefore, when the divided stream STDb2 is distributed without executing the picture replacement, the reference images of the first two B pictures Bbb of the divided stream STDb2 are different between when encoded and when decoded. In this case, the decoded image may be deteriorated.

  For this reason, the stream distribution system DSYS replaces the partial stream RSTbb2 including the first two B pictures Bbb in the divided stream STDb2 with the replacement stream RSTab2 determined from the combination of the divided streams STD before and after switching. As a result, a stream STOb2 for distribution is created. That is, the stream distribution system DSYS creates a stream STOb2 by replacing the stream RSTbb2 of the first two B pictures Bbb of the divided stream STDb2 with the replacement stream RSTab2.

  For example, in the 6 Mbps stream STOb2 after the picture replacement, the first two B pictures Bab (the B picture Bab indicated by a bold line in the figure) uses the last P picture Pa of the stream STOa1 as a forward reference image. In the first two B pictures Bab of the stream STOb2, for example, the first I picture of the stream STOb2 is used as a backward reference image.

  As described above, in the stream STOb2 in which the picture replacement has been performed, the reference images of the first two B pictures Bab are the same at the time of encoding and at the time of decoding. For this reason, in this embodiment, it is possible to prevent the decoded image from deteriorating when the bit rate of the stream STO is switched. In this embodiment, since the first two B pictures Bab of the stream STOb2 are encoded by bidirectional prediction, the image quality is smooth from the last P picture Pa of the stream STOa1 to the first I picture of the stream STOb2. To change. That is, in this embodiment, it is possible to suppress a change in image quality when switching streams.

  FIG. 8 shows an example of the operation of the stream creation device DGEN shown in FIG. The operation shown in FIG. 8 is an embodiment of the operation method of the stream creation device.

  In step S100, the dividing unit DIV divides the content to create a divided stream STD. For example, the dividing unit DIV receives the stream STIN of the content to be distributed from the outside of the stream creation device DGEN. The dividing unit DIV then divides the content stream STIN with the stream bit rate switching point SWP as a boundary. Then, the dividing unit DIV converts each divided stream into all the bit rates included in the selection candidates when selecting the bit rate at the time of distribution. As a result, a plurality of divided streams STD are created for each stream bit rate switching point SWP.

  Note that the boundary of the divided stream STD is encoded with an open GOP. The divided stream STD created in step S100 is transferred to, for example, the replacement stream creation unit RSGEN and the divided stream storage unit MEMD of the stream distribution system DSYS. For example, the replacement stream creation unit RSGEN holds the divided stream STD transferred from the division unit DIV while it is used to create the replacement stream RST. Further, for example, the divided stream storage unit MEMD stores all the divided streams STD transferred from the division unit DIV.

  In step S110, the replacement stream creation unit RSGEN creates a replacement stream RST including a replacement picture obtained by encoding a picture of the divided stream STD before and after the switching point SWP as a reference image for bidirectional prediction. For example, the replacement stream creation unit RSGEN creates, for each bit rate switching point SWP of the stream, the number of replacement streams RST corresponding to the number of combinations of the divided streams STD before and after the switching point SWP.

  That is, the replacement stream creation unit RSGEN creates a replacement stream RST corresponding to all combinations of split streams STD that may be distributed. The replacement stream RST created in step S110 is transferred to, for example, the replacement stream storage unit MEMR of the stream distribution system DSYS.

  In this way, the divided stream STD encoded by the open GOP and the replacement stream RST for replacing the picture preceding the first I picture of the divided stream STD are created. By creating a stream STO for distribution using the divided stream STD and the replacement stream RST, a change in image quality at the time of stream switching is suppressed. Therefore, in this embodiment, a change in image quality at the time of stream switching can be suppressed.

  FIG. 9 shows an example of the operation of the stream distribution system DSYS shown in FIG. The operation illustrated in FIG. 9 is an embodiment of the operation method of the stream distribution system.

  In step S200, the segment stream selection unit SELD selects the segment stream STD to be distributed based on the band information BINF. The selection result is notified to, for example, the divided stream accumulation unit MEMD and the replacement stream selection unit SELR. For example, the divided stream storage unit MEMD selects the divided stream STD according to the selection result received from the divided stream selection unit SELD. Then, the divided stream accumulation unit MEMD outputs the selected divided stream STD to the replacement unit REP. That is, the divided stream storage unit MEMD outputs the divided stream STD determined by the divided stream selection unit SELD to the replacement unit REP.

  In step S210, the segment stream selection unit SELD determines whether or not replacement is necessary. For example, the divided stream selection unit SELD determines whether or not to switch the bit rate of the stream STO before and after the switching point SWP of the divided stream STD. When the bit rate of the stream STO is switched, it is determined that replacement is necessary. If the bit rate of the stream STO does not change before and after the switching point SWP, it is determined that no replacement is necessary.

  When replacement is necessary (Yes in step S210), the operation of the stream distribution system DSYS moves to step S220. On the other hand, when the replacement is not necessary (No in step S210), the operation of the stream distribution system DSYS moves to the process S230. Note that the fact that the replacement is not necessary is notified to the replacement stream selection unit SELR and the replacement unit REP, for example.

  In step S220, the replacement unit REP replaces a part (part to be replaced) of the divided stream STD selected in step S200 with the replacement stream RST. For example, the replacement stream selection unit SELR selects the replacement stream RST based on the selection result received from the segment stream selection unit SELD. The selection result is notified to the replacement stream storage unit MEMR, for example.

  For example, the replacement stream storage unit MEMR selects the replacement stream RST according to the selection result received from the replacement stream selection unit SELR. Then, the replacement stream accumulation unit MEMR outputs the selected replacement stream RST to the replacement unit REP. Further, the replacement unit REP replaces a part (part to be replaced) of the divided stream STD transferred from the divided stream storage unit MEMD with the replacement stream RST transferred from the replacement stream storage unit MEMR.

  That is, when replacement is necessary, the replacement stream selection unit SELR selects the replacement stream RST based on the combination of the divided streams STD before and after the switching point SWP. Then, the replacement unit REP replaces a part (part to be replaced) of the divided stream STD selected by the divided stream selection unit SELD with the replacement stream RST selected by the replacement stream selection unit SELR. Thereby, a stream STO for distribution is created. Then, the replacement unit RST outputs the created stream STO to the distribution unit OPT.

  In step S230, the distribution unit OPT distributes the stream STO received from the replacement unit REP. For example, when replacement is necessary, the distribution unit OPT distributes the stream STO created in step S220. When the replacement is not necessary, the replacement unit REP outputs the divided stream STD selected in step S200 to the distribution unit OPT as the stream STO. That is, when the replacement is not necessary, the distribution unit OPT receives the divided stream STD selected in step S200 via the replacement unit REP. Therefore, when the replacement is not necessary, the distribution unit OPT distributes the divided stream STD selected in step S200 as the stream STO.

  In step S240, the stream distribution system DSYS determines whether or not the content distribution has been completed. When the content distribution is not completed (No in step S240), the operation of the stream distribution system DSYS returns to step S200. On the other hand, when the content distribution is completed (Yes in step S240), the stream distribution by the stream distribution system DSYS ends.

  Thus, when the bit rate of the stream STO is switched, the stream distribution system DSYS replaces a part of the divided stream STD with the replacement stream RST, and creates the switched stream STO. Thereby, in this embodiment, even when the bit rate of the stream STO is switched, the reference image can be made the same at the time of encoding and at the time of decoding. For this reason, in this embodiment, it is possible to prevent the decoded image from deteriorating when the bit rate of the stream STO is switched.

  As described above, in the embodiment illustrated in FIGS. 1 to 9, the stream creation unit DGEN includes the division unit DIV and the replacement stream creation unit RSGEN. The permutation stream creation unit RSGEN creates a permutation stream RST including a permutation picture in which the pictures of the divided streams STD before and after the switching point SWP are encoded as reference pictures for bi-directional prediction for each bit rate switching point SWP of the stream STO. To do. For example, as many replacement streams RST as the number of combinations of the divided streams STD before and after the switching point SWP are created.

  In addition, the stream distribution system DSYS of this embodiment includes a divided stream selection unit SELD, a divided stream storage unit MEMD, a replacement stream selection unit SELR, a replacement stream storage unit MEMR, a replacement unit REP, and a distribution unit OPT. The segment stream selection unit SELD selects a segment stream STD to be distributed from segment streams STD having different bit rates. The replacement stream storage unit MEMR holds a plurality of replacement streams RST created for each bit rate switching point SWP of the stream STO. When the bit rate of the stream STO is switched, the replacement stream selection unit SELR selects a replacement stream including a replacement picture that is encoded using the pictures of the divided streams STD before and after the switching point SWP as reference images for bidirectional prediction. The replacement unit REP replaces a part of the divided stream STD selected by the divided stream selection unit SELD with the replacement stream RST selected by the replacement stream selection unit SELR, and creates a distribution stream STO.

  Thereby, in this embodiment, the reference image of the picture of the stream STO for distribution can be made the same at the time of encoding and at the time of decoding. Therefore, in this embodiment, it is possible to prevent the decoded image from deteriorating when the bit rate of the stream STO is switched. In this embodiment, a picture before the first I picture of the stream STO is encoded by bidirectional prediction. Therefore, in this embodiment, before and after the switching point SWP, the image quality smoothly changes from the last P picture of the stream STO before the switching point SWP to the first I picture of the stream STO after the switching point SWP. That is, in this embodiment, it is possible to suppress a change in image quality when switching streams.

  FIG. 10 is a diagram showing another embodiment of the stream distribution system. The dashed arrows in FIG. 10 indicate the flow of signals and the like. In the stream distribution system DSYS2 of this embodiment, a dividing unit DIV and a replacement stream creating unit RSGEN2 are added to the stream distribution system DSYS shown in FIG. The other configuration of the stream distribution system DSYS2 is the same as that of the stream distribution system DSYS shown in FIG. The same elements as those described in FIGS. 1 to 9 are denoted by the same reference numerals, and detailed description thereof will be omitted.

  The stream distribution system DSYS2 includes, for example, a division unit DIV, a replacement stream creation unit RSGEN2, a divided stream storage unit MEMD, a replacement stream storage unit MEMR, a divided stream selection unit SELD, a replacement stream selection unit SELR, a replacement unit REP, and a distribution unit OPT. Have.

  The dividing unit DIV is the same as the dividing unit DIV shown in FIG. 1 except for the output destination of the divided stream STD. For example, the dividing unit DIV receives the stream STIN of the content to be distributed, and outputs the divided stream STD to the divided stream storage unit MEMD. The divided stream STD created by the dividing unit DIV is the same as the divided stream STD of the embodiment described with reference to FIGS.

  The replacement stream creation unit RSGEN2 is the same as the replacement stream creation unit RSGEN shown in FIG. 1 except that it receives the split stream STD from the split stream storage unit MEMD. For example, the replacement stream creation unit RSGEN2 receives the divided stream STD from the divided stream storage unit MEMD, and creates a replacement stream RST for each switching point SWP of the divided stream STD.

  The replacement stream RST generated by the replacement stream generation unit RSGEN2 is the same as the replacement stream RST of the embodiment described with reference to FIGS. For example, the replacement stream RST includes a replacement picture obtained by encoding the pictures of the divided stream STD before and after the switching point SWP as a bi-directional prediction reference image. In addition, for example, as many replacement streams RST as the number of combinations of the divided streams STD before and after the switching point SWP are created.

  The operation of the stream distribution system DSYS2 is the same as the operation described in FIGS. 8 and 9, for example. For example, the operations of the division unit DIV and the replacement stream creation unit RSGEN2 are illustrated in FIG. 8 by replacing the replacement stream creation unit RSGEN with the replacement stream creation unit RSGEN2. The operations of the divided stream storage unit MEMD, the replacement stream storage unit MEMR, the divided stream selection unit SELD, the replacement stream selection unit SELR, the replacement unit REP, and the distribution unit OPT will be described with reference to FIG.

  Note that the configuration of the stream distribution system DSYS2 is not limited to this example. For example, the stream distribution system DSYS2 may include the replacement stream creation unit RSGEN illustrated in FIG. 1 instead of the replacement stream creation unit RSGEN2. That is, the stream creation device DGEN may be included in the stream distribution system DSYS shown in FIG.

  As described above, also in the embodiment described with reference to FIG. 10, the same effects as those of the embodiment described with reference to FIGS. 1 to 9 can be obtained. For example, in this embodiment, a change in image quality at the time of stream switching can be suppressed. Furthermore, in this embodiment, the stream distribution system DSYS2 includes a replacement stream creation unit RSGEN2. Thereby, the replacement stream creating unit RSGEN2 can use the divided stream STD held in the divided stream storage unit MEMD when creating the replacement stream RST. Therefore, in this embodiment, the capacity of the storage unit in the replacement stream creation unit RSGEN2 can be reduced.

The invention described in the above embodiments is organized and disclosed as an appendix.
(Appendix 1)
A first selection unit that selects a first stream to be distributed from a plurality of first streams having different bit rates created for each stream obtained by dividing a content stream in a time direction;
A first holding unit for holding a plurality of replacement streams created for each bit rate switching point of the first stream;
The picture of the first stream before switching to the first stream selected by the first selection unit is a forward reference image, and the picture of the first stream selected by the first selection unit is backward A second selection unit that selects, from the plurality of replacement streams, a replacement stream including a replacement picture encoded by bi-directional prediction as a reference image;
A replacement unit that replaces a part of the first stream selected by the first selection unit with the replacement stream selected by the second selection unit, and creates a stream for distribution. Stream delivery system.
(Appendix 2)
In the stream distribution system according to attachment 1,
Creation of the replacement stream including the replacement picture in which the pictures of the first stream before and after the switching point are encoded as bi-directional prediction reference images for each combination of the first streams before and after the switching point The stream delivery system characterized by having a part.
(Appendix 3)
In the stream distribution system according to Supplementary Note 1 or Supplementary Note 2,
An information amount of the replacement stream is the same as the partial information amount of the first stream.
(Appendix 4)
In the stream distribution system according to Supplementary Note 1 or Supplementary Note 2,
The stream distribution system, wherein the replacement stream includes only the replacement picture among multiplexed data, audio data, and the replacement picture.
(Appendix 5)
In the stream distribution system according to any one of supplementary notes 1 to 3,
The stream distribution system, wherein the replacement stream includes multiplexed data, audio data, and the replacement picture.
(Appendix 6)
Receiving a plurality of first streams having different bit rates created for each stream obtained by dividing the content stream in the time direction, the first stream before and after the switching point at each switching point of the bit rate of the first stream A stream creation apparatus comprising: a creation unit that creates a replacement stream including a replacement picture obtained by encoding, as a bi-predictive reference image, pictures of the first stream before and after the switching point for each combination .
(Appendix 7)
In the stream creation device according to attachment 6,
The stream creation device characterized in that the creation unit makes the information amount of the replacement stream the same as the information amount of a part to be replaced in the first stream after the switching point.
(Appendix 8)
In the stream creation device according to attachment 6,
The stream creation apparatus, wherein the replacement stream includes only the replacement picture among multiplexed data, audio data, and the replacement picture.
(Appendix 9)
In the stream creation device according to appendix 6 or appendix 7,
The stream creation device, wherein the replacement stream includes multiplexed data, audio data, and the replacement picture.
(Appendix 10)
The first stream to be distributed is selected from a plurality of first streams having different bit rates created for each stream obtained by dividing the content stream in the time direction,
Holding a plurality of replacement streams created for each bit rate switching point of the first stream;
The picture of the first stream before switching to the selected first stream is a forward reference picture, and the selected picture of the first stream is a backward reference picture and is encoded by bidirectional prediction. Selecting a replacement stream including the replaced picture from the plurality of replacement streams;
A stream delivery method, wherein a part of the selected first stream is replaced with the selected replacement stream to create a delivery stream.
(Appendix 11)
In the stream delivery method according to attachment 10,
For each combination of the first streams before and after the switching point, create the replacement stream including the replacement picture obtained by encoding the pictures of the first stream before and after the switching point as a reference image for bidirectional prediction. Stream delivery method characterized by the above.
(Appendix 12)
In the stream delivery method according to appendix 10 or appendix 11,
An information amount of the replacement stream is the same as the partial information amount of the first stream.
(Appendix 13)
In the stream delivery method according to appendix 10 or appendix 11,
The stream distribution method, wherein the replacement stream includes only the replacement picture among multiplexed data, audio data, and the replacement picture.
(Appendix 14)
In the stream distribution method according to any one of appendix 10 to appendix 12,
The stream distribution method, wherein the replacement stream includes multiplexed data, audio data, and the replacement picture.
(Appendix 15)
Receiving a plurality of first streams having different bit rates created for each stream obtained by dividing the content stream in the time direction, the first stream before and after the switching point at each switching point of the bit rate of the first stream A stream creation method, comprising: for each combination, a replacement stream including a replacement picture obtained by encoding a picture of the first stream before and after the switching point as a reference image for bidirectional prediction.
(Appendix 16)
In the stream creation method according to attachment 15,
The stream creation method characterized in that the information amount of the replacement stream is the same as the information amount of the part to be replaced in the first stream after the switching point.
(Appendix 17)
In the stream creation method according to attachment 15,
The stream creation method, wherein the replacement stream includes only the replacement picture among multiplexed data, audio data, and the replacement picture.
(Appendix 18)
In the stream creation method according to supplementary note 15 or supplementary note 16,
The stream creation method, wherein the replacement stream includes multiplexed data, audio data, and the replacement picture.

  From the above detailed description, features and advantages of the embodiments will become apparent. This is intended to cover the features and advantages of the embodiments described above without departing from the spirit and scope of the claims. Also, any improvement and modification should be readily conceivable by those having ordinary knowledge in the art. Therefore, there is no intention to limit the scope of the inventive embodiments to those described above, and appropriate modifications and equivalents included in the scope disclosed in the embodiments can be used.

  DIV: Dividing unit; DSYS, DSYS2: Stream distribution system; MEMD: Divided stream accumulating unit; MEMR: Replacement stream accumulating unit; OPT ... Distributing unit; REP ... Substituting unit; RSGEN, RSGEN2 ... Substitution stream creating unit; Selection part; SELR ... Replacement stream selection part

Claims (8)

A first selection unit that selects a first stream to be distributed from a plurality of first streams having different bit rates created for each stream obtained by dividing a content stream in a time direction;
A first holding unit for holding a plurality of replacement streams created for each bit rate switching point of the first stream;
The picture of the first stream before switching to the first stream selected by the first selection unit is a forward reference image, and the picture of the first stream selected by the first selection unit is backward A second selection unit that selects, from the plurality of replacement streams, a replacement stream including a replacement picture encoded by bi-directional prediction as a reference image;
A replacement unit that replaces a part of the first stream selected by the first selection unit with the replacement stream selected by the second selection unit, and creates a stream for distribution. Stream delivery system. The stream distribution system according to claim 1, wherein
Creation of the replacement stream including the replacement picture in which the pictures of the first stream before and after the switching point are encoded as bi-directional prediction reference images for each combination of the first streams before and after the switching point The stream delivery system characterized by having a part. In the stream delivery system according to claim 1 or 2,
An information amount of the replacement stream is the same as the partial information amount of the first stream. In the stream delivery system according to claim 1 or 2,
The stream distribution system, wherein the replacement stream includes only the replacement picture among multiplexed data, audio data, and the replacement picture. In the stream delivery system according to any one of claims 1 to 3,
The stream distribution system, wherein the replacement stream includes multiplexed data, audio data, and the replacement picture.   Receiving a plurality of first streams having different bit rates created for each stream obtained by dividing the content stream in the time direction, the first stream before and after the switching point at each switching point of the bit rate of the first stream A stream creation apparatus comprising: a creation unit that creates a replacement stream including a replacement picture obtained by encoding, as a bi-predictive reference image, pictures of the first stream before and after the switching point for each combination . The first stream to be distributed is selected from a plurality of first streams having different bit rates created for each stream obtained by dividing the content stream in the time direction,
Holding a plurality of replacement streams created for each bit rate switching point of the first stream;
The picture of the first stream before switching to the selected first stream is a forward reference picture, and the selected picture of the first stream is a backward reference picture and is encoded by bidirectional prediction. Selecting a replacement stream including the replaced picture from the plurality of replacement streams;
A stream delivery method, wherein a part of the selected first stream is replaced with the selected replacement stream to create a delivery stream.   Receiving a plurality of first streams having different bit rates created for each stream obtained by dividing the content stream in the time direction, the first stream before and after the switching point at each switching point of the bit rate of the first stream A stream creation method, comprising: for each combination, a replacement stream including a replacement picture obtained by encoding a picture of the first stream before and after the switching point as a reference image for bidirectional prediction.

Images