JP2007221597A - Stream receiver and stream reception method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress occurrence of overflow or underflow in a buffer for accumulating stream data, even in a system where a stream transmission rate at a transmission side cannot be controlled on the reception side, by eliminating the need for controlling the transmission rate at the transmission side in a configuration, wherein a decoding speed is controlled in accordance with a state of the buffer for accumulating stream data at a stream data receiving side. <P>SOLUTION: A buffer 111 temporarily accumulates received stream data. A decoder 112 decodes the stream data. A control unit 113 accelerates the decoding speed, if it is decided, based on the amount of change in the amount of stream data accumulated in the buffer 111, that the accumulated amount tends to increase, and decelerates the decoding speed, if it is decided that the amount of stream data accumulated in the buffer 111 tends to decrease. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a stream receiving apparatus and a stream receiving method, and more particularly to a stream receiving apparatus and a stream receiving method using a streaming technology for reproducing data such as audio or moving images while receiving the data via a network.

  The streaming technology is a technology for delivering data that requires real-time performance such as audio or moving images via a network and performing reproduction while delivering the data. Streaming technology allows playback without downloading all data, eliminating the need for a large-capacity storage device on the receiving side, and speeding from the start of delivery to the start of playback compared to a method that downloads all data. There is a feature that can be.

  However, since the clock of the stream data transmission side (stream server) and the clock of the stream data reception side (client) are not completely synchronized, the rate at which the stream data transmission side (stream server) performs delivery, There is a slight difference in the rate at which the stream data receiving side (client) performs playback. Due to this clock difference, there is a problem that an overflow or underflow of the reception buffer of stream data occurs. In addition, this problem is likely to occur particularly when reproduction is performed for a long time. In addition, when the stream data transmission side uses the wireless network to deliver the stream data, an overflow or underflow of the stream data reception buffer occurs due to the unstable wireless propagation environment. There are challenges.

  As a prior art for solving this, there is, for example, Patent Document 1. FIG. 21 is a diagram showing the configuration of the stream delivery system disclosed in Patent Document 1. As shown in FIG. In FIG. 21, the stream server 10 is connected to the client 20 via the network 30. A disk 12 for storing stream data is connected to the stream server 10. Further, the stream server 10 includes a delivery server 11 that executes reading and delivery of stream data. The client 20 is connected to a display 22 that outputs an image and a speaker 23 that outputs sound. In the client 20, a playback application 21 that executes reception and playback of stream data is activated.

  Next, the operation of the stream delivery system in Patent Document 1 will be described. The playback application 21 on the client 20 transmits a stream delivery start request via the network 30 to the delivery server 11 on the stream server 10 (ST40). Upon receiving the stream delivery start request, the delivery server 11 sequentially reads the stream data from the disk 12 (ST41) and delivers the stream data to the playback application 21 (ST42). The reproduction application 21 receives the stream data and reproduces the received stream data sequentially on the display 22 and the speaker 23 (ST43).

  The countermeasure in Patent Document 1 for the problem of buffer overflow and underflow will be described below.

  The stream server 10 includes rate change delivery means (not shown) capable of changing the delivery rate of stream data and delivering it. The rate change delivery means is configured to be changeable depending on or not depending on a bit rate (unique bit rate) that is a transmission rate unique to stream data.

  The client 20 uses request rate determination means (not shown) for determining an optimum delivery rate requested from the stream server 10 using the difference between the reception rate of the stream data delivered by the stream server and the specific bit rate. And request rate notifying means (not shown) for notifying the stream server 10 of the delivery rate determined by the request rate determining means.

When the amount of stream data (buffer amount) in the buffer for storing stream data decreases or increases, the client 20 sends a delivery rate change request to the stream server 10, which is desirable for the stream server 10. Request to change to rate (matching rate). Upon receiving the delivery rate change request, the stream server 10 changes the delivery rate to the requested matching rate. With this configuration, in Patent Document 1, buffer overflow and underflow are prevented.
JP 2000-228669 A

  However, in the conventional configuration, the stream data reception side (client) issues a request to the stream data transmission side (stream server) to change the delivery rate, which is the stream data transmission rate, and performs control. There is a problem that it can be applied only to a system that can do this.

  The present invention has been made in view of such points, and it is necessary for the stream data receiving side to control the decoding speed in accordance with the state of the buffer that stores the stream data, and to control the transmission rate on the transmitting side. By providing the stream receiving apparatus, a stream receiving apparatus and a stream receiving method capable of suppressing the occurrence of overflow or underflow of a buffer for storing stream data even in a system in which the receiving side cannot control the stream sending rate on the transmitting side are provided. The purpose is to do.

  The stream receiving apparatus of the present invention includes a receiving unit that receives distributed stream data, a storage unit that temporarily stores the received stream data, a decoding unit that decodes the stored stream data, The decoding speed is increased when it is determined that the accumulation amount is increasing based on the amount of change in the accumulation amount of the stream data, and the decoding is performed when it is determined that the accumulation amount is decreasing. And a control means for slowing down the speed.

  The stream reception method of the present invention includes a reception step for receiving distributed stream data, a storage step for temporarily storing the received stream data, a decoding step for decoding the stored stream data, and a storage step. Further, the decoding speed is increased when it is determined that the accumulation amount is increasing based on the change amount of the stream data accumulation amount, and the decoding speed is decreased when the accumulation amount is decreasing. And a control step.

  According to the present invention, since the stream data receiving side is configured to control the decoding speed in accordance with the amount of change in the stream data accumulation amount in the accumulation means, it is not necessary to control the transmission rate on the transmission side. Even in a system in which the receiving side cannot control the stream transmission rate of the transmitting side, it is possible to suppress the occurrence of overflow or underflow of a buffer for storing stream data.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a diagram showing a streaming network system 100 according to Embodiment 1 of the present invention. The streaming network system 100 includes a stream reception / playback apparatus (client) 101, a server 102, and a network 103. In FIG. 1, the network 103 is a wireless network, but is not limited to this, and may be a wired network.

  The stream reception / playback apparatus 101 includes a communication unit 110, a buffer 111, a decoder 112, and a control unit 113. The server 102 includes a control unit 120, a stream data transmission unit 121, and a communication unit 122.

  First, the configuration of the stream reception / playback apparatus 101 will be described.

  The communication unit 110 receives stream data representing content such as music, for example, via the network 103 and outputs the received stream data to the buffer 111.

  A buffer 111 serving as storage means temporarily stores stream data input from the communication unit 110. Then, the buffer 111 outputs the accumulated stream data to the decoder 112.

  The decoder 112 decodes the stream data input from the buffer 111 at a speed controlled by the control unit 113 and outputs the decoded data to the speaker 114.

  The control unit 113 calculates the change amount of the accumulation amount of the stream data accumulated in the buffer 111, and controls the speed at which the decoder 112 decodes the stream data based on the calculated change amount. Specifically, when the control unit 113 determines that the accumulation amount tends to increase based on the change amount of the accumulation amount of the stream data accumulated in the buffer 111, the control unit 113 determines the decoding speed to the decoder 112. If the accumulation amount is determined to be decreasing based on the change amount of the accumulation amount of the stream data accumulated in the buffer 111, the decoding speed is decreased with respect to the decoder 112. Control to do.

  The speaker 114 outputs music or the like represented by the stream data input from the decoder 112 to the outside.

  Next, the configuration of the server 102 will be described.

  The control unit 120 controls the stream data transmission unit 121.

  The stream data sending unit 121 outputs the stream data to the communication unit 122 based on the control of the control unit 120.

  The communication unit 122 transmits the stream data input from the stream data transmission unit 121 to the stream reception / playback apparatus 101 via the network 103.

  The operation of the streaming network system 100 configured as described above will be described with reference to FIG. FIG. 2 is a flowchart showing the operation of the streaming network system 100.

  In the basic operation of normal streaming playback, the stream reception / playback apparatus 101 starts receiving stream data via the wireless network 103 (step ST201), and stores the stream data received within a certain time (for example, Tini) in the buffer 111. (Step ST202). Note that the stream reception / playback apparatus 101 is not limited to the case where the stream data received within a certain time is stored in the buffer 111, but the stream reception / playback apparatus 101 may be configured to store a certain amount of stream data in the buffer 111. good. When the fixed time Tini elapses or a certain amount of stream data is accumulated in the buffer 111, the control unit 113 instructs the decoder 112 to start decoding, and the decoder 112 receives an instruction from the control unit 113. In response to this, the decoding of the stream data stored in the buffer 111 is started, and the decoded stream data is supplied to the speaker 114. In this way, the stream reception / playback apparatus 101 plays back the stream data, and the music represented by the received stream data starts to sound from the speaker 114.

  During the reproduction of the stream data, the control unit 113 periodically measures the amount of stream data stored in the buffer 111 (hereinafter referred to as “remaining buffer amount”) and based on the measured remaining buffer amount. The amount of change in the remaining buffer amount is periodically calculated and stored (step ST203). The control unit 113 determines whether or not the number of calculations of the remaining buffer amount change amount has reached a predetermined value (step ST204). If the number of calculations has not reached the predetermined value, the processing of steps ST201 to ST204 is performed. repeat. On the other hand, in step ST204, when the number of calculations reaches a predetermined value, the control unit 113 obtains an average value of the amount of change in the remaining buffer amount (step ST205).

  Then, based on the obtained average value, the control unit 113 determines whether or not the amount of change in the remaining buffer amount is increasing (step ST206). The decoding speed is increased (step ST207). In step ST206, the control unit 113 determines whether or not the trend is decreasing when it is determined that the trend is not increasing (step ST208), and the decoder 112 performs decoding when it is determined that the trend is decreasing. The speed is decreased (step ST209). Subsequently, after the decoding speed is increased in step ST207, the decoding speed is decreased in step ST209, or when it is determined in step ST208 that there is no tendency to decrease, the stream reception / playback apparatus 101 finishes receiving the stream data (Step ST210), the operation is stopped when it is determined that the reception of the stream data is completed, and the steps ST201 to ST210 are determined when it is determined that the reception of the stream data is not completed. Repeat the process.

  Next, details of a method by which the control unit 113 determines whether the amount of change in the remaining buffer amount is increasing or decreasing will be described with reference to FIGS. 3 is a diagram showing the time transition of the remaining buffer amount, FIG. 4 is a diagram showing the state of the buffer 111 at each time, and FIG. 5 is a diagram showing the time transition of the decoding speed. FIG. 6 is a diagram illustrating the time transition of the remaining buffer amount.

  As shown in FIG. 3, the control unit 113 measures and stores the remaining buffer amount for each predetermined time Tc with reference to the reference time T0. The control unit 113 calculates and stores the amount of change in the remaining buffer amount every time the fixed time Tc elapses from the reference time T0. Specifically, the control unit 113 calculates the change amount ΔD1 of the remaining buffer amount at time T1 (T1 = T0 + Tc), that is, the change amount ΔD1 of the remaining buffer amount from time T0 to time T1. Subsequently, the control unit 113 calculates a change amount ΔD2 of the remaining buffer amount at time T2 (T2 = T1 + Tc), that is, a change amount ΔD2 of the remaining buffer amount at time T2 when a certain time Tc has elapsed from time T1. Thereafter, the control unit 113 calculates the amount of change in the remaining buffer amount every time the predetermined time Tc elapses from the previous calculation time until it is determined Yes in step ST210.

  Here, when the network 103 is a wireless network, packet loss or retransmission due to radio wave conditions or the like is likely to occur, so the remaining buffer amount is likely to change. In order to suppress the occurrence frequency of overflow or underflow of the buffer 111 due to the clock difference while eliminating these influences as much as possible, the control unit 113 sets the average value of a plurality of changes in the remaining buffer amount in the buffer 111. Based on this, the change tendency of the remaining buffer amount is determined.

  FIG. 4 is a diagram illustrating the state of the buffer 111 at times T0 to T6 as an example of FIG. As shown in FIG. 4, the control unit 113 measures the amount of change in the remaining buffer amount for a predetermined number of times (six times in FIG. 4) within a measurement time (time from time T0 to time T6) that is a fixed time. Then, the average value ΔD of the change amount of the remaining buffer amount for the predetermined number of times measured (six times in FIG. 4) is calculated, and whether the change amount of the remaining buffer amount is increasing based on the calculated average value ΔD. Or it is judged whether it is decreasing. Here, in the following description, the measurement time for calculating the average value is set to N × Tc. Then, the control unit 113 adds the number obtained by dividing the average value ΔD of the time from the time T0 to the time T6 by the unit time Tc to the decoding speed Rout of the time from the time T0 to the time T6. To correct. In the next measurement time (time from time T7 to time T12), the decoder 112 decodes at the corrected decoding speed.

  For example, when the decoding speed of the decoder 112 is Rout = 40 Kbyte / Sec (= 320 Kbps), the average value ΔD of the amount of change in the remaining buffer amount at a certain time Tc (10 seconds) is ΔD as shown in FIG. = -0.5 Kbytes. Further, the control unit 113 calculates Rout + ΔD / Tc as a new decoding speed so as to cancel the average value ΔD of the change amount of the remaining buffer amount. In the case of FIG. 4, since the polarity of the average value ΔD of the calculated change amount of the remaining buffer amount is negative, the control unit 113 determines that the remaining buffer amount is in a decreasing tendency and slows down the decoding speed. The decoder 112 is controlled. That is, the control unit 113 changes the decoding speed after time T6 to the newly calculated decoding speed, that is, 40 + (− 0.5) /10=39.95 Kbyte / Sec (= 319.6 Kbps). The decoder 112 is controlled. As a result, as shown in FIG. 5, the time decoding speed from time Tn to time Tn2 is only ΔD / Tc = −0.05 Kbyte / Sec than the time decoding speed Rout from time T0 to time Tn. Become slow. Then, by reducing the decoding speed Rout by ΔD / Tc, as shown in FIG. 6, the remaining buffer amount from time Tn to time Tn2 is reduced by ΔD from the remaining buffer amount at time T0. It stays constant at.

  In this way, after time Tn, decoding and playback are performed with the decoding speed slower than the time from time T0 to time Tn, so that the tendency of the remaining buffer amount to decrease can be suppressed. In addition, in FIGS. 3 to 6, the case where the change amount of the remaining buffer amount tends to decrease has been described. However, when the change amount of the remaining buffer amount tends to increase, it is the opposite of the case where the change amount is decreasing. Take control. By repeating such control, after the time Tn, the frequency of occurrence of overflow or underflow of the buffer 111 due to the clock difference and the radio propagation environment can be suppressed.

  Incidentally, even when the decoding speed is controlled by the control unit 113, there is a possibility that an overflow or underflow of stream data occurs. In the case of an overflow, in the case of audio, a problem in audibility occurs depending on the stream data that has overflowed. Therefore, when a predetermined amount or more of stream data is accumulated in the buffer 111, some stream data that does not cause a problem in audibility Process to delete. In addition, since the sound is heard as noise in the case of an underflow, the decoding is stopped during a period from when the accumulated amount of stream data in the buffer 111 becomes equal to or less than a predetermined amount until some stream data is accumulated. Inform the user that decoding is stopped. As a result, it is possible to prevent stream data from being output as unbearable sound.

  As described above, according to the first embodiment, it is not necessary to control the transmission rate on the transmission side by controlling the decoding speed of the decoder 112 according to the amount of change in the remaining buffer amount. Even in a system in which the transmission rate cannot be controlled, the occurrence of overflow or underflow of a buffer that accumulates stream data can be suppressed.

  In the first embodiment, the control unit 113 measures the amount of change in the remaining buffer amount every time 10 sec elapses. However, the control unit 113 is not limited to this, and the control unit 113 has a time T1 = 10 sec, a time T2 = 30 sec, etc. The change amount of the remaining buffer amount may be measured at different time intervals. Further, according to the first embodiment, it is determined whether the trend is increasing or decreasing based on the average value of the change amount of the remaining buffer amount, but not limited to this, the change amount of the remaining buffer amount is calculated. You may judge every time whether it is an increasing tendency or a decreasing tendency.

(Embodiment 2)
FIG. 7 is a flowchart showing the operation of the streaming network system 100. In FIG. 7, parts that are the same as those in FIG. The streaming network system according to Embodiment 2 of the present invention is the same as that shown in FIG. 1, and the configuration of the stream reception / playback apparatus (client) and server is the same as that shown in FIG.

  In the second embodiment, in the case where the network 103 is a wireless network, in order to extract only the influence of the buffer overflow or underflow due to the clock difference, the remaining buffer amount due to the packet loss or retransmission due to the radio wave condition Eliminate sudden changes. That is, in the second embodiment, a large change amount greater than or equal to the reference value among the change amounts of the remaining buffer amount is caused by fading that causes rapid level fluctuation or deterioration of radio wave conditions such as interference between the wireless LAN and Bluetooth. This is different from the first embodiment in that it is not used for control judgment when the control unit 113 controls the decoding speed.

  During the reproduction of the stream data, the control unit 113 periodically measures the remaining buffer amount and periodically calculates the change amount of the remaining buffer amount based on the measured remaining buffer amount (step ST203). Then, the control unit 113 determines whether or not the calculated change amount of the remaining buffer amount is equal to or greater than the threshold value (step ST701), and does not store the calculated change amount when the change amount is equal to or greater than the threshold value. (Step ST702). Then, control unit 113 determines whether or not the number of calculation of the remaining buffer amount change amount has reached a predetermined value (step ST204). On the other hand, when the amount of change is not greater than or equal to the threshold value in step ST701, the control unit 113 stores the calculated amount of change in the remaining buffer amount, and whether or not the number of times of calculation of the amount of change in the remaining buffer amount has reached a predetermined value. (STEP ST204).

  Next, details of how the control unit 113 determines whether the amount of change in the remaining buffer amount tends to increase or decrease will be described with reference to FIGS. 8 is a diagram showing the time transition of the remaining buffer amount, FIG. 9 is a diagram showing the state of the buffer 111 at each time, and FIG. 10 is a diagram showing the time transition of the decoding speed. 11 is a diagram showing the time transition of the remaining buffer amount.

  FIG. 8 shows a case where a failure occurs in reception of stream data due to deterioration of the radio wave condition in the wireless network 103 at time Terr between times T1 and T2. Due to the burst error resulting from this reception failure, the amount of stream data (buffer amount) stored in the buffer 111 is greatly reduced. Also, in order to recover the influence of reception failure between time T2 and time T3 after time Terr, retransmission processing of stream data is performed between the stream reception / playback apparatus 101 and the server 102, and the remaining buffer amount is greatly recovered. is doing. As described above, when the radio wave condition in the wireless network 103 deteriorates, the amount of change in the remaining buffer amount becomes very large compared to the normal case.

  FIG. 9 is a diagram illustrating the state of the buffer 111 at times T0 to T6 as an example of FIG. Each time the control unit 113 calculates the change amount of the remaining buffer amount, the control unit 113 determines whether or not the calculated change amount of the remaining buffer amount is a reference value (for example, 10 Kbytes) or more. Do not use for judgment. In FIG. 9, a flag field is provided, and the control unit 113 assigns an “unused” flag to the change amount of the remaining buffer amount determined to be equal to or greater than the reference value, and determines the remaining buffer determined to be less than the reference value. A “use” flag is assigned to the amount of change in the amount. In this way, when the amount of change in the remaining buffer amount is calculated as shown in FIG. 9, the control unit 113 obtains the average value ΔD from the amount of change for four times in which the flag is “used”. The obtained average value ΔD is “+0.5 Kbyte”. At this time, since the polarity of the calculated average value ΔD of the remaining buffer amount change is positive, the control unit 113 determines that the remaining buffer amount change amount is increasing and increases the decoding speed. The decoder 112 is controlled as follows. That is, the control unit 113 controls the decoder 112 to change the decoding speed after time T6 to the newly calculated decoding speed. As a result, as shown in FIG. 10, the time decoding speed from time Tn to time Tn2 is higher by ΔD / Tc than the time decoding speed Rout from time T0 to time Tn. Then, by increasing the decoding speed Rout by ΔD / Tc, as shown in FIG. 11, the remaining buffer amount of time from time Tn to time Tn2 is “at time T0” as shown by the solid line in FIG. It remains constant at “remaining buffer amount” + ΔD + “change amount B caused by burst error or the like due to deterioration of radio wave condition”. In FIG. 11, the broken line represents the time transition of the remaining buffer amount when it is assumed that no burst error or the like has occurred.

  In this way, after time Tn, the decoding speed is made faster than the time from time T0 to time Tn, and decoding and reproduction are performed, thereby suppressing an increase in the buffer amount. 8 to 11, the case where the amount of change in the remaining buffer amount tends to increase has been described. However, when the amount of change in the remaining buffer amount tends to decrease, it is the opposite of the case where the amount of change remains. Take control. By repeating such control, after the time Tn, the frequency of occurrence of overflow or underflow of the buffer 111 due to the clock difference and the radio propagation environment can be suppressed.

  Thus, according to the second embodiment, in addition to the effect of the first embodiment, the streaming reception / playback apparatus tends to increase by eliminating the amount of change in the remaining buffer amount equal to or greater than the reference value, or Because it is judged whether or not there is a tendency to decrease, the influence of burst errors due to radio wave conditions of the network is eliminated, and control only on the stream reception side is caused by the clock difference between the stream transmission and reception and the radio propagation environment The frequency of occurrence of buffer overflow and underflow can be suppressed.

  In the second embodiment, the reference value to be compared with the change amount of the remaining buffer amount has been described with reference to a specific value. However, the reference value is not limited to the above value. In the second embodiment, the control unit 113 measures the amount of change in the remaining buffer amount every time 10 sec elapses. However, the control unit 113 is not limited to this, and the control unit 113 has a time T1 = 10 sec, a time T2 = 30 sec, etc. The change amount of the remaining buffer amount may be measured at different time intervals.

(Embodiment 3)
FIG. 12 is a diagram showing a time transition of the decoding speed controlled by the control unit 113 according to Embodiment 3 of the present invention, and FIG. 13 shows the remaining buffers in the buffer 111 according to Embodiment 3 of the present invention. It is a figure which shows the time transition of quantity. The streaming network system according to Embodiment 3 of the present invention is the same as that shown in FIG. 1, and the configuration of the stream reception / playback apparatus (client) and server is the same as that shown in FIG. Since the operation of the streaming network system 100 is the same as that of FIG. 2 except that the decoding speed is controlled to be variable so that the remaining buffer amount is reduced or recovered, the description thereof is omitted.

  The third embodiment is different from the first embodiment in that the decoding speed is controlled so that the remaining buffer amount is reduced or recovered.

  The control unit 113 in the third embodiment performs control so as to recover the decrease or increase in the remaining buffer amount by correcting the decoding speed using the correction value. For example, the control unit 113 stores a correction value ΔD ′ = ΔD × α (where α is a correction coefficient). At this time, the correction coefficient α can be set variably.

  When the correction coefficient α = 1 is set (when ΔD ′ = ΔD), the corrected decoding speed is Rout + ΔD / Tc, and therefore, as shown in FIG. 6 and FIG. 11, in the time from time Tn to time Tn2. The remaining buffer amount is maintained at a constant remaining buffer amount without decreasing or increasing.

  In addition, when the average value of the change amount of the remaining buffer amount is increasing, the control unit 113 sets the correction coefficient α = 2 (ΔD ′ = 2 × ΔD), so that the corrected decoding speed is Since Rout + 2 × ΔD / Tc, as shown in FIG. 12, the decoding speed can be made faster than the decoding speed when the correction coefficient α = 1 is set. For example, when the average value of the change amount of the remaining buffer amount is obtained as “+0.5 Kbyte”, the control unit 113 determines that the change amount of the remaining buffer amount is increasing and sets the correction coefficient α = 2. Thus, the decoder 112 is controlled to increase the decoding speed. As a result, the new decoding speed is changed to Rout + ΔD ′ / Tc = 40 + (+ 1) /10=40.1 Kbyte / Sec (= 320.8 Kbps). In this way, after time Tn, decoding and reproduction are performed at a speed faster than the decoding speed from the time T0 to the time Tn, thereby suppressing an increase in the buffer amount. When the change amount of the remaining buffer amount tends to increase, the control unit 113 sets the correction coefficient α to “2” which is a value larger than “1” so that the remaining buffer amount is reduced. Control to increase the speed can be performed. As a result, the suppression effect of the increasing tendency can be made higher than in the first and second embodiments. In the case of FIG. 13, by setting the correction coefficient α = 2, the same time interval (time from time Tn to time Tn2) next to the time interval (time from time T0 to time Tn) at which measurement was performed. After the elapse, the remaining buffer amount at the time T0 can be returned to the same remaining buffer amount.

  On the other hand, when the average change amount of the remaining buffer amount tends to decrease, the control unit 113 controls the decoder 112 to set the correction coefficient α = 2 so as to reduce the decoding speed. In this way, after time Tn, decoding and reproduction are performed at a speed slower than the decoding speed from time T0 to time Tn, thereby suppressing a decrease in the buffer amount. When the amount of change in the remaining buffer amount tends to decrease, the control unit 113 sets the correction coefficient α to “2”, which is a value larger than “1”, so that the remaining buffer amount increases. Control to reduce the speed can be performed. As a result, the effect of suppressing the decrease tendency can be made higher than in the first and second embodiments. By such control of the control unit 113, after the same time interval (time from time Tn to time Tn2) after the time interval (time from time T0 to time Tn) has elapsed, the remaining buffer at time T0 The amount of remaining buffer can be returned to the same amount.

  FIG. 14 is a diagram showing the time transition of the decoding speed controlled by the control unit 113 when the correction coefficient α = 1.5, and FIG. 15 shows the case where the correction coefficient α = 1.5. It is a figure which shows the time transition of the remaining buffer amount in the buffer 111 of.

  When the average value of the amount of change in the remaining buffer amount tends to increase, the control unit 113 sets the correction coefficient α = 1.5 (ΔD ′ = 1.5 × ΔD), thereby correcting the decoded data. Since the speed is Rout + 1.5 × ΔD / Tc, as shown in FIG. 14, the decoding speed is higher than the decoding speed when the correction coefficient α = 1 is set and the correction coefficient α = 2 is set. The decoding speed can be slower than the speed. In the case of FIG. 15, by setting the correction coefficient α = 1.5, the same time interval (from time Tn to time Tn2) following the time interval (time from time T0 to time Tn) at which the measurement was performed. Time) and the next time interval (time from time Tn2 to time Tn3) can be returned to the remaining buffer amount equal to the remaining buffer amount at time T0.

  On the other hand, when the average value of the change amount of the remaining buffer amount is decreasing, the control unit 113 sets the correction coefficient α = 1.5 (ΔD ′ = 1.5 × ΔD), thereby correcting the correction coefficient. It is possible to make the decoding speed faster than the decoding speed when α = 1 is set and slower than the decoding speed when the correction coefficient α = 2 is set. By such control of the control unit 113, the same time interval (time from time Tn to time Tn2) next to the time interval (time from time T0 to time Tn) and the next time interval (time) After the elapse of (time from Tn2 to time Tn3), the remaining buffer amount can be returned to the same as the remaining buffer amount at time T0.

  The remaining buffer amount from time Tn to time Tn2 in FIG. 13 and the remaining buffer amount from time Tn to time Tn3 in FIG. 15 are time transitions of the expected remaining buffer amount. That is, the remaining buffer amount when the reception speed (Rin) estimated by the measurement between the times T0 and Tn is actually received after the time Tn.

  In the first embodiment and the second embodiment, the control unit 113 controls the decoding speed (Rout) to be the same as the estimated value of the reception speed (Rin). On the other hand, in the third embodiment, when α = 2, the control unit 113 controls the measurement time (time from time T0 to time Tn) next to a certain time (time from time Tn to time). After the elapse of time (until time Tn2), control is performed so that the remaining buffer amount is the same as the remaining buffer amount at time T0. Further, when α = 1.5, a certain time (time from time Tn to time Tn2 and time Tn2) after the certain time after the measurement time (time from time T0 to time Tn) at which the measurement was performed. After the elapse of time from time Tn3 to time Tn3, control is performed so that the remaining buffer amount is the same as the remaining buffer amount at time T0. In the third embodiment, the time from time T0 to time Tn, the time from time Tn to time Tn2, and the time from time Tn2 to time Tn3 are each set to be, for example, the length of one time slot. be able to. The length is not limited to one time slot, and can be any length.

  Thus, according to the third embodiment, in addition to the effect of the first embodiment, the decoding speed is set using the correction value ΔD ′ = ΔD × α calculated using the correction coefficient α larger than 1. By controlling, the reduced or increased remaining buffer amount can be recovered. In addition, according to the third embodiment, if the decoding speed is changed steeply, the change in frequency becomes large, resulting in a problem with audibility. However, by adjusting the correction coefficient α, the frequency of occurrence of audibility problems is suppressed. can do.

  In the third embodiment, the case where the correction coefficient α is set to 2 and 1.5 has been described. However, the present invention is not limited to this, and the correction coefficient α is set to an arbitrary value within a range where no audibility problem occurs. Can be set. In the third embodiment, the control is performed so that the remaining buffer amount at time T0, that is, the original remaining buffer amount is restored. However, the present invention is not limited to this, and the average value of the remaining buffer amount changes tends to increase. In order to reduce the remaining buffer amount, the decoding speed is increased, and when the average value of the remaining buffer amount change is decreasing, the decoding speed is controlled to increase so that the remaining buffer amount increases. It is not necessary to control to return to the original remaining buffer amount. Further, the third embodiment can be applied to the first embodiment and the second embodiment.

(Embodiment 4)
FIG. 16 is a flowchart showing the operation of the streaming network system 100 according to Embodiment 4 of the present invention. In FIG. 16, parts that are the same as those in FIG. 2 are given the same reference numerals, and descriptions thereof are omitted. The streaming network system according to Embodiment 4 of the present invention is the same as that shown in FIG. 1, and the configuration of the stream reception / playback apparatus (client) and server is the same as that shown in FIG.

  In the fourth embodiment, the control unit 113 controls the decoding rate Rout by calculating the average value ΔD of the amount of change in the remaining buffer amount in the same manner as in the first embodiment. The difference from the first embodiment is that a sharp change in the decoding speed is suppressed by providing an upper limit and a lower limit determined by a certain threshold.

  In FIG. 16, after the decoding speed is increased in step ST207, after the decoding speed is decreased in step ST209, or when it is determined that there is no tendency to decrease in step ST208, the control unit 113 determines the amount of change in the remaining buffer amount. It is determined whether or not the absolute value | ΔD | of the average value ΔD is equal to or greater than (Rout × Th%) × Tc (step ST1601). That is, assuming that the threshold is Th%, the control unit 113 controls the decoding speed so that the rate of change in the decoding speed Rout falls within Th%. Specifically, when ΔD ≦ − (Rout × Th%) × Tc, the control unit 113 controls the decoding speed as ΔD = − (Rout × Th%) × Tc, and ΔD ≧ + (Rout × In the case of (Th%) × Tc, the decoding speed is controlled as ΔD = + (Rout × Th%) × Tc (step ST1602). On the other hand, when the absolute value of the average value ΔD of the remaining buffer amount change amount is not equal to or greater than (Rout × Th%) × Tc in step ST1601, the control unit 113 determines the decoding speed set in step ST207 or step ST209. To maintain. Subsequently, the stream reception / playback apparatus 101 determines whether or not the reception of the stream data has ended (step ST210). When the stream reception and playback apparatus 101 determines that the reception of the stream data has ended, the stream reception / playback apparatus 101 stops the operation and receives the stream data. When it is determined that the process has not been completed, the processes of steps ST201 to ST209, step ST1601, step ST1602, and step ST210 are repeated.

  FIG. 17 is a diagram illustrating an example of decoding speed control when the absolute value | ΔD | of the average value ΔD of the remaining buffer amount change amount is | ΔD | <(Rout × Th%) × Tc. FIG. 18 is a diagram illustrating an example of decoding speed control when | ΔD | ≧ (Rout × Th%) × Tc. As shown in FIG. 18, ΔD ≧ + (Rout × Th%) × Tc, and when ΔD exceeds the threshold, ΔD = + (Rout × Th%) × Tc, and the corrected decoding speed exceeds the threshold. Control so that there is no. When ΔD does not exceed the threshold value, the control unit 113 performs the control as described in the first embodiment.

  To explain using specific values, when Th = 0.1% and Rout = 40 Kbyte / sec, the average value ΔD of the change amount of the remaining buffer amount is ΔD ≧ + (Rout × Th%) × Tc = In the case of 40 × 0.1 (%) × 10 = 0.4 Kbytes, the control unit 113 controls the decoding speed as ΔD = 0.4 Kbytes. When the average value ΔD of the change amount of the remaining buffer amount is ΔD ≦ − (Rout × Th%) × Tc = −40 × 0.1 (%) × 10 = −0.4 Kbyte, the control unit 113 The decoding speed is controlled as ΔD = −0.4 Kbytes.

  As described above, according to the fourth embodiment, in addition to the effect of the first embodiment, by controlling the change amount of the decoding rate Rout by providing the upper limit and the lower limit determined by a certain threshold value, It is possible to suppress the frequency of occurrence of audible problems due to a large change in frequency.

  In the fourth embodiment, Th is described as being 0.1%. However, the present invention is not limited to this, and Th can be set to an arbitrary value within a range in which a problem in audibility does not occur. Further, the fourth embodiment can be applied to the second embodiment or the third embodiment. When applied to the third embodiment, when the absolute value | ΔD ′ | of the correction value ΔD ′ is equal to or greater than (Rout × Th%) × Tc, ΔD ′ = + (Rout × Th%) × Tc or The decoding speed is controlled as ΔD ′ = − (Rout × Th%) × Tc. In the fourth embodiment, whether or not | ΔD | ≧ (Rout × Th%) × Tc is determined in step ST1601. However, not limited to this, | ΔD | <(Rout) in step ST1601. X Th%) x Tc is determined. If | ΔD | <(Rout × Th%) × Tc, ΔD = + (Rout × Th%) × Tc or ΔD = − (Rout × Th% ) × Tc, the decoding speed may be controlled.

(Embodiment 5)
19 and 20 are diagrams showing a time transition of the decoding speed controlled by the control unit 113 according to Embodiment 5 of the present invention. The streaming network system according to Embodiment 5 of the present invention is the same as that shown in FIG. 1, and the configuration of the stream reception / playback apparatus (client) and server is the same as that shown in FIG. Since the operation of the streaming network system 100 is the same as that of FIG. 2 except that the decoding speed is continuously changed, the description thereof is omitted.

  In the fifth embodiment, similarly to the first embodiment, the control is performed by calculating the average value ΔD of the change amount of the remaining buffer amount, but the decoding speed is changed from Rout to Rout + ΔD / Tc at a certain time Tn. The difference from Embodiment 1 is that the control is performed so that the decoding speed changes continuously, not the change is not performed discontinuously.

  In FIG. 19, the control unit 113 performs control so that the change in the decoding speed continues at time Tn, and slightly changes so that the change in the decoding speed becomes linear in the time from time Tn to time Tn2. Change it step by step. In FIG. 20, the control unit 113 controls the decoding speed to change continuously at time Tn, and the decoding speed change becomes non-linear within the time from time Tn to time Tn2. Change little by little.

  As described above, according to the fifth embodiment, in addition to the effect of the first embodiment, the decoding speed is changed little by little so that the decoding speed changes continuously. , Tn2...) Can be reduced.

  In the fifth embodiment, the decoding speed is changed little by little within the time from time Tn to time Tn2. However, the present invention is not limited to this, and decoding is made little by little within the time from time Tn to time Tn3. The time for changing the decoding speed little by little can be arbitrarily set. The fifth embodiment can be applied to the first to fourth embodiments.

  In the first to fifth embodiments, the case where the stream data is audio has been described. However, the present invention is not limited to this, and the present invention may be applied to stream data of any data type such as when the stream data is a moving image. it can.

  In the first to fifth embodiments, the operation procedure or the stream reception method of the stream reception / playback apparatus may be expressed by a computer program, and the computer program may be executed by the computer. A computer program expressing the operation procedure of the apparatus or the stream reception method is recorded on a recording medium such as a CD-ROM or DVD, or the computer program expressing the operation procedure or the stream reception method of the stream reception / playback apparatus is connected to an electric communication line The program may be transmitted to a computer and the computer program transmitted using the destination computer may be executed.

  The present invention can be applied to a stream receiving apparatus and a stream receiving method using a streaming technique for reproducing data while receiving data such as audio or moving images via a network.

The figure which shows the streaming network system which concerns on Embodiment 1 of this invention. The flowchart which shows operation | movement of the streaming network system which concerns on Embodiment 1 of this invention. The figure which shows the time transition of the remaining buffer amount which concerns on Embodiment 1 of this invention. The figure which shows the state of the buffer in each time which concerns on Embodiment 1 of this invention The figure which shows the speed of the decoding which concerns on Embodiment 1 of this invention The figure which shows the time transition of the remaining buffer amount which concerns on Embodiment 1 of this invention. The flowchart which shows operation | movement of the streaming network system which concerns on Embodiment 2 of this invention. The figure which shows the time transition of the remaining buffer amount which concerns on Embodiment 2 of this invention. The figure which shows the state of the buffer in each time which concerns on Embodiment 2 of this invention. The figure which shows the speed of the decoding which concerns on Embodiment 2 of this invention The figure which shows the time transition of the remaining buffer amount which concerns on Embodiment 2 of this invention. The figure which shows the speed of the decoding which concerns on Embodiment 3 of this invention. The figure which shows the time transition of the remaining buffer amount which concerns on Embodiment 3 of this invention. The figure which shows the speed of the decoding which concerns on Embodiment 3 of this invention. The figure which shows the time transition of the remaining buffer amount which concerns on Embodiment 3 of this invention. The flowchart which shows operation | movement of the streaming network system which concerns on Embodiment 4 of this invention. The figure which shows the speed of the decoding which concerns on Embodiment 4 of this invention. The figure which shows the speed of the decoding which concerns on Embodiment 4 of this invention. The figure which shows the speed of the decoding which concerns on Embodiment 5 of this invention. The figure which shows the speed of the decoding which concerns on Embodiment 5 of this invention. Diagram showing a conventional streaming network system

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Streaming network system 101 Stream receiving / reproducing apparatus 102 Server 103 Network 110 Communication part 111 Buffer 112 Decoder 113 Control part

Claims (7)

Receiving means for receiving the distributed stream data;
Storage means for temporarily storing the received stream data;
Decoding means for decoding the accumulated stream data;
When it is determined that the accumulated amount is increasing based on the change amount of the accumulated amount of the stream data, the decoding speed is increased, and when it is determined that the accumulated amount is decreasing, Control means to slow down the decoding speed;
A stream receiving apparatus comprising:   The control means calculates the amount of change a plurality of times within a predetermined measurement time to obtain a plurality of calculated values, and stores the accumulation when an average value of the obtained plurality of calculated values tends to increase. The stream reception according to claim 1, wherein the decoding speed is increased as the amount tends to increase, and the decoding speed is decreased as the accumulation amount tends to decrease when the average value is decreasing. apparatus.   The stream receiving apparatus according to claim 2, wherein the control unit obtains the average value by excluding a change amount in which the change amount is equal to or greater than a threshold value.   The control means increases the decoding speed so that the accumulation amount of stream data in the accumulation means decreases when the accumulation amount tends to increase, and the accumulation means when the accumulation amount tends to decrease. The stream receiving apparatus according to claim 1, wherein the decoding speed is decreased so that an accumulation amount of stream data increases.   The stream receiving apparatus according to claim 1, wherein the control unit changes the decoding speed so that the decoding speed falls within a predetermined range.   The stream receiving apparatus according to claim 1, wherein the control unit gradually changes the decoding speed. A receiving step for receiving the distributed stream data;
An accumulation step for temporarily accumulating the received stream data;
A decoding step for decoding the accumulated stream data;
The decoding speed is increased when it is determined that the accumulated amount is increasing based on the change amount of the accumulated amount of the stream data, and the decoding speed is increased when the accumulated amount is decreasing. Control steps to slow down,
A stream receiving method comprising:

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