JP4742836B2 - Receiver - Google Patents

Description

  The present invention relates to a stream data receiving apparatus and a stream data receiving method for receiving and decoding a data stream including video / audio via an IP (Internet Protocol) network such as the Internet and displaying the data stream on a television or the like.

  In recent years, so-called IP streaming, in which an AV stream including video and audio is transmitted from a transmitter such as a video server via an IP network such as the Internet and streaming reproduction is performed on the receiver side, is spreading. Conventionally, the use of IP streaming with a PC (personal computer) as a receiver has been the mainstream, but in order to increase the number of IP streaming users, the use of IP streaming with a home appliance such as a television as a receiver It is necessary to realize.

  In this way, in order to increase the number of IP streaming users who use home appliances as receivers, the buffer memory for temporarily storing AV streams received by the receiving device is limited to the one with as little capacity as possible. It is necessary to keep the unit price as low as possible. Also, in order to shorten the time from the start of AV stream reception until it is displayed, it is necessary to reduce the amount of data stored in the buffer as much as possible. In order to reduce the capacity of the buffer memory, the transmission speed at which the transmitter transmits the AV stream and the speed at which the receiver decodes the AV stream are synchronized, and the amount of AV stream stored in the buffer memory is reduced. It is necessary to keep it low. In order to synchronize such speed, a technique for recovering the transmission timing of the AV stream of the transmitter on the receiver side based on the received AV stream and synchronizing the timing of the decoding process on the receiver side with this. Is required.

  However, in the transmission of an AV stream via an IP network, the data rate arriving at the receiver depends on transmission characteristics (burst characteristics) on the transmitter side, such as a video server, and transmission characteristics (transmission delay fluctuation) of the IP network. Shake greatly. In order to perform stable timing recovery on the receiver side even under such conditions, it is necessary to extremely increase the time constant of the timing recovery circuit of the receiver (usually composed of a PLL or the like). It may take a long time to stabilize. As a result, it may take a long time to recover the timing of the receiver.

  As a technique for shortening the time until the timing recovery of the receiver, for example, with respect to a digital television broadcast receiver, the control voltage of the VCO at the time when the timing recovery circuit is stabilized is stored and stored at the next stream reception. There has been proposed a technique for shortening the time until the timing recovery circuit is stabilized by applying the control voltage as an initial offset (see, for example, Patent Document 1).

  This technique is effective in conventional digital broadcasting not via an IP network. In general, transmission facilities for satellite digital broadcasting and terrestrial digital broadcasting are required to have high frequency accuracy, and therefore use a very high-accuracy clock source. Therefore, the frequency error between broadcasting stations is small. Therefore, even when the receiver receives an AV stream of a channel different from the previous time, the control voltage of the VCO is likely to be a value close to the previous value.

However, in a video server or the like used for IP streaming via an IP network, a frequency accuracy as high as that of a broadcasting facility is not required, and thus a high-accuracy clock is not always used. (For example, in a PC-based video server, the CPU operation clock with relatively low required accuracy may be used for time measurement as it is.) As a result, the error between the video servers becomes large and the receiver is different from the previous one. When receiving an AV stream from a video server, there is a possibility that the effect of shortening the time until the timing recovery circuit is stabilized may not be obtained even if the same control voltage of the VCO as before is used.
JP-T-08-509346

  The present invention is for solving the above-described problem, and even when there is a large error between AV stream transmission sources as in IP streaming over an IP network, the time until the timing of the received stream at the receiver is recovered. The purpose is to provide technology for shortening.

  In order to solve the above-described problems, a video server according to the present invention includes a storage unit that stores compressed stream data, a storage unit that stores synchronization reference information that identifies a synchronization signal being referred to, and the storage unit. Transmission means for transmitting the stream data read from the storage means and the synchronization reference information read from the storage means to the receiving apparatus via a network.

  The receiving apparatus according to the present invention includes a receiving means for receiving stream data and synchronization reference information, a receiving buffer means for temporarily storing the received stream data, and a stream output from the buffer means to the decoding means. Control means for controlling data; storage means for associating and storing the synchronization reference information and a control parameter indicating a ratio between a bit rate value of received stream data and a bit rate value of stream data output by the control means; A receiving device including a decoding unit that decodes stream data received from the control unit and outputs the decoded data to a display unit, wherein the control unit controls the corresponding control parameter when the synchronization reference information is stored in the storage unit. Control the output bit rate value of the stream data according to When not stored quasi information in the storage means and controls the output bit rate value of the stream data according to the bit rate value of the stream data received.

  As a result, even when the error between the AV stream transmission sources is large as in IP streaming via the IP network, it is possible to shorten the time until the timing of the received stream at the receiver is recovered.

(Embodiment 1)
FIG. 1 is a diagram showing a configuration of a system including a video server 22 and a stream receiving device 21 which are stream transmitting devices in the first embodiment of the present invention. Reference numeral 22 denotes a video server which is a stream transmitting device, 21 is a stream receiving device, 23 is an NTP server, and 24 is an IP network.

  The video server 22 can refer to external synchronization criteria in order to transmit the AV stream at the most accurate rate possible. In this example, an NTP (Network Time Protocol) server is used as a synchronization reference. The NTP server 23 has a very high-precision clock, and devices on the IP network 24 can refer to an accurate time from the NTP server 23 using the NTP protocol.

  In the video server 22 of FIG. 1, 501 is a packet transmission / reception unit, 502 is a stream multiplexing unit, 503 is a stream reading unit, 504 is a stream storage unit, 506 is a synchronization reference information table, 507 is a time management unit, and 508 is time information acquisition. Part. In the synchronization reference information table 506, synchronization reference information indicating the synchronization reference referred to by the video server 22 (in this example, the IP address of the NTP server 23) is stored in advance. In the stream storage unit 504, the required number of AV streams are stored in advance.

  In the video server 22, the time information acquisition unit 508 reads the IP address of the NTP server 23 as the synchronization reference information from the synchronization reference information table 506, and periodically uses the NTP protocol from the NTP server 23 specified by the IP address. The time information is acquired and notified to the time management unit 507. The time management unit 507 smoothes the obtained time information in the time direction and synchronizes the internal clock with the NTP server 23 in order to avoid the influence of errors due to communication fluctuations of the NTP protocol. The stream reading unit 503 reads the AV stream from the stream storage unit 504 at a rate (Rsrv) specific to each AV stream according to the time indicated by the clock of the time management unit 507. On the other hand, the stream multiplexing unit 502 reads the synchronization reference information from the synchronization reference information table 506 and multiplexes it with the AV stream read by the stream reading unit 503. For example, when the AV stream format is MPEG2 Transport Stream (hereinafter referred to as MPEG2-TS), the synchronization reference information is described in a section format table compliant with MPEG2-TS, converted into TS packets, and multiplexed into the AV stream. To do.

  The AV stream multiplexed by the stream multiplexing unit 502 is converted into an IP packet format by the packet transmission / reception unit 501 and transmitted to the stream receiving device 21 via the IP network 24.

  FIG. 2 is a diagram showing in detail the configuration of the stream receiving device 21 of the device of the present invention in the same system as FIG. Reference numeral 21 denotes a stream receiving device as a receiver, 101 denotes a packet receiving unit, 102 denotes a reception buffer, 103 denotes an output control unit, 105 denotes an output rate calculation unit, and 107 denotes a synchronization reference information table. 110 is an AV decoder that decodes the AV stream, and 111 is a display unit such as a display that displays video and audio decoded by the AV decoder 110.

  First, an outline of the operation of the receiving apparatus in FIG. 2 is shown. The packet receiving unit 101 of the stream receiving device 21 receives the AV stream transmitted from the video server 22. The reception buffer 102 temporarily stores the AV stream received by the packet reception unit 101 and transmits the AV stream to the AV decoder 110 according to the control of the output control unit 103. The output rate calculation unit 105 calculates the rate to be output by monitoring the amount of staying data in the reception buffer 102 and notifies the output control unit 103 of the calculated rate.

The output control unit 103 reads the AV stream from the reception buffer 102 at a rate corresponding to the output rate value obtained from the output rate calculation unit 105 and transmits the AV stream to the AV decoder 110. The AV decoder 110 includes a PLL circuit that monitors the time stamp of the AV stream (PCR in the case of MPEG2-TS), and synchronizes the decode clock generator 120 with the rate input from the output control unit 103. The AV stream is decoded at a speed corresponding to the input rate. The display unit 111 displays the video and audio decoded by the AV decoder 110 on the screen. A detailed procedure will be described below using the flowchart of FIG.

(1) When the synchronization reference information notified from the video server 22 is not registered in the synchronization reference information table 107:
First, the output rate calculation unit 105 in the stream receiving device 21 sends the bit rate value Rsrv to the video server 22 together with information necessary for receiving the desired AV stream, and the RTSP (Real Time Streaming Protocol) protocol. Use to get. Next, when the stream receiving device 21 similarly requests the video server 22 to transmit an AV stream using the RTSP protocol, the video server 22 starts transmitting the AV stream to the stream receiving device 21.

  The stream reception device 21 receives the AV stream by the packet reception unit 101 and accumulates it in the reception buffer 102. At that time, the stream separation unit 106 acquires synchronization reference information from the received AV stream, that is, the address (IP address) of the NTP server 23 referred to as the synchronization reference by the video server 22 (step S1).

  Subsequently, the output rate calculation unit 105 searches whether the address of the NTP server 23 acquired from the video server 22 is registered in the synchronization reference information table 107 (step S2).

  The synchronization reference information table 107 stores synchronization reference information and control parameters (details will be described later) for controlling the output of the output control unit 103 in association with each other. FIG. 4A is a diagram showing an example of the contents stored in the synchronization reference information table 107.

  As a result of the search, if the address of the NTP server 23 acquired from the video server 22 is not registered in the synchronization reference information table 107, the value of the bit rate Rsrv acquired from the video server 22 is sent to the output control unit 103 as the initial bit rate. (Step S3).

  The output control unit 103 reads the AV stream from the reception buffer 102 at a speed corresponding to the bit rate value specified by the output rate calculation unit 105, and outputs the AV stream to the AV decoder 110 (step S4).

FIG. 6 is a diagram showing details of an interface between the output control unit 103 and the AV decoder 110. The two are connected by three types of signals: interface clock, data enable, and AV stream data. In order to stably control the output rate of the AV stream, the output control unit 103 performs the control by keeping the interface clock constant and increasing / decreasing the number of data enables. If the period for controlling the number of data enables is N (clock), and the maximum rate of the output interface is Rmax, the output control unit 103
(Equation 1)
R = Rmax (n / N)
Is determined so as to be closest to the desired output rate, and control is performed so that the enable signal is set high for n clocks during N clocks. Here, Rmax is a value obtained from the frequency of the interface clock. For example, when the output of the output control unit 103 is an 8-bit parallel interface, Rmax is eight times the frequency of the interface clock.

  When such a method is not used, a method of directly controlling the output rate using, for example, a VCO (Voltage Control Type Variable Frequency Oscillator) is also possible. In that case, if the relationship between the control voltage of the VCO and the output frequency is obtained in advance, a desired rate R can be obtained by controlling the control voltage. However, in the case of the method using the VCO, since the VCO has a large error in the transmission frequency due to changes in ambient environment such as temperature, the transmission frequency may change with time even when the same control voltage is applied. In the case of streaming using the IP network 24, it takes time to recover the timing as described above, so even a slight frequency error may take extra time. In the method shown in FIG. 6, the fixed frequency oscillator 104 has higher frequency stability than the VCO, and thus there are few such problems.

  Note that the rate obtained by Equation 1 may not necessarily match the desired value, but in this case as well, the error between the two can be made sufficiently small by sufficiently increasing N.

  Next, a mechanism for synchronizing the transmission rate of the video server 22 and the decoding rate of the receiver will be described with reference to FIG.

  As shown in FIG. 5A, the input rate and output rate of the reception buffer 102 are Rin and Rout, respectively. In step S4, the output control unit 103 of the stream reception device 21 reads the AV stream from the reception buffer 102 at a rate of Rsrv when Rmax obtained from the oscillation frequency of the transmitter 104 is used as a reference. On the other hand, the video server 22 transmits the AV stream at a rate of Rsrv when the clock of its own time management unit 507 is used as a reference. The former is equal to Rout and the latter is equal to Rin. Since the clock of the video server 22 and the output of the transmitter 104 of the stream receiving device 21 are not necessarily synchronized, an error occurs between Rin and Rout. Due to this rate difference, the amount of data retained in the reception buffer 102 gradually increases or decreases with time, and if left as it is, the reception buffer 102 overflows or underflows and is input to the AV decoder 110. If a part of the data is lost, the video / audio displayed on the display unit 111 may be disturbed. Therefore, the output rate calculation unit 105 monitors the change in the amount of data retained in the reception buffer 102 so that the rate (= Rout) read by the output control unit 103 matches Rin by the following procedure. Fine adjustment is performed (step S5).

FIG. 5B shows an example of a change in the amount of retained data in the reception buffer 102, and FIG. 5C shows an example of a change in the output rate of the output control unit 103. As shown in FIG. 5B, when the observation time is T and the change in the amount of staying data is D, the difference Rdif between the rate Rin input to the reception buffer 102 and the output rate Rout is:
(Equation 2)
Rdif = Rin−Rout = D / T
It is represented by Therefore, by changing the output rate Rout of the output control unit 103 by Rdif, it can be brought close to Rin. That is, if the amount of staying data tends to increase (that is, the sign of D is positive), the output rate of the output control unit 103 is increased, and if the amount of staying data tends to decrease (that is, the sign of D is negative). Case.) Control to reduce the output rate. Actually, it is rare that Rout coincides with Rin by a single control due to measurement errors of D and T. However, by repeating this control, the two can be gradually matched. As described above, the AV decoder 110 has a built-in PLL circuit that monitors the time stamp (PCR in the case of MPEG2-TS) of the input AV stream, and uses the oscillation frequency of the decode clock generator 120 as the input stream rate. The AV stream is decoded at a speed corresponding to the input rate. With the above-described mechanism, the decoding rate of the stream receiving device 21 can be synchronized with the transmission rate of the video server 22. That is, Rout gradually converges to a specific rate Rout0. Here, Rout0 represents the rate of the AV stream with reference to the reference clock of the stream receiving device 21 (in this example, the oscillation frequency of the transmitter 104). On the other hand, Rsrv is the AV stream rate based on the reference clock of the video server 22 (in this example, the clock of the NTP server 23 referred to as the synchronization reference). Although these operating frequencies do not necessarily match, each may be considered to be almost constant at all times, so even if the receiver receives another AV stream, if the synchronization reference referred to by the video server 22 is the same, The ratio between Rsrv and Rout0 is a substantially constant value. Therefore, when the stream receiving device 21 finishes receiving the AV stream, the ratio between the output rate Rout0 of the output control unit 103 immediately before the end and the rate Rsrv first obtained from the video server 22,
(Equation 3)
Ratio = Rout0 / Rsrv
Is stored in the synchronization reference information table 107 in association with the address of the NTP server 23 as a control parameter (step S6).

(2) When the synchronization reference information notified from the video server 22 is registered in the synchronization reference information table 107:
Next, an operation when the address of the NTP server 23 is registered in the synchronization reference information table 107 in step S2 described above will be described.

In this case, the ratio, which is the control parameter associated with the acquired address of the NTP server 23, is read from the synchronization reference information table 107, and the bit rate value Rsrv of the AV stream acquired from the video server 22 is
(Equation 4)
Rdec = Rsrv × Ratio
Is set in the output control unit 103 as an initial rate (step S7). Thereafter, the operation is the same as in steps S4 to S6.

  Through the above procedure, the stream receiving device 21 accurately matches the bit rate of the received stream data of the received AV stream even when the video server 22 and the stream receiving device 21 are not synchronized. Output can be realized. In addition, when the video server 22 acquires the information of the signal source that is referred to as the synchronization reference and already stores the control information related to the signal source, by controlling according to the parameter that stores the initial output rate, It is possible to shorten the time until the timing recovery of the received stream in the receiver. That is, even when receiving a stream from a different video server 22, when synchronized with the same NTP server 23, the value of Ratio in Equation 3 can be expected to be substantially constant. By using the Rdec obtained in the above as the initial rate of the output control unit 103, the output rate of the output control unit 103 can be converged in a short time.

  In the present embodiment, the case where each element is provided inside the stream receiving device 21 is illustrated, but some of these elements may be provided outside the stream receiving device 21. For example, the AV decoder 110, the display unit 111, and the synchronization reference information table 107 may be provided outside the stream receiving device 21. Moreover, the structure which some or all of these elements united may be sufficient. For example, the output control unit 103 may have the function of the output rate calculation unit 105 or may store synchronization reference information.

(Embodiment 2)
FIG. 7 is a diagram showing the configuration of the receiving apparatus according to the second embodiment of the present invention. In FIG. 7, reference numeral 203 denotes an output control unit, which is different from the output control unit 103 of the first embodiment in the control method of the output timing of the AV stream. 205 is a count speed calculation unit, and 208 is a counter. The rest is the same as in the case of the first embodiment.

  In this embodiment, as shown in FIG. 8, when transmitting an AV stream from the video server 22, time information that each AV packet should be input to the AV decoder 110 into a packet (AV packet) constituting the AV stream. Is granted. For example, in the case of MPEG2-TS, time information with 27 MHz accuracy is inserted for each TS packet that is an AV packet. The counter 208 counts up with a 27 MHz clock, and the output control unit 203 outputs the packet to the AV decoder 110 at the timing when the time information of the AV packet at the head of the reception buffer 102 matches the count value of the counter 208.

However, since the speed of the counter for time information provided by the video server 22 and the speed of the counter 208 of the stream receiving device 21 do not necessarily coincide with each other, the amount of retained data in the reception buffer 102 is caused by an error between the two. Gradually increases or decreases. Therefore, the count speed calculation unit 205 adjusts the operation clock of the counter 208 according to the change in the amount of retained data in the reception buffer 102. That is, if the change in the amount of data retained in the reception buffer 102 at the observation time T is D, the difference Rdif in the input / output rate of the reception buffer 102 is as expressed by Equation 2, and this is the operation clock of the counter 208. Is converted to
(Equation 5)
Rdif ′ = (D / T) × (Rcnt / Rsrv)
It becomes. Here, Rcnt is the center frequency of the operation clock of the counter 208, which is 27 MHz in this embodiment. That is, by changing the operation clock of the counter 208 by Rdif ′, the output rate of the reception buffer 102 can be brought close to the reception rate.

  By repeating this control, the operation speed of the counter 208 gradually converges to a constant value Rcnt0. This value is considered to be the same even when another AV stream is received as long as the synchronization standard referred to by the video server 22 is the same. Therefore, in step S6, the operation speed Rcnt0 of the counter 208 immediately before the end of the stream is stored as a control parameter in the synchronization reference information table 107 in association with the synchronization reference information of the AV stream. Next, when the reception of the AV stream is started, the same effect as that of the example of the first embodiment is obtained by using the stored control parameter Rcnt0 as the initial value of the operating frequency of the counter 208 in step S7. Can be obtained. FIG. 4B shows an example of the contents stored in the synchronization reference information table 107.

  In the second embodiment, the operation speed of the counter 208 is adjusted by controlling the clock frequency of the counter 208. However, like the rate adjustment mechanism in the output control circuit of FIG. 6, the clock frequency is fixed. It is also possible to adjust the operating speed of the counter 208 by controlling the enable signal.

(Embodiment 3)
FIG. 9 is a diagram showing the configuration of the receiving apparatus according to the third embodiment of the present invention.

  In FIG. 9, reference numeral 305 denotes a decode rate calculation unit. 310 is an AV decoder, but unlike the case of the first and second embodiments, the AV decoder 310 mainly reads data necessary for decoding from the reception buffer 102. 320 is a decode clock generator that generates a decode clock of the AV decoder 310, but does not have a mechanism for adjusting the oscillation frequency according to the input rate, and changes the oscillation frequency according to the output of the decode rate calculation unit 305. Let Others are the same as in the case of the first embodiment.

In the present embodiment, the decode rate calculation unit 305 adjusts the decode rate of the AV decoder 310 by adjusting the speed of the decode clock oscillator 320 based on the change in the AV stream accumulation amount in the reception buffer 102. As a result, the video / audio rate output from the AV decoder 310 is adjusted. That is, if the change in the amount of data retained in the reception buffer 102 at the observation time T is D, the difference Rdif in the input / output rate of the reception buffer 102 is as expressed by Equation 2, When converted to frequency error,
(Equation 6)
Rdif ″ = (D / T) × (Rsys / Rsrv)
It becomes. Here, Rsys is the center frequency of the decode clock generated by the decode clock oscillator 320, and is 27 MHz in the case of MPEG2. That is, by changing the speed of the decode clock oscillator 320 by Rdif ″, the decode rate of the AV decoder 110 can be brought close to the reception rate. By repeating this control, the frequency of the decode clock oscillator 320 gradually converges to a constant value Rsys0. This value is considered to be the same even when another AV stream is received as long as the synchronization standard referred to by the video server 22 is the same. Therefore, in step S6, the frequency Rsys0 of the decode clock oscillator 320 immediately before the end of the stream is stored as a control parameter in the synchronization reference information table 107 in association with the synchronization reference information of the AV stream. Next, when the reception of the AV stream is started, the stored control parameter Rsys0 is used as the initial value of the operating frequency of the decode clock oscillator 320 in step S7, so that it is the same as the example of the first embodiment. The effect of can be obtained. FIG. 4C shows an example of the contents stored in the synchronization reference information table 107.

  In the third embodiment, the decode rate calculation unit 305 adjusts the video / audio rate output from the AV decoder 310 by controlling the decode clock oscillator 320 of the AV decoder 310. Can control the output clock of the AV decoder 310 to control the output rate of video / audio, and the AV decoder 310 can be configured to decode according to the output rate.

  In each of the embodiments described above, as a method for transmitting the synchronization reference information from the video server 22 to the receiving device, the mode of multiplexing in the AV stream in the MPEG2 section format has been described, but multiplexing in other formats is also described. Is also possible. In addition, a method of transmitting the synchronization reference information to the receiving apparatus by a method other than multiplexing the AV stream is also possible. For example, in the communication of the RTSP protocol used for controlling the video server 22 from the receiving apparatus, the SDP is used. It is also possible to send a description. It is also possible to obtain a program from a program guide server different from the video server 22 in advance when the program is reserved, or to distribute it in advance by digital television data broadcasting.

  Further, although the case where the address of the NTP server 23 is used as the synchronization reference information has been described, it is possible to use the address of another server as long as the synchronization reference has a reliable accuracy. In addition to the IP address, the synchronization reference information may be any information as long as it can identify a server or device referred to as the synchronization reference, such as a domain name or URL.

  As the synchronization reference, it is not always necessary to use an NTP server 23 having absolute time information. For example, an ISDN reference clock or a transmission clock of a specific channel of digital television (or radio) broadcasting is used. It is also possible to use GPS radio waves. In this case, information for specifying these signals may be described as the synchronization reference information.

  Further, when the video server 22 does not particularly specify an external synchronization reference, the video server 22 itself is regarded as a synchronization reference, and the address of the video server 22 and the ratio are stored in the synchronization reference information table 107 in association with each other. It is also possible.

  The apparatus and method for receiving stream data according to the present invention shortens the time until the timing recovery of the received stream in the receiver even when the error between the AV stream transmission sources is large, as in IP streaming over an IP network. This is useful as a stream data receiving apparatus and a stream data receiving method via an IP network.

The block diagram which showed the stream transmission apparatus in 1st embodiment of this invention The block diagram which showed the stream receiver in 1st embodiment of this invention Flowchart in the first embodiment of the present invention The figure which showed the memory content of the synchronous reference | standard information table in 1st to 3rd embodiment of this invention The figure which showed the change of the data retention amount in the receiving buffer in 1st embodiment of this invention, and the change of the output rate of an output control part The figure explaining the detail of the interface of the output control part and AV decoder in 1st embodiment of this invention The block diagram which showed the stream receiver in 2nd embodiment of this invention The figure which showed the structure of AV stream in 2nd embodiment of this invention The block diagram which showed the stream receiver in 3rd embodiment of this invention

Explanation of symbols

21 Stream receiver 22 Video server 23 NTP server 24 IP network 101 Packet receiver 102 Reception buffer 103, 203 Output controller 104 Transmitter 105 Output rate calculator 106 Stream separator 107, 506 Synchronization reference information table 110, 310 AV decoder DESCRIPTION OF SYMBOLS 111 Display part 120,320 Decoding clock transmitter 205 Count rate calculation part 208 Counter 305 Decoding rate calculation part 501 Packet transmission / reception part 502 Stream multiplexing part 503 Stream reading part 504 Stream accumulation part 507 Time management part 508 Time information acquisition part

Claims (12)

Receiving means for receiving stream data and synchronization reference information from a video server;
Receiving buffer means for temporarily storing stream data received by the receiving means;
An output rate calculating means for calculating a control parameter indicating a ratio between a bit rate value of the stream data received by the receiving means and an output bit rate value of the stream data output by the output control means described later;
Storage means for storing the synchronization reference information and the control parameter in association with each other;
When the synchronization reference information is stored in the storage means, an output bit rate value is set based on a control parameter corresponding to the synchronization reference information and a bit rate value of stream data received by the reception means, and the synchronization When the reference information is not stored in the storage means, the output bit rate value is set based on the bit rate value of the stream data received by the receiving means, and the stream data output from the reception buffer means to the decoding means Output control means for controlling;
Decoding means for decoding the stream data received from the output control means and outputting to the display unit;
A receiving apparatus. 2. The receiving apparatus according to claim 1 , wherein the output control means increases or decreases an output bit rate value of stream data output to the decoding means in accordance with a data accumulation level of the reception buffer means. The receiving apparatus according to claim 1 , wherein the output rate calculating means calculates a ratio between a bit rate value of the received stream data and a bit rate value of the stream data output at the end of reception of the stream data. The synchronization reference information, the receiving apparatus according to claim 1, characterized in that the time information providing server address on the IP network 3. The synchronization reference information, the receiving apparatus according to any one of claims 1 to 3, characterized in that the ISDN reference clock. The synchronization reference information, the receiving apparatus according to any one of claims 1 to 3, characterized in that the channel transmission clock of the television or radio broadcast. The synchronization reference information, the receiving apparatus according to any one of claims 1 to 3, characterized in that the GPS time information. The receiving apparatus according to any one of claims 1 to 3 , wherein the receiving apparatus obtains the synchronization reference information from encoded stream data transmitted from a video server. The receiving apparatus, the receiving apparatus according to any one of claims 1 to 3, characterized in that obtaining the synchronization reference information by the session other than the reception of the stream data and the video server. The receiving apparatus, the receiving apparatus according to any one of claims 1 to 3, characterized in that it receives from another server connected to the synchronization reference information to the network. The receiving apparatus, the receiving apparatus according to any one of claims 1 to 3, characterized in that to receive the synchronization reference information from the television or radio broadcast waves. The receiving apparatus, the receiving apparatus according to any one of claims 1 to 3, characterized in that to receive the synchronization reference information from the communication line.

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