KR20150142350A - Method for Measuring Variation of Transmission Delay Time of Network for Rate Adaptation and Realtime Video Service System Using the Same - Google Patents

Abstract

The present invention relates to a method for measuring a variation of network transmission delay time for rate adaptation of a real time video service, and a real time video service providing system using the same. The method for measuring a variation of network transmission delay time for rate adaptation comprises the following steps: including a first system clock in a first packet and transmitting the first system clock from a transmitter to a receiver at a transmission time of the first packet, wherein the first system clock is used for detecting a change in relative transmission delay time through a comparison with a second system clock of the receiver-; receiving information about the congestion degree of a network according to the change from the receiver; and adjusting a beat rate of a video encoder according to the information about the congestion degree.

Description

TECHNICAL FIELD [0001] The present invention relates to a network transmission delay time variation measurement method for rate adaptation and a real-time video service provision system using the same,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a network transmission delay time variation measurement technique, and more particularly, to a network transmission delay variation measurement method for rate adaptation of a real-time video service and a real-time video service provision system using the same.

For a real-time video service requiring a delay of less than a certain level between a transmitting device and a receiving device, such as a video call, a TCP (Transmission Control Protocol) -based protocol having a retransmission characteristic for lost packets in case of packet loss of a video call, Similar implementations can be used, but in this case there may be a problem with real-time performance due to normal acknowledgment (ACK) and time delays due to packet retransmission.

For this reason, real-time image transmission is mainly performed in the form of a Real-time Transport Protocol (UDP) UDP (User Datagram Protocol). However, since UDP is a protocol that is not guaranteed to be transmitted, packet loss occurs when transmission is performed at a bit rate higher than the network bandwidth or when the network congestion becomes high, thereby deteriorating quality such as deterioration of image quality of real time image.

In real - time video services such as video calls, it is a good idea to use a network that guarantees high - priority quality of the video and voice packets. That is, in a network or a wireless environment or a mobile communication environment in which quality is not guaranteed, packet loss can not be prevented due to a change in signal strength. Therefore, it is possible to estimate the transmission bandwidth without network congestion through rate adaptation and continuously change the transmission bit rate, and additionally compensate for lost packets through Forward Error Correction (FEC). .

In the conventional rate adaptation method, a feedback packet containing information necessary for adjusting the transmission bit rate from the reception apparatus to the transmission apparatus is transmitted to adjust the transmission bit rate. For example, information such as packet loss, jitter, and the amount of received data may be transmitted from the receiving apparatus to the transmitting apparatus through the feedback packet, and information related to packet loss among the transmitted information may control the transmission bit rate Is used as key information. The feedback packet may be implemented using standard RTCP (RTP control protocol) packets. However, the rate adaptation based on packet loss information has a disadvantage in that the transmission bit rate is adjusted only after the loss of the packet occurs and the quality is significantly degraded.

As for the reason of packet loss, when network congestion becomes high, packets are accumulated in a queue of a relay device such as a router, thereby causing a transmission delay of a packet. When a packet is accumulated over a queue size, packet loss occurs. That is, a packet transmission delay occurs before a packet loss, and a packet transmission delay time is measured by considering this principle and used as a parameter for rate adaptation.

A conventional method of estimating a packet transmission delay time is to use a half value of RTT (Round Trip Time) obtained using an RTCP packet. 1 is a view for explaining an RTT measurement method using a standard RTCP packet.

As shown in FIG. 1, a transmitting apparatus periodically transmits an RTCP SR (Sender Report) packet to a receiving apparatus, and a receiving apparatus periodically transmits an RTCP RR (Receiver Report) packet to a transmitting apparatus upon receiving an RTCP SR packet . Since the receiving apparatus does not send the RTCP RR packet directly to the transmitting apparatus as a response immediately after receiving the RTCP SR packet, the difference between the time when the receiving apparatus receives the RTCP SR packet and the time when the receiving apparatus transmits the RTCP RR packet is delayed (Td) And then transmitted in an RTCP RR packet.

The RTT that can be measured at the transmitting apparatus side can be obtained by the following formula (1).

The packet transmission delay time can be defined as the half value of RTT, but there are disadvantages of the following 1 ~ 3.

1. Because RTT is affected by two-way network condition, it is not suitable for multimedia sharing such as unidirectional transmission, video call, etc., and it may be more error in mobile communication network as asymmetric network.

2. For RTT calculation, RR (Receiver Report) needs to be sent in pairs with SR (Sender Report). In particular, when the RTCP packet is lost, it is generally impossible to update the status information until the SR retransmission.

3. Standard RTCP packets can cause unnecessary amount of information and cause waste of network bandwidth.

International Application Publication No. WO 2012/125008 A2 (September 20, 2012)

SUMMARY OF THE INVENTION The present invention has been made in order to solve the disadvantages of the prior art, and it is an object of the present invention to provide a rate adaptation scheme which can be applied simply by using the measurement of the packet transmission delay time, do. That is, an embodiment of the present invention provides an efficient network transmission delay time variation measurement method for rate adaptation of a real-time image service and a real-time image service system using the same.

According to an aspect of the present invention, there is provided a method for measuring network transmission delay time variation for rate adaptation of a real-time image service, the method comprising: transmitting a first system clock to a first packet at a transmission time of a first packet; Wherein the first system clock is used to detect a change in the relative transmission delay time through comparison with a second system clock of the receiving apparatus; Receiving congestion information of network congestion according to a change trend from a receiving apparatus; And adjusting the bit rate of the video encoder according to the congestion information.

According to another aspect of the present invention, there is provided a network transmission delay time variation measurement method for rate adaptation of a real-time image service, the method comprising: receiving a transmission packet from a transmission apparatus in a reception apparatus; The method comprising the steps of: detecting a change in the relative transmission delay time, estimating a network congestion according to a change trend, and transmitting the estimated congestion information to a transmission apparatus. Here, the congestion information is used in the rate adjuster of the transmitting apparatus to adjust the bit rate of the video encoder of the transmitting apparatus.

In one embodiment, the network transmission delay time variation measurement method for rate adaptation of a real-time image service further comprises increasing the reference clock in the reception apparatus gradually to correct the system clock increase rate difference between the transmission apparatus and the reception apparatus . Here, the reference clock is obtained by subtracting the first system clock from the second system clock.

In one embodiment, the network transmission delay variation measurement method for rate adaptation of a real-time image service further comprises estimating a change in network congestion through a linear regression analysis of the relative transmission delay time at the receiving apparatus.

In one embodiment, the first system clock may be added to replace the time stamp of a User Datagram Protocol (UDP) packet.

According to another aspect of the present invention, there is provided a transmission system for providing a real-time image service through a network, the system comprising: a video encoder for encoding an image to be transmitted to a receiver; A packetizer for packetizing image data encoded by a video encoder; A packet transmitter for transmitting a packetized first packet to a receiving device in a packetizer; A system time injector coupled to the packet transmitter for adding a first system clock to a first packet before transmission of the first packet; And a rate adjuster for receiving the congestion information of the network congestion estimated based on the first system clock from the receiving apparatus and controlling the bit rate of the video encoder based on the received congestion information.

According to another aspect of the present invention, there is provided a system for providing a real-time image service, the system comprising: a packet receiver for receiving a first packet from a transmitter; A packetizer for parsing a first packet of a packet receiver; An image decoder for decoding the image data parsed in the depacketizer; A system time injector for generating a second system clock for a reception time of a first packet received at a packet receiver; A relative transmission delay time calculator for calculating a relative transmission delay time by comparing the first system clock included in the first packet with the second system clock; And a network congestion estimating unit for estimating a change trend by analyzing a relative transmission delay time and transmitting congestion information of a network congestion degree according to the estimated change trend to a transmission apparatus, wherein the congestion degree information is transmitted from the rate adjuster of the transmission apparatus And adjusting the bit rate of the video encoder.

In one embodiment, the receiving device gradually increases the reference clock to compensate for the system clock increase rate difference with the transmitting device, where the reference clock is the second system clock minus the first system clock.

In one embodiment, the network congestion estimator estimates a change in network congestion through linear regression analysis of relative transmission delay time.

In one embodiment, the first system clock may be inserted in the UDP packet instead of the timestamp.

According to the present invention, it is possible to easily apply the present invention using the measurement of the packet transmission delay time, which is considered to be most effective for adjusting the transmission rate, before the image quality deterioration among elements considered in the conventional rate adaptation method for stable image service And provides a scheme for implementing rate adaptation with little additional network load, thereby realizing efficient video transmission service.

That is, in order to provide a stable image service, it is necessary to apply a rate adaptation adaptable to a change in the network state, but the application is not simple for a method in which a sufficient effect is expected. Particularly, when the image transmission function has already been implemented, it is necessary to make various modifications to the transmission apparatus, the reception apparatus and the network. However, according to the present embodiment, there is an effect that the rate adaptation function can be effectively implemented without applying a lot of modifications to the existing environment or matter as a method which is relatively simple and has little additional network load.

In addition, according to the present invention, a service for transmitting a large amount of data using UDP (User Datagram Protocol) is basically a network transmission delay for rate adaptation that can be applied to a communication system that needs to adjust a transmission rate according to a network situation A time variation measurement method and system can be provided.

Also, according to the present invention, there is provided a network transmission delay time variation measuring method and system for rate adaptation, which can be applied to all services that require mainly video transmission, .

In addition, according to the present invention, it is possible to apply the present invention to a real-time image sharing service that performs image transmission simultaneously with a normal voice call, A transmission delay time variation measurement method and system can be provided.

1 shows an example of a RTT (Round Trip Time) measurement method using a standard RTCP (RTP control protocol) packet
2 is a block diagram of a real-time image service providing system using a network transmission delay time variation measurement method for rate adaptation of a real-time image service according to an embodiment of the present invention.
3 is a flowchart of a relative delay time measurement process of a network transmission delay time variation measurement method for rate adaptation of a real-time image service according to another embodiment of the present invention

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

The network transmission delay time variation measurement method according to an embodiment of the present invention is a technique required to implement rate adaptation that adjusts a transmission bit rate according to a change in a network state in real time multimedia transmission.

The rate adaptation method implemented in the network transmission delay time variation measuring method of the present embodiment is compared with the existing rate adaptation method and the characteristic parts thereof will be described as follows.

In the transmitting apparatus, the system clock at the time of packet transmission is injected into the packet to be transmitted.

The receiving apparatus extracts the system clock at the transmission time in the received packet, sets or updates the reference clock, and calculates the relative transmission delay time of the packet.

Also, the reference clock is gradually increased in order to automatically correct the error due to the difference in the system clock increase rate between the transmitting apparatus and the receiving apparatus.

Further, the receiving apparatus calculates a change in the detected transmission delay time and sends a feedback packet to the transmitting apparatus.

According to the present embodiment, in real-time image transmission method implementation, rate adaptation is applied to prevent deterioration of image quality by dynamically changing a transmission bit rate according to a change in network congestion. Particularly, In applying a rate adaptation scheme using a rate adaptation scheme, that is, an increase in the packet transmission delay time when the network congestion degree increases, it is possible to check the relative change in the packet transmission delay time rather than the absolute value of the packet transmission delay time itself A method of rate adaptation in an effective real-time video service can be provided.

Example 1

2 is a block diagram of a real-time image service providing system using a network transmission delay time variation measurement method for rate adaptation of a real-time image service according to an embodiment of the present invention.

In general, the flow of a video transmission service consists of a video encoder, a packetizer, and a packet transmitter in a transmitting device, and a packet receiver in a receiving device, a depacketizer, and a video decoder .

Referring to FIG. 1, a real-time image service providing system according to the present embodiment includes a transmitting apparatus 10 and a receiving apparatus 20 connected via a network, and the transmitting apparatus 10 includes a video encoder 11, A packetizer 12, a packet transmitter 13, a system time injector 14 and a rate adjuster 15. The receiver 20 includes a packet receiver 21, a packetizer 22, A video decoder 24, a system time injector 24, a relative transmission delay time calculator 25, and a network congestion estimator 26.

The system time injector 14 may be referred to as a first system time injector and may be coupled to the packet transmitter 13 to provide a first system time injector 14 for the first transmission time point of the RTCP SR packet transmitted from the transmitting device 10 to the receiving device 20. [ Time is injected into the corresponding transmission packet.

The rate adjuster 15 applies a control signal to the video encoder 11 so that the bit rate of the real time video service is adjusted based on the congestion degree information received from the network congestion estimating unit 26 of the receiving apparatus 20. [ Here, the congestion information may be a reference value for adjusting the bit rate of the transmission video signal for the real-time image service.

The system time injector 24 may be referred to as a second system time injector and may be coupled to the packet receiver 21 to transmit a second time for the reception time of the RTCP SR packet received from the transmission device 10 to a relative transmission delay time And provides it to the calculation unit 25.

The relative transmission delay time calculator 25 calculates the relative delay time of the specific packet received from the transmitting apparatus 10 based on the first time obtained by parsing the RTCP SR packet and the second time obtained from the system time injector 24 . The relative transmission delay time calculator 25 may be implemented as a unit that calculates the relative delay time variation of the received packet or a configuration unit that performs a function corresponding to such a unit.

The network congestion estimating unit 26 estimates the change in the network congestion by analyzing the relative delay time calculated by the relative transmission delay time calculating unit 25. [ The transition of the network congestion degree estimated by the network congestion estimating unit 26 is transmitted to the rate adjuster 15 of the transmitting apparatus 10 as congestion information.

According to this embodiment, the packet transmitter 13 injects the system time into the packet, calculates the relative transmission delay time from the system time of the transmitting apparatus injected into the packet at the packet receiver, modifies the system time of the receiving apparatus The rate adaptation of the real-time image service can be efficiently optimized by estimating the congestion degree of the network and transmitting the change of the congestion degree to the transmission apparatus to adjust the bit rate of the transmission image.

Example 2

An accurate measurement of the packet transmission delay time is defined as a difference between a clock at the time of packet transmission and a clock at the time of packet reception when the system clock of the transmitting apparatus and the receiving apparatus are accurately synchronized using a separate apparatus. However, even if the system clocks between the two devices are not synchronized, it is also possible that the transmission rate of the transmitting device and the receiving device are equal to each other, If you do, you can find the relative change.

That is, the difference between the transmission delay time of the N-th packet and the transmission delay time of the M-th packet can be defined as Equation (2).

In Equation 2, TS _M is the system clock of the transmitting device when sending the M-th packet, TR _M is the system clock of the receiver when receiving the M-th packet, D _M represents respectively the actual transmission delay time of the M-th packet, TS _N represents the system clock of the transmitting apparatus at the time of transmitting the Nth packet, TR _N represents the system clock of the receiving apparatus at the time of receiving the Nth packet, and D _N represents the actual transmission delay time of the Nth packet. Where N is a natural number greater than M.

In Equation (2), if the actual transmission delay time of the Nth packet is set to 0 and the relative transmission delay time of the Mth packet is defined as DRel _M , the following equation (3) can be simply defined.

In Equation (3), T _diffbase is the transmission delay time of the Nth packet and can be defined as Equation (4), and can be set to 0 as a reference clock.

As described above, when the transmitting apparatus measures the system clock at the time of packet transmission and transmits the measured system clock to the receiving apparatus, the receiving apparatus can measure the relative transmission delay time by parsing the received packet. In particular, if the transmitted protocol is Real-time Transport Protocol (RTP), the RTP time stamp can be used to store the system clock at the transmission time.

Compared with the standard RTP implementation method, since the RTP timestamp is not the transmission time but the reproduction time of the media, it is insufficient to use the RTP timestamp as a criterion for accurate network delay time change measurement by factors such as an encoder, a decoder, and a play buffer. Therefore, in this embodiment, the RTP time stamp can be used as a criterion for measuring the network delay time change by overwriting the RTP time stamp with the system clock of the transmitting apparatus instead of the reproduction time.

In case of RTP UDP (User Datagram Protocol), since the size of one frame of an image is larger than the maximum transmission unit (MTU), a frame of the image is composed of a plurality of UDP packets. That is, according to the present embodiment, a plurality of packets constituting an image of one frame have the same time stamp.

Therefore, when a plurality of packets constitute one frame of an image, the transmission time is measured for the first RTP packet of the frame, the RTP time stamp is overwritten, and the time stamp of the remaining RTP packets is overwritten with the transmission time of the first RTP packet Write. According to this configuration, since it does not deviate from the RTP standard specification, it can be reproduced by a general player.

The time stamp of the received packet is the system clock of the transmitting apparatus at the transmitting time of the packet, so that the receiving apparatus can obtain the delay time variation of the packet by the simple method as shown in FIG.

3 is a flowchart illustrating a relative delay time measurement process of a network transmission delay time variation measurement method for rate adaptation of a real-time image service according to another embodiment of the present invention.

Referring to FIG. 3, the relative delay time measurement process in the receiving apparatus according to the present embodiment first receives a packet (S31) and determines whether it is a packet to be calculated (S32). The determination of the packet to be computed refers to determining whether a plurality of packets have the same timestamp.

Next, it is determined whether the packet is the first packet among a plurality of packets to be computed (S33). In this step, it is determined whether or not the packet to be computed is a remaining packet having the same timestamp as the first packet of the single frame, as in the case where a plurality of RTP packets constitute one video frame in step S32. .

If it is determined in step S33 that the packet is the first packet of the calculation target packet, the reference clock is set using the time stamp of the first packet (S34). That is, the reference clock setting step S34 is a step of obtaining the difference between the system clock of the transmitting apparatus and the system clock of the receiving apparatus, and may be simply expressed by the following equation (5).

Next, the relative delay time of the previous or previous packet of the packet used for the reference clock setting is calculated by applying the reference clock (S35). The relative delay time calculation step S35 can be obtained by the following Equation (6) by obtaining the relative delay time of the previously received packet.

As can be seen from Equation (6), if the delay time of the received packet is less than 0, that is, if the delay time is the longest among the previously received packets, the reference clock is reset So that the minimum value of the packet transmission delay time can be maintained to be zero.

Next, it is determined whether the relative delay time is less than 0 (S36). In this step S36, the relative delay time obtained through the above process is checked for the change of the delay time by linear regression analysis or the like to check the change of the delay time.

For example, in the case of linear regression analysis using the simplest least squares method, where the x-axis is time and the y-axis is delay time, when the result of relative delay time calculation is analyzed by slope and intercept, And the network congestion is decreasing if it is smaller than 0.

Next, the congestion information is transmitted to the transmitting apparatus for resetting the reference clock (S37). In this step S37, when the slope of the linear regression analysis result with respect to the relative delay time is greater than or equal to a specific threshold value, the feedback packet including the congestion information is transmitted to the transmission apparatus so as to reduce the transmission bit rate, .

Example 3

On the other hand, there is a possibility that the initial reference clock may not be set properly when transmitting at the initially set bit rate without knowing the network status, which may cause a malfunction. In a typical network environment, since the transmission delay of a small IP (Internet Protocol) packet is smaller than that of a large IP packet, the packet of the minimum size is transmitted before the start of transmission of the actual video packet, You can access close values. In addition, since it is necessary to update the minimum delay time in order to correct the clock increase rate difference between the transmitting apparatus and the receiving apparatus described above with reference to FIG. 2, it may be necessary to periodically transmit a small size packet.

As described above, the accurate measurement of the packet transmission delay time is defined as the difference between the clock of the transmission timing of the packet and the reception clock when the system clocks of the transmission apparatus and the reception apparatus are exactly the same. On the other hand, even if the clocks of the transmitting apparatus and the receiving apparatus are exactly synchronized once, the system clock of the transmitting apparatus and the system clock of the receiving apparatus do not increase at the same speed.

If the system clock of the transmitting apparatus is Cs and the system clock of the receiving apparatus is Cr in a state where the synchronization of the system clock is stabilized, the relationship between the system clocks of the two apparatuses can be represented by a function form of Equation 7, which is a simple linear function.

In Equation (7), when A is 0, the increase rate of two clocks is exactly the same, and when A is larger than 0, the system clock of the receiving apparatus operates faster than the transmitting apparatus system clock. If A is smaller than 0 The system clock of the transmitting apparatus operates faster than the system clock of the receiving apparatus.

Since a difference between system clocks may occur between the two devices as time goes by, a separate device is required to correct the system clock. As a rule, if two system clocks are synchronized, There is an increasing number of factors to consider such as how to perform the actual packet transmission during synchronization, whether to use the network to synchronize the system clock, and whether it affects the image transmission using the same network.

That is, the difference in the system clock increase rate between the transmitting apparatus and the receiving apparatus may cause a problem in the relative packet delay time measuring method. However, the difference in the system clock increase rate between the two devices in a general situation is not so large, and therefore, in this embodiment, the above-mentioned problem is avoided simply by operating the system clock of the receiving apparatus as if it is operating at a slower speed than the actual one.

The above-mentioned working principle will be described in the following 1 and 2.

1. When the system clock of the receiving apparatus operates more slowly, if there is no change in the actual packet delay time, the relative delay time is measured to be gradually decreased since Equation (6) is satisfied. As a result, the relative delay time becomes negative. In this case, the reference clock is updated according to the packet, so that the system clock of the receiving apparatus can be corrected and synchronized with the transmitting apparatus.

2. If the system clock of the receiving device operates more quickly and the actual packet transmission delay time does not change at all, then the system time of the receiving device will operate faster than the sending device's system time, It becomes smaller than the increase of the system time of the apparatus, and therefore, the transmission delay time is measured to increase gradually. In other words, it is judged that the network congestion rate continues to increase.

Therefore, to compensate for this, the system time of the receiving apparatus is always adjusted so that it operates artificially a little slower. According to this measure, the system clock of the receiving apparatus will increase more slowly than the system clock of the transmitting apparatus, so that the system clock of the receiving apparatus can be corrected naturally by the same principle as the above-mentioned correction function of 1. above.

According to the above operation principle, the formula for calculating the reference clock of Equation (5) can be modified as shown in Equation (8) below.

In Equation (8), the reference clock corresponds to subtracting the first system clock from a value obtained by adding the increment to the second system clock, where A is the time at which the system clock increase rate of the calibrated receiver is always faster than the system clock increase rate of the transmitter (Natural number) that can be set.

It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims . It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

10: Transmitter
14: System time injector
15: Rate adjuster
20: Receiver
24: System time injector
25: relative transmission delay time calculation unit
26: Network congestion degree estimation unit

Claims (8)

Transmitting a first system clock at a transmission time of a first packet to the reception apparatus by including the first system clock in the first packet, wherein the first system clock is compared with a second system clock of the reception apparatus Used to detect a change in the relative transmission delay time;
Receiving congestion information of network congestion according to the change trend from the receiving apparatus; And
And adjusting the bit rate of the video encoder according to the congestion information. A reception apparatus receives a transmission packet from a transmission apparatus, detects a change in relative transmission delay time by comparing a first system clock included in the received transmission packet with a second system clock of the reception apparatus, Wherein the congestion degree information includes at least one of a network transmission delay for rate adaptation used for adjusting the bit rate of the video encoder of the transmission apparatus in the rate adjustor of the transmission apparatus, Method of measuring time variation. The method according to claim 1 or 2,
Further comprising a step of gradually increasing a reference clock in the receiving apparatus to correct a system clock increasing speed difference between the transmitting apparatus and the receiving apparatus, wherein the reference clock is a value obtained by adding the increment to the second system clock, Lt; RTI ID = 0.0 > 1 < / RTI > system clock. The method according to claim 1 or 2,
Further comprising estimating a change in the network congestion through a linear regression analysis of the relative transmission delay time at the receiving apparatus. A transmitting apparatus connected to a receiving apparatus via a network,
A video encoder for encoding an image to be transmitted to the receiver;
A packetizer for packetizing the image data encoded by the image encoder;
A packet transmitter for transmitting a packetized first packet in the packetizer;
A system time injector coupled to the packet transmitter for adding a first system clock to the first packet before transmission of the first packet; And
A rate adjuster for receiving the congestion degree information of the network congestion estimated based on the first system clock from the receiving apparatus and controlling the bit rate of the video encoder based on the received congestion degree information;
And a real-time image service providing system. A receiving apparatus connected to a transmitting apparatus via a network,
A packet receiver for receiving a first packet from the transmitting apparatus;
A packetizer for parsing a first packet of the packet receiver;
An image decoder for decoding image data parsed in the depacketizer;
A system time injector for generating a second system clock for a reception time of a first packet received at the packet receiver;
A relative transmission delay time calculator for calculating a relative transmission delay time by comparing the first system clock included in the first packet with the second system clock; And
A network congestion estimating unit that analyzes the relative transmission delay time to estimate a change trend and transmits network congestion information according to the estimated change trend to the transmission apparatus, Used to adjust the bit rate of the video encoder of the transmitting device;
And a real-time image service providing system. The method of claim 6,
Wherein the receiving apparatus gradually corrects the system clock increase rate difference with the transmission apparatus by gradually increasing the reference clock, wherein the reference clock is obtained by subtracting the first system clock from a value obtained by adding the increment to the second system clock Real - time video service delivery system. The method according to claim 6 or 7,
Wherein the network congestion estimator estimates a change in the network congestion through a linear regression analysis of the relative transmission delay time.

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