JP2007104569A - Data receiving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain video streaming which has a short reproduction delay time and in which neither an underflow nor an overflow frequently occurs. <P>SOLUTION: Video data distributed through an IP (Internet Protocol) network are input to a package receiver 101. Time information is inserted into the encoded packet data on a transmission side, so a system clock 111 in a receiver is continuously contrasted with the inserted time information inserted to know the state of jitters on a transmission line. The amount of data received within a time of the difference between the maximum delay jitters and mean delay jitters is defined as an optimum readout storage amount, and decoding and reproduction are started after data are stored in a receiving buffer by the amount after the reception is started. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

This apparatus relates to a data receiving apparatus suitable for receiving and reproducing video in real time via, for example, an IP network.

As a method of viewing digital video data on a client such as a PC via an IP network, the video data is downloaded in batch by the client, and after all the downloads are completed, the file is opened and played back. There is a method of sequentially reproducing video data while the client receives the transmitted video data. However, the former requires an enormous amount of time to download all of the huge video data, even with advanced compression technology, and with the current IP network transfer speed, it is too real-time. It will be far away. In view of this, a technique (video streaming) that can reproduce video without waiting for completion of the download, such as the latter, has attracted attention.

In video streaming, video data packets continuously received via an IP network are stored in a buffer such as a memory in the client in consideration of transmission delay jitter related to transmission, and a certain amount of data is stored. After that, the video data is read out, decoded, and displayed as reproduction data on the display of the client.

In the following standard technology collection, a technical example using a buffer to deal with transmission delay jitter in an Internet protocol telephone is described.
Standard Technology Collection "Internet Protocol Telephone (IP Telephone) Technology" 1-1-3 (Technical Trends Group, Technical Research Section, General Affairs Department, Patent Office)

Further, in Patent Document 1 below, if there is a buffer failure in streaming, if underflow occurs, the accumulated amount until the first read is increased, and if overflow occurs, the accumulated amount until the first read is decreased. The technology is described.
JP 2002-330136 A

The packet data transmission delay jitter fluctuation to the client is a short-term fluctuation such as fluctuation due to IP network traffic congestion and error correction, so that the average jitter amount does not change, There are fluctuations in which the average value of the jitter amount changes due to long-term factors such as increase / decrease in nodes and changes in transmission paths in the IP network.

A method in which a certain amount of data is stored in the client reception buffer and then decoded and played back is effective in absorbing transmission delay jitter, but the exact amount of jitter cannot be predicted, so the stored data in the buffer In order to avoid an underflow state in which playback is interrupted due to emptying, it is necessary to set a large storage amount based on an empirical amount, which causes a problem that playback delay increases. However, underflow has not been able to eradicate until now due to the unpredictability of accurate jitter.

In addition, in the method of manually setting the accumulation amount as an empirical amount or adjusting the accumulation amount only when there is a buffer failure as described in Patent Document 1, the long-term transmission delay jitter as described above is used. In the case of frequent fluctuations, there has been a problem that quality degradation due to continuous buffer failures cannot be improved. Further, in these conventional methods, since the main idea is to reduce the frequency of underflow, the concept of reducing the read accumulation amount as much as possible, that is, reducing the time delay during reproduction is thin. For example, if the transmission delay jitter is a constant value for a long time, it does not reflect that the read accumulation amount may be zero.

In order to solve the above problems, the present invention takes the following means.

(1) a packet receiving unit that receives an encoded stream in which reproduction time information of a stream is inserted at a predetermined packet interval and outputs the encoded stream to a reception buffer;
A reception buffer having a memory for storing an encoded stream, a read accumulation amount calculation unit for calculating the amount of packet data stored in the reception buffer, and a packet data amount output to the reception buffer by the packet reception unit are constantly monitored. When the total amount of packet data stored in the reception buffer reaches the read accumulation amount after the device starts operation, there is an accumulation amount monitoring unit that outputs a read request signal, and a read request signal from the accumulation amount monitoring unit. A decoding / reproducing unit that reads out the packet data from the reception buffer at the timing of the reproduction time information added to the received encoded stream and starts reproduction.

(2) The read accumulation amount calculation unit calculates the average over the time width T from the reproduction time information inserted in the encoded stream received by the packet reception unit and the system clock in the receiving device when the encoded stream is received. A delay amount is calculated, a difference between the maximum delay jitter amount and the average delay jitter amount is set as a read accumulation amount, and an accumulation amount calculation unit that performs processing for notifying the read accumulation amount to the accumulation amount monitoring unit is provided. The data receiving device.

(3) The read accumulation amount calculation unit calculates the average over the time width T from the reproduction time information inserted into the encoded stream received by the packet reception unit and the system clock in the receiving apparatus when the encoded stream is received. A delay amount is calculated, a difference between the maximum delay jitter amount and the average delay jitter amount is set as a read accumulation amount, and an accumulation amount calculation unit that performs processing for notifying the read accumulation amount to the accumulation amount monitoring unit is provided. In addition to when the read accumulation amount is reached for the first time since the start of operation of the device, the amount calculation unit is used when the encoded stream becomes empty in the reception buffer (underflow) or the encoded stream overflows in the reception buffer. A data receiving device that calculates a read accumulation amount even after a state such as overflow (overflow) occurs and the reception buffer fails A.

(4) The read accumulation amount calculation unit is a data reception apparatus that sets a positive value N smaller than the size of the reception buffer instead of 0 as an initial value of the read accumulation amount at the start of processing. .

(5) The read accumulation amount calculation unit is a data receiving device characterized in that when the determined read accumulation amount exceeds an abnormally large value M, the read accumulation amount is set to M.

(6) The read accumulation amount calculation unit is a data receiving device characterized in that it always calculates the average delay jitter and recalculates the read accumulation amount as soon as an underflow or overflow occurs.

(7) The read accumulation amount calculation unit always calculates the maximum delay jitter and the average delay jitter, and the difference A between the maximum delay jitter and the average delay jitter is less than the read accumulation amount B set at the start of processing of the apparatus. Further, the data receiving apparatus is characterized in that the read accumulation amount is A.

According to the first aspect of the present invention, the amount of packet data received from the IP network can be automatically set in the buffer, and the reproduction delay can be reduced. Also, since the amount of storage cannot be adjusted until the buffer fails, underflow can occur even when short-term delay jitter or long-term delay jitter occurs frequently due to changes in the IP network. It is possible to prevent frequent occurrences.

According to the second aspect, it is possible to quantify the timing for notifying the decoding / playback unit of the read permission signal for starting the reading of the packet data from the buffer, thereby realizing automation of the apparatus.

Further, according to the third aspect, even if the storage amount is less than the read storage amount, it is possible to quickly cope with the buffer failure.

According to the fourth aspect of the present invention, it is possible to prevent a buffer failure immediately after the operation of the apparatus by setting the non-zero value N as an initial value.

According to the fifth aspect of the present invention, when the transmission delay jitter becomes so large as to exceed the size of the buffer, it is possible to prevent the buffer failure from continuing for a certain period of time.

Further, according to claim 6, since it is possible to calculate the average delay jitter and the maximum delay jitter immediately after the buffer failure without waiting for a certain fixed time necessary for calculating the average delay jitter, It is possible to shorten adverse effects such as stop of image reproduction due to buffer failure.

According to the seventh aspect of the present invention, the read accumulation amount is returned to a small value again when a time elapses after the read accumulation amount has become a large value, such as when a large maximum delay jitter occurs. Thus, the delay time of image reproduction in the decoding / reproducing unit can be returned to a small value about the initial setting value.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a data receiving apparatus according to an embodiment of the present invention. FIG. 2 is a process flowchart in the data receiving apparatus according to the embodiment of the present invention.

In this embodiment, an encoded stream into which playback time information has been inserted is received by a receiving apparatus, the optimum packet accumulation amount is calculated from the respective values of average delay jitter and maximum delay jitter, and the frequency of underflow is reduced. It is what I did.

In FIG. 1, encoded packet data of video data distributed via an IP network is input to a packet receiving unit 101. Since time information is inserted into the encoded packet data on the transmission side, the jitter in the transmission path can be reduced by continuously comparing the system clock 111 in the receiver with the time information inserted in the received data. It becomes possible to know the situation.

If {inserted time information: system clock}, for example, if three packets are received and {1: 2}, {2: 3}, and {3: 4}, respectively, the transmission delay jitter is It can be seen that it is always 1, and if it is {1: 3}, {2: 4}, {3: 5}, the transmission jitter is always 2. In this case, as will be described later, the average delay jitter and the maximum delay jitter are each 1.

If {1: 2}, {2: 3}, {3: 5}, {4: 6}, the transmission delay jitter is often 1, but 2 is also present. In this case, as will be described later, the average delay jitter is (1 + 1 + 2 + 1) /4=1.25, and the maximum delay jitter is 2.

The input encoded packet data is stored in the reception buffer 103. When the read accumulation amount is accumulated in 103 and the read request signal arrives at the decode reproduction unit 105 from the accumulation amount monitoring unit 109, the encoded packet data is transmitted from 103 to 105, decoded at 105, and reproduced on the client monitor or the like. Is done.

It is the read accumulation amount calculation unit 107 that calculates how much encoded packet data is stored in 103. Since time information is inserted into the encoded packet data on the transmission side, the data receiving device checks the continuity between the time information and the system clock in the data receiving device, thereby reducing the delay jitter generated in the transmission path. It can be known as shown in equation (1).


Here, ENCt (i) is a value obtained by converting the time information of the packet I into the receiving system clock, and DECt (i) is the receiving system clock when the packet I is received.

Next, based on the transmission delay jitter, the average delay jitter Ja is obtained as in equation (2).


Further, the maximum jitter amount among the transmission delay jitters during the time width T is defined as the maximum delay jitter Jm.

Here, an event that may occur when the amount stored in the buffer is not suitable will be described. The encoded stream is input to the receiver, accumulated in the reception buffer, and after a certain amount (A: read accumulation amount) has been accumulated, reading of the packet from the reception buffer is started. The transmission path is a short-term variation such as fluctuation due to IP network traffic congestion or packet retransmission due to error correction, so that the average jitter amount does not change, and the increase or decrease of nodes in the IP network or transmission path There are fluctuations in which the average value of the jitter amount changes due to a long-term change.

When A is smaller than these transmission delay jitters, if a large jitter occurs, the encoded stream packet in the reception buffer disappears (underflow), and decoding / reproduction becomes impossible in the reproduction unit. If A is larger than the size of the reception buffer, naturally, the encoded stream packet overflows from the reception buffer (overflow), packet loss occurs, and this cannot be decoded and reproduced by the reproduction unit. Become. For this reason, it is desirable that the preferable amount of A is larger than the transmission delay jitter and smaller than the reception buffer.

Even if this condition is satisfied, if the read accumulation amount is increased too much because the safety aspect is too important, the reproduction delay is increased and the real-time property is impaired. Thus, it is desirable that the ideal read accumulation amount is larger than the transmission delay jitter, smaller than the reception buffer, and as small as possible.

Therefore, in the present invention, the amount of data B received at the time of the difference between the maximum delay jitter and the average delay jitter shown in Equation (2) is set as the optimum read accumulation amount, and B packets are accumulated in the reception buffer after the start of reception. After that, decoding / reproduction is started. In step 107, equation (3) is calculated.


According to the equation (3), if the delay jitter in the transmission line is completely stable for a long time and keeps a constant value, B is set to 0 and decoding and reproduction can be performed.

The calculation result of 107 is transmitted to 109, and the accumulation amount of 103 is monitored in 109. When the accumulation corresponding to the calculation result of 107 is accumulated, a read request signal is transmitted to 105, and 105 starts reading. .

The timing for calculating the read accumulated amount and reflecting the result in the decode / playback unit is the case where the read accumulated amount reaches the initial set value of the read accumulated amount after the apparatus starts operation, and underflow and This is the case when the receive buffer fails, such as when an overflow occurs.

However, in this case, if a larger underflow occurs, it will be reflected in the decoding / playback unit. Therefore, if the processing continues, the read accumulation amount will only increase. For this reason, when the read accumulation amount is small, such as when the line is stable, there is a disadvantage that the reproduction delay is larger than necessary. Therefore, in the present invention, the read accumulation amount is further below the initial set value. Even in this case, it is reflected in the decoding / playback unit to prevent an increase in playback delay.

FIG. 2 summarizes the processing steps for determining the read accumulation amount from the start of the operation. The delay jitter is calculated for the time T, and when T elapses, the maximum delay jitter and the average delay jitter are calculated based on the delay jitter value sequence, and the read accumulation amount of Expression (3) is calculated.

In the present invention, not only when the delay jitter is calculated during the time T from the time of buffer failure, but as described above, the average delay jitter is always calculated, so that the read and accumulate immediately after the buffer failure occurs. A method of calculating quantity is also proposed.

FIG. 3 is a diagram for explaining the average delay jitter 301 and the maximum delay jitter 303. The read accumulation amount is a packet data amount corresponding to the difference between 303 and 301. When 303 becomes a large value, underflow occurs unless the read accumulation amount is increased. When 303 matches 301, the read accumulation amount is 0, and the encoded packet data received at 101 is reproduced at 105 in real time.

... Processing block diagram of data receiver ... Processing step for calculating the read accumulation ... graph of transmission delay jitter

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Packet receiving part 103 ... Reception buffer 105 ... Decoding reproduction | regeneration part 107 ... Read accumulation amount calculation part 109 ... Accumulation amount monitoring part 111 ... System clock 301 ... Average delay jitter 303 ... Maximum delay jitter

Claims (7)

A packet receiving unit that receives an encoded stream in which reproduction time information of the stream is inserted at a predetermined packet interval and outputs the encoded stream to a reception buffer;
A receive buffer with a memory for storing the encoded stream;
A read accumulation amount calculation unit for calculating the amount of packet data stored in the reception buffer;
The packet receiving unit constantly monitors the amount of packet data output to the reception buffer, and outputs a read request signal when the total amount of packet data stored in the reception buffer reaches the read storage amount for the first time after the device starts operating. An accumulated amount monitoring unit;
A decode reproduction unit that reads and decodes packet data from the reception buffer at the timing of reproduction time information added to the received encoded stream when a read request signal is received from the accumulation amount monitoring unit; and
A data receiving apparatus.
The read accumulation amount calculation unit calculates the average delay jitter amount in the time width T from the reproduction time information inserted in the encoded stream received by the packet reception unit and the system clock in the receiving apparatus when the encoded stream is received. 2. The data according to claim 1, further comprising: calculating a difference between the maximum delay jitter amount and the average delay jitter amount as a read accumulation amount, and performing a process of notifying the read accumulation amount to an accumulation amount monitoring unit. Receiver device.
The read accumulation amount calculation unit calculates the average delay jitter amount in the time width T from the reproduction time information inserted in the encoded stream received by the packet reception unit and the system clock in the receiving apparatus when the encoded stream is received. The difference between the maximum delay jitter amount and the average delay jitter amount is used as a read accumulation amount, and the read accumulation amount is notified to the accumulation amount monitoring unit. The accumulation amount calculation unit starts the operation of the device. In addition to when the read accumulation amount is reached for the first time after that, there are situations where the encoded stream is empty in the receive buffer (underflow) or the encoded stream overflows in the receive buffer (overflow). The data receiving apparatus according to claim 1, wherein the read accumulation amount is calculated even after the reception buffer fails, such as
The read accumulation amount calculation unit sets a positive value N smaller than the reception buffer size instead of 0 as an initial value of the read accumulation amount at the start of processing of the apparatus. Data receiver.
The data receiving apparatus according to claim 1, wherein the read accumulation amount calculation unit sets the read accumulation amount to M when the determined read accumulation amount exceeds M.
The data receiving apparatus according to claim 1, wherein the read accumulation amount calculation unit always calculates an average delay jitter and recalculates the read accumulation amount as soon as underflow or overflow occurs.
The read accumulation amount calculation unit always calculates the maximum delay jitter and the average delay jitter, and when the difference A between the maximum delay jitter and the average delay jitter is less than the read accumulation amount B set at the start of processing of the apparatus, The data receiving apparatus according to claim 1, wherein an accumulation amount is A.