KR19990043437A - Decoding Control Method of VAudio Client - Google Patents

Abstract

According to the present invention, when the client receives the encoded bit stream from the server and decodes the encoded bit stream for restoring to the original signal, the present invention actually estimates the server based on data fullness status information in the reception buffer. The present invention relates to a decoding control method of a VOD client capable of controlling a decoding rate based on a transmission rate. To this end, the present invention provides a reception buffer when decoding a coded bit stream for restoration to an original signal. By estimating the actual data rate in the server based on the data fullness (bit stream state) information in the system, and adaptively controlling the decoding rate based on the estimated actual data rate, the encoder system clock and the server as in the conventional method Error between system clock or client system clock and server system Due to the error between Luck will be capable to reliably prevent overflow or OY eonteo flow phenomenon which may be caused in the receive buffer on the client side, to effectively suppress the image quality degradation in the reproduced image resulting.

Description

Decoding Control Method of VAudio Client

The present invention relates to a method of controlling a decoding speed of a stream provided from a server under a client-server system environment, and more particularly, a client receiving a video on demand (VOD) service from a server is synchronized with a server system clock. The present invention relates to a decoding control method of a VOD client suitable for adaptively adjusting the decoding speed.

Recently, the development of interactive cable television (I-CATV), an advanced form of cable television (CATV), has been accelerated everywhere.

On the other hand, using digital interactive cable television service technology instead of analogue, Video On Demand ensures that television viewers get the information they need (e.g., video information) at the right time. : VOD) service is available. In order to realize such on-demand video service, an information provider consisting of a large capacity server capable of storing and transmitting information, a service provider such as a television broadcasting station, and a high-speed information request from a service provider through a network are provided. This requires a client using a delivery system provider and service information provided from a delivery system provider for simultaneous delivery to multiple television users (ie clients).

In order to implement the VOD service, the client requests remote servo to provide information such as a program to be serviced according to a user's operation, for example, a movie, news, or English conversation program, and the server responds to the client's request. The video and audio data of the program, ie, a stream of video, audio, and text, are fetched from the database and delivered to the client requesting the service.

At this time, the stream transmitted from the server to the client is data encoded and compressed based on the MPEG-2 algorithm, for example, and in DAVIC, a standard organization of the current interactive multimedia system, asynchronous transmission method is used to improve transmission performance. (native) I am using ATM.

Meanwhile, the encoded bit stream transmitted from the server to the client in response to the client's VOD service request and the bit stream of the header information include the data rate of the server. The client may restore the encoded bit stream to the original signal before encoding. When the rate information contained in the bit stream is extracted and the decoding rate at the time of restoration is determined based on the extracted rate information, the decoding rate is determined as 10 Mbps when the bit rate extracted from the bit stream is 10 Mbps. .

At this time, in the server, due to an error between the system clock of the encoder that compresses and encodes video and audio signals, and the system clock of the server itself, the bit rate of the bit stream transmitted from the server to the client exceeds or is lower than the preset rate. Can be sent. For example, even though the set rate is actually 10 Mbps, the data rate to the client may be 10.1 Mbps or 9.9 Mbps due to an error between the encoder's system clock and the server's own system clock.

In this case, since the bit stream transmitted from the server to the client includes predetermined rate information, that is, 10 Mbps rate information, the client determines the decoding rate as 10 Mbps, where the system clock and the server system clock are determined. If a change in the actual transmission rate (that is, increase or decrease of the transmission rate) occurs due to the error between the data, an overflow or underflow phenomenon of data may occur in the reception buffer at the client side.

In addition, the client may decode the encoded bit stream at a speed of 10.1 Mbps or 9.9 Mbps even though the preset transmission rate extracted from the bit stream is 10.1 Mbps due to an error between its system clock and the system clock of the server.

In this case, as described above, an overflow or underflow phenomenon of data may occur in the client-side reception buffer.

Therefore, in the above-described conventional method, due to an error between the encoder system clock and the server system clock or the error between the client system clock and the server system clock, an overflow or an underflow phenomenon occurs in the reception buffer on the client side, resulting in deterioration in image quality of the reproduced video. Has a problem.

Accordingly, the present invention is to solve the above-mentioned problems of the prior art, the client side receives the encoded bit stream from the server, and when the decoding of the encoded bit stream to restore to the original signal in the receiving buffer It is an object of the present invention to provide a decoding control method of a VOD client capable of estimating an actual data rate in a server based on data fullness (bit stream) state information of a server and controlling a decoding speed based on the estimated actual data rate. .

In order to achieve the above object, the present invention provides a method for controlling decoding of an encoded bit stream provided from a server in response to a VOD service request from a client having a receive buffer and a decoder in a client-server system. A first step of the server, in response to the VOD service request of the server, transmitting the encoded bit stream to the client, and extracting the rate information contained in the bit stream while storing the transmitted bit stream in the reception buffer; A second process of determining an initial decoding rate of the decoder based on the extracted rate information; A third step of storing data in the reception buffer until the current data amount stored in the reception buffer becomes a preset decoding start reference buffer amount; A fourth step of restoring the encoded bit stream sequentially extracted from the reception buffer to the original signal before encoding when the current amount of data in the reception buffer is the predetermined decoding start reference buffer amount; A fifth step of repeatedly checking the data increase / decrease amount of the current buffer stored in the reception buffer in predetermined reference buffer increments during the decoding operation; The decoder based on the increase / decrease state of the receive buffer when the current data increase / decrease amount of the receive buffer is increased or decreased by the predetermined predetermined data amount unit corresponding to the check result of the fifth process. A sixth step of sequentially increasing and decreasing the decoding speed at; And a seventh process of repeatedly performing the fourth to sixth processes until the VOD service is terminated.

1 is a schematic block diagram of a client-server system suitable for applying a method for controlling decoding of a VOD client in accordance with the present invention;

2 is a flowchart illustrating a decoding control process of a VOD client according to an embodiment of the present invention;

3 is a diagram for describing a process of preventing data overflow in a buffer by increasing a decoding speed as an example of an increase in the amount of data stored in a buffer.

* Explanation of symbols for main parts of the drawings

100: client 102: client control block

104: buffer 106: MPEG decoding block

110: server 112: server control block

114: Stream Pump

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

1 shows a schematic block diagram of a client-server system suitable for applying a method for controlling decoding of a VOD client according to the present invention.

As shown in the figure, the client 100 includes a client control block 102, a buffer 104 and an MPEG decoding block 106, and the server 110 includes a server control block 112 and a stream pump ( 114).

Referring to FIG. 1, the client control block 102 includes, for example, a microprocessor for performing overall operation control of a client system, and includes an operation signal according to a user's operation, for example, a video resume. Receive a command such as video pause, and perform a corresponding operation.

That is, the client control block 102 generates a VOD service request message when the operation signal for the VOD service request is input, transmits the VOD service request message to the server control block 112 on the server 110 through the line L11, and transmits the line L13. When transmitted from the server 110 side stream pump 114 to the bit stream, the rate information contained in the received bit stream is extracted to determine the initial decoding rate. Here, the buffer 104 is to prevent data loss that may be caused by the bit rate variation of the bit stream, and temporarily stores the bit stream received through the line L13.

In addition, the client control block 102 checks the state of the bit stream (ie, the full state) stored in the buffer 104 to adjust, i.e., vary, the decoding speed in the MPEG decoding block 106.

Next, the MPEG decoding block 106 performs a function of restoring a bit stream that has been compressed and encoded according to the MPEG encoding standard received through the buffer 104 to the original signal before encoding, where the decoding speed is substantially Adaptive to the decoding control signal provided from the client control block 102 via the line L17.

On the other hand, the server control block 112 on the server 110, for example, includes a microprocessor for performing overall operation control of the server system, instructions provided from the client control block 102 via the line L11, That is, instructing the stream pump 114 to continue or stop the stream transmission based on the message, and the stream pump 114 generates an encoded bit stream for the pre-stored program according to the instruction from the server control block 112. It is withdrawn and transmitted to the client 100 through the line L13.

Next, a process of controlling the decoding speed of the client based on the data full state information of the buffer in the client-server system having the above-described configuration will be described.

2 is a flowchart illustrating a decoding control process of a VOD client according to an exemplary embodiment of the present invention.

Referring to FIG. 2, when an operation signal for a VOD service request according to a user operation is input from a key input unit (not shown), a client control block 102 on the client 100 generates a VOD service request message on a line L11. (Step 202).

Therefore, the server control block 112 on the server 110 side instructs the stream pump 114 to continue the stream transmission in response to the VOD service request message received through the line L11, and as a result, the stream pump 114 receives the line. The bit stream encoded through L13 is transmitted to the client 100 (step 204). In this case, the transmitted bit stream includes predetermined rate information (eg, a 10 Mbps transmission rate).

Meanwhile, the client control block 102 extracts the rate information contained in the bit stream received through the line L13 (step 206), determines the initial decoding rate based on the extracted rate information (step 208), and the line The amount of data stored in the buffer 104 is checked through L15 to determine whether or not the amount of data in the buffer has reached the start of decoding.

That is, as an example, as shown in FIG. 3A, it is assumed that the buffer 104 is a buffer having a capacity of 10 M bits and starts a decoding operation for data recovery when the buffer 104 is filled with 5 M bits of data. In step 210, it is checked whether the current buffer amount is filled by the reference buffer amount L which is a predetermined decoding start start point.

As a result of the check in the step 210, if it is determined that the current buffer amount is not filled by the predetermined reference buffer amount L, step 210 and step (b) until the buffer 104 is filled by the predetermined reference buffer amount L. Repeat 212).

On the other hand, if it is determined in the step 210 that the current buffer amount is filled by the predetermined reference buffer amount L, the client control block 102 generates a bit stream fetch control signal on the line L15 and at the same time the line A decoding control signal determined based on the rate information extracted from the bit stream is generated through L17. As a result, the MPEG decoding block 106 encodes the encoded stream provided from the buffer 104 at the decoding rate provided through the line L17. The original signal is restored (step 214).

On the other hand, when performing the reception of the bit stream and decoding the received bit stream as described above, the client control block 102 checks the amount of data currently stored in the buffer 104 at regular intervals, that is, the current buffer. It is checked in predetermined units (e.g., 1 megabit, 2 megabits, etc.) whether the amount is more or less than the predetermined buffer increase / decrease amount M (step 216).

As a result of the check in the step 216, the current buffer amount is not more or less than 1 megabit assuming that the error tolerance of the preset reference buffer amount L (i.e., the data increase / decrease of the buffer is checked in units of 1 megabit). If no end of the VOD service is detected (step 220), the decoding operation of the encoded bit stream is continuously performed through repeating the above-described step 214. Here, the service termination is detected when the bit stream transmission for the program for which the user has requested the VOD service is terminated or the service is requested to be stopped by the user.

On the other hand, if it is determined in the step 216 that the current buffer increase / decrease is outside the error tolerance of the preset reference buffer increase / decrease amount M, the client control block 102 determines the decoding speed according to the increase / decrease information of the data amount. Increase or decrease the decoding speed by one step when the current buffer increase or decrease exceeds the preset reference buffer increase or decrease M, and decrease the decoding speed by one step when the current buffer increase or decrease is smaller than the preset reference buffer increase or decrease M. The amount of data filled in 104 is controlled to remain constant within the error tolerance (step 218), and then the decoding speed is adaptively adjusted until the VOD service is terminated by repeating the step 214.

As an example, in the state in which the preset transmission rate extracted from the bit stream is 10 Mbps, the capacity of the buffer 104 is 10 megabits, and the preset reference buffer amount, which is the time point at which the decoding operation is started, is set to 5 megabits, as shown in FIG. 3B. As shown, approximately 5 seconds, assuming that the actual transmission rate is 10.1 Mbps due to an error between the system clock of the encoder and the system clock of the server, and that the actual decoding rate is 9.9 Mbps due to an error between the system clock of the server and the system clock of the client. Afterwards, one megabit plus six megabits of data will accumulate in the buffer 104.

Accordingly, the client control block 102 will check the amount of data in this buffer 104 and increase the decoding rate by one step from 9.9 Mbps to 10 Mbps, as shown in FIG. 3B. However, since the actual data rate at the server 110 is 10.1 Mbps, after about 10 seconds, 7 megabits of data plus 1 megabit will be accumulated in the buffer 104.

Therefore, the client control block 102 increases the decoding speed by one step from 10 Mbps to 10.1 Mbps, so that the actual transmission rate from the server 110 and the decoding rate at the client 100 coincide with each other. By being synchronized, as shown in Fig. 3C, in the buffer 104, the data amount of 7 mega bits will remain constant within the tolerance range. Therefore, in the present invention, the overflow or underflow phenomenon in the client-side reception buffer is reliably prevented.

As described above, according to the present invention, when performing decoding to restore the original signal of the encoded bit stream on the client side, the actual transmission rate is estimated on the server based on the data fullness state information in the reception buffer. By adaptively controlling the decoding rate based on the estimated actual data rate, the overflow that can be caused in the receive buffer on the client side due to an error between the encoder system clock and the server system clock or between the client system clock and the server system clock. Alternatively, the underflow phenomenon can be reliably prevented.

Claims (2)

A method for controlling decoding of an encoded bit stream provided from a server in response to a VOD service request from a client having a receive buffer and a decoder in a client-server system, the method comprising: A first step in which the server transmits an encoded bit stream to the client in response to a VOD service request from the client, and extracts rate information contained in the bit stream while storing the transmitted bit stream in the reception buffer; A second process of determining an initial decoding rate of the decoder based on the extracted rate information; A third step of storing data in the reception buffer until the current data amount stored in the reception buffer becomes a preset decoding start reference buffer amount; A fourth step of restoring the encoded bit stream sequentially extracted from the reception buffer to the original signal before encoding when the current amount of data in the reception buffer is the predetermined decoding start reference buffer amount; A fifth step of repeatedly checking the data increase / decrease amount of the current buffer stored in the reception buffer in predetermined reference buffer increments during the decoding operation; The decoder based on the increase / decrease state of the receive buffer when the current data increase / decrease amount of the receive buffer is increased or decreased by the predetermined predetermined data amount unit corresponding to the check result of the fifth process. A sixth step of sequentially increasing and decreasing the decoding speed at; And And a seventh process of repeatedly performing the fourth to sixth processes until the VOD service is terminated. The method of claim 1, wherein the decoding rate is gradually increased or decreased at a rate corresponding to the preset reference buffer increase / decrease unit.