KR19980020687A - Method of determining multiplexing rate of variable bit rate signal - Google Patents

Abstract

The present invention relates to a method of determining a multiplexing rate of a variable bit rate signal, and more particularly, to a method of determining a multiplexing rate of a variable bit rate signal by considering multiplexing bit rates of respective encoders in consideration of transmission delays and buffer states of bit strings of multiplexed video ≪ / RTI >

The present invention relates to a method and an apparatus for decoding data, the method comprising: determining a minimum multiplexing bit rate and a maximum multiplexing bit rate so that a decoder buffer does not underflow and overflow due to a transmission delay and an excessive transmission; the sum of the minimum-multiplexed bit rate and r ^r _i obtained in step the steps to obtain the ^{r r} _i (?) by the maximum multiplex bit rate to minimize the variance of the buffer status of all the encoders to be multiplexed comprises a step determining the multiplexing bit rate for .

Description

Method of determining multiplexing rate of variable bit rate signal

FIG. 1 is a diagram illustrating a process of determining a multiplexing bit rate;

2 shows a multiplexing system.

Description of the Related Art [0002]

21: Transmission controller 22: i-th encoder buffer

23: multiplexing buffer 24: multiplexing system controller

More particularly, the present invention relates to a method of determining a multiplexing rate of a variable bit rate signal, which determines a multiplexing bit rate of each encoder by taking into account the transmission delay and the buffer state of a bit stream of all multiplexed video signals .

With the completion of standardization of video encoding centering on MPEG, development of a transmission protocol and a transmission system capable of efficiently transmitting bit streams of compressed video data is actively underway. In addition, demand for video services for users will increase rapidly in broadcasting and communication using wired, wireless, satellite and B-ISDN networks. In particular, when digital broadcasting is started, a broadcasting station compresses and multiplexes video signals of a plurality of channels, and multiplexes and transmits the video signals into a single bit stream. In a receiver, a desired video channel can be selected and demultiplexed through demultiplexing and decoding. In multiplexing and transmitting video signals of various channels, efficient use of bandwidth and efficient management of traffic for each video signal can be achieved as compared with a method of independently transmitting each channel. An identity rate encoder in the same place needs a buffer because it must transmit the encoded variable rate data to the fixed channel. In the existing system, it is suitable to store and edit the multiplexed bit stream by constructing the same multiplexed stream of each stream area occurring during one access time interval. However, since the multiplexing bit rate of each video does not take into account the state of the buffers of other video and the amount of traffic, the heavy traffic of one encoder affects other encoder buffers. Such a buffer state affects the quality of the image to be encoded, which may result in image quality degradation if the image is complex or a scene change occurs. Therefore, multiplexing multiple channels in a fixed bandwidth, such as broadcasting, is not suitable for efficient bandwidth distribution and maintaining uniform image quality.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a method for effectively preventing data loss in a buffer and efficiently transmitting data even in a small buffer.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above problems, and it is an object of the present invention to provide a method of multiplexing a bit stream encoded by a variable rate and multiplexing a bit stream of each encoder through control of a buffer used when the bit stream is transmitted at an identity rate. That is, the present invention provides a method for controlling an encoder buffer, the method comprising: determining a minimum multiplexing bit rate and a maximum multiplexing bit rate so that a decoder buffer does not underflow and overflow due to a transmission delay and an excessive transmission; A step of obtaining R ^r _i by a maximum multiplexing bit rate so as to minimize a variance value of buffer states of all encoders to be multiplexed and a step of setting a sum of a minimum multiplexing bit rate and R ^r _i obtained in the step to a multiplexing bit rate .

The multiplexing bit rate of each encoder is determined considering the transmission delay and the buffer state of the bit streams of all multiplexed video. Therefore, the multiplexing bit rate and the bit generation rate do not coincide with each other, and one multiplexed stream may be composed of a bit stream encoded at another time.

The buffer used for multiplexing can be divided into an encoder buffer and a multiplexer buffer. The multiplexing buffer transfers data from the buffer of each encoder into a multiplexed stream and transmits it to the network. The size of the multiplexing buffer can be determined according to the transmission rate R _T of the multiplexed bit stream transmitted to the network and the multiplexing bit rate R _i allocated to each video. If n is the number of multiplexed encoders and R _T = R _{i, the} multiplexing buffer only needs to compensate for the difference between the clock provided by the network and the clock used by the system. Therefore, even a small system buffer can be multiplexed. In the present invention, R _T = R _i , the system buffer is assumed to be smaller than that of each video buffer.

Generally, the encoder has two methods to satisfy the buffer condition. One is to control the amount E _i of the encoded bit stream through the rate control and the other is to appropriately determine the multiplexing bit rate R _i according to the state of the buffer of each encoder. In the present invention, an algorithm for optimizing the buffer control is considered by determining the multiplexing bit rate R _i with a coded non-stream having a rate control using a virtual buffer.

In the proposed scheme, since the compression layer and the multiplexing layer have independent structures, the configuration of one multiplexed stream can be composed of bit streams having different coding times. However, in order to obtain the time stamp information for providing the presentation time of the configuration of the compression layer, each encoder notifies the multiplexing controller of the position in the video buffer when this position occurs.

The larger the size of the packet, the less header information needed to transmit each elementary stream is required. Therefore, the transmission efficiency is good, but the encoder buffer is required and the transmission delay is increased. Therefore, it is not suitable for low-latency coding and a large amount of data may be lost at a time when a transmission error occurs. On the contrary, when the packet size is small, a large amount of header information necessary for transmission is required. However, since it requires less encoder buffer, it is advantageous for low delay transmission and can efficiently cope with transmission error. Since each buffer state can be smoothly adjusted, it is possible to obtain a more uniform image quality by determining the quantization parameters necessary for encoding the image in the encoder, by checking the buffer status. In the proposed scheme, the time unit constituting the packet is defined as the slice rate. This is advantageous in that the size of the packet can be adjusted according to the size of the buffer of the system. For example, if the size of the buffer is small, the packet is constructed in a time that can express one slice. If the size of the buffer is large, the packet is constructed in a time that can express several slices.

In the present invention, in order to obtain the multiplexing rate, a minimum multiplexing bit rate ^Rm _i and a maximum multiplexing bit rate R ^M _i are obtained so that a transmission delay and an over-transmission occur first and a decoder buffer does not underflow and overflow. Second, the encoder buffer and the ^M R _i care not to overflow with reference to seek the R ^r _i, and finally, final multiplexing rate is met _{^{R i = R m i + R}} r i is the formula (1).

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features, and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 1 conceptually shows the process of obtaining R _i after finding R ^m _i and R ^r _i . R ^m _i is determined according to the amount of data delayed after checking the state of each encoder buffer B _i (t). R ^r _i is the number of predicted bits to occur during B _i (t) - R ^m _i and the multiplexing period Δt for the video source _i is determined so as to minimize the variance of the buffer state at t +? t. At t +? t, the buffer states of the four video sources A, B, C, and D are all the same.

Figure 2 shows the structure of the multiplexing system. [Delta] t is the multiplexing period for n video sources. That is, the multiplexer determines the multiplexing bit rate of each of the encoders during [Delta] t, and each encoder transmits the encoded bit stream in the buffer to the multiplexing buffer 23 after making the packet. The multiplexer makes each packet into a multiplexed bit stream and transmits it to the network. In the experiment, Δt was defined as the slice rate. Since the number of slices is 30 in the 704x480 image and 15 slices in the 352x240 image, the slice rate is 30x30 and 30x15, respectively, when the image rate corresponding to one second is 30.

R _T is the identity transmission rate when the multiplexed bit stream is transmitted to the network. R _{i (t)} is the multiplexing bit rate assigned to each video according to the traffic state of each video. B ^e _i (t) (22) is the current buffer of the i-th encoder, and E _i (t) is the incidence rate of the encoded bit stream. _i is the number of prediction bits to occur during? t. During Δt, R _i (t) becomes R _i . During? T, a packet P _i of each bitstream is multiplexed with a multiplexing bit rate R _i , and the number of bits of P _i can be represented by R _i × Δt. The transmission controller 21 of each video is connected to the controller 24 of the multiplexing system _i . _i , B ^e _i (t) and the previous multiplexing bit rate R _i (tj Δt) (1 ≤ j ≤ k-1), the multiplexer finally obtains the value of R _i .

The multiplexed bit stream is transmitted to the demultiplexer with the identity bit rate R _T. Therefore, it is assumed that the channel delay from the multiplexer to the demultiplexing is constant. The minimum end-to-end delay from the encoder buffer to the decoder buffer is defined as kΔt. The size of the encoder buffer of each video is B ^e _max = × k Δt, the buffer size of the decoder is B ^d _max = × k Δt × δ (?).

In order to prevent overflow and underflow of the decoder buffer, the following equation must be satisfied.

_{^{0≤B d i (t- △ t)}} + R i (tk △ t) △ tE i (t) △ t≤B d max (3)

The buffer state of the decoder at time t is expressed by the following equation.

The conditions under which the buffer underflow does not occur due to the transmission delay from Equation (3) will be described. To avoid underflow, equation (5), which is the first inequality condition of equation (3), must be satisfied.

E _i (t) ΔtB ^d _i (t- Δt) ≤R _i (t + k Δt) Δt (5)

By combining Eqs. (4) and (5), the multiplexing bit rate satisfying the given minimum delay without buffer underflow can be expressed as Eq. (6).

Since B ^e _i (t) can be expressed by equation (7), equation (6) can be expressed as equation (8).

_{^{B e i (t + △ t}} ) = B e i (t) + E i (t) △ tR i (t) △ t (7)

Therefore, in order to satisfy the end-to-end delay, the minimum multiplexing bit rate ^Rm _i can be obtained as follows.

If R ^m _i is less than 0, then R ^m _i becomes zero. In the above equation, R ^m _i is the amount of data that is stored in the buffer of the encoder before k △ t is transmitted from time (k-1) Δt to before - Δt. This value can be easily understood intuitively in a system where the transmission delay is k △ t.

In the second step, the maximum multiplexing bit rate R ^M _i of each video encoder is obtained from the condition that buffer overflow of the decoder due to transmission delay does not occur. To avoid overflow, equation (10), the second inequality condition of equation (3), must be satisfied.

_{R i (t + k △ t} ) △ t≤B d max + E i (t) △ tB d i (t- △ t) (10)

By combining Eqs. (4) and (10), R _i can be expressed as Eq. (11).

Since B ^e _i (t) can be expressed by Eq. (7), Eq. (11) can be expressed as Eq. (12).

Therefore, R ^M _i can be obtained as follows.

The sum of the data transmitted from R ^M _i and the time (k-1) Δt to before Δt is equal to the sum of the data stored in the encoder buffer before B ^d _max and k Δt Able to know. If R ^m _i has a value greater than 0, R ^M _i can be expressed as Eq. (14).

Since R ^m _i is the minimum multiplexing bit rate at which the decoder does not underflow, R ^M _i , where the decoder overflows, And R ^m _i .

In order to determine R ^r _i , the state of the buffers of all multiplexed encoders and the traffic of the encoded bit stream must be considered. It is not known which encoder and when to transmit the bit stream to each buffer. Therefore, in order to efficiently cope with arbitrary traffic of arbitrary video, the transmission rate R ^r _i should be determined so that the states of all multiplexed buffers are the same. In the present invention, the dispersion is determined to be zero. If B _i (t) = B ^m _i + B ^r _i and B ^m _i = B ^m _i Δt and B ^r _i = R ^r _i Δt, then B _i (t + Δt) Can be roughly obtained.

R ^r _i minimizes the variance of the buffer to prevent encoder buffer overflow and underflow at time t + Δt. At time t +? T, the average value of the state of the encoder buffer And variance value σ can be expressed as follows.

If B _i (t +? T) is less than (t +? t), the variance value? (t +? t) will be zero. To minimize the value of σ (t + Δt), R ^r _i is the value of B _i (t + Δt) (t + [Delta] t). B _i (t + Δt) can be expressed as Eq. (18).

B` _i (t +? T) = _i x? t + B ^r _i = B _min + B _i (t +? t)

However, _Bmin = min (B` _i (t +? T))

B _i (t +? T) = B _min +? B _i (t +? T) -R ^r _i ? T (18)

Approximately B _i (t +? T) is B _min Will be close to zero and σ will be B _min if the condition R ^r _i × Δ t = ΔB _i (t + Δt) is satisfied.

The sum of △ B _i value, and R ^r _i △ t is the following relationship is always satisfied.

R ^t _i is obtained to obtain R ^r _i . R ^t _i is a value that does not refer to R ^M _i . In this case, Does not become zero. In such a case, R ^t _i is determined in proportion to the difference from the minimum buffer state as follows.

In the case of Can be zero. R ^t _i is determined as shown in equation (21).

Since R _i can not be larger than R ^M _i , R ^r _i is obtained by referring to R ^M _i as follows.

R ^m is _{^{i + R t i R M i}} R r i = R t i,

R ^m + R _i ^t _i R is _{^{M i R r i = R M}} i - R m i (22)

Finally, the multiplexing bit rate R _i is expressed as R _i = R ^m _i + R ^r _i .

As described above, according to the present invention, when multiplexing a plurality of video signals, it is possible to avoid the overflow and underflow of the encoder and decoder buffers of each video traffic and to minimize the dispersion value of each video buffer, . This algorithm is expected to be widely used in broadcasts where multiple video signals having a variable rate are multiplexed and transmitted at an identity rate.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. will be.

Claims (4)

Determining a minimum multiplexing bit rate and a maximum multiplexing bit rate so that a transmission delay and an over-transmission occur and the decoder buffer does not underflow and overflow; Obtaining R ^r _i by a maximum multiplexing bit rate so that a dispersion value of a buffer state of all multiplexed encoder buffers is minimized in order to prevent data loss due to an overflow of an encoder buffer multiplexing; And And determining a sum of the minimum multiplexing bit rate and the R ^r _i obtained in the step to a multiplexing bit rate. The method according to claim 1, Wherein the minimum multiplexing bit rate ^Rm _i satisfies the following formula: (? T: multiplexing period for video source B ^e _i : Current buffer status of the i th encoder k △ t: Minimum end-to-end delay time from encoder buffer to decoder buffer R _i : multiplexing rate assigned to each video) The method according to claim 1, Wherein the maximum multiplexed bit rate R ^M _i satisfies the following equation: (B ^d _max : maximum size of decoder buffer Δt: Multiplexing cycle for video source B ^e _i : Current buffer status of the i th encoder k △ t: Minimum end-to-end delay time from encoder buffer to decoder buffer R _i : multiplexing rate assigned to each video) The method according to claim 1, ^Wherein the R ^r _i satisfies the following equation. R ^m is _{^{i + R t i R M i}} R r i = R t i, If ^m _i + R ^t _i R R ^M R _i ^r _{i i} = R ^M - R ^m _i, (R ^m _i : minimum multiplexing bit rate R ^M _i : maximum multiplexing bit rate)