JPH09139720A - Multiplex method and multiplexer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a multiplexed stream suitable for recording plural data such as moving image and voice signals to a recording medium such as a disk or for transmission of the data to a transmission line. SOLUTION: The device stores plural input coded signals in 1st buffer memories 41, 42 tentatively for each input coded signal and calculates a generating period of packets obtained based on a multiplexing rate applied in advance and the size of packets to be multiplexed, then calculates the transmission information amount of each input coded signal to be sent for the period based on a coding rate applied in advance and adds the transmission information amount to a virtual packet buffer supplement amount of each input coded signal to obtain a virtual buffer supplement amount of each of input data for each packet generation period. Then a control means 1 controls transfer of the input coded signal in the 1st buffer memory to a means 6 adding a header to the signal based on the supplement amount and subtracts the transferred information amount from the virtual buffer of the input coded signal transferred to the addition means 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for recording a plurality of encoded data such as moving images and voices on a recording medium such as a disc or sending the data on a transmission line.
The present invention relates to a multiplexer that generates a suitable multiplexed stream.

[0002]

2. Description of the Related Art An important point in data (information) multiplexing processing is that the decoder buffer must be multiplexed so as not to cause underflow or overflow. In the decoder buffer, when an underflow occurs, there is no data to decode, so when the data is time-series data, there is no data (information) at the time when the underflow occurs. Further, when overflow occurs, data (information) is lost, so that correct decoding cannot be performed.

Therefore, in the conventional multiplexing, in order to multiplex each input data at a rate such that an underflow or an overflow does not occur in a decoder, each input data is temporarily stored in a buffer memory and packetized. The buffer memory for each input data is inspected at the cycle of multiplexing, and the input data in which the amount of data to be inserted into the packet is accumulated is packetized, and the amount of data is erased from the buffer memory to control multiplexing. Was there.

[0004]

Here, an example of a multiplexing device for performing multiplexing control by managing and controlling the filling amount of the input buffer memory will be shown. It is assumed that this multiplexer performs fixed-length packet multiplexing and generates a packet when the filling amount of the input buffer memory reaches a predetermined value. FIG. 5 shows how packets are generated when the input data has a constant rate, and FIG. 6 shows how packets are generated when the input data is bursty. In FIGS. 5 and 6, (a) shows the input rate to the multiplexer, (b) shows the change of the filling amount of the input buffer memory, and (c) shows the occurrence degree of the generated packet, respectively. Shows.

As can be seen from FIGS. 5 and 6, when the input data has a constant rate, the generated packets have a constant interval, and when the input data is bursty,
It can be seen that the cycle of the generated packet has a locally concentrated portion and a quiet portion. Next, FIG.
FIG. 7 shows a case where the audio data and the moving image data are input to the above-mentioned multiplexing device at a constant input rate. Also,
FIG. 9 shows a burst-like input rate to the above multiplexer.
The situation where voice data and moving image data are input is shown. However, it is assumed that both voice and moving image data are multiplexed in fixed length packets, and the total number of packets generated in a fixed time is the same in both FIGS.

(A) shows the generation of a packet (V) of moving image data, and (b) shows the generation of a packet (A) of audio data. (c) shows a stream in which (a) video packets and (b) audio packets are multiplexed. When an audio packet and a moving image packet are generated at the same time, the audio packet is preferentially multiplexed, and when both the audio packet and the moving image packet do not exist, the stuffing packet (P) is multiplexed.

(D) shows the transition of the buffer memory for moving image data in the decoder, and (e) shows the transition of the buffer memory for audio data in the decoder. In the method of controlling the multiplexing by the filling amount of the input buffer memory, the interval of the data packets to be multiplexed becomes almost constant for the input data of the constant rate, and the processing speed of the decoder and the input to the decoder are performed. Since it is multiplexed so that the data rates can be matched,
No overflow or underflow occurs in the decoder buffer memory.

On the other hand, in the case of a burst-like input, the packets of specific data are locally concentrated or scattered, so that in the locally concentrated part, the processing speed of the decoder is higher than the processing speed. Since data is input at a rate,
In the buffer memory, where overflow occurs and packets are locally scattered, data is supplied at a speed lower than the processing speed of the decoder, so underflow occurs. In order to decode the multiplexed data as shown in FIG. 9 (c) without causing overflow, the buffer memory of the decoder is made large enough to eliminate the mismatch between the processing speed of the decoder and the data speed of the transferred data. As a countermeasure against underflow, the decoding delay is increased and the size of the buffer memory of the decoder corresponding to the delay is required.

As described above, in order to decode a multiplexed stream with an inappropriate multiplexing interval, not only the buffer memory of the decoder is required to have an unnecessarily large size but also an unnecessarily long delay occurs. Become. Increasing the buffer memory results in high cost, and large delay is very disadvantageous in system operation. However, in general, when encoding moving image data and audio data, in order to collectively process images and audio in a certain unit, wait until data to be processed is accumulated, and data to be processed is accumulated. Since the batch processing is performed at the time of sending, the output of the encoder becomes a burst-like output.

Therefore, it is possible to multiplex burst input data in the multiplexer without changing the size of the buffer memory of the decoder without causing underflow or overflow in the buffer memory of the decoder. , A device for converting a burst input into a constant rate input is required. However, in order to operate the device for converting the bursty input to the constant rate input for various input rates, it is necessary to generate various clocks, so that the device is very expensive. Becomes
An object of the present invention is to convert bursty input into a constant rate in the preceding stage of the multiplexer without changing the size of the buffer memory of the decoder even for bursty input data as described above. It is an object of the present invention to perform multiplexing without providing such a device and prevent an underflow or an overflow of the buffer memory in the decoder.

Further, in a multiplexing device which performs multiplexing on the assumption that the clock of the output transmission line is synchronized with the clock of the input data, the clock of the output transmission line is asynchronous with the clock of the input data. In some cases, the mismatch of clocks causes excess or deficiency in the output data to the transmission line. When dummy data is inserted or multiplexed data is deleted to eliminate the excess or deficiency of output data caused by the clock mismatch, the time information existing in the multiplexed data is calculated on the premise of synchronization. Therefore, the time information is displaced, and the decoder cannot reproduce the correct time. Therefore, it is an object of the present invention to enable a decoder to reproduce a correct time even if they are not synchronized.

[0012]

Conventionally, the packetization timing of input data has been performed by managing and controlling the actual buffer memory filling amount, but in the present invention, the packetization timing of each input data is calculated. It is managed by. This is the same as managing the virtual buffer memory, not the actual buffer. FIG. 7 shows how packets are generated according to the present invention when data is input at a burst rate. FIG. 7A shows a burst-like input rate. (c) shows a transition of the amount of sufficiency of the virtual buffer memory calculated by calculation, and packetization is performed when the amount of virtual buffer reaches a predetermined amount. FIG. 7D shows how packets are generated, but packets are generated at regular intervals in spite of burst-like input. (b) shows the state of the input buffer memory. As described above, in the present invention, instead of managing / controlling the actual buffer memory filling amount for each input data and performing packetization, the virtual buffer memory filling amount is calculated and the filling amount is managed / controlled. By performing packetization by means of packetizing, it is possible to provide a multiplexer capable of accurately multiplexing even a burst-like input signal.

Further, in order to achieve such an object,
The output of the multiplexer is input to the buffer at a specified rate in synchronization with the clock of the input data, read from the buffer at a specified rate in synchronization with the transmission line clock, and dummy data is inserted or multiplexed data is added depending on the buffer fill amount. After deleting the data, the time information in the multiplexed data is corrected to generate multiplexed data with accurate time information even when the input data clock and the transmission path clock are asynchronous. To provide a rectification device.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the multiplexer of the present invention will be described below with reference to the drawings. (Embodiment 1) Input data is single moving image coded data and single voice coded data, and moving image coded data and voice coded data are multiplexed in a fixed length data area of a fixed length packet. A case will be described as Example 1 with reference to FIGS. 1, 2, and 3.

The moving picture data coding unit 2 compresses and codes the inputted moving picture data in units of one picture, and at the time when the coding of each picture is completed, the coded data is burst-stored in the buffer memory 41. Send out. In addition, the moving image data coding unit 2 supplies the average coding rate information for each certain period to the control unit 1.

The audio data encoding unit 3 compresses and encodes the input audio data in a certain unit (hereinafter referred to as a frame), and when the encoding of each frame is completed, the encoded data is buffered in a burst form. It is sent to the memory 42.
Further, the audio data encoding unit 3 supplies the average encoding rate information for each certain period to the control unit 1.

The multiplexing rate is Rmax [bytes / sec],
The size of packets to be multiplexed Stp [bytes] has a fixed length. The multiplexing unit time Tp, which is the time per one multiplexing packet, is calculated from the above multiplexing rate and the size of the multiplexing packet by the following equation (Equation 1).

[0018]

(Equation 1)

As shown in FIG. 2, the control unit 1 determines from the coding rate information supplied from the data coding units 2 and 3 that
Virtual buffer increase amount calculation units 12 and 13 that calculate the virtual buffer increase amount in the multiplexing unit time Tp, and virtual buffer fill amount calculation units 14 and 15 that calculate the virtual buffer fill amount in each of the multiplexing unit time Tp , And an output data determination unit 11 that determines the data to be transferred to the header addition unit 6 by checking the virtual buffer filling amount.

The time to start the multiplexing of the moving image data and the audio data is converted into a virtual buffer amount as in the following equation (Equation 2) based on the first coding rate information. By doing so, the multiplexing start time of each input data can be managed by the virtual buffer filling amount.

[0021]

(Equation 2)

When the coding rate is the initial value, the virtual buffer increment calculation units 12 and 13 calculate the virtual buffer increment from the coding rate from the data encoders 2 and 3 and the multiplexing unit time Tp. It is calculated by the formula (Equation 3). Also, if the encoded data has a variable rate,
Even if the coding rate is changed, the variable rate can be dealt with by calculating the virtual buffer increase amount by the following equation.

[0023]

(Equation 3)

The virtual buffer sufficiency calculation units 14 and 15 calculate the virtual buffer sufficiency by the following equation (Equation 4) for each multiplexing unit time Tp.

[0025]

(Equation 4)

Next, the output data determination unit 11 checks the virtual buffer filling amount Bv_v (n) of moving image data and the virtual buffer filling amount Bv_a (n) of audio data. That is, the output data determination unit 11 determines that the virtual buffer filling amount Bv_v (n) of the moving image data has not reached the data amount to be inserted into the packet, and the virtual buffer filling amount Bv_a (n) of the audio data is
If the amount of data to be inserted into the packet has not reached, the data to be transferred to the header addition unit 6 is determined to be stuffing data.

Further, the output data judgment unit 11 determines that the virtual buffer filling amount Bv_v (n) of the moving image data has reached the data amount to be inserted into the packet, and the virtual buffer filling amount Bv_a (n) of the audio data is the packet amount. If the amount of data to be inserted into the header has not reached, the data to be transferred to the header adding unit 6 is determined to be moving image data.

Furthermore, the virtual buffer filling amount B for voice data
If v_a (n) has reached the amount of data to be inserted into the packet and the virtual buffer fill amount Bv_v (n) of the moving image data has not reached the amount of data to be inserted into the packet,
The data transferred to the header adding unit 6 is determined as audio data. Furthermore, the virtual buffer filling amount B for moving image data
If v_v (n) has reached the amount of data to be inserted in the packet and the amount of virtual buffer for voice data Bv_a (n) has also reached the amount of data to be inserted in the packet, the amount of virtual buffer for each input data is filled. The quantity is weighted by the following equation (Equation 5).

[0029]

(Equation 5)

The weighted values are compared, and it is determined that the larger value (the one that has reached the amount of data to be inserted into the packet earlier in time) is the data to be transferred to the header adding unit 6. If the data transferred to the header adding unit 6 is moving image data, the virtual buffer filling amount calculation unit 14 subtracts the virtual buffer filling amount as in the following equation (Equation 6).

[0031]

(Equation 6)

If the data transferred to the header adding unit 6 is voice data, the virtual buffer filling amount calculation unit 15 subtracts the virtual buffer filling amount from the following equation (Equation 7).

[0033]

(Equation 7)

Further, the output data judging section 11 sends information of the data judged to be outputted (type and data amount) to the switch 5 and the header adding section 6. The switch 5 transfers the data designated by the control unit 1 to the header adding unit 6 by the designated data amount. The header addition unit 6 adds header information suitable for the type of data designated by the control unit 1 and transfers the header-added (packetized) data to the output interface 7.

If there is an instruction from the control unit 1, the stuffing data sending unit 43 sends the stuffing data via the switch 5 in a designated amount (that is, at a time when the switch 5 is connected to the stuffing data sending unit 43). Only the determined amount) is transferred to the header addition unit 6.

As shown in FIG. 3, the output interface 7 comprises an output control unit 71, a smoothing unit 72, an output buffer memory 73, a stuffing packet sending unit 74, a switch 75, and a header changing unit 76.

The smoothing unit 72 transfers the packet transferred from the header adding unit 6 to the output buffer memory 73 at a predetermined constant rate.

The output buffer memory 73 temporarily stores the packets transferred from the smoothing unit 72, and if there is an instruction from the output control unit 71, the designated packet is switched to the switch 7.
Send to 5.

The output control unit 71 operates in synchronism with the output transmission line clock, and if there is a request for packet transmission from the output transmission line, it checks the filling amount of the output buffer memory 73,
When the filling amount of the output buffer memory 73 has reached the predetermined amount, the output buffer memory 73 is instructed to transfer the packet existing in the output buffer memory 73 for the longest period to the switch 75. Here, if the synchronization between the output transmission line clock and the input signal is guaranteed, the output control unit 71 may operate in synchronization with the input signal.

At this time, if the filling amount of the output buffer memory 73 exceeds a certain upper limit value, the least necessary packet is deleted from the output buffer memory 73. Also,
The output control unit 71 also instructs the switch 75 to send a packet to the header changing unit 76.

The header changing unit 76 has a counter (not shown) which operates with a clock synchronized with the input signal, and when the header of the packet sent from the output buffer memory 73 contains time information. In addition, since the time information is calculated on the premise that the input signal clock and the output transmission path clock are synchronized, if the input signal clock and the output transmission path clock are asynchronous, In consideration of this, the time information is corrected to the time information actually measured by the counter of the header changing unit 76.

The stuffing packet transmitter 74 outputs the stuffing packet when the switch 75 is connected to the stuffing packet transmitter 74. Further, the switch 75 switches between the output of the output buffer memory 73 and the output of the stuffing packet transmitter 74 according to an instruction from the output controller 71.

Here, in order to control so that a packet containing certain special information is always inserted in an even-numbered packet, it is output for an even-numbered packet for a longer period than a packet containing the special information. Buffer memory 73
Even if there is a packet inside, the output buffer memory 73 is instructed to immediately transfer the packet containing the information to the switch 75.

In the case of odd-numbered packets, even though the packet containing the special information remains in the output buffer memory 73 for the longest period, it remains in the output buffer memory 73 for the next longest period. The output buffer memory 73 is instructed to transfer the existing packet to the switch 75.

The header changing unit 76 changes the header contents according to the instruction from the output control unit 71 when there is a packet to be changed in the header of the packet sent from the output buffer memory 73.

The switch 75 transfers the packet designated by the output control unit 71 to the header changing unit 76. The stuffing packet transmitter 74 outputs a stuffing packet when instructed by the output controller 71.

(Embodiment 2) As Embodiment 2 of the present invention, the input data is two moving image data, two audio data and three additional information data, and all the moving image data and audio data are encoded data. However, it is assumed that one piece of additional information data includes time-series data and the other additional information data does not include time-series data.All data is multiplexed in the fixed-length data area of the fixed-length packet. The case of being converted will be described below with reference to FIG.

The basic structure is the same as that of the first embodiment. When the number of input data is increased in this way, the virtual buffer filling amount of each input data is calculated for each multiplexing unit time, resulting in a huge calculation amount. Here, when the coding rate of the data to be multiplexed is very small compared to the multiplexing rate, the increment of the virtual buffer filling amount per multiplexing unit time is very small, so that Even if the virtual buffer amount is inspected, it is very unlikely that the sufficiency amount has reached the amount to be inserted into the packet.

Therefore, the calculation of the virtual buffer filling amount of the input data having a low coding rate is not performed every time the multiplexing unit time is increased, but the increase amount of the virtual buffer filling amount is calculated by the increase amount of the virtual buffer filling amount. The virtual buffer filling amount is calculated in a range that does not exceed. For example, when calculating once in 16 multiplexing unit time, the virtual buffer filling amount is calculated by the following equation (Equation 8).

[0050]

(Equation 8)

By doing so, the amount of calculation per unit time can be greatly reduced. However, if the calculation interval is increased, the multiplexing delay may occur, and special care must be taken when the multiplexing interval of the packet is rigorously determined or when the buffer on the decoder side has no margin. is there.

[0052]

Since the present invention is configured as described above, it has the following effects. (1) Instead of checking the filling amount of the real buffer memory, by checking the filling amount of the virtual buffer, the size of the decoder buffer can be increased without increasing the size of the decoder buffer even for burst input data. Provides a method (apparatus) for performing multiplexing without providing a device for converting a burst-like input into an averaged rate in the preceding stage, without causing buffer underflow or overflow in a decoder. .

(2) Further, by inserting a specific type of multiplexed signal into a specific position of the multiplexed stream, the position of the specific type of multiplexed signal can be recognized quickly and easily when decoding. It can be decoded. (3) Furthermore, by changing the coding rate used for the calculation of the virtual buffer filling amount every predetermined period, it is possible to deal with the case where the input coded signal has a variable rate.

(4) Instead of simply comparing the virtual buffer filling amount, the time required for the virtual buffer filling amount to reach a predetermined amount is
By weighting and comparing, the state of the decoder buffer is taken into consideration, that is, the multiplexing control in which overflow or underflow does not occur can be performed. (5) By converting the multiplexing start time into the initial filling amount of the virtual buffer, the data to be multiplexed can be accurately synchronized.

(6) Furthermore, the calculation amount can be reduced by lengthening the period for calculating the virtual buffer filling amount,
More complex judgment and multiplexing control can be performed. (7) By changing the time in the multiplexed data to the time of the output transmission line, the correct time can be reproduced even in the decoder when the clock of the output transmission line is asynchronous with the clock of the input data. A multiplexing method (apparatus) can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a multiplexing device of the present invention.

FIG. 2 is a diagram showing an embodiment of a multiplexing device of the present invention.

FIG. 3 is a diagram showing an embodiment of a multiplexing device of the present invention.

FIG. 4 is a diagram showing an embodiment of a multiplexing device of the present invention.

FIG. 5 is a diagram showing how packets are generated when input data has a constant rate.

FIG. 6 is a diagram showing how packets are generated when input data is bursty.

FIG. 7 is a diagram showing a state in which audio data and moving image data are supplied to the multiplexing apparatus of the present invention at a burst-like input rate.

FIG. 8 is a diagram showing a state in which audio data and moving image data are supplied to the multiplexing device at a constant input rate.

FIG. 9 is a diagram showing a state in which audio data and moving image data are supplied to the multiplexer at a burst-like input rate.

FIG. 10 is a diagram showing an embodiment of a multiplexing device of the present invention.

[Explanation of symbols]

1 Control Unit 2, 21A, 21B Moving Image Data Encoding Unit 3, 31A, 31B Audio Data Encoding Unit 4, 41, 41A, 41B, 42, 42A, 42B, 4
4A, 44B, 44C Buffer memory (first buffer memory) 5,75 Switch 6 Header addition unit 7 Output interface 11 Output data determination unit 12, 13 Virtual buffer increase amount calculation unit 14, 15 Virtual buffer filling amount calculation unit 43 Stuffing Data sending unit 71 Output control unit 72 Smoothing unit 73 Output buffer memory (second buffer memory) 74 Stuffing packet sending unit 76 Header changing unit 81A, 81B, 81C Additional information data generating unit

[Procedure amendment]

[Submission date] August 12, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a multiplexing device of the present invention.

FIG. 2 is a diagram showing an embodiment of a multiplexing device of the present invention.

FIG. 3 is a diagram showing an embodiment of a multiplexing device of the present invention.

FIG. 4 is a diagram showing an embodiment of a multiplexing device of the present invention.

FIG. 5 is a diagram showing how packets are generated when input data has a constant rate.

FIG. 6 is a diagram showing how packets are generated when input data is bursty.

FIG. 7 is a diagram showing a state in which audio data and moving image data are supplied to the multiplexing apparatus of the present invention at a burst-like input rate.

FIG. 8 is a diagram showing a state in which audio data and moving image data are supplied to the multiplexing device at a constant input rate.

FIG. 9 is a diagram showing a state in which audio data and moving image data are supplied to the multiplexer at a burst-like input rate.

[Description of Codes] 1 control unit 2, 21A, 21B moving image data coding unit 3, 31A, 31B audio data coding unit 4, 41, 41A, 41B, 42, 42A, 42B, 4
4A, 44B, 44C Buffer memory (first buffer memory) 5,75 Switch 6 Header addition unit 7 Output interface 11 Output data determination unit 12, 13 Virtual buffer increase amount calculation unit 14, 15 Virtual buffer filling amount calculation unit 43 Stuffing Data sending unit 71 Output control unit 72 Smoothing unit 73 Output buffer memory (second buffer memory) 74 Stuffing packet sending unit 76 Header changing unit 81A, 81B, 81C Additional information data generating unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04N 5/92 H04N 5/92 H 7/24 7/13 Z

Claims (11)

[Claims] 1. A multiplexing method for multiplexing coded signals, wherein a plurality of input coded signals are temporarily accumulated in a first buffer memory for each input coded signal, and a previously declared multiplexing rate is set. Is calculated from the size of the packet to be multiplexed, and the transmission information amount of each input coded signal transmitted during the packet generation period is calculated based on the previously declared coding rate. Calculate, add the respective transmission information amount to the virtual buffer filling amount of each input coded signal, obtain the virtual buffer filling amount of each input data for each packet generation period, based on the virtual buffer filling amount A virtual buffer of the input coded signal transferred to the step of adding the header, controlling the transfer of the input coded signal of the first buffer memory to the step of adding the header Multiplexing method being characterized in that so as to have a step of subtracting et the transferred amount of information. 2. The multiplexing method according to claim 1, wherein the multiplexed signal to which the header is added is temporarily stored in a second buffer memory, and the multiplexed signal stored by the second buffer memory is stored. Among them, a multiplexing method characterized in that a predetermined type of multiplexed signal is made to stand by for a predetermined period. 3. The multiplexing method according to claim 1, further comprising a step of changing a coding rate used for calculation of a virtual buffer filling amount every predetermined period. Method. 4. The multiplexing method according to claim 1, wherein when the step of controlling the transfer to the step of adding the header is performed, the virtual buffer filling amount is determined by the coding rate of the input coded signal. A multiplexing method comprising a weighting step. 5. The multiplexing method according to claim 1, wherein the virtual buffer initial amount is set as a multiplexing start time of each coded signal. 6. The multiplexing method according to claim 1, wherein when the step of calculating the virtual buffer filling amount is performed, the calculation of the virtual buffer filling amount is performed every integer multiple of the cycle. A multiplexing method characterized by. 7. A multiplexing device for multiplexing coded signals, wherein a plurality of input coded signals are temporarily stored in a first buffer memory for each input coded signal, and a previously declared multiplexing rate is set. Is calculated from the size of the packet to be multiplexed, and the transmission information amount of each input coded signal transmitted during the packet generation period is calculated based on the previously declared coding rate. Calculate, add the respective transmission information amount to the virtual buffer filling amount of each input coded signal, obtain the virtual buffer filling amount of each input data for each packet generation period, based on the virtual buffer filling amount Controlling the transfer of the input coded signal of the first buffer memory to the means for adding a header, and from the virtual buffer of the input coded signal transferred to the means for adding the header, Multiplexer being characterized in that so as to comprise means for subtracting the transmission information amount. 8. The multiplexing device according to claim 7, wherein the multiplexed signal to which the header is added is temporarily stored in a second buffer memory, and the multiplexed signal stored by the second buffer memory is stored. The multiplexing apparatus according to claim 1, characterized in that a multiplexed signal of a predetermined type is held in a standby state for a predetermined period. 9. The multiplexing device according to claim 7, further comprising means for changing a coding rate used for calculation of a virtual buffer filling amount at every predetermined cycle. apparatus. 10. The multiplexing method according to claim 1, wherein the multiplexed signal added with the header is temporarily stored in a second buffer memory, and the multiplexed signal stored by the second buffer memory is added. A multiplexing method characterized in that a deviation between the included time information and the time when the time information is actually output to the output transmission line is measured and corrected. 11. The multiplexing device according to claim 7, wherein the header-added multiplexed signal is temporarily stored in a second buffer memory, and the multiplexed signal stored in the second buffer memory is stored. The multiplexing apparatus according to claim 1, further comprising means for measuring and correcting a deviation between the included time information and the time when the time information is actually output to the output transmission path.