KR19980026747A - MPEG-2 transport stream remultiplexer (PCR corrector of MPEG-2 transport stream remultiplexer) - Google Patents

Abstract

The present invention relates to a TS packet remultiplexer conforming to the MPEG-2 system, and its object is to provide a TS packet remultiplexer which complies with the MPEG-2 system, in which PCR jitter due to packet multiplexing in the re- . The composition is as follows. The re-multiplexing scheduler unit receives the first TS enable signal, the second TS enable signal, the PCR1 detection flag, and the PCR2 detection flag, determines one packet to be re-multiplexed at present, outputs the result to the packet selection code, Output packet intervals. The PCR compensation value calculation unit calculates and outputs the re-multiplexing delay time using the PCR packet intervals, and the multiplexer outputs the third TS by re-multiplexing the null packet, the first TS and the second TS according to the packet selection code. The PCR packet detecting unit detects the PCR packet included in the third TS and outputs the original PCR value, the third TS, the PCR1 detection flag and the PCR2 detection flag. In order to eliminate the PCR jitter, the PCR correcting code unit newly encodes and outputs the PCR in the third TS with the PCR correction value plus the PCR compensation value corresponding to the PCR delay time and the original PCR value. The effect is that it can be widely used in applications such as digital broadcasting adopting MPEG-2 by encoding PCR timestamp accurately by removing PCR jitter.

Description

MPEG-2 transport stream remultiplexer (PCR corrector of MPEG-2 transport stream remultiplexer)

FIG. 1 is a PCR timing diagram of an MPEG-2 transport bit stream re-multiplexing process,

FIG. 2 is a block diagram of a PCR correcting device of a demultiplexer,

FIG. 3 is a block diagram of the re-multiplexing scheduler;

FIG. 4 is a block diagram of a PCR packet detecting unit,

FIG. 5 is a block diagram of the PCR correction code unit. FIG.

Description of the Related Art [0002]

10: re-multiplexing scheduler unit 11: re-multiplexing scheduler

12, 14, 16: Packet counters 13, 15, 17: Packet interval calculator

20: PCR compensation value calculation unit 30: MUX

40: PCR packet detector 41: PID comparator

42, 52: Shift register 43: PCR value decoder

50: PCR correction code part 51: modified PCR value calculator

The present invention relates to a TS packet remultiplexer conforming to the MPEG-2 system, and more particularly to a PCR correcting apparatus of an MPET-2 transport bit stream remultiplexer.

In general, the MPEG-2 standard is an international standard for ISO / IEC and is a compression standard for video and audio. This is widely adopted in applications including video services such as TV broadcasting, video communication, and computers. This standard has three kinds of video, audio, and system. The system part is a standard for multiplexing for transmitting encoded program information, and enables the synchronized program to be reproduced without a buffer error in the decoder.

The MPEG-2 transport bit stream remultiplexer multiplexes two or more MPEG-2 transport stream streams (hereinafter abbreviated as TS) to output one transport bit stream. Re-multiplexing is a time-division multiplexing on a packet-by-packet basis, in which packet jitter is generated. This packet jitter means that the relative position in time of an arbitrary packet before re-multiplexing is changed after re-multiplexing. Likewise, PCR jitter occurs due to the temporal relative positional change of the PCR field in which a program clock reference (hereinafter abbreviated as PCR) value is carried. PCR is a time stamp for restoring the encoder's system time clock (abbreviated as stc hereinafter) as specified in the MPEG-2 standard.

In a real-time digital data transmission system such as an MPEG-2 codec, it is very important to synchronize the decoding and reproduction of application service data such as video or audio in the decoder. The transmitted data should be processed according to the specific rate associated with its generation and transmission. If the synchronization is read out, a buffer deficiency or an overflow error occurs and eventually the reproduction and decoding motivation is lost. MPEG-2 solves the synchronization problem by separately transmitting the time information used as a reference in the decoder to the determined packet syntax. That is, the PCR is encoded and transmitted with a value obtained by sampling the STC of the encoder, and this value represents a time instant when the decoder completely restores the field from the transmission bit stream. The decoder uses the PCR value to recover the decoder STC. By using the recovered STC as a reference clock, real-time decoding and reproduction can be performed at a specific rate associated with transmission and generation of the transmitted data without buffer error of the decoder. The PCR is transmitted one or more times within 0.1 second to synchronize the STC of the decoder with the STC of the encoder. All PCRs transmitted at this time should always have a certain delay from generation to decoding.

The re-multiplexing is packet multiplexing in units of TS packets, and the relative time position of packets changes in the process. That is, a timing jitter that changes the transmission delay of the data bit stream occurs in the re-multiplexing process of the transport bit stream. Similarly, the time interval between the PCR fields in the transport bit string after multiplexing is different from the time interval when the original encoding is performed. The change in the transmission delay of this PCR field is called PCR jitter in particular.

Therefore, the PCR jitter over the allowable range makes it difficult for the decoder to recover the system clock synchronized with the encoder, thereby causing a problem of the decoder buffer.

The present invention for solving the above problem is to eliminate the PCR jitter due to packet multiplexing in the re-multiplexing process in a TS packet remultiplexer compliant with the MPEG-2 system, thereby encoding an accurate PCR time stamp.

According to an aspect of the present invention, there is provided an apparatus and method for receiving a first TS, a second TS, a null packet, a first TS enable signal, and a second TS enable signal, And a PCR 2 detection flag and a PCR 2 detection flag are received from the first TS enable signal, the second TS enable signal, the PCR 1 detection flag, and the PCR 2 detection flag in the PCR corrector of the second transport bit stream remultiplexer, A PCR compensation value calculator for calculating and outputting a re-multiplexing delay time using the PCR packet intervals, and a PCR compensation value calculator for calculating a re-multiplexing delay time using the PCR packet intervals, A multiplexer for re-multiplexing the null packet, the first TS, and the second TS according to a selection code and outputting the third TS; and a multiplexer for detecting the PCR packet included in the third TS, A PCR packet detection unit for outputting the third TS, the PCR1 detection flag and the PCR2 detection flag, and a PCR correction value obtained by adding the PCR compensation value corresponding to the PCR delay time and the original PCR value to eliminate PCR jitter And a PCR correction code unit for newly encoding and outputting the third TS.

A re-multiplexing scheduler, an MUX, a PCR packet detector, a PCR compensation value calculator, and a PCR correction code unit. The PCR correction is a process of newly encoding the PCR field by compensating the PCR value corresponding to the delay time by the re-multiplexing. The re-multiplexing scheduler determines the types of TS packets to be re-multiplexed at present and the MUX re-multiplexes the selected packets. When the PCR packet detecting unit detects the PCR packet included in the third TS, the remultiplexing scheduler outputs the PCR packet intervals, and the PCR compensation value calculating unit outputs the PCR value corresponding to the delay time. The PCR correction code section newly codes the PCR field with the PCR correction value.

FIG. 1 is a PCR timing diagram of an MPEG-2 transport bit stream re-multiplexing process. The PCR timing relationship of the MPEG-2 transport bit stream re-multiplexing process will be described with reference to FIG.

The two transport bit streams included in the remultiplexing are denoted by a first TS and a second TS, respectively, and they transmit PCR fields at time intervals of T _{1, i} , T _{2, and i} , respectively. In one program transport bit stream, the intervals of the PCR fields may be the same but are generally different. Here, T _{1, i} represents the time between PCR _{1, i, which} is the i-th PCR of the first TS _, and PCR _{1, (i + 1), which is the (i + 1) th} PCR. T _{2, i} likewise represents the time interval between PCR fields in the second TS. Assuming that the transport bit string in which the first TS and the second TS are remultiplexed is the third TS, the multiplexed PCRs in the first TS and the second TS are transmitted to the third TS at time intervals of T _{31, i} , T _32, . Here, T _{31, i} is the PCR between the i-th PCR _{31, i} of the first TS in the third TS and the PCR _{31, (i + 1)} of the i + 1-th PCR of the first TS in the third TS It represents time. At this time, the original time interval is not maintained and the additional delay time as shown in Equation (1) is included. This is called a re-multiplexing delay time and is represented by DELTA T. ΔT _{1, i} represents the re-multiplexing delay time of the i-th PCR of the first TS.

[Equation 1]

T _{1, i} = T _{31, i} - T _{1, i}

T _{2, i} = T _{32, i} - T _{2, i}

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

FIG. 2 is a configuration diagram of a PCR correcting device of the demultiplexer. Referring to FIG. 2, the configuration of a PCR correction device of the demultiplexer will be described.

The PCR correction apparatus of the remultiplexer includes a re-multiplexing scheduler unit 10, a PCR compensation value calculation unit 20, a MUX 30, a PCR packet detection unit 40 and a PCR correction code unit 50.

The PCR correction is a process of newly encoding the PCR field by compensating the PCR value corresponding to the re-multiplexing delay time as shown in Equation (1). At this time, the PCR may be included in a packet having a predetermined payload. It is assumed that the packet constitutes an independent packet having a unique PID, and the packet is referred to as a PCR packet. If the byte position of the PCR field is always constant in the PCR packet, the interval of the PCR field can be expressed in units of TS packets. Knowing the TS rate and knowing the number of packets at the desired interval, the time corresponding to the interval can be known. The operation principle of the whole PCR correction device is as follows.

First, the remultiplexing scheduler 10 determines a TS packet type of 188 bytes to be re-multiplexed at present and outputs the result to the packet selection code. The MUX 30 re-multiplexes the null packet, the first TS, and the second TS according to the packet selection code, and outputs the third TS. The PCR packet detector 40 detects a PCR packet included in the third TS and outputs a PCR1 detection flag and a PCR2 detection flag to the remultiplexing scheduler 10 when a PCR packet is detected. The re-multiplexing scheduler 10 outputs the PCR packet intervals N ₁ , N ₂ , N ₃₁ and N ₃₂ when the flag signal is valid and the PCR compensation value calculator 20 calculates Calculates a multiplexing delay time, calculates a PCR value corresponding thereto, and outputs the result to the PCR correcting code unit 50. The PCR correction code unit 50 newly encodes the PCR field with the PCR correction value obtained by adding PCR_org, which is the original PCR value detected by the PCR packet detection unit 40, and? PCR, which is the PCR compensation value.

FIG. 3 is a configuration diagram of a re-multiplexing scheduler; FIG. The configuration of the re-multiplexing scheduler unit will be described with reference to FIG.

The re-multiplexing scheduler 10 is implemented as a state machine. The re-multiplexing scheduler 10 receives the first TS enable signal and the second TS enable signal as a state transition control signal, transitions the state, Coded by the packet selection code and output. The transition state indicates a packet to be re-multiplexed at present. The state machine's drive clock occurs once for every 188 clips of the third TS transmit clock because the TS packet is 188 bytes. That is, it performs re-multiplexing scheduling in units of one TS packet.

The packet selection method for re-multiplexing selects one packet of the first TS if the first TS enable signal is valid, and if the first TS enable signal is invalid and the second TS enable signal is valid, If one of the first TS enable signal and the second TS enable signal is invalid, a null packet is selected. When the first TS packet is determined, the re-multiplexing scheduler 11 generates a first TS packet counter enable signal to drive the first TS packet counter 12. The first TS packet counter 12 counts the number of first TS packets multiplexed so far. Similarly, the second TS packet counter 14 is driven by the second TS packet counter enable and counts the number of the second TS packets multiplexed so far. The third TS packet counter 16 counts all the re-multiplexed TS packets so far, and is driven by the third TS packet counter enable.

When the PCR1 detection flag signal is generated, the first TS packet interval calculator 13 stores the counter value of the first TS packet counter 12 and outputs the most recent first TS packet counter Value, which represents the number of packets between the PCR packet currently detected in the first TS and the PCR packet detected immediately before, and outputs the result as N ₁ . Likewise, when a PCR2 shedding flag signal is generated, the second TS packet interval calculator 15 stores the counter value of the second TS packet counter 14, obtains the difference from the previously stored second TS packet counter value N ₂ . When the PCR1 detection flag signal is generated, the third TS packet interval calculator 17 stores the counter value of the third TS packet counter 16, and when the PCR1 detection flag signal is generated, the third TS packet counter And outputs the difference as N ₃₁ , which represents the interval of the PCR packets re-multiplexed from the first TS in the third TS by the number of packets. Likewise, when the PCR2 detection flag signal is generated, the third TS packet interval calculator 17 stores the counter value of the third TS packet counter 16, and when the PCR2 detection flag signal is generated, The difference from the counter value is obtained and output as N ₃₂ .

This operation is performed every time a PCR packet is detected for all the PCR packets. Therefore, the number of packets between the i-th PCR packet and the (i + 1) th PCR packet of the first TS is N _{1, i} , when said number of packets N _{31, i,} and outputs the N _{l, i} and N _{31, i} for any i th PCR packet. Likewise _, N _{2, i} and N _{32, i} are output to the second TS.

The PCR compensation value calculation unit 20 will be described without reference to the drawings.

The PCR compensation value calculation unit 20 obtains a PCR compensation value for compensating PCR jitter. First, the re-multiplexing delay time corresponding to the PCR delay variation after re-multiplexing is obtained. That is, if the time T _{1, i} between the i-th PCR packet and the (i + 1) -th PCR packet of the first TS and the time T _{31, i} between the i-th PCR1 packet and the (i + The difference becomes the re-multiplexing delay time of the i-th PCR packet of the first TS. Assuming that the first TS transmission rate is R first TS and the third TS transmission rate is R third TS, T _{1, i} and T _{31, i} are expressed by the following equation (2). The delay time of PCR1 is obtained from equations (1) and (2). The delay time of PCR2 can also be obtained by the same method.

&Quot; (2) "

Second, the PCR value corresponding to the delay time, DELTA T, and PCR are obtained. The PCR shows 27 MHz STC using a 9-bit basic field PCR_base and an extension field PCR_ext. PCR1 _{, i} is represented by Equation (3) as a PCR value corresponding to [Delta] T1 _{, i} . Here, DIV means dividing by an integer and discarding the rest.

&Quot; (3) "

Δ PCR _1, i_base = {(27 MHz × ΔT _{1, i} ) DIV 300}% 2 ²³

? PCR _1, i_ext = {(27 MHz x? T _{1, i} ) DIV 1}% 2 ²³

? PCR1 _{, i} =? PCR1 _, i_basex300 +? PCR1 _, i_ext

The PCR output from the PCR compensation value calculation unit 20 is obtained as shown in Equations (2) to (3) above, and PCR1 _{, i} is the i-th PCR compensation value of the first TS. Similarly, the PCR compensation value is calculated for all the PCR packets of the second TS.

FIG. 4 is a configuration diagram of a PCR packet detecting unit. The configuration of the PCR packet detecting unit will be described with reference to FIG.

The PCR packet detector 40 detects the PCR packets of the first TS and the second TS in the re-multiplexed transport bit stream third TS. The data passed through the MUX 30 is input to the PCR packet detecting unit 40 as a transmission clock of the third TS in parallel by one byte. The inputted third TS data passes through the shift register 42 for 10 clocks by one byte per clock. The shift register 42 includes, in order from input to output, sr1, sr2, ..., and sr10, and outputs the sync signal sync_byte and the packet identifier PID (packet ID) to sr4, sr3_t and sr2 signals to the PID comparator 41 in order to detect the PCR packet. The final data having passed through the 10-byte shift register 42 is output to sr10.

The PID comparator 41 reads the necessary data from the shift register 42 and detects the PCR packet. In order to detect a PCR packet, a synchronization signal of a TS packet must be searched first, which is found by comparing sr4 with sync_byte and Ox47.

If packet synchronization is found, the PID is compared. That is, PID [12..0], which is the 13 bits of the PCR packet PID of the first TS and the second TS, is compared with sr3 [7..4] and sr2 [7..0]. sr3_t represents sr3 [7..4], and sr2 represents sr2 [7..0]. sr3 [7..4] represents the upper 4th bit to the 8th bit in sr3 data in byte units, and sr3 [7..4] and sr2 [7..0] represent 13-bit data, and sr3 [3..0] indicates the upper 4 bits of the 13-bit data, and sr2 [7..0] indicates the lower 8 bits of the 13-bit data. sync_byte is detected and the PCR PID of the first TS is detected at the same time, the packet is a PCR packet of 1 TS and generates a PCR1 detection flag signal informing PCR packet detection. Similarly, when the PID of the second TS is detected, a PCR2 detection flag signal is generated. PCR packets are detected and PCR values are stored in sr5 to sr10 after 10 clocks. The PCR value decoder 43 decodes the original PCR value from these data and outputs it as PCR_org.

PCR_org is obtained by the following equation (4).

&Quot; (4) "

PCR_org = PCR_base × 300 + PCR_ext

FIG. 5 is a block diagram of the PCR correction code unit. Referring to FIG. 5, the configuration of the PCR correction code unit will be described.

The PCR correcting code unit 50 replaces the PCR field included in the third TS with the corrected value. The input third TS is temporarily stored in the shift register 52. The modified PCR value calculator 51 obtains a modified PCR value as shown in Equation 5 by adding PCR_org, which is an original PCR value, and? PCR, which is a compensated PCR value, and newly codes the PCR_base and PCR_ext fields to replace the original value of the shift register do. PCR modification of the second TS can also be performed as described above.

&Quot; (5) "

PCR _1, i_corr = PCR _1, i_org +? PCR _{1, i}

PCR _1, i_base = {(PCR _1, i_corr) DIV 300}% 2 ²³

PCR _1, i_ext = {(PCR _1, i_corr) DIV 1}% 2 ²³

Therefore, the present invention as described above can be applied to a digital video broadcasting system such as digital broadcasting or the like which adopts MPEG-2 by encoding the accurate PCR time stamp by removing PCR jitter due to packet multiplexing in the re-multiplexing process in a TS packet remultiplexer compliant with the MPEG- It can be widely used in applications.

Claims (3)

A PCR correction device of an MPEG-2 transport bit stream remultiplexer that receives a first TS, a second TS, a null packet, a first TS enable signal, and a second TS enable signal and corrects the packet to output a third TS As a result, Receives the first TS enable signal and the second TS enable signal, the PCR1 detection flag and the PCR2 detection flag, determines one packet to be re-multiplexed at present, outputs the result to the packet selection code, A re-multiplexing scheduler 10 for outputting the re-multiplexed data; A PCR compensation value calculation unit 20 for calculating and outputting a re-multiplexing delay time using the PCR packet intervals; A multiplexer (30) for re-multiplexing the null packet, the first TS and the second TS according to the packet selection code and outputting the third TS; A PCR packet detector (40) for detecting a PCR packet included in the third TS and outputting an original PCR value, the third TS, the PCR1 detection flag and the PCR2 detection flag; And And a PCR correcting code unit 50 for newly encoding and outputting the third TS with a PCR correction value obtained by adding the PCR compensation value corresponding to the PCR delay time and the original PCR value in order to eliminate the PCR jitter Characterized by an MPEG-2 transport bit stream remultiplexer PCR correction device. The apparatus of claim 1, wherein the PCR packet detector (40) The first TS data is input to the first TS data one byte at a time, and the first TS data is transmitted while being shifted while being shifted, and a synchronous signal and a packet identifier are output in order to detect the PCR packet, the original PCR value is stored, A shift register 42; A PID comparator (41) for receiving the synchronization signal and the packet identifier and analyzing the packet identifier to output the PCR1 detection flag and the PCR2 detection flag; And And a PCR value decoder (43) for decoding the original PCR value from the modified PCR data and outputting the decoded original PCR value. The apparatus according to claim 1, wherein the PCR correcting code unit (50) A second shift register (52) for receiving and storing a third TS; And a modified PCR value calculator 51 for newly coding the modified PCR value obtained by adding the original PCR value and the compensated PCR value and replacing the corrected PCR value with the original value of the second shift register 52. [ -2 transport bit-stream remultiplexer PCR correction device.