CN1314269C - Method and device for regulating program reference clock of motion image expert group 2 - Google Patents

Abstract

The present invention relates to a method and a device for regulating a program reference clock of a moving picture expert group-2, which belongs to the field of digital video-audio transmission. The method comprises the steps: obtaining proportional relation of code rates before and after multiplexing transmission streams; obtaining change rate-Rpcr with the unit of bag of PCR of multiplexed and outputted programs among input transmission streams in relation to the input transmission streams; regulating the PCR in the multiplexed output transmission streams. The device comprises m buffering-counting-latching units, a buffering-counting unit and a multiplexing-processing unit. The method and the device of the present invention can reduce the complexity of hardware designs, enhance the smoothness of the regulated PCR, reinforce the anti-interference capability of a system, and enhance flexibility.

Description

The method of adjustment and the device that are used for the Program Clock Reference of motion image expert group 2

Affiliated field

The invention belongs to the digital video-audio transmission field, be specifically related to when motion image expert group 2 (MPEG-2) transmission stream remultiplexing, carry out the method and apparatus that Program Clock Reference (PCR) is adjusted.

Background technology

Mpeg 2 transport stream is being carried out again all adopt usually when multiplexing method that time reference is adjusted so that image and voice keep end-to-end delay consistently after through coding, transmission and decoding, thus the correct reproduction of assurance video/audio signal.The field relevant with time reference is Program Clock Reference (PCR) in the mpeg 2 transport stream system, shows time stamp (PTS) and decoding time stamp (DTS), and wherein PCR is used for the clock at decoding end recovery coding side, and PTS and DTS all with PCR as reference.Usually when adjusting time reference, PTS and DTS are not made an amendment, and only this significant field of PCR is adjusted, so that stably keep synchronously with encoded clock through the PCR after multiplexing.

U.S. Pat 5905732 " PCR restamper " discloses a kind of method of PCR being carried out again mark, this method need be measured the code check of input transport stream, also need with hardware the transport stream packets (being designated hereinafter simply as the PCR bag) of carrying the PCR field to be carried out real-time analysis, the final adjustment of PCR still needs hardware to finish.

U.S. Pat 6233238 " Method for updating clock references in adigital data stream and a remultiplexer " discloses the method for revising reference clock in a kind of reuse device, this method principle is simple, but also need to use hardware that the PCR bag is analyzed when realizing, and can't eliminate the PCR shake that encoded clock or Network Transmission are brought.

In general, present time reference adjustment technology mostly needs the transport stream of input is carried out real-time analysis, find out PCR and wrap also and then obtain the system status parameters in this moment, the final adjustment of PCR also requires to carry out in real time in the moment of output, with present technical merit, these work can only be finished by hardware, and this must cause the hardware complexity, and cost improves.In addition, some principle complexity, operation times is many, need pay bigger cost for the precision of retention time benchmark.

Summary of the invention

Technical problem to be solved by this invention is to overcome prior art algorithm complexity, realization difficulty, the not good shortcoming of technique effect, proposes a kind of this method of methods and applications of carrying out the PCR adjustment when mpeg 2 transport stream is multiplexing again and carries out the device that PCR adjusts.

The multiplexing again Program Clock Reference of mpeg 2 transport stream (PCR) method of adjustment that is used for that the present invention proposes may further comprise the steps:

The first step: the proportionate relationship that obtains transmission stream remultiplexing front and back code check, input transport stream code check before multiplexing again is designated as CodeRateIn, output transport stream code check after multiplexing again is designated as CodeRateOut, according to following formula (1) the definition ratio Kcr of the code check of multiplexing front and back again:

$\mathrm{Kcr}=\frac{\mathrm{CodeRateIn}}{\mathrm{CodeRateOut}}---\left(1\right);$

Second step: obtaining in the input transport stream by the PCR of the program of multiplexing output again is the rate of change Rpcr of unit with the bag with respect to the input transport stream, the transport stream packets quantity of two middle processes of PCR bag in the input transport stream is designated as Δ PacketNumIn, and the difference of PCR field in these two PCR bags is designated as Δ PCRIn, then obtain Rpcr according to following formula (2):

$\mathrm{Rpcr}=\frac{\mathrm{\ΔPCRIn}}{\mathrm{\ΔPacketNumIn}}---\left(2\right);$

The 3rd step: the result who obtains according to preceding two steps adjusts the PCR in the output transport stream after multiplexing again, and this step can be divided into following two steps:

1. the some PCR bag that will participate in again multiplexing program is considered as initial PCR bag, this bag is not adjusted and directly exports, and the value of the PCR field that this bag is carried is designated as PCROut0;

2. the transport stream packets quantity of process is designated as Δ PacketNumOut (n) between each PCR bag that initial PCR bag is occurred afterwards and the initial PCR bag, and the value after the PCR field adjustment that will wrap is designated as PCROut (n), calculates according to following formula (3):

PCROut(n)＝PCROut0+Kcr×Rpcr×ΔPacketNumOut(n) …(3)。

A kind of adjusting device that is used for the multiplexing again Program Clock Reference of mpeg 2 transport stream comprises:

With input transport stream m buffering-counting-latch units one to one, be used for the input transmit flow data is cushioned and counts, and under the control of latch control signal, count value is latched, latched value and latching is refreshed sign offer multiplexing process unit again;

Buffering-counting unit, be used to cushion from the output transport stream of multiplexing process unit again, simultaneously the output transport stream data are counted, latch control signal just is set when counting has increased predefined fixed value (being designated as CONSTCNT), and this signal is provided for buffering-counting-latch units of respectively importing on the transport stream;

Multiplexing process unit again, be used in time reading latched value, latching information such as refreshing sign and input transmit flow data from described buffering-counting-latch units, all double latched values that read are added up as the input transmit flow data counting of inside modules use, the output transport stream data counts that inside modules is used (initial value is zero) adds the fixed value CONSTCNT that chooses in buffering-counting unit simultaneously, and then the ratio of input, the counting of output transport stream data in the identical time period is exactly again the ratio Kcr of the code check of multiplexing front and back; And read the input transmit flow data from buffering-counting-latch units, handle obtaining the rate of change Rpcr of PCR with respect to the input transport stream packets; Output transport stream is carried out PCR to be adjusted.

Adopt the method for the invention and device, can not need PCR is carried out real-time analysis, reduced the complexity of hardware designs, and can improve the smoothness of adjusted PCR, the antijamming capability of enhanced system; Can reduce the difficulty of realization, to reduce owing to realizing being not good at causing the unfavorable probability of result; Overwhelming majority work can be finished by software, is easy to exploitation and debugging, also is convenient to algorithm and improves and increased functionality, has improved flexibility.

Description of drawings

Fig. 1 is the schematic diagram of functional block that is used to illustrate the method for adjustment of Program Clock Reference of the present invention;

Fig. 2 is the schematic diagram that is used for the functional block that key diagram 1 code check ratio obtains;

Fig. 3 is the schematic diagram that is used for the functional block that key diagram 1 input PCR rate of change obtains;

Fig. 4 is the schematic diagram that is used for the functional block of key diagram 1 output-pcr processing;

Fig. 5 is the schematic diagram of PCR adjusting device;

Fig. 6 is the schematic diagram of buffering-counting among Fig. 5-latch units 1;

Fig. 7 is the schematic diagram of buffering-counting unit among Fig. 5;

Fig. 8 is the functional schematic of multiplexing process unit again among Fig. 5;

Fig. 9 is the flow chart of latch information receiving function among Fig. 8;

Figure 10 is the flow chart of transport stream processing capacity among Fig. 8;

Figure 11 is the flow chart of PCR bag processing capacity among Figure 10.

Embodiment

Execution mode below in conjunction with accompanying drawing and example is described in further detail method of adjustment and device thereof according to Program Clock Reference of the present invention.

At first, describe the method for adjustment of Program Clock Reference of the present invention in detail referring to Fig. 1 to 4.

As shown in Figure 1, the method of adjustment of Program Clock Reference of the present invention can be divided into three functional blocks: code check ratio acquisition module, input PCR rate of change acquisition module and output-pcr processing module, and these three modules realize three steps of the method for the invention respectively:

1, input transport stream byte clock ByteClkIn and output transport stream byte clock ByteClkOut are analyzed, obtain the proportionate relationship of the code check of transmission flow multiplex front and back;

2, input transport stream packets PacketIn is analyzed, obtain importing the PCR rate of change;

3, output transport stream PacketOut is analyzed, the parameter that obtains according to first two steps is adjusted the PCR in the transport stream of multiplexing output again, obtains adjusted PCR (PCROut among Fig. 1);

Fig. 2 is the schematic diagram of code check ratio acquisition module among Fig. 1, is used to the step that illustrates that the code check ratio is obtained:

Input transport stream byte counter is counted input transport stream byte clock ByteClkIn;

The output transport stream byte counter is counted output transport stream byte clock ByteClkOut;

The byte counter control module is controlled above two counters, obtains the variation delta ByteNumIn of input transport stream byte counter in the identical time period and the variation delta ByteNumOut of output transport stream byte counter;

Δ ByteNumIn and Δ ByteNumOut are output to the output-pcr processing module among Fig. 1.

Fig. 3 is the schematic diagram of input PCR rate of change acquisition module among Fig. 1, is used to the step that illustrates that input PCR rate of change obtains:

Input transport stream packets counter is counted input transport stream packets PacketIn, offers input PCR processing module;

Input PCR processing module is handled the PCR bag of the program that is re-used, and calculates the difference DELTA PCRIn of the PCR field of two PCR bags, obtains the bag quantity Δ PacketNumIn of process between these two PCR bags again according to the value of input transport stream packets counter;

Δ PCRIn and Δ PacketNumIn are output to the output-pcr processing module among Fig. 1.

Fig. 4 is the schematic diagram of output-pcr processing module among Fig. 1, is used to illustrate the method for the PCROut that obtains output:

The output transport stream package counting facility is counted output transport stream bag PacketOut, obtains PacketNumOut;

The output-pcr adjusting module is analyzed output transport stream PacketOut, identify the PCR bag, read the corresponding output packet counting of each PCR bag from the output transport stream package counting facility simultaneously, thereby calculate Δ PacketNumOut (n), the parameter that provides according to the code check ratio acquisition module among Fig. 1 and input PCR rate of change acquisition module again is according to formula (3)

PCROut(n)＝PCROut0+Kcr×Rpcr×ΔPacketNumOut(n) …(3)

Calculate adjusted PCR value (being designated as PCROut), and replace PCR field in this bag with the PCR value that calculates.

In the superincumbent computational process, Kcr and Rpcr calculate according to following formula:

$\mathrm{Kcr}=\frac{\mathrm{\ΔByteNumIn}}{\mathrm{\ΔByteNumOut}},\mathrm{Rpcr}=\frac{\mathrm{\ΔPCRIn}}{\mathrm{\ΔPacketNumIn}};$

Then formula (3) deformability is following formula (4):

$\mathrm{PCROut}\left(n\right)=\mathrm{PCROut}0+\frac{\mathrm{\ΔByteNumIn}\×\mathrm{\ΔPCRIn}\×\mathrm{\ΔPacketNumOut}\left(n\right)}{\mathrm{\ΔByteNumOut}\×\mathrm{\ΔPacketNumIn}}---\left(4\right).$

Input PCR is exactly in fact the rate of change of program encoded clock with respect to the input transport stream packets that be re-used with respect to the rate of change of input transport stream packets, the ratio of this rate of change and input and output code check is multiplied each other, what obtain is exactly the rate of change of program encoded clock with respect to the output transport stream bag that be re-used, thereby calculate certain output-pcr bag (the PCR value that will wrap is considered as the PCROut0 in the inventive method description) changing value of any one output transport stream bag (the output transport stream bag quantity that will wrap the middle process of the bag corresponding with PCROut0 is designated as Δ PacketNumOut (n)) corresponding codes clock afterwards, with the PCROut0 addition, be the corresponding PCR value of this bag again.

In order to make adjusted PCR satisfy the requirement of Moving Picture Experts Group-2 to the PCR precision, the ratio of input PCR rate of change and input and output code check all should be with the form preservation of the ratio of two integers, and the figure place of these integers also should reach certain length; According to formula (4) when calculating, the multiplication of same priority and division arithmetic are calculated division after should calculating multiplication earlier.

PCR adjusting device of the present invention is as shown in Figure 5: comprise with each input transport stream TS 1, TS2 ..., TS (M) M buffering-counting-latch units, multiplexing process unit and buffering-counting unit more one to one; Each import transport stream TS 1, TS2 ..., TS (M) is through after corresponding buffering-counting-latch units is handled, offer multiplexing process unit again, buffering-counting unit receives the output of multiplexing process unit again, under the control of external output transport stream byte clock CLKOut, generate output transport stream TSOut, buffering-counting unit is counted CLKOut simultaneously, the overflow indicator OVFLG of counter offers each buffering-counting-latch units, as latch control signal.

Fig. 6 is the schematic diagram of buffering-counting among Fig. 5-latch units: comprise a FIFO (first in first out) chip, 20 digit counter, 20 bit register, one latch control unit.In buffering shown in Figure 6-counting-latch units 1, the data byte of input transport stream is written into FIFO1, and offering counter 1, counts its byte clock CLK1, latch control unit at the rising edge control register 1 of the LCKCTL of latch control signal from counter 1 reading, and be provided with to latch and refresh sign LCKFLG1, this sign offers multiplexing process unit again with the output DATA1 of the output CNT1 of register 1 and FIFO1 as the output of whole buffering-counting-latch units, latchs to refresh sign and be latched control unit remove after the content of register 1 is read away.

Fig. 7 is the schematic diagram of buffering-counting unit among Fig. 5: comprise one as the fifo chip of output buffer and 16 digit counters of a band overflow indicator; FIFO receives the output DATAOut of multiplexing process unit again, and under the control of output transport stream byte clock CLKOut, send output transport stream TSOut, counter is counted CLKOut simultaneously, overflow indicator OVFLG is its output, be introduced into and latch control unit as latch control signal LCKCTL among Fig. 6, after overflow indicator is set up, when arriving, removes automatically the next count pulse of CLKOut.

Fig. 8 is multiplexing process unit a functional schematic that first via input transport stream is handled again among Fig. 5: be divided into that latch information receives and two functional blocks of transport stream processing, the latch information receiver module receives latch information (CNT1, LCKFLG1) and handles from buffering-counting-latch units 1, result offers the transport stream processing module, and the transport stream processing module is handled the input transmit flow data (DATA1) from buffering-counting-latch units 1 in view of the above.

The multiplexing process unit is handled each input transport stream repeatedly again, generates output transport stream TSOut by the transport stream processing unit at last.

Fig. 9 has provided the flow process (it is similar with it that other input transport stream latch information receives flow process, the latch information receiving function in all each road input transport stream latch information receiving function pie graphs 8) of first via input transport stream latch information receiving function:

Beginning 901;

Judge that at first latch information refreshes sign LCKFLG1 902, do not change step 909 if this sign is set, otherwise continue to carry out;

Read the count value CNT1 903 of register 1;

Judge whether it is to read register 904 for the first time, be then to continue to carry out, otherwise change step 906;

It is with the zero clearing of two counter initial values that latch information receives initialization, and the value of preserving CNT1 simultaneously calculated difference 905 when being used for reception latch information is next time changeed step 909 then;

The difference of all double CNT1 values added up has been used as first via input transport stream with the input byte count Δ ByteNumIn1 906 (corresponding to the Δ ByteNumIn in the formula (4)) in the equal time, order:

Number of times * 2 that Δ ByteNumOut1=CNT1 difference adds up ¹⁶

Δ ByteNumOut1 is with the counting of the output byte in the equal time (corresponding to the Δ ByteNumOut in the formula (4)), 2 ¹⁶Coefficient be for corresponding with the figure place of counter in the counting-latch units among Fig. 7, and in inside, multiplexing process unit again, integer and 2 ¹⁶Multiply each other and to realize with byte shift easily.

Judge whether input or output byte counter will overflow 907, be then to continue to carry out, otherwise change step 909;

In the time will overflowing, will import byte count and output byte counting and move to right 16 908 simultaneously;

Finish 909.

Be not difficult to find out: the buffering-counting-latch units among Fig. 6, buffering-counting unit among Fig. 7 and the latch information receiving function among Fig. 9 cooperatively interact, realized the function of the code check ratio acquisition module of Fig. 2, it should be noted: counter counts from zero the time of overflowing and must count from zero the time of overflowing less than counter in buffering-counting-latch units in the counting-latch units, and when realizing the latch information receiving function, detect the time interval that latch information refreshes between the sign for twice must count from zero the time of overflowing less than counter in the counting-latch units again.

Referring now to Figure 10,, Figure 10 is the flow chart according to transport stream processing capacity of the present invention.

Beginning 1001;

Wrap synchronously, analyze input transport stream 1002;

Carry out multiplexing process, generate output transport stream, and safeguard package counting facility and the output transport stream package counting facility 1003 of respectively importing transport stream;

Judge whether it is PCR bag 1004, be then to continue to carry out, otherwise change step 1006;

Call PCR packet handing module 1005;

Judge whether dispose 1006, be then to change 1008 if respectively importing transport stream, otherwise continue to carry out;

Prepare 1007 for handling next road transport stream, change step 1002 then;

Finish 1008.

Figure 11 only provided the program A that is re-used PCR bag process chart, the flow process that the PCR bag of other program is handled is similar with it:

Beginning 1101;

From input PCR bag, extract the PCR value, take out affiliated input transport stream of this program and 1102 values of output transport stream counter simultaneously;

Judge whether first PCR bag 1103, be then to continue to carry out, otherwise change step 1105 for this program;

For adjusting, PCR carries out initial work 1104: with the initial value PCROutA0 (corresponding to PCROut0 in formula (4)) of current PCR value as output-pcr, the value that reads the output transport stream package counting facility is as PacketNumOut0, to import PCR variation delta PCRInA (corresponding to the Δ PCRIn in the formula (4)) and input package counting facility variation delta PacketNumInA (corresponding to the Δ PacketNumIn in the formula (4)) zero clearing, change step 1106 then;

Upgrade the rate of change 1105 of PCR: this PCR is deducted previous PCR with respect to the input transport stream packets, the result who obtains adds the new value of Δ PCRInA as Δ PCRInA, count according to the input transport stream packets of correspondence again, through calculating the new value of Δ PacketNumInA, thereby the function of PCR rate of change acquisition module among realization Fig. 3, also to take simultaneously with Fig. 9 in similarly method prevent overflowing of internal storage unit;

Preparation is carried out PCR and is adjusted calculating 1106, and the value of output transport stream package counting facility deducts PacketNumOut0 as Δ PacketNumOut (n) with this moment, simultaneously some data is preserved in order to calculating next time and uses;

Whether the denominator in the judgment formula (4) is 0 1107 (guaranteeing that division is meaningful), is then to change step 1109, otherwise continues to carry out;

Carry out PCR according to formula (4) and adjust calculating 1108, and revise the PCR field in this bag in view of the above;

Finish 1109.

Generally, just can obtain the value of code check proportionate relationship before beginning is multiplexing again, the denominator in the formula (4) is zero when handling first PCR bag so have only, and do not make an amendment to this PCR bag this moment.Above situation be equivalent to temporarily can't to determine that the Kcr in the formula (3) is long-pending with Rpcr because Δ PacketNumOut this moment (n) is zero, so though the PCR that exports can't calculate but still coincidence formula (3) according to formula (4).

Claims (4)

1. be used for the method for adjustment of the Program Clock Reference of motion image expert group 2, may further comprise the steps:

At first obtain the proportionate relationship of code check before and after the transmission stream remultiplexing, the ratio Kcr of the code check of multiplexing front and back is according to following formula definition again:

$\mathrm{Kcr}=\frac{\mathrm{CodeRateIn}}{\mathrm{CodeRateOut}},$

CodeRateIn is again the input transport stream code check before multiplexing in the formula, and CodeRateOut is again the output transport stream code check after multiplexing;

Be the rate of change Rpcr of unit by the Program Clock Reference of the program of multiplexing output again with the bag with respect to the input transport stream in the input transport stream of reentrying, this rate of change Rpcr calculates according to following formula:

$\mathrm{Rpcr}=\frac{\mathrm{\ΔPCRIn}}{\mathrm{\ΔPacketNumIn}},$

Δ PCRIn is the difference of Program Clock Reference field in two Program Clock Reference bags in the input transport stream in the formula, and Δ packetNumIn be the transport stream packets quantity of these two Program Clock Reference bags centre processes;

The result who obtains according to preceding two steps adjusts the Program Clock Reference in the output transport stream after multiplexing again, comprises the steps:

A Program Clock Reference bag that participates in multiplexing again program is considered as initial Program Clock Reference bag, this bag is not adjusted and directly exports, and the value of the Program Clock Reference field that this bag is carried is designated as PCROut0;

Each Program Clock Reference bag to the appearance after the initial Program Clock Reference bag, the transport stream packets quantity of process between this bag and the initial Program Clock Reference bag is designated as Δ PacketNumOut (n), and the value after the Program Clock Reference field adjustment that will wrap is designated as PCROut (n), then:

PCROut(n)＝PCROut0+Kcr×Rpcr×ΔPacketNumOut(n)，

Kcr is the ratio of the code check of multiplexing front and back in the formula, and Rpcr is for being the rate of change of unit by the Program Clock Reference of multiplexing output again with the bag with respect to the input transport stream in the input transport stream.

3. the adjusting device that is used for the Program Clock Reference of motion image expert group 2 is characterized in that it comprises:

With input transport stream m buffering-counting-latch units one to one, be used for the input transmit flow data is cushioned and counts, and under the control of latch control signal, count value is latched, latched value and latching is refreshed sign offer multiplexing process unit again;

Buffering-counting unit, be used to cushion from the output transport stream of multiplexing process unit again, simultaneously the output transport stream data are counted, latch control signal just is set when counting has increased a predefined fixed value, and this signal is provided for buffering-counting-latch units of respectively importing on the transport stream;

The multiplexing process unit is used in time reading latched value, latching information such as refreshing sign and input transmit flow data, through handling the ratio of the code check that obtains again multiplexing front and back from described buffering-counting-latch units again; And read the input transmit flow data from buffering-counting-latch units, handle obtaining the rate of change of PCR with respect to the input transport stream packets; Output transport stream is carried out PCR to be adjusted.

4, the adjusting device that is used for the Program Clock Reference of motion image expert group 2 according to claim 3, it is characterized in that described buffering-counting-latch units comprise a first in first out chip, counter, register, one latch control unit;

The data byte of input transport stream is written into the first in first out chip, and offering counter, counts by its byte clock, latch control unit at the rising edge control register of latch control signal from meter reading, and be provided with to latch and refresh sign, this sign offers multiplexing process unit again with the output of the output of register and first in first out chip as the output of whole buffering-counting-latch units, latchs to refresh sign and be latched control unit remove after the content of register is read away.

5,, it is characterized in that described buffering-counting unit comprises as a first in first out chip of output buffer and a counter of band overflow indicator according to claim 3 or the 4 described adjusting devices that are used for the Program Clock Reference of motion image expert group 2; The first in first out chip receives the output of multiplexing process unit again, and under the control of external output clock, send output transport stream, counter is counted the output clock simultaneously, overflow indicator is its output, be introduced into and latch control unit as latch control signal, after overflow indicator is set up, when arriving, removes automatically the next count pulse of output clock.

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