CN101257623A - Method for correcting MPEG-2 transmission stream PCR twitter based on accounting device setting number - Google Patents

Abstract

The present invention is a counter based MPEG-2 transmission stream PCR shake correction method, facing to digital television system MPEG-2 transmission stream in communication. PCR parameter represents system clock of transmission stream. The technical problems needed to be solved are to correct the PCR shake produced by the transmission stream passing through the code stream processing system. The present invention designs a novel method for correcting PCR shake based on the substance of PCR and original scheme, namely counter based PCR shake correction method. The method sets the PCR counter to be the current number when the data packet containing PCR parameters enter into the system, performs counter extraction of PCR parameter when outputting data packet, thereby accomplishing correction of PCR parameter. Compared with the original scheme, complexity of the scheme is reduced. And the synthetic result of the method is superior greatly to the original scheme, due to use simple logic, and without complex adder implementation, and with less system resource occupation.

Description

Put several mpeg 2 transport stream PCR method of compensating for hand shake based on counter

Technical field

The communication system digital tv network

Background technology

Mpeg 2 transport stream

Summary of the invention

Proofread and correct the PCR shake in the mpeg 2 transport stream.

Description of drawings

Fig. 1 PCR jitter correction system block diagram

Fig. 2 sliding window schematic diagram

Fig. 3 PCR counter status transition figure

Embodiment

PCR is the part in the MPEG-2TS stream, i.e. timer reference of programs (Program Clock Reference), and 42 bits, is made up of two parts: a part of 1/300 (90kHz) with system clock (27MHz) is unit, is called the PCR essential part, 33 bits; A part is a unit with the system clock, is called the PCR expansion, 9 bits.The PCR value is a time value t (i), and i is the sequence number of byte in whole transport stream that contains last bit of essential part among this PCR, and what promptly the PCR value was represented is the time that this byte arrives System Target Decoder.After all sounds, video sampling enter encoder, export respectively in decoder end through a constant delay end to end.Because in the process that transmits flow transmission, the transmission delay of each field is not strict identical, and can produce situations such as code stream reorganization and rate adapted, the PCR field that is used for synchronization mechanism like this in the TS stream is just possible different from the transmission delay that encoder arrives decoder.Will produce so-called PCR shake like this.

The present invention at first carries out the extraction of PCR.After extracting original PCR parameter, to putting number with the inside PCR counter of this packet correspondence, promptly the initial value of this counter is set to current PCR value.After this, this counter begins to count according to inner 27MHz clock.This corresponding data Bao Ze carries out rate adapted, as enters FIFO etc.When this packets need output, system detects and the inside PCR counter of this packet correspondence, and this PCR counter current count value is embedded in the packet according to standard code, and the respective byte in the code stream is rewritten, thereby finish the renewal of PCR parameter, system configuration such as Fig. 1.

In transport stream, because multi-channel program multiplexing, the nearer several packets that might occur being separated by all contain the situation of PCR, before this packet PCR upgrades, former extraction value need be kept, and the present invention uses four counters.Each counter recycles, and resolves end at input code flow and resolves the sliding window that end adopts identical grid number with output code flow.

The function that setting counter at first needs to realize is the positive transition that judges whether to exist pcr_en, and this saltus step 27MHz clock common and module is asynchronous.The present invention has adopted the pre_state register.When a 27MHz rising edge clock stimulating module, we still detect pcr_en state this moment, and with reference to pre_state, when pcr_en is a high level, when pre_state is low level, we think that pcr_en may produce positive transition, but immediately counter is not put number, when next 27MHz rising edge clock encourages then, we detect the state of pcr_en again, if still be 1, then be sure of to have produced saltus step, counter is changed to the numerical value (because in fact PCR just counter should be put several at last one-period) of PCR+1, this status change can be described as Fig. 2.

Sliding window is a kind of mechanism that is used to receive and dispatch asynchronous control.For situation of the present invention, when carrying out the input code flow parsing,, then need the counter of first label is carried out set if contain PCR in first packet, simultaneously window is slided backward once.When receiving the packet that contains PCR for the second time, again second counter carried out set.Resolve end in code stream output, such sliding window mechanism is also arranged.Receiving terminal carries out code stream analyzing equally, finds out whether to contain PCR, when finding for the first time, just the current count value of first counter is deposited in the code stream as the PCR that upgrades.Sliding window is represented with one 2 bit wide register buffer_state towards the realization of hardware.This register just adds one whenever finishing after start-stop counter is put number or read operation.The addition of two registers is equivalent to mould 4 additions, has so just realized function.This functional schematic as shown in Figure 3.

Claims (3)

1. usage counter is put severally to the PCR parameter correction in the mpeg 2 transport stream, does not use adder.

2. use sliding window mechanism that the output sequence number is handled, seek corresponding PCR value.

3. counter is put to count and is adopted the PCR of clock sampling method detection for a long time to enable.

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