CN100421449C - Control Method of Clock Synchronization in Network Digital TV System - Google Patents

Abstract

A control method for network digital TV system clock synchronization maintenance, which introduces digital TV programs into the broadband IP network development process, and maintains time information in the demultiplexing and remultiplexing units. The information in the transport stream restores the original time information, and the effective data of the program can be transmitted in the network at a variable bit rate rate, and the system clock synchronization at the encoding end and the decoding end can be achieved with a time information model at a constant bit rate rate. The present invention makes the demultiplexing and remultiplexing processing simpler, and does not need to correct the time information; the single-program system transmission stream with time synchronization information is more suitable for transmission in the IP network, and the original multi-program can be recovered The same time synchronization information as the system transport stream can be used as a synchronous system decoder clock to eliminate various phenomena caused by codec asynchrony.

Description

Control Method of Clock Synchronization in Network Digital TV System

technical field

The present invention relates to a control method used in the technical field of network digital TV transmission, in particular to a control method for maintaining clock synchronization of a network digital TV system.

technical background

At present, the common digital TV coding technology adopts the MPEG-2 video and audio coding standard, which is established by ISO/IEC

13818 file description, which also defines the system layer structure of the encoded output stream, and also defines a time model to keep the codec clock synchronized. At the same time, the standard also defines a program reference clock (PCR) value in the code stream to mark the system clock of the program code stream, but the standard stipulates that the processing of the code stream, such as demultiplexing, re-multiplexing and bit rate During the change processing, the PCR value of the time information parameter of the code stream must be strictly corrected according to the standard regulations. With the development of digital TV and broadband IP network, the development of digital TV business in IP network has become an important application. At the same time, experiments have proved that the transmission of digital TV programs in IP network should adopt the single-program system transmission stream that only transmits the effective data of the program. Such a form often leads to a single-program system transport stream with a variable bit rate at the system layer. Such a system transport stream will be more efficient than a system transport stream that maintains a constant bit rate (CBR) by adding empty packets. Effective, not only improves channel utilization, but also fits the service mode of IP network "Best-effort". This means that when digital TV programs are introduced into the network, the multi-program system transport stream must be demultiplexed to generate a single-program system transport stream for transmission in the network. At the same time, it is necessary to ensure that the transmission after these processes is more effective while maintaining the standard The defined time model for clock synchronization is still valid. In order to keep these time information valid, the traditional multi-program demultiplexer not only needs to perform strict (PCR) time information correction, but also needs to pass Adding empty packets to maintain a constant bit rate (CBR) output is not suitable for effective transmission in a shared IP network, and it also increases the complexity of bit stream processing.

In the ISO/IEC13818 document of the MPEG-2 standard, Appendix D "ITU-T H.222.0|ISO/IEC13818-1Systems Timing Model and Application Implications" describes in detail the implementation and significance of the system clock synchronization model, and points out that in PCR jitter (JITTER) will be introduced during the processing and transmission of the code stream. Some of these jitters are caused by the processing of the code stream, and some are caused by network transmission. Appendix D suggests that strict PCR correction should be performed when processing the code stream, and it is recommended to use Smoothing Buffer to smooth the jitter caused by the network after the code stream is transmitted. In the ISO/IEC13818 document of the MPEG-2 standard, Appendix K "Interfacing Jitter-Inducing Networks to MPEG-2 Decoders" recommends using FIFO and PLL to eliminate the jitter of CBR in network transmission, and also recommends another method using network layer Timestamp to help eliminate jitter caused by network transmission. However, the above methods are all based on the idea of correcting processing jitter and transmission jitter separately, which not only complicates the processing and cannot eliminate all jitter, but also does not fully integrate the service mode of network transmission.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies and defects of the prior art, and provide a control method for network digital TV system clock synchronization maintenance, which can realize that digital TV programs only transmit the effective data of the program in the network, and return to a constant value at the receiving end. The code rate is high, and the system clock is synchronized with the correct PCR value. The structure is simple, and it has a good degree of expansion. It is suitable for introducing digital TV services into broadband IP networks.

The present invention is realized through the following technical solutions. The present invention introduces digital TV programs into the broadband IP network development process, and maintains time information in the demultiplexing and remultiplexing units. The information in the stream restores the original time information, and the effective data of the program can be transmitted in the network at a variable bit rate rate, and the system clock synchronization at the encoding end and the decoding end can be achieved with a time information model at a constant bit rate rate.

The "demultiplexing and re-multiplexing" means that when the digital TV program system transport stream of the traditional digital TV broadcasting network is input, the de-multiplexing and re-multiplexing processing unit re-demultiplexes according to the information of the input system transport stream. Generate a single-program system transport stream with time synchronization information. The single-program system transport stream only contains the effective video and audio data of the program and is transmitted in the broadband IP network. Such a system transport stream will maintain a constant bit rate than by adding empty packets. The system transmission stream is more effective, which not only improves the channel utilization rate, but also conforms to the "Best-effort" service mode of the IP network. At the receiving end, the recovery time information processing unit transmits the system according to the received single program with time synchronization information Return to the code stream of constant code rate rate again, the time synchronization information PCR value of this constant code rate code stream is the same as the position before entering the input demultiplexing and multiplexing processing unit, so that the system of the program code stream decoder Clock synchronization.

The "system clock synchronization" includes a front-end demultiplexing and remultiplexing processing unit, a network transmission processing unit, and a receiving end recovery time information processing unit. The demultiplexing and remultiplexing processing unit refers to the effective network The transmitted digital TV system transport stream is processed to generate the corresponding single-program digital TV system transport stream; the network transmission processing unit refers to the protocol processing performed during network transmission in order to effectively transmit the digital TV system transport stream; the receiving end The recovery time information processing unit refers to the processing performed by the terminal to correctly recover the system time information of the system transport stream after receiving the network data of the transport stream of the digital television system.

When the input is a digital TV program system transmission stream of a traditional digital TV broadcasting network, the receiving end recovers to a constant bit rate rate, and synchronizes the system clock with the PCR value of the correct time information, including the following steps:

① Demultiplex and re-multiplex the input digital TV multi-channel program system transmission stream. In the process of demultiplexing, there is no need to correct the PCR value of the time information, only need to keep the time information of the original program and insert some The information is used to record the relative position of the program transmission packet; also, in the process of multiplexing, it is not necessary to correct the PCR value of the time information, and generate a single program transmission stream that does not contain empty packets;

②The generated single-program transmission code stream without empty packets is transmitted at a variable bit rate in the network;

③ At the receiving end, the recovery time information processing unit restores the code stream with a constant bit rate rate according to the information contained in the single program system transport stream, and the time synchronization information PCR value of the constant bit rate rate bit stream and input demultiplexing It is the same as the position before reusing the processing unit.

The implementation scheme of network digital TV system clock synchronization maintenance in the present invention performs demultiplexing and remultiplexing in a more convenient manner when developing digital TV network services to generate corresponding single-program system transmission streams to be transmitted, and the network The transmission processing unit processes with a more effective and convenient network protocol, which can transmit and transmit the effective data of the program in the network at a variable bit rate, and decode and play at the receiving end at a constant bit rate. At the terminal, the receiving end restores the time information processing unit to perform corresponding processing according to the received network data information, and can recover the time information as accurate as the original transmission stream entering the demultiplexing and remultiplexing processing unit. The structure realized by the operation processing of the present invention is simple, and has good expansibility. Regardless of whether it is relative to the code stream demultiplexing and remultiplexing processing for developing network digital TV services, or relative to only transmitting effective code stream code rates in the network, accurate system time information can be recovered at the receiving end. methods are applicable.

Description of drawings

Fig. 1 System block diagram of introducing digital TV programs from digital TV broadcasting network in broadband IP network to develop network digital TV services

Description: The transmission packet (TP) of the digital TV single program N is marked as TSN, N=1, 2...; the empty transmission packet (TP) mark bit is NULL; the transmission of the system time information PCR value containing the digital TV single program N Small packets (TP) are marked as PCRN, N=1, 2.... In Fig. 1, it includes a demultiplexing and remultiplexing processing unit. After the input digital TV program system transport stream is demultiplexed and remultiplexed, a single program system transport stream with time synchronization information is generated. After being processed by the network transmission processing unit, the transmission stream of the single program system is transmitted in the broadband IP network in the form of IP stream. After the receiving end receives the transmitted IP stream, it first performs network jitter removal processing, and then processes the received single-program system transport stream with time synchronization information to restore the same time synchronization as the original multi-program system transport stream information.

Figure 2 Block diagram of demultiplexing and remultiplexing processing

In Fig. 2, a single-program system transport stream with time synchronization information is schematically generated.

Figure 3 Block diagram of recovery time information processing unit

In Fig. 3, it is schematically shown that the same time synchronization information as that of the original multi-program system transport stream is recovered.

Fig. 4 is an application scenario and a specific system block diagram according to an embodiment of the present invention.

Fig. 4 is an application scenario and a specific system block diagram of an embodiment of the present invention, which is applied to a broadband IP network and introduces digital TV programs from a digital TV broadcasting network to develop network digital TV services.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Since the digital TV service transmission mode of the digital TV broadcasting network is a broadcast form, while the broadband IP network service transmission mode is a two-way, shared, best-effort service form, so it is more suitable to transmit the single program system transmission stream in the broadband IP network The transmission operation mode of the IP network. Therefore, it is necessary to extract and analyze the information of the digital TV programs entering the broadband IP network, as well as demultiplex and re-multiplex the digital TV programs to generate a single-program system transport stream suitable for IP network transmission.

As shown in Figures 1 and 4, in the process of implementing IP network transmission of digital TV services, digital TV programs can come from traditional broadcast networks such as terrestrial broadcasting, satellite transmission, and digital cable. The multi-program system transport stream of time information is first demultiplexed and re-multiplexed. In this process, it is not necessary to perform complex and strict time information correction as stipulated in the standard, but to fully consider network processing, transmission and reception. The synergistic cooperation of the recovery processing realizes the Internet TV service in a more efficient, simple and network transmission efficiency manner.

Perform the demultiplexing and re-multiplexing processing in Figure 2 on the received multi-program system transport stream, generate a single-program system transport stream with time synchronization information, and perform packet identification (PID) on the input digital TV program system transport stream Carry out analysis, as shown in the figure, if the corresponding transmission packet (TP) constitutes the transmission stream of the single program system to be transmitted, then keep it; if the corresponding transmission packet (TP) is an empty packet, replace it with a byte synchronization position Tag (Tag), if the corresponding transport packet (TP) is a single program system transport stream that constitutes other transmissions, it is also replaced with a one-byte synchronous position tag (Tag). The single-program system transport stream with time synchronization information generated in this way only contains valid data constituting the program and a small amount of time synchronization information, which will not waste IP network transmission bandwidth.

The network transmission processing unit performs the protocol encapsulation processing required for network transmission on the single-program system transmission stream with time synchronization information. For example, it can encapsulate 7 small transmission packets in one data frame for network transmission after the processing shown in Figure 2. Protocol encapsulation processing and transmission can be performed with fixed frame length data.

At the receiving end, the recommendations in the MPEG-2 standard can be applied for network jitter removal. The received data is processed as shown in Fig. 3, Fig. 3 is that the present invention carries out recovery time information processing to the received single program system transmission with time synchronization information, check the received data as shown in the figure, if it is synchronous The position mark (Tag) is then replaced with an empty packet, and then the data stream recovered out only contains the data of a single program compared with the data stream that originally entered the demultiplexing and multiplexing unit. The position is the same as the position in the original data stream, so that the time information (PCR value) corresponding to the single program can be recovered as a synchronous system decoder without any processing. From the correspondence between Figure 3 and Figure 2, it can be seen that the position of the time information packet in the code stream is exactly the same, indicating that no jitter of time information is introduced in the process of code stream processing and network transmission. In the transmitted IP data stream, only valid data of a digital TV program and a small amount of time information synchronization marks are included, which indicates that the constant bandwidth and fixed delay of traditional digital TV broadcasting network transmission have been changed in digital TV IP network transmission. mode, which is transmitted in a more bandwidth-efficient mode.

Claims (3)

1. A control method for network digital television system clock synchronization maintenance, characterized in that, in the process of introducing digital television programs into a broadband IP network, time information is maintained in demultiplexing and remultiplexing units, and transmitted through the network Later, at the receiving end, the original time information can be restored according to the information in the transport stream, and the effective data of the program can be transmitted in the network at a variable bit rate rate, and the time information model with a constant bit rate rate can be used to achieve the encoding end and The system clock at the decoding end is synchronized. When the input is the digital TV program system transport stream of the traditional digital TV broadcasting network, the demultiplexing and re-multiplexing processing unit regenerates the unit with time synchronization information according to the information of the input system transport stream. The program system transport stream, the single program system transport stream only contains the effective video and audio data of the program and is transmitted in the broadband IP network. At the receiving end, the recovery time information processing unit re- Return to the code stream of constant code rate rate, the time synchronization information PCR value of this constant code rate code stream is the same as the position before entering the input demultiplexing and multiplexing processing unit, so that the system clock of the program code stream decoder Synchronize. 2. The control method for network digital TV system clock synchronization maintenance as claimed in claim 1, wherein said "system clock synchronization" includes front-end demultiplexing and re-multiplexing processing, network transmission processing, receiving end Recovery time information processing, demultiplexing and re-multiplexing processing refers to the processing of digital TV system transmission streams that need to be effectively transmitted over the network to generate corresponding single-program digital TV system transmission streams; network transmission processing refers to effective network transmission Transmission of digital TV system transport stream, protocol processing during network transmission; receiving end recovery time information processing refers to the system for correctly recovering the system transport stream after receiving the network data of the transmitted digital TV system transport stream at the terminal processing of time information. 3. the control method of network digital television system clock synchronization maintenance as claimed in claim 1, is characterized in that, when inputting as the digital television program system transmission stream of traditional digital television broadcasting network, return to constant code rate rate at the receiving end , and synchronize the system clock with the PCR value of the correct time information, including the following steps: ① Demultiplex and re-multiplex the input digital TV multi-channel program system transmission stream. In the process of demultiplexing, there is no need to correct the PCR value of the time information, only need to keep the time information of the original program and insert some information to record the relative position of the program transmission packet; also in the process of multiplexing, it is not necessary to correct the PCR value of the time information, and generate a single program transmission stream that does not contain empty packets; ②The generated single-program transmission code stream without empty packets is transmitted at a variable bit rate in the network; ③ At the receiving end, the recovery time information processing unit restores the code stream with a constant bit rate rate according to the information contained in the single program system transport stream, and the time synchronization information PCR value of the constant bit rate rate bit stream and input demultiplexing It is the same as the position before reusing the processing unit.

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