1 Introduction MPEG- as a motion picture has been widely used international standard, digital video broadcasting (DVB) has MPEG- as a source format. In many practical applications, including satellite broadcasting, digital cable and high-definition television HDTV, MPEG- group synchronous interface through the encoder input to the channel. In broadband digital communications network as ADSL, FTTC and broadband IDSL is MPEG- group into another network transmission packet, in this case, a certain number of transport stream packet to be compressed into a ATMAAL-5PDU unit When the packet switching, PDU is broken down into several ATM cells. As the number of transport stream packet compression as ATMAAL-5PDU units, mainly with the ATM network protocol, generally 2 transport stream packet is compressed into a single AAL-5PDU unit. A transmission network, MPEG-2 transport stream packet within required time delay for the control, this control is mainly to send a program reference clock to the receiver to decode the system when the system clock to recover. But also avoids the decoder input buffer overflow and underflow.
A video delivery system in the design time of the MPEG- transport stream bit rate the implementation of precise control is particularly important. When the MPEG- group of direct transmission, the system of time control is relatively simple, the key question is how to input the video source for accurate calculation of the time. If you solved the problem, the decoder, the decoder system clock or system clock input layer of multiplexer and encoder essential to synchronize the system clock. If the current network can tolerate a certain amount of packet delay, then the result of network congestion and packet delay is not the goal we are concerned, therefore, the bit rate MPEG- were measured for the entire decoder or the video delivery system is not looked very key issue. But when the MPEG- transport stream packet into another format, such as ATMAAL-5PDU unit time on the inside due to network congestion caused by packet delay or even packet loss on the effectiveness of decoding a very key issue. Here we present a simple and effective way, can the decoder or receiver system layer multiplexing for effective bit rate of MPEG- measurement. Through the use of MPEG decoder chip and an embedded processor on the MPEG- program transport stream clock reference for unified management. As the program transport stream MPEG- reference clock is based on a certain set encoder system reference clock, so you can by its real-time monitoring to determine the flow of the basic bit rate, while the current reference clock and the decoder reference clock procedures ? PCR? comparison, it can be measured to verify the network congestion. And the design of a hardware testing and evaluation card to validate the method to verify the results are consistent with the requirements of the current CATV or HDTV.
2 network congestion and system reference clock recovery MPEG-
according to international standards, reference encoder system clock (27MHz) of 1 / 33 encoding, the encoded data must expand and treated as a program reference clock? PCR embedded in the transport stream packet. At the decoder, therefore, PCR recovery by the system clock to determine the encoding, decoding so as to achieve synchronization. As in the transport stream, the packet containing PCR field PID? Value in the program mapping table (PMT) were identified. According to this with? PCR PID packets field set to refer to the first packet containing the PCR system clock STC as a reference PCR, and then the rest of the transmission packet contains a PCR field in the PCR? Of value through a certain way Treatment can restore the system clock. Restore the system clock as follows:
(1) will be the first? PCR to initialize the value of the STC. ?
(2) consider the decoder input buffer overflow and underflow effects, some estimates of its size, to determine the decoding input buffer. BOLA TANGKAS