Abstract

In a system that transmits packets containing timestamps and information from a transmission site to a reception site at a transmission bit rate the packets may experience jitter, i.e. variable delay, during transmission. In such a case, the packets are temporally shifted relative to the timestamps and to other packets. Where the timestamp values are inserted into selected packets prior to transmission and that timestamp represent the value of the transmission site clock, the method and apparatus of the present invention substantially removes the jitter and adjusts the timestamp values prior to reception of the packets at the reception site. The present invention achieves this goal by receiving the packets at an intermediate site that has a local clock operates at a nominal frequency substantially equal to the nominal frequency of the transmission site clock and uses that clock as a jitter-free clock to correct the packets. The packets are stored in a buffer at the intermediate site and output from the buffer at a controlled rate to maintain a substantially constant average transit time of packets through the buffer. Before the packets are output for reception at the reception site the timestamps of selected packets are modified to reflect the new temporal relationship between packets due to the controlled rate of output from the intermediate site.

Other References

• "MPEG-2 Systems" Standard, Generic Coding of Moving Pictures and Associated Audio:Systems International Organisation for Standardisation ISO/IEC JTC1/SC29/WG11 Nov. 1994
• Wasilewski, A., "The MPEG-2 Systems Specification: Blueprint for Network Interoperability", Jan. 3, 199