Program clock reference correction in transport stream processors with rate adaptation

Abstract

The program clock reference (PCR), which is carried by MPEG-2 transport streams, is commonly used for synchronizing different media types, in receivers. In summary, it is a snapshot of the transmitter's 27 MHz counter and is employed to adapt the local clock. However, the PCR may present inaccuracies on its time base information, known as jitter, given that the processing chain between transmitter and receiver often modifies relative distances among time stamps. In order to correct such a behavior, some authors have suggested PCR-jitter control schemes, which are able to compensate for new PCR positions, in streams. Nevertheless, as none of them takes into account the asynchronism among all elements involved in this procedure, there is often an increase in jitter. The present paper addresses this problem and introduces a methodology for joint rate adaptation and PCR correction, which has the potential to reduce the output jitter, when it is caused by stream modifications due to a rate adaptation module. Simulation results show that the proposed method is effective and outperforms traditional and more recent schemes presented in the literature, by keeping the output jitter level as close as possible to the one at the input and, consequently, avoiding large clock deviations.