PCR - Program Clock Reference
Synchronization of the receiver System Time Clock (STC) with the transmitter STC depends on transmitting PCRs through a constant-delay portion of the system. Thus, PCRs are inserted following the encoder buffer and extracted before the receiver buffer. PCRs are inserted with a maximum interval of 100ms.
Synchronization can be adversely affected by transmission over links having a variable delay or time jitter, and the accuracy of clock recovery must be studied if such an application is contemplated.
PCRs are also affected by the multiplexing of multiple program streams. In this case, there is additional buffering in the multiplexer, and it may become necessary to re-stamp the PCR values of data that is transmitted earlier or later than expected. Although the MPEG standards provide the means to maintain synchronization in this case, they do not specify the jitter limits, suggesting only that it is "intended" to be +/-4 ms maximum in a well-designed system.
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