system clock reference (digital TV) (SCR)

The transport stream ofdigital television consists of many multiplexed television programs, each of which must be synchronized on the receiving side.

Each individual decoder must be synchronized to the received television signal. This synchronization is done with the Program Clock Reference( PCR).

In addition, the program stream from all programs must be synchronized so that the decoder operates with only one time reference. This synchronization mechanism is provided by the System Clock Reference ( SCR). This is a time stamp that is transmitted with the program stream and from which the decoder of digital TV derives its reference time. In most cases, the SCR and PCR values are identical. However, the permissible internal deviations between the system clock references are 700 ms, whereas they may be 1,000 ms for the program clock references.