1.9 Timebase Recovery in Interfacing

Unlike generic data, audio-visual data is only meaningful when reproduced with an appropriate timebase, both in the long term and the short term . Whatever means may be used to deliver the data, there must also be a means to recover the timebase. In audio and video installations it is common practice to distribute master clocks from a central generator. When this is done, the interfaces essentially become data transmissions, because timebase correction will be used at any receiving device in order to align the signal timing with the master reference.

This approach is feasible within a building complex, but not over long distances. Where data networks are used, packets may be routed over different physical paths between the same points and the time taken will be subject to some variation, known as packet jitter. Under these conditions it is much more difficult to recreate the correct timebase in the receiving device. Where several signal formats are possible, the receiver may need metadata that help it generate the correct timing.