A method and apparatus for synchronizing an event produced at a digital
television receiver with an instant of a transmitted video, audio, or
data element of a digital television program is disclosed. In a digital
television system, a system time clock generates a timeline that is used
to synchronize the presentation of the video, audio, and data elements of
the television program. An application time is used in program production
to synchronize instants of the several program elements. To synchronize a
receiver generated event with an instant of a transmitted video, audio,
or data program element, samples of the application time are transmitted
to a receiver in a synchronized data service. A reconstructed application
time is generated at the receiver as a function of the current system
time, the application time sample, and the presentation time stamp of the
data access unit in which the application time sample was transmitted.
The presentation time of the program instant is associated with an
application time correlating the event and the instant. The correlating
application time is transmitted to the receiver as part of a synchronous
or asynchronous data service and the event is instigated when the
reconstructed application time corresponds to the correlating application
time. A clock for generating a reconstructed application time
synchronized to the system time is also disclosed.