Exclusive playlist (excl)
The exclusive playlist allows up to one of its children to play. The start of one media object causes the currently playing item to either pause or stop.
The priorityClass tag further defines interrupt priorities and behavior (pause, defer, or stop) of media objects when interrupts occur.
The starting of a media object may be triggered by an event such as a key press or a Wallclock time, as the following sample code illustrates.
<excl> <priorityClass> <seq begin="wallclock(R/2010-01-01/PT1H)"> <video src="hour.mpg" /> </seq> </priorityClass> <priorityClass higher="pause" pauseDisplay="hide"> <seq repeatCount="indefinite" begin="0"> <video src="ad1.mpg" /> <video src="ad2.mpg" /> <video src="ad3.mpg" /> </seq> </priorityClass> </excl>
This exclusive playlist contains two priority classes.
The first (higher) priority class contains a single video "hour.mpg" that begins on the top of each hour, starting on midnight of January 1, 2010. See Wallclock for detailed ISO-8601 specification.
The second (lower) priority class contains a sequential playlist, that begins at "zero" seconds (immediately as the <excl> playlist is entered). While the sequence plays, when a higher priority class is triggered, the then playing item is "paused" as the interrupting media object plays. After it finishes, the paused media object resumes.
This achieves the effect of looping three videos, and interrupting with another on the top of every hour.