Inside Macintosh: QuickTime Reference

A Note to Authors of Media Handlers

QuickTime developers who may author media handlers should take note of the following:

Specifically, consider a containing movie of duration 10 with a movie media track that contains a media element, which is active from time 4 to 6. At time 4, the embedded movie is at its time zero. But because the embedded movie is actually instantiated in advance of its play time (up to fifteen seconds) it will be active at times when its time is actually negative. (For more information on embedded movies, see the section "Introducing Embedded Movies".)

Because the embedded movie's time base has its start time set to zero, however, those negative times are pinned to zero. However, the rate is non-zero. So there is a strange situation where time is stopped at zero and the rate is moving. Some media handlers can misinterpret this situation and start playing before their actual start time. Media handlers can detect this situation by calling GetTimeBaseStatus instead of GetTimeBaseTime.

Inside Macintosh: QuickTime Reference