NOTE: This Technical Q&A has been retired. Please see the Technical Q&As page for current documentation.

Technical Q&A QTW49
Determining QTW Time Values

Q When you use MCActionSetSelectionDuration and MCActionSetSelectionBegin to set the duration and starting point of a selection, what are the units for these two values? I tried a start value of 0 and a duration value of 5 and the movie did not play at all. With a duration value of 50, it lasted 1/10 of a second. I call Play Every Frame beforehand, and SetPlaySelection is set to TRUE somewhere beforehand.

A The number of time units that pass in one second is equal to the time scale times the play rate. If you are playing the movie at a rate of 1.0, the number of time units per second is just the timescale. You can get a movie's time scale with a call to GetMovieTimeScale(). 600 is a typical value. Thus, a duration of 50 would be 1/12 of a second. Check out page 3 of the QuickTime 2.0 Developer Guide for Windows. It describes the QTW time coordinate system in detail.

[Aug 01 1995]


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