Technical Q&A

QTW 43 - Synchronization Problems and Data Skips with QuickTime for Windows 2.0.1 (1-July-95)

Q I am experiencing a playback problem with QuickTime for Windows 2.0.1 that did not occur with version 1.01. This is an example of what happens: movie_1 plays fine the first time, but after I play movie_2, movie_1 plays back audio only at first, and then I get jerky video playback after a two-to three second delay. The movies are 150K, Cinepak-compressed files with 10 frames/second and 22.050KHz audio. The movies have been movie-shopped and analyzed in movie analyzer, and they appear to be OK. I examined memory usage, and there are no leaks during playback. The movies play back with no problems using the Movie Player.

A You can experience synchronization problems, data skips, and so on if no pre-rolling takes place when the movie rate is changed from 0 to a non-zero value (e.g., fixed 1.0 for normal-speed forward). Try adding a pre-roll call (the second line in the following example) ahead of any call to "MCDoAction(mc, mcActionPlay, and (LPVOID)lfxRate)":

    SetMovieActive (mMovie, TRUE);
    PreRollMovie   (mMovie, 0, MAKEFIXED(1,0));
    MCDoAction     (mcMovie, mcActionPlay, (LPVOID)MAKELFIXED(1,0);

Note that the movie state must be active when prerolling is called.

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