mvPlaySpeed(3dm)                                              mvPlaySpeed(3dm)


NAME
     mvSetPlaySpeed, mvGetPlaySpeed, mvGetCurrentDirection - Control rate of
     playback for a movie instance


SYNOPSIS
     #include <dmedia/moviefile.h>
     #include <dmedia/movieplay.h>


     void mvSetPlaySpeed(MVid movieId, double newPlaySpeed);

     double mvGetPlaySpeed(MVid movieId);

     MVdirection mvGetCurrentDirection(MVid movieId);


DESCRIPTION
     mvSetPlaySpeed(3dm) changes the movie play speed, expressed as a fraction
     of the movie's natural image frame rate.  This frame rate is stored in
     the movie file (SGI and QuickTime only) and it may be determined by
     calling mvGetImageRate(3dm).  For example, if you call
     mvSetPlaySpeed(3dm) with a value of 2.0, the movie plays twice as fast as
     it normally would.

     For movies with audio, the Movie Playback Library attempts to resample
     the audio to match the requested playback speed.  This changes the pitch
     of the audio.  Be aware that the current implementation uses software
     techniques to perform audio resampling; thus, changing the speed of
     playback for a movie with an audio sound-track will consume more
     processor time.

     If you specify a negative value for newplayspeed, the movie plays in
     reverse.  You should use mvGetCurrentDirection(3dm) to determine the
     direction the movie is actually playing, because the swinging loop mode
     may cause the movie to play in a direction other than that indicated by
     the sign of the current speed. See mvPlayLoop(3dm) for details.

     The default movie speed is always 1.0.

     mvGetPlaySpeed(3dm) returns the current play speed.

     The results of mvSetPlaySpeed(3dm) depend on whether or not the movie is
     playing every frame (see mvSetPlayEveryFrame(3dm)).  If the movie is not
     playing every frame, then mvSetPlaySpeed(3dm) acts as described above.
     If the movie is playing every frame, then mvSetPlaySpeed(3dm) will have
     no effect.

     You may call these functions for a specified movie instance regardless of
     whether or not the movie is playing.


NOTES
     The method the Movie Playback Library uses to resample audio for variable
     speed playback does not perform any filtering.  Thus, the pitch-shifted
     audio may have aliasing artifacts.


SEE ALSO
     mvBindOpenGLWindow(3dm), mvIntro(3dm), mvPlay(3dm), mvPlayLoop(3mv),
     mvSetPlayEveryFrame(3dm).


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