MediaPreroll The MediaPreroll function allows the Movie Toolbox to prepare your media handler for playback. Contains the starting time of the media segment to play. This time value is expressed in your media's time scale. The MediaSetRate function allows the Movie Toolbox to set your media's playback rate. This effective rate accounts for any master time bases that may be in use with the current movie.
Positive values represent forward rates and negative values indicate reverse rates.
The Movie Toolbox calls your derived media handler's MediaSetRate function whenever the movie's playback rate changes. The Movie Toolbox provides you with a new effective rate for your media. This effective rate accounts for any master time bases that may be in use with the current movie. Consequently, you may use this rate without having to further transform it. You obtain the initial rate information from the effectiveRate field of the movie parameter structure that the Movie Toolbox provides to your MediaInitialize function.