Just incase it helps, this is from the manual.
_"Some video formats can take a noticeable fraction of a second to start play; The Video Preload actor helps you to avoid that delay by "preloading" a small chunk of the specified movie or movies into your computer's main memory, thus reducing as much as possible the delay in starting playback. Note however that the preload function will only work if snd out, dir stage, and into RAM parameters exactly match the equivalent settings in the Movie Player used to play the movie._
_Input Properties_
mode: This property can be set to either play or forever.
When set to play, the video is kept in memory until a Movie Player actor starts and then stops playing it. Once that actor stops playing the video, it is removed from memory.
_When set to forever, the video is kept in memory until it is preloaded again with the mode set to play, or until Isadora quits. Use this option with caution! It is easy to fill up your RAM with videos that you no longer need to play." _