[8.3] I don't want to loop this QT, but I need it to play again. What do I do?

To rewind and play again, reset the movieTime to the beginning and restart it using the movieRate:

  on backToStart
    set the movieTime of sprite myVideoSprite = 0
    set the movieRate of sprite myVideoSprite = 1
  end backToStart

It may sometimes be necessary, especially if you're also switching castmembers at the same time, to kickstart this process with liberal use of the updateStage command.