MediaPlayback works only sometimes

I am trying to create a stand-alone video presentation with a video on almost every slide. After the file got way too big when I used embedded video, I now started to use the MediaPlayback component. It works on some slides now, but on some it just doesn't, or it starts working after 20 sec, but already progressing in the timelinebar of the MediaPlayback.

Is there a way to add a preloader to the MediaPlayback component so it starts only when it is finished loading?
Is there a way to loop the MediaPlayback component?

Thanks alot.
I am pretty new to Flash so please be a little more explicit in your answers.