Symbol
make a movie symbol the size you want for the movie
now instead of embedding video, export the video as a sequence of images
a 4min video should be around 3000 images.
enter the symbol and leave layer 1 as the core rectangle you made
insert a new layer, import the first image in the folder to the stage it will say something to the effect of "this image is part of a sequence import all images in sequence?"
yes you want to do this.
now pull the keyframe from the layer 1 rectangle to the end of the images frames
mask layer 1 to layer 2
click out of the symbol
now you can move that around as you wish. so if you have a 400x200 rectangle it will be a 400x200 swf for you to imput into dreamweaver or whatever you are using.
this swf will be larger than you probably want, but embedding video is about the same size or comperable to this process.
I did a paintball movie integrated into a header for a webpage and it turned out to be 2800 frames, and a 1.4 meg .swf.